Control of Innate and Adaptive Immune Responses during Infectious Diseases ppt

This book covers several aspects of induction, control and evasion of host immune response during infectious eases.. 1Julio Aliberti 2 Mechanisms of Host Protection and Pathogen Evasion

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Control of Innate and Adaptive Immune Responses during Infectious Diseases

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Julio Aliberti

Editor

Control of Innate and

Adaptive Immune Responses during Infectious Diseases

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Julio Aliberti

Associate Professor

Divisions of Molecular Immunology and Pulmonary Medicine

Cincinnati Children’s Hospital Medical Center and School of Medicine

Springer New York Dordrecht Heidelberg London

Library of Congress Control Number: 2011936972

NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis Use in connection with any form of information storage and retrieval, electronic adaptation, computer software,

or by similar or dissimilar methodology now known or hereafter developed is forbidden.

The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identiﬁed as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights.

Printed on acid-free paper

Springer is part of Springer Science+Business Media (www.springer.com)

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Upon infection, pathogen and host perform a complex interaction that ultimately aims to achieve elimination of the invading microbe with the least amount of dam-age to host tissues and organs Interestingly, both sides of this equation co-evolved several mechanisms that mediate pathogen recognition, initiation and expansion of immune responses, neutralization of toxic elements and elimination of replicating organisms and ﬁnally healing and remodeling of damaged tissues On one side pathogens evolved mechanisms to evade recognition and killing, while on the other side, host express numerous (sometimes redundant) mechanisms of recognition and elimination of the pathogen Nonetheless, it is clear that an absolute successful strategy on the pathogen side would be lethal to both host and pathogen Therefore, several evasion mechanisms are seen among several microbes The most successful ones are not necessarily the most abundantly found within the host, but those that can achieve transmission On the other hand, hosts need a robust and extended immune response in order to expand memory cells This critical balance is where the co-evolution between host and pathogens lies This book covers several aspects

of induction, control and evasion of host immune response during infectious eases Multiple aspects are covered and each chapter focuses on one prominent infectious agent

Preface

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1 Resolution of Inﬂammation During Toxoplasma gondii Infection 1Julio Aliberti

2 Mechanisms of Host Protection and Pathogen

Evasion of Immune Response During Tuberculosis 23Andre Baﬁca and Julio Aliberti

3 NKT Cell Activation During (Microbial) Infection 39Jochen Mattner

4 Regulation of Innate Immunity

During Trypanosoma cruzi Infection 69Fredy Roberto Salazar Gutierrez

5 B Cell-Mediated Regulation of Immunity

During Leishmania Infection 85

Katherine N Gibson-Corley, Christine A Petersen,

and Douglas E Jones

6 Control of the Host Response to Histoplasma Capsulatum 99George S Deepe, Jr

7 Modulation of T-Cell Mediated Immunity by Cytomegalovirus 121

Chris A Benedict, Ramon Arens, Andrea Loewendorf,

and Edith M Janssen

8 T Cell Responses During Human Immunodeﬁciency

Virus (HIV)-1 Infection 141

Claire A Chougnet and Barbara L Shacklett

Index 171

Contents

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Julio Aliberti, Ph.D. Associate Professor, Divisions of Molecular Immunology and Pulmonary Medicine, Cincinnati Children’s Hospital Medical Center and School of Medicine, University of Cincinnati, Cincinnati, OH, USA

Chris A Benedict Division of Immune Regulation, La Jolla Institute

for Allergy and Immunology, La Jolla, CA, USA

benedict@liai.org

Claire A Chougnet Division of Molecular Immunology, Cincinnati Children’s Hospital Research Foundation and Department of Pediatrics, University of Cincinnati, Cincinnati, OH, USA

Claire.Chougnet@cchmc.org

George S Deepe Jr, M.D. Professor, Veterans Affairs Hospital, Cincinnati, OH, USA; Division of Infectious Diseases, University of Cincinnati College of Medicine, Cincinnati, OH, USA

george.deepe@uc.edu

Katherine N Gibson-Corley Department of Veterinary Pathology,

College of Veterinary Medicine, Iowa State University, Ames, IA, USA

Fredy Roberto Salazar Gutierrez, M.D., Ph.D. Assistant Professor,

School of Medicine, Antonio Nariño University, Bogotá, Colombia

salazarfrg@gmail.com

Contributors

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x Contributors

Edith M Janssen Division of Molecular Immunology, Cincinnati Children’s Hospital Research Foundation, University of Cincinnati College of Medicine, Cincinnati, OH, USA

Christine A Petersen Department of Veterinary Pathology,

College of Veterinary Medicine, Iowa State University, Ames, IA, USA

Barbara L Shacklett Department of Medical Microbiology and Immunology, School of Medicine, University of California, Davis, CA, USA

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J Aliberti (ed.), Control of Innate and Adaptive Immune Responses

during Infectious Diseases, DOI 10.1007/978-1-4614-0484-2_1,

Abstract Upon Toxoplasma gondii host infection, a powerful immune response

takes place in order to contain dissemination of the parasite and prevent mortality Once parasite proliferation is contained by IFN-J-dependent responses, nevertheless , parasite immune escape prevents complete clearance characterizing the onset of the chronic phase of infection, with a continuous (and powerful) cell-mediated immu-nity Such potent responses are kept under tight control by several, non-redundant mechanisms that control pro-inflammatory mediators Including cytokines, such as members of the IL-10 family, TGF-beta, the membrane receptors, ICOS, CTLA4 and a class of anti-inflammatory eicosanoids, the lipoxins In this chapter we address the host strategies that keep pro-inflammatory responses under control during chronic disease On the other hand, we approach the perspective of the pathogen, which pirates the host’s machinery to its own advantage as a part of the pathogen’s immune-escape mechanisms

1.1 Introduction

Toxoplasmosis is caused by the protozoan parasite, Toxoplasma gondii The pathogen

can be found worldwide and is particularly prevalent in the United States, where it

is estimated that more than 60 million people may be infected Among those who are infected, few develop symptoms due to healthy immune system that usually prevents the parasite from causing illness Nevertheless, within the high risk group are pregnant women and individuals with compromised immune systems

J Aliberti ( * )

Divisions of Molecular Immunology and Pulmonary Medicine,

Cincinnati Children’s Hospital Medical Center and School of Medicine,

University of Cincinnati, Cincinnati, OH, USA

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2 J Aliberti

Felines, including the house cat are deﬁnitive hosts in which it is observed the

sexual stages of T gondii and thus, are considered to be the main parasite reservoirs Cats become infected with T gondii by carnivorism (Fig 1.1) After tissue cysts or oocysts are ingested, viable organisms are released and invade epithelial cells of the small intestine, where they undergo an asexual cycle followed by a sexual cycle and then form oocysts, which can be excreted The unsporulated oocyst takes 1–5 days after excretion to sporulate (become infective) Although cats shed oocysts for only 1–2 weeks, large numbers may be shed

Oocysts can survive in the environment for several months and are remarkably resistant to disinfectants, freezing, and drying, but are killed by heating to 70°C for

10 min The persistency of oocysts in the environment may enhance the infectious potential of the parasite

Humans may acquired T gondii via different routes (Fig 1.1):

(a) Ingestion of: raw or undercooked and infected meat containing Toxoplasma

cysts; oocysts from fecally contaminated hands or food;

(b) Organ transplantation or blood transfusion from infected humans;

(c) Transplacental transmission from an infected mother; and

(d) Accidental inoculation of tachyzoites

predation Ingestion of oocysts

Ingestion of infected raw meat

or water/food contaminated with oocysts

Congenital transmission Feces

Fig 1.1 Toxoplasma gondii life cycle Cats become infected with T gondii through predation of

infected mice or rats After cysts or oocysts are ingested the organisms are released and spread throughout the small intestine and then form oocysts, which are excreted and can potentially survive for long periods in the environment Human acquire infection via in several routes: ingestion

of infected food containing Toxoplasma cysts; ingestion of oocysts from contaminated hands or

food; organ transplantation or blood transfusion from infected humans; transplacental sion from an infected mother; and accidental inoculation of tachyzoites

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1 Resolution of Inﬂammation During Toxoplasma gondii Infection

Toxoplasma gondii, a protozoan apicomplexa parasite is highly virulent and can

potentially invade and subsequently replicate within any nucleated host cell Under natural conditions infection occurs by ingestion of parasite oocyst-contaminated food or water Oocysts are complex structures formed in the digestive tract of the deﬁnitive host – felines which protect the parasites from heat and dehydration and can remain infective within the environment for long periods of time Once ingested, oocyst rupture occurs within the host digestive system and the released parasites enter host cells through an active process mediated by the apical complex (Morisaki

et al 1995) Host cells include epithelial cells, resident macrophages and dendritic cells (Fig 1.1, Life Cycle) Once intracellular, the parasites (tachyzoites) quickly replicate Although deﬁnitive evidence is still required, it is proposed that circulat-ing infected host cells (probably macrophages or DCs) might mediate spread of the parasite to several organs, including the liver One current hypothesis proposes that the acute phase of infection resolves when the remaining fast-replicating parasites switch, probably as a response to immune attack, to a slow replicating form known

as bradyzoites and seclude themselves in cysts in certain tissues, such as the central nervous system (CNS) and the retina (known as chronic or persistent infection) (Black and Boothroyd 2000)

For a long time it was widely accepted that cysts containing bradyzoites were latent, biologically inactive structures that eventually died off or in some cases re-activated parasite replication Today, however this concept has been challenged as it has been shown that cysts are dynamic structures, where parasites convert to tachyzoites The conclusion is that this “dripping” effect in which tachyzoites are slowly released, con-tinuously stimulating immune response Therefore, when immune suppression caused

by drugs or other infections, such as HIV, can lead to reversion from bradyzoites back

to the fast replicating tachyzoites, which rupture cysts causing local tissue necrosis, thus characterizing the main pathology resulting from this infection If reactivation occurs in the CNS, it is often lethal During the early years of the AIDS epidemic,

encephalitis due to reactivation of chronic T gondii infection was one of the most

relevant pathologies affecting immuno-depressed patients (Martinez et al 1995)

