Innate Immune Responses to LCMV Armstrong and Clone 13 and Their Influence on the Development of Acquired Immunity Pubblico

Abstract

Infection of mice with LCMV Armstrong (ARM) or Clone 13 (C13), results in acute and chronic infections respectively. However the early cellular and molecular mechanisms that mediate these disparate outcomes are poorly understood. We have characterized the innate immune responses that occur during acute and chronic LCMV infection, with a view to identifying early correlates and mechanisms of the later immune responses and viral loads. Two temporally distinct phases of innate immune response were observed: early DC responses during the first 72 hours of infection, and later myeloid cell expansion peaking at day 14 post infection.

During the first 72h of infection with ARM or C13, dendritic cells (DCs) upregulated activation markers, and produced innate cytokines independent of viral strain. CD8α+ and CD8α− DC populations decreased following activation, with CD8α+ DC nearly absent by 72h post infection. Finally, DCs and myeloid cells enriched during the first two days of ARM and C13 infection similarly stimulated OT-1 T cells in vitro.

In the second phase, by day 7, myeloid cells were expanded in the spleen and the blood during both infections. However, while myeloid cells contracted during ARM infection, C13 infection increased and sustained high numbers myeloid cells, peaking at day 14. Ly6Chi monocytic cells expanded during C13 infection had the morphology and phenotype of myeloid-derived suppressor cells (MDSC) and potently suppressed T cell proliferation. Blocking iNOS or IFN-γ abrogated the suppressive function of these cells. CCR2−⁄− mice showed impaired mobilization of myeloid cells during C13 infection, and had enhanced anti-viral T cell function. By administering anti-Gr-1 antibody to C13 infected mice we were able to temporarily deplete myeloid cells, leading to increased cytokine production by LCMV-specific CD8+ T cells. Early innate immune responses to ARM and C13 are indistinguishable by classical methods of measuring activation and T cell stimulatory function. However, during chronic infection myeloid cells become massively expanded and are able to inhibit T cell proliferation and function, contributing to viral persistence.

Table of Contents

TABLE OF CONTENTS ITEM PAGE DISTRIBUTION AGREEMENT I APPROVAL SHEET II ABSTRACT COVER III ABSTRACT IV COVER PAGE V ACKNOWLEDGEMENTS VI

TABLE OF CONTENTS VIII

LIST OF FIGURES XI LIST OF ABBREVIATIONS XIII CHAPTER 1: Introduction 1

Part I: Innate Immune Receptors and Innate

Immune Cells 1

Pattern Recognition Receptors (PRRs) and

Modulating Adaptive Immunity 1

Toll-like receptors (TLRs) 2 TLR adaptor molecules 2 TLR polarize adaptive responses 3 RIG-I like Receptors (RLRs) 4 NOD-like Receptors 5 Innate Immune Cells 6 Granulocytes 7 Natural Killer Lymphocytes 11 Macrophages 13 Dendritic cells 16 Monocytes 18

Innate Cells During Chronic Inflammation:

Myeloid Derived Suppressor cells 20

Identifying MDSC 21 Expansion 21 Gaining Suppressive Function 22 Mechanism of suppression 23

Part II: Lymphocytic Choriomeningitis Virus (LCMV)

as a Model for Acute and Chronic Viral Infections 26 Basic Virology of LCMV 26

LCMV genome 27

Cellular Receptor aDG 27

Persistent LCMV strain Clone13 28

LCMV tropism 28

The Cellular Immune Response to LCMV 29

CD8⁺ T cell mediated immunity 29

Memory subpopulations 30

CD4⁺ T cell responses 31

Anti-viral immune responses during

C13 infection 31

Molecular markers and characteristics

of exhaustion and immunosuppression 32

The Innate Immune Response to LCMV 34

Innate responses to acute LCMV infection 34

Type I IFN and innate immune responses 35

References 38

CHAPTER 2: Chronic, but not acute viral infections, induce

sustained expansion of myeloid suppressor cells that inhibit

viral-specific T cell immunity 83

Summary 84 Introduction 85 Results 88 Discussion 103 Experimental Procedures 108 Acknowledgements 113 Figures 114 Figure Legends 125 References 132 CHAPTER 3: Summary, Discussion and Future Directions 140 Figures 151 Figure Legends 152 References 153

About this Dissertation

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School	Laney Graduate School
Department	Biological and Biomedical Sciences
Degree	PhD
Submission	Dissertation
Language	English
Research Field	Biology, General Biology, Virology Health Sciences, Immunology
Parola chiave	Myeloid Suppressor Cells chronic LCMV T cell exhaustion
Committee Chair / Thesis Advisor	Pulendran, Bali, Emory University
Committee Members	Evavold, Brian, Emory University Grakoui, Arash, Emory University Jacob, Joshy, Emory University Mittler, Robert S, Emory University

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