In nature, the main route for T gondii transmission is through predation (i.e

felines preying on rodents), therefore an evolutionary advantage would be among pathogens that populate the host and simultaneously provide conditions to protect the host to carry as many parasites without killing it In other words, this means to proliferate while promoting host survival To achieve this, the parasite has evolved several mechanisms to induce a powerful immune response by the host, which pre-vents host death by controlling parasite growth However, to avoid the potential collateral damage of such powerful pro-inﬂammatory reaction, the pathogen sub-verts the immune system allowing it to persist through the chronic phase of the disease, which can last for many years (Hay and Hutchison 1983) Herein, we dis-

cuss the immune response triggered by T gondii and how hosts and pathogens make

use of immune-regulatory pathways to promote host survival, which increases the probability of parasite transmission

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1.2 Experimental T gondii Infection

1.2.1 Microbial Recognition and IL-12 Induction

A balanced interrelationship between host and parasite is highly dependent on the early induction of immune response after infection Too much immune response and pathogen is swiftly cleared without causing disease On the other hand, the absence of a proper timely host response may lead to uncontrolled pathogen replica-tion and spread, often leading to the death of the host Nevertheless, this is an

over-simpliﬁcation of the rather complex scenarios that take place during T gondii

infection Although signiﬁcant protection is achieved after infection, a relevant proportion of invading parasites evade immune effector mechanisms, i.e tachyzoites turn infected cells incapable to secrete pro-inﬂammatory mediators (Walker et al

2008), bradyzoites, hidden within tissue cysts populate immune privileged sites,

such as the retina or the CNS Therefore, T gondii parasites can persist in the host

even in the presence highly powerful immune response To add further complexity

to this interaction, several lines of evidence indicate that without innate immune responses, such as following NK-cell depletion, the initial IFN-J-dependent control

of parasite replication is compromised and, in the case of NK-cell-depletion of T-cell-deﬁcient mice, host resistance is lost resulting in host death, which indicates an important role for NK cells in the induction of a response (Sher et al 1993; Hunter

et al 1994)

IL-12 is a cytokine produced during pathogen recognition that is essential to trigger both NK cell as well as T cell-derived IFN-J production during T gondii infection The biological relevance of this cytokine was evidenced by the ﬁnding that

IL-12-deﬁcient animals are extremely susceptible to T gondii infection (Gazzinelli

et al 1994)

B cells, macrophages, neutrophils and DCs are known to produce IL-12 in vitro and in vivo (Denkers 2003) During T gondii infection, macrophages, neutrophils and DCs can all produce detectable amounts of IL-12 after T gondii infection

(Denkers 2003) However, DCs – abundant producers of IL-12 in vivo – are the most

relevant cell population for the development of a parasite-speciﬁc type 1 immune response Reis e Sousa and colleagues observed that splenic mouse CD8D+ DCs

produce IL-12 in response to T gondii in the absence of co-stimulatory signals (Reis e

Sousa et al 1997) While macrophages require a cognate priming signal, i.e IFN-J and neutrophil IL-12 production levels are relatively low when compared to DCs

In summary, DCs can either activate the immune system by recognition of derived molecules or can harbor initial replication of the intracellular parasites

parasite-A cellular homogenate from culture-derived tachyzoites (STparasite-Ag) was used in order to decipher which are the parasite components and their respective host recep-

tors involved in DC IL-12 induction by T gondii Such approach seemed feasible

since STAg was capable to induce markedly higher levels of IL-12 from in vitro stimulated splenic DCs than when the same cell populations are exposed to several other microbial products Although the mechanisms underlying such responses are

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not completely understood, one potential interpretation came from studies showing that the chemokine receptor CCR5 plays an important role in the induction of IL-12

synthesis following stimulation with T gondii STAg (Aliberti et al 2000) The logical relevance of the unusual requirement for a chemokine receptor to participate

bio-in microbial recognition by DCs is supported by the fact that decreased IL-12 production is observed during acute infections in CCR5-deﬁcient animals although defects in cell migration could also contribute to this susceptible phenotype

The phenotype of CCR5-deﬁcient mice infected with T gondii cannot be solely

explained by the IL-12 production defects, other studies indicated that NK cells show defective migration patterns after oral infection, leading to a weaker initial NK-derived IFN-J secretion, resulting in susceptibility to infection (Khan et al

2006) In summary, it seems clear that CCR5 plays several critical roles for the

development of innate immunity after T gondii infection Both at the DC IL-12

induction level as well as inducing NK cell migration to infection foci

In the pursuit to identify the ligands with IL-12-inducing activity from T gondii,

a thorough analysis of this activity was performed in fractionated suspensions of secreted parasite proteins Such analysis identiﬁed cyclophillin-18 (C-18) as one

such component T gondii C-18 is a secreted prolyl-isomerase that can bind avidly

to the immunosuppressant cyclosporine, which was therefore initially pursued as a potential therapeutic target for the treatment of toxoplasmosis (Aliberti et al 2003b) C-18 was found to bind directly to human and mouse CCR5 with afﬁnities compa-rable to its prototype ligand, the chemokine CCL4 (MIP-1E) Indeed, C-18 competed with the natural ligand CCL4 for binding to CCR5 It has been shown that endoge-nous CCR5 ligands can trigger IL-12 production Nevertheless, the low levels of cytokine secretion observed under these conditions indicate that it may not have a critical inﬂuence on determining resistance to infection Given that CCR5 is a co-receptor for HIV invasion, further studies showed that toxoplasma C-18 could inhibit the infection of monocytes by CCR5-tropic primary and laboratory HIV isolates (Golding et al 2003, 2005)

However, despite the evident stimulating activity of C-18 triggering IL-12 production by murine DCs, the resulting IL-12 levels observed after stimulation of DCs with C-18 are consistently lower than those seen after stimulation with whole parasite lysate or with a pool of tachyzoite-secreted proteins, indicating that path-ways other than those initiated by CCR5/C-18 might also be important for IL-12 production by DCs (Aliberti et al 2003b) Toll-like receptors (TLRs) have been investigated as a likely candidate for such cytokine induction Mice deﬁcient for the TLR adaptor protein MyD88 were found to have a pronounced defect in IL-12 production in response to STAg stimulation in vivo and in vitro Moreover, upon

T gondii infection, MyD88-deﬁcient hosts had high mortality due to a lack of

protective IFN-J-mediated immunity (Scanga et al 2002) Suggesting that the residual IL-12 produced in response to CCR5 was clearly not sufﬁcient to provide any level of protection after infection Obviating the predominant role of TLR’s in initiating innate IL-12 production in the presence of parasite derived molecules.TLR2 has been found to be involved in the development of resistance to infection

with a large inoculum of T gondii cysts (300 cysts/mouse) (Mun et al 2003)

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Apparently, the defect seen in TLR2-deﬁcient mice is related to inefﬁcient activation

of microbicidal functions, as a defect in nitric oxide production by macrophages was reported, whereas no defect in the production of IL-12 or any other pro-inﬂammatory cytokines, which are typical of innate microbial recognition, was seen (Mun et al 2003)

In an attempt to identify the TLR ligands present in STAg, a CCR5-independent IL-12-inducing activity was puriﬁed from parasite preparations, further analysis indicated the cytoplasmic protein proﬁllin was the key molecule inducing CCR5-independent, MyD88-sensitive DC IL-12 production in mice (Yarovinsky et al

2005) In fact, a thorough evaluation of a panel of TLR-responsive elements in a cell reporter assay allowed for the identification of mouse TLR11 as the receptor of profillin (Yarovinsky et al 2005) In the absence of TLR11, DC’s showed major reduction in IL-12 responses Interestingly, no residual IL-12 was detected under these conditions, something seen previously with STAg-stimulated MyD88-deficient cells Although the effects are dominant and TLR11-deficiency completely abol-ishes resistance to infection, some points remain unanswered, including the identity

of the human TLR involved in T gondii recognition – given that the human TLR11

homolog is a pseudogene Moreover, proﬁllin is not a secreted protein it is released only after tachyzoite rupture, suggesting that it may not necessarily be present at the initial stages where the killing mechanisms are still not active Taken together, the recognition steps that lead to full IL-12 responses is a rather complex interaction that assures the host to produce vigorous DC-derived IL-12 when in the presence of parasite molecules Such responses are essential for the development of protective adaptive immunity

The biochemical basis for the induction of the IL-12 genes has been studied extensively (for review see (Trinchieri 2003)) However, the transcription factors that are directly involved in IL-12 induction during in vivo infection with intracel-

lular parasites, including T gondii it is still not completely elucidated deﬁcient mice cannot produce IL-12 during infection with T gondii and fail to

IRF-8-develop resistance to infection (Scharton-Kersten et al 1997) This observation would directly implicate IRF-8, an interferon-inducible transcription factor that binds to interferon consensus sequences and promotes gene transcription, in the induction of IL-12 gene expression, but recent reports have pointed out that besides their IL-12-induction defect, IRF-8-deﬁcient mice fail to develop the major DC subset involved in IL-12 production in response to STAg stimulation, the CD8D+subset (Aliberti et al 2003a; Tsujimura et al 2003) Furthermore, the remaining DC subsets also had severe defects in response to microbial stimuli Further studies are required to clarify whether the defect in IL-12 production in these mice precludes the DC developmental defect NF-kB family members have been studied during

T gondii infection models, it is clear that NF-kB activation is a required step for the

development of protective immune response to infection (Tato et al 2006) However, the developmental abnormalities seen in animals genetically deficient of NF-kB make dendritic cell specific responses rather complex due to environmental and developmental deficiencies

It has been reported that p38 MAP kinases are required for macrophage IL-12 responses to STAg stimulation (Mason et al 2004) On the other hand, JNK family

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of MAP kinases while have been associated with induction of IL-12 by some (Sukhumavasi et al 2007), while other studies indicate that the play a negative, inhibitory role (Sukhumavasi et al 2010) A more comprehensive analysis of this enzyme activity, targets and function remains to be reported

The unusual combination of receptors triggered by T gondii molecules, i.e

CCR5 and TLR11 suggests that the transcriptional machinery might be unique, which could explain, at least in part, the unusually high IL-12 levels seen after expo-sure of DCs to STAg

An interesting paradox has been unveiled while studying cytokine responses in infected cells In other words, both dendritic cells and macrophages failed to pro-duce signiﬁcant levels of IL-12 when exposed to live tachyzoites (Butcher et al

2001) Such studies led to the hypothesis that dendritic cells may serve as a parasite shuttle during in vivo infection, providing protection while migrating throughout the host (Denkers and Butcher 2005) This set of reports support a scenario in which microbial recognition takes place through released proteins from live free-ﬂoating parasites or from infected cells The mechanistic that leads to inhibition of infected cell responsiveness to microbial stimulation is still not clear, but it has been shown that intracellular parasites disrupt the cytoskeleton of the host cells, specially mem-brane proximal structures It is possible that such disruption decouples the biochem-ical signaling apparatus that is associated with the recognition receptors Another possibility is that infected cells produce an autocrine suppressive factor, although this possibility has not been fully investigated

1.2.2 IFN- g, Th1 Cells and Microbicidal Activity

Once present in the infected host, IL-12 activates NK cells to produce IFN-J and drives the proliferation of type 1 CD4+ and CD8+ T cells, which produce even more IFN-J IFN-J-producing cells is a central component to induce and maintain control

of parasite proliferation and dissemination during both acute and chronic infection (Yap and Sher 1999) Several factors are driven by IFN-J activation that have been

to shown to be involved in controlling intracellular parasite growth Macrophages harboring intracellular parasites and activated with IFN-J can produce nitric oxide, which, in turn, is responsible for microbicidal/microbiostatic control of intracellular parasite growth Intriguingly, even though IFN-J-induced microbicidal mechanisms are potent, the machinery is not 100% effective at eliminating parasites (Yap and Sher 1999) During the chronic phase, some parasites evade immunity and survive within the host for long periods, despite the continuing survey of the immune system

in search of released parasites

Interestingly, among the genetic clusters upon which the strains of T gondii are

grouped, some present extremely high virulence, leading to rodent host death prior

to opportunity for viable transmission Such parasite strains have shown weaker innate immune activating properties Suggesting that for the lack of some evolution-ary pressure, those strains present little to no adaptation to mouse hosts

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With the onset of the chronic phase parasites make use of two major mechanisms

to evade immune responses:

1 Parasites become less susceptible to host microbicidal activity; and/or,

2 Parasites induce immunosuppressive factors that dampen immune effector activity, including the production of pro-inﬂammatory mediators

As an example of an evasion of immune response mechanism, it is well-known that a several microbes escape effector immunity through the actions of membrane receptors or cytoplasmic enzymes that inactivate or neutralize effector molecules, including a complement factors (Karp and Wills-Karp 2001), superoxide or nitric

oxide As an example, during T gondii infection, complement receptors are activated

inducing expression of peroxiredoxins (Son et al 2001) It seems obvious to late that those evasion strategies may increase the frequency of persisting parasites within the host, despite ongoing potent immunity As an alternative, modulatory or anti-inﬂammatory factors could be selectively enhanced by the pathogen leading to inhibition of the migration, proliferation or differentiation of effector cells at the infection foci, favoring the evasion of the pathogen from protective immunity and progression towards the development of chronic disease

specu-1.3 Pro-resolution Strategies as a Mechanism

to Prevent Immunopathology

1.3.1 Resolution Phase of the Inﬂammatory Response

In general, protective pro-inflammatory response ultimately clears the tissues of both the cause and consequences of tissue injury that can accompany host defense (Cotran and Pober 1990) If unresolved, acute inflammation may lead to chronic inflammation, scarring and eventual loss of function (Majno and Joris 1995)

A growing list of reports indicated that, in addition to classic diseases associated with inflammation, for example psoriasis, periodontal disease and arthritis, uncon-trolled inflammation governs the pathogenesis of many widely prevalent diseases including infectious, cardiovascular and cerebrovascular disease, cancer, obesity and Alzheimer’s disease (Libby 2002; Calder 2006) (Van Dyke and Serhan 2003) Prostaglandins and leukotrienes are initially produced locally at the inflammation site and are key in promoting the cardinal signs of inflammation Of interest, another class of arachidonic acid-derived mediators, the lipoxins (LXs) and aspirin- triggered lipoxins (ATLs), are mediators recently recognized to perform both endogenous anti-inflammatory and pro-resolving actions (Serhan 2005, 2007)

In the recent years, multiple previously unknown enzymatic pathways were tiﬁed to be present during the resolution phase Those are derived from the precursors EPA and DHA Both EPA and DHA are major n-3 fatty acids also widely known as the omega-3 PUFA or ﬁsh oils The new mediators are biosynthesized during the

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evolution of locally contained inflammatory exudates They possess potent actions in controlling the resolution (Serhan et al 2000, 2002; Hong et al 2003) Resolvins are endogenous, local-acting mediators that carry potent anti-inflammatory and immu-noregulatory signals (Serhan et al 2002) These include novel actions that are tar-geted to promote resolution, namely reducing neutrophil infiltration and regulating the cytokine-chemokine axis and reactive oxygen species and stimulating the uptake and clearance of apoptotic PMN as well as lowering the magnitude of the inflamma-tory response and associated pain (Serhan et al 2000, 2002; Svensson et al 2007) Protectins are biosynthesized in many organs and perform potent anti-inflammatory (Hong et al 2003) as well as protective actions demonstrated for the novel and potent DHA-derived 10,17-docasatriene in animal models of stroke (Marcheselli et al

2003) and Alzheimer’s disease (Lukiw et al 2005) Both families, the resolvins and protectins, are potent local-acting agonists of endogenous anti-inﬂammation and promote resolution speciﬁc processes (Serhan 2007)

IFN-J-dependent immune and its derived pro-inﬂammatory responses are tially extremely toxic to the host As an example, during chronic inﬂammatory dis-eases such as arthritis or Crohns’ disease, sustained or uncontrolled type 1 cytokine responses has been shown to cause serious damage to host tissues and organs In order

poten-to prevent that potential damage, several host mediapoten-tors and receppoten-tors have evolved poten-to counter host-damaging responses The homeostasis of the immune response is abso-lutely dependent on the presence of such counter regulatory pathways This complex network of anti-inﬂammatory pathways, given its actions, has been seized by patho-gens and used to their own beneﬁt to prevent parasite eradication

1.3.2 Interleukin-10

IL-10 is one of the most biologically active cytokine with anti-inﬂammatory ties besides TGF-E and IL-35 It can be produced by a growing list of activated immune cells, in particular monocytes/macrophages and T cell subsets including Tr1, Treg, and Th1 cells It acts via activation of a transmembrane receptor complex, which is composed of IL-10R1 and IL-10R2, and controls the activities of several immune cells In monocytes/macrophages, IL-10 inhibits the production of pro-inﬂammatory mediators and antigen processing and presentation Furthermore, IL-10 plays a relevant role in the differentiation/proliferation of B and T cells In general, its physiological relevance lies in the preventing over-whelming immune responses and, consequently, of tissue damage Simultaneously, IL-10 enhances the

proper-“scavenger”-like activities

To highlight its relevance in inhibiting immune responses during infectious eases, IL-10 is used by pathogens to evade the development of protective immunity Viruses, such as EBV, encode a viral IL-10-homologue that can initiate the signaling cascade as the one triggered by the mammalian cytokine (Salek-Ardakani et al

dis-2002) Poxviruses carry genes that encode IL-10 receptor homologues; therefore, cells expressing such receptors when in the presence of IL-10 become refractory to

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pro-inﬂammatory signals (Haig 1998) Moreover, IL-10 gene transfer has been shown to have anti-inﬂammatory actions in various pathologies associated with increased IFN-J, IL-1 or TNF production (van de Loo and van den Berg 2002, Wille

disease succumbing to T gondii infection in the earlier to mid-acute phase The

animals show severe inﬁltration of leukocytes and hepatic necrotic lesions in the liver as well as focal necrosis in small intestines, concomitant to high levels of IFN-J and TNF production (Suzuki et al 2000, Gazzinelli et al 1996) (Fig 1.2)

IL-10 was hypothesized to mediate immune evasion during T gondii infection,

given its immune modulatory activities Conversely, IL-10 has not been found to be directly related to the elements that potentially contribute to the mechanisms of

T gondii virulence Furthermore, the over-production of IL-10 has been shown to

perform no clear role in the pathways involved in driving persistence of T gondii in

the chronic stage (Wille et al 2001) In summary, it is clear that, besides IL-10, several other mechanisms of immune modulation/evasion used by the parasite and by the host are relevant to allow mutual survival (host and pathogen) for enough time to permit successful transmission and, ultimately for parasite survival as a species (Fig 1.3)

IL-12

NOIFN-

tachyzoite

C-18

Fig 1.2 Induction of pro-inﬂammatory responses during T gondii infection Immediately after

infection, host dendritic cells (DCs) produce IL-12 in response to products secreted by T gondii,

via the CCR5-binding cyclophillin-18 and the TLR11-activating proﬁllin IL-12 promotes the ferentiation and proliferation of type 1, IFN-J-producing T cells (CD4 + and CD8 + ) and NK cells

dif-In turn, IFN-J triggers host cells, including macrophages (MM) to exert microbicidal activity, such

as the production of nitric oxide, expression IDO and tryptophan depletion or autophagy

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During the interaction with macrophages, T gondii tachyzoites expose phosphatidyl

serine leading to the release of active TGF-E by infected macrophages (Seabra et al

2004) TGF-E is a well-known macrophage deactivator, including inhibition of NOS2 expression Neutralization of TGF-E abolished the inhibition of NO production, thus

reducing the persistence of intracellular T gondii in activated macrophages

Furthermore, the up-regulation of Smad 2 and 3 in infected macrophages conﬁrms that a TGF-E autocrine effect was caused by the T gondii infection It is clear that TGF-E is present during host/parasite interaction and that affects key aspects of host immune protective responses

The peroral route T gondii infection – an experimental model for the mucosal

host/pathogen interation that is characterized by ileitis mediated both by mediated tissue destruction as well as by the host immune responses Buzoni-Gatel

parasite-et al 2001 showed that intraepithelial lymphocytes present in the gut mucosa are the main producers of TGF-E (Butcher et al 2001) CD8+ T cells differentiate into TGF-E-producing cells The presence of this cytokine inhibits CD4+ T lymphocyte inﬁltration, macrophage activation and tissue destruction mediated by excessive IFN-J production (Mennechet et al 2004) Consequently, the hallmarks of TGF-E exposure are indeed present in lamina propria-resident CD4+ T cells, the up-regulation

of Smad2 and Smad3 (Fig 1.4)

1.3.4 IL-22

IL-22 is a member of the IL-10 cytokine family and signals through a heterodimeric receptor composed of the common IL-10R2 subunit and the IL-22R subunit IL-10 and IL-22 both activate the STAT3 signaling pathway Unlike IL-10, which is produced by a variety of cell types, IL-22 is made by only a subset of activated immune cells, preferentially by Th17 T cells, but also by Th1 cells and conventional

DC

M

4 8 IL-12

Fig 1.3 Central role of IL-10 in controlling pro-inﬂammatory responses during acute phase of

T gondii infection The potential cytotoxic effects of such activity are controlled, during the

mid-to-late acute phase, by IL-10 production at sites of high-level parasite replication, such as the liver and spleen IL-10 down-regulates pro-inﬂammatory cytokine and chemokine expression, as well

as the microbicidal activities of DCs, T cells, NK cells and macrophages

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12 J Aliberti

NK cells, JG CD3+ T cells, noncytolytic NK cells, lymphoid tissue inducer cells, and skin-homing IL-13+ T cells The receptor for IL-22 is distinct and consists of IL-22R, which most studies indicate is restricted to the surfaces of epithelial cells, keratino-

cytes, and some ﬁbroblasts, and IL-10R2, which is ubiquitous In fact, T gondii oral

infection triggers IL-22-mediated protection of the gut mucosal surfaces Suggesting

an additional mediator that provides an immune suppressive environment to control gut inﬂammation (Wilson et al 2010)

1.3.5 IL-27

IL-27 is a heterodimeric cytokine composed of Epstein-Barr virus–induced gene

3 (EBI3) and p28 It is known to signal through a receptor complex composed of the IL-27 receptor and gp130 Expression of IL-27R is confined to immune cells, its partner gp130, a shared receptor component of several cytokines including IL-6, is widely expressed both in and out of the immune system While IL-27 was initially known to promote T cell proliferation and the development of TH1 responses; it was subsequently indicated that it could suppress TH1 and TH2 responses during various parasitic infections In agreement with this observation, IL-27R-deficient mice develop exaggerated T helper cell responses during the acute stages of toxoplasmo-sis, Chagas disease and leishmaniasis and after helminth challenge Moreover, it was found that IL-27R-deficient mice develop exuberant CD4 + T cell responses in the CNS during chronic toxoplasmosis, in which the majority of the cells are expressing the pro-inflammatory cytokine IL-17 (Stumhofer et al 2006) In fact, IL-27 could inhibit in vitro differentiation of nạve T cells into the Th17 subset Thus, unveiling

a new mechanism to control inﬂammation in a very sensitive environment, the central nervous system (Fig 1.5)

Fig 1.4 The role of TGF-E and IL-22 in controlling gut mucosal immune responses after oral

infection with T gondii (a) During the interaction with macrophages, T gondii tachyzoites expose

phosphatidyl serine leading to the release of active TGF-E by infected macrophages (b) Gut mucosa intraepithelial lymphocytes produce TGF-E that inhibits CD4+ T lymphocyte inﬁltration, macrophage activation and tissue destruction mediated by excessive IFN-J production (c) IL-22 is made preferentially by Th17 T cells The receptor for IL-22 is distinct and consists of IL-22R, which is expressed by epithelial cells and the ubiquitous IL-10R2 IL-22 mediates protection

against mucosal damage during oral infection with T gondii

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challenge, which downregulated IL-12 production by DCs (Reis e Sousa et al

1999) The injection of STAg was found to trigger the endogenous release of an eicosanoid known as lipoxin A4 (LXA4) This mediator inhibited STAg-induced DC migration and IL-12 production in vivo and in vitro (Aliberti et al 2002a) Lipoxins have been show to have potent anti-inﬂammatory properties in several disease mod-els (Samuelsson 1991; Goh et al 2003; Van Dyke and Serhan 2003; Kieran et al

2004) Their actions include inhibition of leukotriene function, NK-cell function, leukocyte migration, TNF-induced chemokine production, NF-NB translocation, and chemokine receptor and adhesion molecule expression (Ramstedt et al 1985; Clish et al 1999; Hachicha et al 1999; Bandeira-Melo et al 2000; Ohira et al

2004) Lipoxins are known to bind to two main receptors — a seven-transmembrane G-protein coupled receptor, ALX/FPRL-1 (Maddox et al 1997), and a nuclear receptor, AhR (Schaldach et al 1999) Evidence indicating that ALX is mediating some, if not all, of the anti-inflammatory actions of lipoxins in vivo came from observations reporting that mice over-expressing human ALX have shorter and less severe inflammatory responses (Devchand et al 2003) Despite intense investiga-tion, it is not yet clear which of the two receptors are most important for the trigger-ing of lipoxin-derived anti-inflammatory responses There is evidence of a role for suppressors of cytokine signaling (SOCS) molecules in the induction of the anti-inflammatory effects seen after lipoxin exposure (Leonard et al 2002) The SOCS-family proteins, SOCS-1, -2 and -3, are thought to mediate their actions by binding

to the intracellular domains of cytokine or hormone receptors, thereby blocking activation of downstream signaling pathways (Alexander and Hilton 2004) On the other hand, these proteins may act as part of a ubiquitin ligase molecular complex that lead to proteasome-dependent degradation of transcription factors via their poly-ubiquitinylation (Kile et al 2002; Alexander and Hilton 2004) The molecular basis for lipoxin-induced SOCS expression and the control of pro-inﬂammatory responses is poorly understood (Fig 1.6)

4 8

IL-6TGF-IL-27

Th17

4

Fig 1.5 IL-27 and suppression of immune pathogenic cells in the central nervous system during

chronic toxoplasmosis Naive T cells suppressed the development Th17 cells mediated by IL-6 + TGF-E after exposure to IL-27

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14 J Aliberti

The biosynthetic cascades for the generation of lipoxin involve several complex trans-cellular pathways and therefore, it is unlikely to be only one cellular source for this mediator Nevertheless, production of LXA4 seen upon STAg stimulation is completely dependent of 5-lipoxygenase, indicating that the biosynthetic pathways involving this enzyme were crucial in this experimental setting for the production of LXA4 (Aliberti et al 2002b) 5-lipoxygenase is produced as a pro-peptide that is activated by cleavage, however, low levels of active 5-lipoxygenase are found in different cell types, including macrophages, platelets, DCs and neutrophils (Funk

et al 2002) The expression of a 5-lipoxygenase-activating protein (FLAP) seems to

be the key signal for induction of 5-lipoxygenase activity Although, at the moment,

it is not completely clear which cells are the source of lipoxygenase activity in vivo

during T gondii infection, it is evident that 5-lipoxygenase is required for

biosyn-thesis of LXA4 During T gondii infection, serum levels of LXA4 were found to steadily increase over most of the acute phase, and plateau at high levels through chronic disease (Aliberti et al 2002b) 5-lipoxygenase-deﬁcient animals succumbed

to T gondii infection at the early onset of chronic disease Immune responses against

the parasite were found to be increased in the absence of 5-lipoxygenase, with nificantly less brain cyst formation than in control animals By contrast, excessive pro-inflammatory cytokine secretion and massive brain inflammatory cell infiltra-tion was found The excessive pro-inflammatory response in the brain ultimately caused the death of the 5-lipoxygenase-deficient hosts (Aliberti et al 2002b)

sig-1.3.7 Redundancy and Control of Inﬂammation

IL-10, IL-27, TGF-E and lipoxins share several biological functions in terms of controlling inﬂammation Although it is tempting to suggest that they might play redundant roles, in vitro and in vivo evidence suggest otherwise For example,

the treatment of T gondii-infected 5-lipoxygenase-deﬁcient mice with IL-10 was

DC

M

48IL-12

Fig 1.6 Lipoxins and control of pro-inﬂammatory cytokine production during chronic toxoplasmosis

With the onset of chronic disease, LXA4 is produced and controls pro-inﬂammatory cytokine responses, mostly at sites where parasite replication might be occurring, such as the CNS, without interfering with the microbicidal activity of macrophages

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able to control some of the inﬂammation, but concomitant reactivation of parasite proliferation resulted in failure to rescue animals from mortality (Aliberti et al

2002b) In fact, it was also observed that IL-10 but not LXA4, effectively inhibited the microbicidal activity of macrophages (Aliberti et al 2002b) Another interesting apparent discrepancy between IL-10 and LXA4 biological actions was associated

with the pathological ﬁndings seen during T gondii infections of IL-10- versus

5-lipoxygenase-deficient mice While the former showed generalized lymphocytic infiltration and massive hepatic necrosis after infection, with little to no inflamma-tion in the brain; both liver and CNS infiltration was observed during infection of 5-lipoxygenase-deficient mice, indicating that these two anti-inflammatory mediators are released in a time and organ controlled fashion and play differentiated intracellular inhibitory pathways

The biochemical pathways involved in inhibition of pro-inﬂammatory responses during infection also support the concept that regulatory mechanisms follow distinct intracellular targets On one hand, while lipoxins trigger expression of the regula-tory protein SOCS2, IL-10 mediate their inhibition via up-regulation of SOCS1/SOCS3 and IL-27 do so via up-regulation of STAT3 (Machado et al 2006) TGF-E,

on the other hand, seems to mediate its functions via Smad proteins, including Smad2 and Smad3 It is likely that the particular aspects associated with each regu-latory mediator, i.e induction of tolerance, apoptosis, suppression of chemotaxis, can be traced back to their respective biochemical signature

1.3.8 Induction of Endogenous LXA4 as an Pathogen

Evasion Pathway

Several lines of evidence show that the anti-inﬂammatory actions of lipid mediators are used by pathogens, including fungi and helminths The modulation of host

immune responses is the desired effect The 5-lipoxygenase activity after T gondii

infection was known to be associated with splenic macrophages (Aliberti et al

2002b), the 15-lipoxygenase-expressing cell population was not known In order to identify the cell populations involved in mediating 15-lipoxygenase activity after

T gondii infection, Bannenberg and colleagues isolated an enzymatic activity in

tachyzoites exposed to calcium ionophore in the presence of arachidonic acid

in vitro (Bannenberg et al 2004) Moreover, proteomics analysis of derived lysates revealed the presence of peptides homologous to plant-derived type

tachyzoite-1 lipoxygenases (Bannenberg et al 2004) Therefore, it seems that the induction of

lipoxin biosynthesis by T gondii has been selected through the carrying of a plant-like

lipoxygenase gene, which together with the actions of host-derived 5-lipoxygenase results in lipoxin production High levels of lipoxin, subsequently, suppress immune responses providing hosts the ability to control parasite proliferation without suffering the damaging consequences of exuberant inﬂammation or tissue necrosis The molecular basis for 5-lipoxygenase induction after parasite stimulation has not been clariﬁed, it is known that this enzyme can be induced after leukocyte exposure to a

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16 J Aliberti

variety of stimuli, including PGE2 (Levy et al 2001) The interplay between these mediators, the induction of 5-lipoxygenase and the control of immune responses

in vivo await further investigation Another interesting observation that supports

the argument for a role of T gondii 15-lipoxygenase in immune evasion is the

presence of such enzymatic activity in an organism that does not have lipids that could serve as substrates for lipoxygenases Therefore, the substrate has to come from infected host cells

Pseudomonas aeruginosa 15-lipoxygenase-like enzyme is another example of a

pathogen carrying an enzyme whose substrate is only present in host cells (Vance

et al 2004) P aeruginosa is most commonly associated with chronic lung

infec-tions in patients with cystic fibrosis It is possible that the bacteria may use the 15-lipoxygenase pathway leading to lipoxin biosynthesis to promote suppression of inflammation and persist throughout chronic disease However, patients with cystic fibrosis fail to generate lipoxins in the lungs and the continuing proliferation of bacteria results in uncontrolled accumulation of activated neutrophils that ultimately lead to serious tissue damage with organ failure (Karp et al 2004) This constitutes the major pathology for the lung form of cystic fibrosis The relevance of pathogen-derived 15-lipoxygenase given the lack of lipoxin generation in the lungs of patients with cystic fibrosis and the severity of disease still remains to be elucidated (Fig 1.7)

Mycobacterium tuberculosis is another example of a lung-invading bacterium

that leads to a chronic disease, human tuberculosis is among the top infectious

dis-eases worldwide with enormous public health relevance M tuberculosis infection

is usually asymptomatic, granulomatous reaction in the lungs contain the bacilli and

O(O)H COOH OOH

COOH

OH OH HO

COOH

OH OH HO

O(O)H COOH OOH

COOH

COOH OOH

Fig 1.7 General and pathogen-dependent LXA4 biosynthetic pathways (a) General pathways for

LXA4 biosynthesis Arachidonic acid (AA), which is released in response to inﬂammatory stimuli,

is catalysed by 5-lipoxygenase (LO) to generate LTA4 This compound, secreted by leukocytes, is captured by neighboring platelets or endothelial cells, and, through the actions of 12- or 15-LO, respectively, is converted to LXA4 (b) Pathogen-dependent LXA4 biosynthetic pathway After the generation of LTA4 in a 5-LO-dependent manner, it is catalyzed by pathogen-secreted 15-LO into LXA4, which is then secreted by the infected cell

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prevents its spreading, and a readily-detectable cell-mediated immunity is usually found in exposed patients (Chan and Flynn 2004) However, mycobacterial growth increases and transmission of viable bacilli occurs, along with granuloma disruption and organ function is compromised whenever the immunological status of the hosts is suppressed (Flynn and Chan 2003) Initial pulmonary colonization by M tuberculosis

is a latent process with very little reaction occurring in the organ With the pathogen slowly establishing into the organ and with almost no intervention from the host innate immune system (Flynn and Chan 2003) Interestingly, it has been shown that

in the absence of endogenously generated LXA4, mice become more resistant to infection, with longer survival rates, lower bacterial counts and higher type 1 cell-mediated immunity against the bacilli (Baﬁca et al 2005) The mechanisms involved

in control of the immune response during tuberculosis is approached in detail in another chapter of this book

When comparing the outcomes of infections by T gondii versus M tuberculosis

in 5-lipoxygenase-deﬁcient animals a clear discrepancy becomes evident This cates a protective versus a host detrimental role for endogenously produced lipoxins,

indi-respectively While T gondii – a fast-replicating pathogen – that depends on keeping the host alive so that transmission can occur through predation, M tuberculosis –

slow growing, silent pathogen – requires high proliferation rates in lungs of infected hosts for transmission to occur Nevertheless, both cases indicate that lipoxin-dependent inhibition of pro-inﬂammatory type 1 responses provides a favorable environment for pathogen transmission Therefore, both the host and the pathogen rely on driving a well-balanced immune response

1.4 Conclusions

In summary, mechanisms that contain the breadth, intensity and duration of inﬂammatory functions of the immune system play apparent redundant roles Nevertheless, animal knockout models indicate otherwise A large body of evidence clearly establishes that TGF-E is a key player in modulating immune speciﬁc

pro-responses in the gut mucosal surfaces during oral infection with T gondii Another

organ highly sensitive to the presence of inﬂammatory reactions is the brain, geted by the parasite during chronic infection In this case, evidence point to the protective effects of IL-27 by inhibiting the differentiation of pathogenic Th17 cells

tar-in the nervous tissue While these mediators seem to play a localized role, several reports indicate that IL-10 plays a systemic role, with animals lacking IL-10 or its receptor showing widespread leukocyte inﬁltration, liver necrosis and mortality

after T gondii infection Although the presence of lipoxins in the serum is preceded

by IL-10, there is no evidence that the two mediators cross-regulate each other Moreover, their anti-inﬂammatory actions are overlapping but not redundant The emerging body of evidence including lipoxins as immune-regulatory mediators, and the potential use of their inhibitory effects for pathogen survival and replication, is still a poorly understood area of research Relevant questions including the nature of

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18 J Aliberti

the pathogen-derived signal (s) that induces lipoxin production, or whether the anti-inﬂammatory actions of lipoxins play a role in modulating the balance between Th1, Th2, Th17 and regulatory T cell responses await to be answered And, in addi-tion, the use of the lipoxygenase system and its mediators by pathogenic microbes

as a general mechanism for evasion and manipulation of immune responses as well

as pathogen persistence

The further investigation on the roles played by all of these mediators, their cellular sources, biochemical and cellular targets may provide the basis the develop-ment of novel therapeutic intervention strategies to enhance weak or inhibit undesirable pro-inﬂammatory immune responses in vivo

Acknowledgements Julio Aliberti is funded by grants from NIH (AI075038 and AI078969).

References

Alexander, W S and D J Hilton (2004) “The role of suppressors of cytokine signaling (SOCS)

proteins in regulation of the immune response.” Annu Rev Immunol 22: 503–29.

Aliberti, J., S Hieny, et al (2002) “Lipoxin-mediated inhibition of IL-12 production by DCs:

a mechanism for regulation of microbial immunity.” Nat Immunol 3(1): 76–82.

Aliberti, J., C Reis e Sousa, et al (2000) “CCR5 provides a signal for microbial induced production

of IL-12 by CD8 alpha + dendritic cells.” Nat Immunol 1(1): 83–7.

Aliberti, J., O Schulz, et al (2003) “Essential role for ICSBP in the in vivo development of murine

CD8alpha + dendritic cells.” Blood 101(1): 305–10.

Aliberti, J., C Serhan, et al (2002) “Parasite-induced lipoxin A4 is an endogenous regulator of

IL-12 production and immunopathology in Toxoplasma gondii infection.” J Exp Med 196(9):

1253–62.

Aliberti, J., J G Valenzuela, et al (2003) “Molecular mimicry of a CCR5 binding-domain in the

microbial activation of dendritic cells.” Nat Immunol 4(5): 485–90.

Baﬁca, A., C A Scanga, et al (2005) “Host control of Mycobacterium tuberculosis is regulated

by 5-lipoxygenase-dependent lipoxin production.” J Clin Invest 115(6): 1601–6.

Bandeira-Melo, C., P T Bozza, et al (2000) “Cutting edge: lipoxin (LX) A4 and aspirin-triggered

15-epi-LXA4 block allergen-induced eosinophil trafﬁcking.” J Immunol 164(5): 2267–71.

Bannenberg, G L., J Aliberti, et al (2004) “Exogenous pathogen and plant 15-lipoxygenase initiate

endogenous lipoxin A4 biosynthesis.” J Exp Med 199(4): 515–23.

Black, M W and J C Boothroyd (2000) “Lytic cycle of Toxoplasma gondii.” Microbiol Mol Biol

Rev 64(3): 607–23.

Butcher, B A., L Kim, et al (2001) “Toxoplasma gondii tachyzoites inhibit proinﬂammatory cytokine induction in infected macrophages by preventing nuclear translocation of the tran-

scription factor NF-kappa B.” J Immunol 167(4): 2193–201.

Buzoni-Gatel, D., H Debbabi, et al (2001) “Murine ileitis after intracellular parasite infection is

controlled by TGF-beta-producing intraepithelial lymphocytes.” Gastroenterology 120(4):

914–24.

Calder, P C (2006) “n-3 polyunsaturated fatty acids, inﬂammation, and inﬂammatory diseases.”

Am J Clin Nutr 83(6 Suppl): 1505 S–1519 S.

Chan, J and J Flynn (2004) “The immunological aspects of latency in tuberculosis.” Clin

Immunol 110(1): 2–12.

Clish, C B., J A O’Brien, et al (1999) “Local and systemic delivery of a stable aspirin-triggered

lipoxin prevents neutrophil recruitment in vivo.” Proc Natl Acad Sci USA 96(14): 8247–52.

Trang 30

Cotran, R S and J S Pober (1990) “Cytokine-endothelial interactions in inﬂammation, immunity,

and vascular injury.” J Am Soc Nephrol 1(3): 225–35.

Deckert-Schluter, M., C Buck, et al (1997) “Interleukin-10 downregulates the intracerebral

immune response in chronic Toxoplasma encephalitis.” J Neuroimmunol 76(1-2): 167–76.

Denkers, E Y (2003) “From cells to signaling cascades: manipulation of innate immunity by

Toxoplasma gondii.” FEMS Immunol Med Microbiol 39(3): 193–203.

Denkers, E Y and B A Butcher (2005) “Sabotage and exploitation in macrophages parasitized

by intracellular protozoans.” Trends Parasitol 21(1): 35–41.

Devchand, P R., M Arita, et al (2003) “Human ALX receptor regulates neutrophil recruitment in

transgenic mice: roles in inﬂammation and host defense.” Faseb J 17(6): 652–9.

Flynn, J L and J Chan (2003) “Immune evasion by Mycobacterium tuberculosis: living with the

enemy.” Curr Opin Immunol 15(4): 450–5.

Funk, C D., X S Chen, et al (2002) “Lipoxygenase genes and their targeted disruption.”

Prostaglandins Other Lipid Mediat 68-69: 303–12.

Gazzinelli, R T., M Wysocka, et al (1994) “Parasite-induced IL-12 stimulates early IFN-gamma

synthesis and resistance during acute infection with Toxoplasma gondii.” J Immunol 153(6):

2533–43.

Gazzinelli, R T., M Wysocka, et al (1996) “In the absence of endogenous IL-10, mice acutely infected with Toxoplasma gondii succumb to a lethal immune response dependent on CD4+ T cells and accompanied by overproduction of IL-12, IFN-gamma and TNF-alpha.” J Immunol

157(2): 798–805.

Goh, J., C Godson, et al (2003) “Lipoxins: pro-resolution lipid mediators in intestinal inﬂammation.”

Gastroenterology 124(4): 1043–54.

Golding, H., J Aliberti, et al (2003) “Inhibition of HIV-1 infection by a CCR5-binding cyclophilin

from Toxoplasma gondii.” Blood 102(9): 3280–6.

Golding, H., S Khurana, et al (2005) “CCR5 N-terminal region plays a critical role in HIV-1

inhibition by Toxoplasma gondii-derived cyclophilin-18.” J Biol Chem 280(33): 29570–7.

Hachicha, M., M Pouliot, et al (1999) “Lipoxin (LX)A4 and aspirin-triggered 15-epi-LXA4 inhibit tumor necrosis factor 1alpha-initiated neutrophil responses and trafﬁcking: regulators of

a cytokine-chemokine axis.” J Exp Med 189(12): 1923–30.

Haig, D M (1998) “Poxvirus interference with the host cytokine response.” Vet Immunol

tumor necrosis factor alpha.” Infect Immun 62(7): 2818–24.

Karp, C L., L M Flick, et al (2004) “Defective lipoxin-mediated anti-inﬂammatory activity in

the cystic ﬁbrosis airway.” Nat Immunol 5(4): 388–92.

Karp, C L and M Wills-Karp (2001) “Complement and IL-12: yin and yang.” Microbes Infect

3(2): 109–19.

Khan, I A., S Y Thomas, et al (2006) “CCR5 is essential for NK cell trafﬁcking and host survival

following Toxoplasma gondii infection.” PLoS Pathog 2(6): e49.

Kieran, N E., P Maderna, et al (2004) “Lipoxins: potential anti-inﬂammatory, proresolution, and

antiﬁbrotic mediators in renal disease.” Kidney Int 65(4): 1145–54.

Kile, B T., B A Schulman, et al (2002) “The SOCS box: a tale of destruction and degradation.”

Trends Biochem Sci 27(5): 235–41.

Leonard, M O., K Hannan, et al (2002) “15-Epi-16-(para-ﬂuorophenoxy)-lipoxin A(4)-methyl ester, a synthetic analogue of 15-epi-lipoxin A(4), is protective in experimental ischemic acute

renal failure.” J Am Soc Nephrol 13(6): 1657–62.

Trang 31

20 J Aliberti

Levy, B D., C B Clish, et al (2001) “Lipid mediator class switching during acute inﬂammation:

signals in resolution.” Nat Immunol 2(7): 612–9.

Libby, P (2002) “Inﬂammation in atherosclerosis.” Nature 420(6917): 868–74.

Lukiw, W J., J G Cui, et al (2005) “A role for docosahexaenoic acid-derived neuroprotectin D1

in neural cell survival and Alzheimer disease.” J Clin Invest 115(10): 2774–83.

Machado, F S., J E Johndrow, et al (2006) “Anti-inﬂammatory actions of lipoxin A4 and

aspirin-triggered lipoxin are SOCS-2 dependent.” Nat Med 12(3): 330–4.

Maddox, J F., M Hachicha, et al (1997) “Lipoxin A4 stable analogs are potent mimetics that stimulate human monocytes and THP-1 cells via a G-protein-linked lipoxin A4 receptor.”

J Biol Chem 272(11): 6972–8.

Majno, G and I Joris (1995) “Apoptosis, oncosis, and necrosis An overview of cell death.” Am

J Pathol 146(1): 3–15.

Marcheselli, V L., S Hong, et al (2003) “Novel docosanoids inhibit brain

ischemia-reperfusion-mediated leukocyte inﬁltration and pro-inﬂammatory gene expression.” J Biol Chem 278(44):

43807–17.

Martinez, A J., M Sell, et al (1995) “The neuropathology and epidemiology of AIDS A Berlin

experience A review of 200 cases.” Pathol Res Pract 191(5): 427–43.

Mason, N J., J Fiore, et al (2004) “TRAF6-dependent mitogen-activated protein kinase activation differentially regulates the production of interleukin-12 by macrophages in response to

Toxoplasma gondii.” Infect Immun 72(10): 5662–7.

Mennechet, F J., L H Kasper, et al (2004) “Intestinal intraepithelial lymphocytes prevent driven inﬂammation and regulate the Smad/T-bet pathway of lamina propria CD4+ T cells.” Eur J

pathogen-Immunol 34(4): 1059–67.

Morisaki, J H., J E Heuser, et al (1995) “Invasion of Toxoplasma gondii occurs by active

penetration of the host cell.” J Cell Sci 108 ( Pt 6): 2457–64.

Mun, H S., F Aosai, et al (2003) “TLR2 as an essential molecule for protective immunity against

Toxoplasma gondii infection.” Int Immunol 15(9): 1081–7.

Ohira, T., G Bannenberg, et al (2004) “A stable aspirin-triggered lipoxin A4 analog blocks

phos-phorylation of leukocyte-speciﬁc protein 1 in human neutrophils.” J Immunol 173(3): 2091–8.

Ramstedt, U., J Ng, et al (1985) “Action of novel eicosanoids lipoxin A and B on human natural killer cell cytotoxicity: effects on intracellular cAMP and target cell binding.” J Immunol

135(5): 3434–8.

Reis e Sousa, C., S Hieny, et al (1997) “In vivo microbial stimulation induces rapid CD40 independent production of interleukin 12 by dendritic cells and their redistribution to T cell

ligand-areas.” J Exp Med 186(11): 1819–29.

Reis e Sousa, C., G Yap, et al (1999) “Paralysis of dendritic cell IL-12 production by microbial

products prevents infection-induced immunopathology.” Immunity 11(5): 637–47.

Salek-Ardakani, S., J R Arrand, et al (2002) “Epstein-Barr virus encoded interleukin-10 inhibits HLA-class I, ICAM-1, and B7 expression on human monocytes: implications for immune eva-

sion by EBV.” Virology 304(2): 342–51.

Samuelsson, B (1991) “Arachidonic acid metabolism: role in inﬂammation.” Z Rheumatol 50

protein-interleukin 12 p40 induction.” J Exp Med 186(9): 1523–34.

Seabra, S H., W de Souza, et al (2004) “Toxoplasma gondii exposes phosphatidylserine inducing

a TGF-beta1 autocrine effect orchestrating macrophage evasion.” Biochem Biophys Res

Commun 324(2): 744–52.

Serhan, C N (2005) “Novel eicosanoid and docosanoid mediators: resolvins, docosatrienes, and

neuroprotectins.” Curr Opin Clin Nutr Metab Care 8(2): 115–21.

Trang 32

Serhan, C N (2007) “Resolution phase of inﬂammation: novel endogenous anti-inﬂammatory

and proresolving lipid mediators and pathways.” Annu Rev Immunol 25: 101–37.

Serhan, C N., C B Clish, et al (2000) “Novel functional sets of lipid-derived mediators with inﬂammatory actions generated from omega-3 fatty acids via cyclooxygenase 2-nonsteroidal

anti-antiinﬂammatory drugs and transcellular processing.” J Exp Med 192(8): 1197–204.

Serhan, C N., S Hong, et al (2002) “Resolvins: a family of bioactive products of omega-3 fatty acid transformation circuits initiated by aspirin treatment that counter proinﬂammation signals.”

J Exp Med 196(8): 1025–37.

Sher, A., I P Oswald, et al (1993) “Toxoplasma gondii induces a T-independent IFN-gamma response in natural killer cells that requires both adherent accessory cells and tumor necrosis

factor-alpha.” J Immunol 150(9): 3982–9.

Son, E S., K J Song, et al (2001) “Molecular cloning and characterization of peroxiredoxin

from Toxoplasma gondii.” Korean J Parasitol 39(2): 133–41.

Stumhofer, J S., A Laurence, et al (2006) “Interleukin 27 negatively regulates the development

of interleukin 17-producing T helper cells during chronic inﬂammation of the central nervous

system.” Nat Immunol 7(9): 937–45.

Sukhumavasi, W., C E Egan, et al (2007) “Mouse neutrophils require JNK2 MAPK for Toxoplasma

gondii-induced IL-12p40 and CCL2/MCP-1 release.” J Immunol 179(6): 3570–7.

Sukhumavasi, W., A L Warren, et al (2010) “Absence of mitogen-activated protein kinase family member c-Jun N-terminal kinase-2 enhances resistance to Toxoplasma gondii.” Exp Parasitol

126(3): 415–20

Suzuki, Y., A Sher, et al (2000) “IL-10 is required for prevention of necrosis in the small intestine and mortality in both genetically resistant BALB/c and susceptible C57BL/6 mice following

peroral infection with Toxoplasma gondii.” J Immunol 164(10): 5375–82.

Svensson, C I., M Zattoni, et al (2007) “Lipoxins and aspirin-triggered lipoxin inhibit

inﬂamma-tory pain processing.” J Exp Med 204(2): 245–52.

Tato, C M., N Mason, et al (2006) “Opposing roles of NF-kappaB family members in the regulation

of NK cell proliferation and production of IFN-gamma.” Int Immunol 18(4): 505–13.

Trinchieri, G (2003) “Interleukin-12 and the regulation of innate resistance and adaptive

immu-nity.” Nat Rev Immunol 3(2): 133–46.

Tsujimura, H., T Tamura, et al (2003) “ICSBP/IRF-8 retrovirus transduction rescues dendritic

cell development in vitro.” Blood 101(3): 961–9.

van de Loo, F A and W B van den Berg (2002) “Gene therapy for rheumatoid arthritis Lessons from animal models, including studies on interleukin-4, interleukin-10, and interleukin-1 receptor

antagonist as potential disease modulators.” Rheum Dis Clin North Am 28(1): 127–49.

Van Dyke, T E and C N Serhan (2003) “Resolution of inﬂammation: a new paradigm for the

pathogenesis of periodontal diseases.” J Dent Res 82(2): 82–90.

Vance, R E., S Hong, et al (2004) “The opportunistic pathogen Pseudomonas aeruginosa carries

a secretable arachidonate 15-lipoxygenase.” Proc Natl Acad Sci USA 101(7): 2135–9.

Walker, M E., E E Hjort, et al (2008) “Toxoplasma gondii actively remodels the microtubule

network in host cells.” Microbes Infect 10(14-15): 1440–9.

Wille, U., E N Villegas, et al (2001) “Interleukin-10 does not contribute to the pathogenesis of a

virulent strain of Toxoplasma gondii.” Parasite Immunol 23(6): 291–6.

Wilson, M S., C G Feng, et al (2010) “Redundant and pathogenic roles for IL-22 in mycobacterial,

protozoan, and helminth infections.” J Immunol 184(8): 4378–90.

Yap, G S and A Sher (1999) “Cell-mediated immunity to Toxoplasma gondii: initiation,

regula-tion and effector funcregula-tion.” Immunobiology 201(2): 240–7.

Yarovinsky, F., D Zhang, et al (2005) “TLR11 activation of dendritic cells by a protozoan

proﬁlin-like protein.” Science 308(5728): 1626–9.

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J Aliberti (ed.), Control of Innate and Adaptive Immune Responses

during Infectious Diseases, DOI 10.1007/978-1-4614-0484-2_2,

Abstract An integrated response of the host is essential in health and disease Upon microbial exposure, infected hosts strictly regulate immune responses to both contain pathogen dissemination and modulate immunopathology-associated effects, thus preventing mortality In addition to a variety of molecules, such potent responses are kept under tight control by a class of anti-inﬂammatory eicosanoids, the lipoxins Lipoxins are induced following exposure to several infectious agents and can func-tion as immuno-modulatory molecules A number of observations made in animal models of infection and human studies indicate that such lipid mediators play a critical role in controlling early as well as chronic immune responses This chapter summarizes the role of cytokines and lipoxins in regulating innate immune responses

to a major human pathogen, Mycobaterium tuberculosis.

2.1 Introduction

Despite more than 100 years of research, tuberculosis is still the most important

bacterial infection worldwide The discovery of Mycobacterium tuberculosis as the

causative agent of TB was announced by Robert Koch in 1882 (Koch 1891) In his lecture Koch, who received the 1905 Nobel Prize for his discoveries, reminded his audience that one in seven human beings died of tuberculosis Every year, it is estimated that tuberculosis causes around 1.5 million mortalities with 8 million new cases reported (Barber et al 2009) In general, most infections are controlled by the host’s immune system, leading to latency with persistent/dormant bacteria The World Health Organization estimates that one-third of the world population

A Baﬁca ( * )

Department of Microbiology, Immunology and Parasitology,

Federal University of Santa Catarina, Florianopolis, SC, Brazil

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24 A Baﬁca and J Aliberti

carries the bacilli however only 10% of them will develop clinical disease Acquired immunodeﬁciency syndrome (AIDS) and other immune-compromising conditions greatly increases the risk of developing active tuberculosis, supporting the observa-

tion that protective immunity suppress M tuberculosis infection.

The only vaccine against tuberculosis, M bovis Bacillus Calmette Guerin (BCG),

has proven to be of low efﬁcacy against the most frequent outcome of tuberculosis, lung infection in adults (Fine 1995) Furthermore, with the current treatment requiring

up to three drugs and a high degree of patient compliance, the number of multi drug resistant (MDR) isolates is on the rise in many areas of the world The urgency to develop more effective vaccines or immunotherapies requires potent immune activating strategies at the interface of innate and adaptive immunity

2.2 Infection and Innate Immunity

2.2.1 Neutrophils

In the presence of pro-inﬂammatory stimulus, neutrophils are among the ﬁrst innate immune cells to migrate from the blood to the foci Neutrophils are professional phagocytes and express a range of receptors that can recognize opsonized and non-opsonized microbes, which are rapidly killed upon fusion of the phagosome with lysosomal compartments and specialized cytoplasmic granules that contain a vast arsenal of antimicrobial effector molecules including D-defensins, proteases as well

as iron and siderophore-binding molecules, i.e lactoferrin and lipocalin, tively (Segal 2005; Appelberg 2007) In addition to direct microbicidal activity, neutrophils drive cell migration via production of chemokines as well as produce pro-inﬂammatory cytokines in response to microbial pattern recognition receptor stimulation

respec-Neutrophillic inﬁltrates had been reported during acute pulmonary tuberculosis both in clinical studies and experimental infections (non-aerosol infection models) (Appelberg 1992; Condos et al 1998; Schluger and Rom 1998; Lasco et al 2004) However, the role of neutrophils during tuberculosis is still controversial The lack

of a selective neutrophil deﬁcient model has stiﬂed the studies in this area However, investigators have used antibody-mediated depletion models to question the role of neutrophils during tuberculosis Pedrosa and colleagues studied BALB/c infected

with a high intravenous dose of M tuberculosis Erdmann and the effect of early

(days 0, 2 and 4 post infection) and late (days 16, 18 and 20 post infection) depletion

of neutrophils (Pedrosa et al 2000) While later neutrophil depletion did not show a

quantiﬁable effect on M tuberculosis proliferation in the lungs, earlier neutrophil

depletions impaired development of protection against mycobacterial challenge Further evidence in favor of an early protective role for neutrophils is provided by the observation that intra-tracheal injection of pre-activated neutrophils protected

Fischer rats from infection with M tuberculosis Kurono (Sugawara et al 2004)

On the other hand, other studies failed to show any protective effect when C57Bl/6

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2 Mechanisms of Host Protection and Pathogen Evasion of Immune Response…

mice were challenged via the aerosol route (Seiler et al 2000), suggesting that neutrophils do not play an essential part in the early control of infection with

M tuberculosis Yet in another report, the investigators compared the mouse strains

genetically resistant (A/Sn) versus susceptible (I/St) to M tuberculosis and concluded that upon aerosol infection with M tuberculosis H37Rv, neutrophils con-

tribute to pathology rather than protection (Eruslanov et al 2005) This controversy may be partially explained by genetic differences among strains of experimental

animals as well as different laboratory strains of M tuberculosis.

Another approach to the potential role of neutrophils during tuberculosis has been raised by a series of studies where it has been shown that apoptotic neutrophils can modulate the induction of acquired immunity by dendritic cells (Aleman et al

2002, 2005, 2007; Tan et al 2006), or provide “help” to M tuberculosis-infected

macrophages in vitro (Tan et al 2006), via delivery of antimicrobial contents of

neutrophil granules to M tuberculosis-containing phagosomes shortly after uptake

of apoptotic neutrophils, leading to improved killing of mycobacteria mediated by the neutrophil D-defensin HNP-1

2.2.2 T Cells

The in vivo mouse model of low-dose aerosol M tuberculosis exposure produces a

very low cellular response, especially when comparing to those responses seen after some viral or other fast-replicating bacteria These differences in robustness of responses may reﬂect an immune-modulatory activities triggered by the pathogen

or may simply result from the inoculum route and dose During natural as well as

during experimental aerosol exposure, M tuberculosis enters the lung in droplets of

3–5 Pm of diameter (typically generated by a cough of a diseased individual), only

a few bacilli might be found within these droplets Furthermore, those droplets will

most likely settle within the alveolar space It should also be noted that M tuberculosis

is relative slow grower, with estimated duplication time of approximately 28 h to double in vivo (Dunn and North 1995) Therefore, the optimal conditions for an invading bacilli to initiate the cascade that lead to powerful cellular immune response are extremely low and greatly dependent on the inoculum dose as well as the poten-tial to reach professional antigen-presenting cells and secondary lymphoid tissues, such as the draining lymph nodes Consistent with this observation is the fact that it

is possible to detect early T-cell activation in the lymph nodes draining the lung but not within the lung itself (Chackerian et al 2001) In order to investigate mycobac-teria antigen-specific T cell activation, T-cell receptor transgenic (TCRTg) T cells specific for an IAb-restricted epitope of the early secreted antigenic target 6 kDa protein (ESAT-6) or for an IAb-restricted epitope of the essential mycolyl trans-ferase of Mtb, Ag85The activation of naive T cells has been had been used The published data show a significant up-regulation of an early marker of T cell activation (CD69) as well as proliferation of nạve T cell in the draining nodes of the lung, which is concomitant to the arrival of the bacilli in the node (Reiley et al 2008;

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Wolf et al 2008) The lag between bacterial proliferation in the lungs and the growth and differentiation of effector T cells constitute the basis for the apparent slow

cellular immune response during M tuberculosis.

2.2.3 Dendritic Cells

Fluorescent bacteria delivered by aerosol can be seen within dendritic cells (DCs) and cannot be detected in the lymph node (Wolf et al 2007) More importantly, if the chemotactic signals responsible for DC migration towards the lymph node are absent,

the appearance of M tuberculosis in that organ is inhibited (Wolf et al 2007) It has recently been shown that appearance of microbially activated (or infected) DCs in the lymph node is dependent on the presence of homodimers of IL-12p40 (Khader

et al 2006), previously supposed to act as an endogenous antagonist for the promoting cytokine IL-12p70 This was supported by the ﬁndings that while mice that deﬁciency of IL-12p70 or IL-23 could induce accumulation of activated CD41 T cells in the lung 21 days after infection, mice that lacked IL-12p40 could not (Khader

Th1-et al 2006) The investigators found that this IL-12p40(2) was very rapid (under 3 h) and drove DC migration via up-regulation of responsiveness to CCL19/CCL21 (CCR7 ligands) If DC did not produce IL-12p40, then migration in response to CCL19 and CCL21 remained at the level of the non-activated DC, despite presence

of M tuberculosis (Khader et al 2006) On the other hand, DCs lacking IL-12p35, IL-23p19, or both of these cytokine components respond to CCL19 and CCL21

when incubated with M tuberculosis (Khader et al 2006) The mechanisms by which IL-12p40(2) mediated up-regulation of CCR7 responsiveness is not yet understood

DC accumulation in the lymph node provides environmental cues to the immune system Notably, bacterially activated DCs will drive the nạve T cell activation, growth and differentiation In agreement with this observation, it was shown that

M tuberculosis-exposed DCs adoptively transferred to the lung could provide the

signals to drive T-helper 1 cell development (Bhatt et al 2004) These data also support the paradigm that the mechanisms that modulate the appearance of functional effector

T cells depend directly upon the DC activation status and subset and that there are no redundancies that could compensate for by the intact host cells within the node

2.2.4 Natural Killer Cells

Natural killer (NK) cells are innate granular lymphocytes (Lodoen and Lanier 2006; Newman and Riley 2007; Moretta et al 2008) known to play a role in mediating in allograft rejection and killing of transformed and virus-infected cells Additionally,

NK cells secrete pro-inﬂammatory cytokines, most prominently IFN-J NK cell activity is controlled by cytokines (IL-12, IL-18 and IFN-D in particular) and a complex repertoire of activating (e.g NKG2D, natural cytotoxicity receptors) and inhibitory receptors (e.g CD94-NKG2A)

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It has become evident that NK cells are capable of mounting a vigorous

response to M tuberculosis Human NK cells express granulysin within their

intra- cytoplasmic granules and it has been shown that this peptide could directly

kill M tuberculosis (Stenger et al 1999) Moreover, human NK cells are known to

directly lyse M tuberculosis-infected monocytes and macrophages in vitro (Denis

1994; Vankayalapati et al 2002) The activation occurs via triggering of NKG2D and NKp46 that bind to the stress-induced ligands UL16-binding protein 1 (ULPB1) and vimentin, respectively (Vankayalapati et al 2002, 2005; Garg et al 2006) Human NK cells can also actively inhibit mycobacterial growth via induction of apoptotic cell deaths (Brill et al 2001; Millman et al 2008)

During experimental infections with M tuberculosis it was found that NK cells

accumulate start to accumulate in the lungs and secrete IFN-J after approximately

2 weeks after low dose aerosol infection with M tuberculosis Erdmann

(Junqueira-Kipnis et al 2003) NK cell depletion showed no effect on control of mycobacterial growth Feng and colleagues provided evidence for this hypothesis when they demonstrated that NK cells are the principal source of IFN-J in T cell-deﬁcient

RAG2−/− animals after low-dose M tuberculosis H37Rv infection Most

impor-tantly, that NK cell-derived IFN-J was essential for controlling the pathology (Feng

et al 2006) In the absence of both NK and T cells (RAG2−/− Jc−/−), the control of mycobacterial growth was severely abolished, indicating that NK cells can drive cellular responses against mycobacteria

2.2.5 Regulatory T Cells

Regulatory T cells (T regs) were found to accumulate in the lungs of mice during

experimental M tuberculosis infection and bacterial control is improved after their

depletion (Scott-Browne et al 2007) In humans, it was shown that mannose-capped lipoarabinomannan (ManLAM) drove expansion of CD4 + CD25 + FoxP3+ cells in samples from tuberculin responders but not from nạve individuals (Garg et al

2008) ManLAM is thought to trigger macrophages to produce PGE2, which in turn allows for further Treg expansion (Garg et al 2008) Interestingly, TB patients show higher frequency of Treg cells than in healthy tuberculin responders (Garg et al

2008) During anti-viral therapy, AIDS/TB patients, show an increase in both effector T cells and T regs, however the regulatory activity of the T regs is defective (Seddiki et al 2009)

2.3 Granuloma Formation and Containment of Bacilli

Granuloma is an organized collection of immune cells, including a large proportion

of macrophages, within a tissue as a result of chronic unresolved/persistent inﬂammatory stimulus The purpose of the granuloma for the host is two-fold

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Firstly, through a ﬁbrous capsule is thought to provide a physical containment of the infected area while preventing pathogen spread Secondly, it aggregates a collection

of immune effector cells including APCs, lymphocytes and granulocytesa crucial step during the development of immunity to infection The tuberculous granuloma has been described by Ghon in 1912, however only in recent years an accurate depiction of primary human granulomas has allowed a better understanding of their role during tuberculosis

Frequently, an area of necrosis if found at the inner region of the tuberculosis granuloma This is thought to be a consequence from previous extensive macrophage infection and killing However, the granuloma also allows the chronic maintenance

of M tuberculosis in infected macrophages Notably, while the core of the

granu-loma carries few antigen-presenting cells containing mycobacterial antigens, the periphery of the granuloma is enriched with organized aggregates of APC and pro-liferating lymphocytes and are thought to be a site of active immunity (Ulrichs and Kaufmann 2006) In summary, tuberculosis granuloma can be considered both an essential player in the protective immune response to the pathogen and a facilitator

in the development of latency during chronic disease, which is hard for the immune system to tackle and is notoriously difﬁcult to treat by conventional methods

2.3.1 TNF

TNF has extensively studied during experimental mouse M tuberculosis infections

It has been shown that it is central for the development of protective immune response both during acute and chronic disease, notably from the poor granuloma formation observed in vivo as well as defective macrophage activity (Flynn et al

1995; Mohan et al 2001; Algood et al 2005) Other experimental M tuberculosis

infection models, such as zebraﬁsh and nonhuman primate have shown that TNF is relevant for the mechanisms involved in overcoming acute infection and to prevent disease reactivation, however, granuloma formation is not affected by TNF deple-tion (Lin et al 2010; Clay et al 2008) More importantly, genetic polymorphism of the TNF receptor in humans has been associated with increased susceptibility to active TB in Africa (Moller et al.), which is strongly supported by the increased frequency of re-activated tuberculosis among patients treated with TNF antagonists (Keane 2004) Despite the majority of these cases were from tuberculosis reactiva-tion, there is increased concern over the risk of fulminant acute tuberculosis within highly endemic areas

TNF is a pleiotropic cytokine that can affect several arms of the immune system During early tuberculosis infection, it has been associated with the induction of adhesion molecules (Windish et al 2009) and chemokines (Peters et al 2001; Scott and Flynn 2002; Algood et al 2004), which can perform potentially protective roles during the initiation and expansion of immune responses Another possible aspect that can be affected by TNF is programmed cell death, as a mediator of apoptosis, TNF can be directly detrimental to the survival of mycobacteria within macrophages

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Human TNF production by M tuberculosis infected alveolar macrophages triggers

apoptotic cell death, thereby reducing intracellular bacterial burden (Keane et al

1997) Moreover, attenuated M tuberculosis strains were found to increase apoptosis

and, consequently induce stronger CD8 T cell protective responses, indicating that apoptosis is associated with a better outcome of infection (Hinchey et al 2007)

2.3.2 IFN- g

IFN-J is a central cytokine in the initiation and effector function of cellular immune

responses During experimental M tuberculosis infection, the absence of IFN-J

leads to uncontrolled bacilli growth and mortality (Cooper et al 1993) The stream IFN-J-inducible enzymes required for generation of nitrogen and oxygen radicals, nitric oxide synthase 2 (NOS2) and p47phox, are also relevant for control

down-of immunopathology (Cooper et al 2002)

2.3.3 Lipoxins

We have reported evidence for the role of a pathway involving the 5-LO–dependent

production of lipoxins that dampens M tuberculosis–driven pro-inﬂammatory

immune responses and regulates bacterial growth Lung tissue from 5-LO-deﬁcient animals display higher production of IL-12 and other pro-inﬂammatory cytokines, suggesting that 5-LO-dependent eicosanoids counter-balance such secreted pro-teins Since 5-LO is required for both leukotriene and lipoxin biosynthesis, recon-stitution experiments were performed to more directly assess the role of the latter group of eicosanoids in the regulation of mycobacterial growth in vivo Importantly,

administration of the stable lipoxin analog – ATLa2 to M tuberculosis-infected

5-LO-deficient mice, restored both pulmonary mycobacterial loads and matory cytokine production These observations demonstrated that deficiency in lipoxins is sufficient to explain the effects on bacterial growth and host response seen in the infected 5-LO–deficient animals Interestingly, granuloma formation in 5-LO-deficient mice was found to be altered suggesting that lipoxins regulate chemotaxis of inflammatory monocytes to the site of infection and/or activation of macrophages in vivo (Bafica et al 2005) Nevertheless, whether lipoxins directly control influx/efflux of lung antigen presenting cells is still unclear

pro-inflam-A role for products derived from 5-LO, encoded by pro-inflam-ALOX5 gene, in pulmonary tuberculosis was further supported in human association studies In humans, ALOX5 gene comprises 14 exons and 13 introns approximately 82 kb on chromosome ten (10q11.2) ALOX5 promoter is GC-rich, and the region between 79 and 56 bp is essential for gene expression (Herb et al 2008) In that region, a variable number of tandem repeats (VNTR) has been identified, consisting of [5c-GGGCGG-3c]2–8, which are targets for binding of the transcription factor Sp1 Insertions or deletions

Tiêu đề	Control of Innate and Adaptive Immune Responses during Infectious Diseases
Người hướng dẫn	Julio Aliberti, Editor
Trường học	University of Cincinnati
Chuyên ngành	Molecular Immunology and Pulmonary Medicine
Thể loại	Book
Năm xuất bản	2012
Thành phố	Cincinnati

Định dạng
Số trang	189
Dung lượng	2,5 MB