DEATH AND T CELLS: AN EVALUATION OF HOST CONTRIBUTIONS TO MURINE CYTOMEGALOVIRUS PATHOGENESIS AND EXTRINSIC CELL DEATH TO T CELLS Open Access

Abstract

Cytomegaloviruses (CMVs) establish a lifelong persistent infection in their hosts. They rarely cause disease in the immunocompetent but are a significant source of morbidity and mortality in immunocompromised hosts as well as following transplacental transmission during pregnancy. Due to strict species specificity, studies of pathogenesis or the immune response to CMV rely on murine CMV (MCMV). MCMV induces a potent T cell response that helps control viral replication. MCMV infection also activates innate immunity, including extrinsic apoptotic and programmed necrotic pathways. Caspase 8 (Casp8) is the apical caspase controlling extrinsic apoptosis while simultaneously suppressing programmed necrosis mediated by receptor interacting protein (RIP)1 and RIP3. In this dissertation, I describe work evaluating host contributions to MCMV pathogenesis and contributions of extrinsic cell death pathways to the antiviral T cell response.

Host factors involved in CMV pathogenesis remain poorly understood. I found that antiviral T cells mediate a lethal hepatitis during MCMV infection. Lethality is associated with increased cytokine production by hepatic CD8 T cells at day four. Thus, the antiviral T cell response contributes to or protects from MCMV disease depending on the context and antiviral T cells exert their effects in the periphery at earlier times that previously appreciated.

RIP3 mediates programmed necrosis and its inhibition is required for productive in vivo replication of MCMV, but its contribution to the immune response is unknown. I found that, at low doses, RIP3 is dispensable for the antiviral T cell response and control of infection. However, RIP3 helps to protect mice from a Casp8-dependent death following high dose inoculation. Thus, under certain conditions, programmed necrosis restricts extrinsic apoptosis and can protect from disease.

CD8 T cells lacking Casp8 undergo a RIP1/RIP3 mediated programmed necrosis upon TCR ligation, but functions of Casp8 in T cells outside of regulating this necrotic pathways remain unexplored. Utilizing Casp8^-/-Rip3^-/- mice, I found that Casp8 is required for homeostatic turnover of CD8 T cells, but is dispensable for a robust CD8 T cell response to MCMV. Thus, during an antiviral CD8 T cell response, extrinsic apoptosis is completely dispensable.

Table of Contents

Abstract.............................................................................................................................. iii

Acknowledgements........................................................................................................... v

Table of Contents ............................................................................................................. vi

List of Figures and Tables ............................................................................................. viii

Abbreviations..................................................................................................................... x

Chapter 1: Introduction

A. Betaherpesvirinae Background .......................................................................... 2

Taxonomy, genome and structure ........................................................................... 2

Tropism................................................................................................................... 2

Viral life cycle .......................................................................................................... 3

Pathogenesis ........................................................................................................... 4

B. HCMV and Disease ........................................................................................... 7

HCMV epidemiology and disease in the immunocompetent ................................... 7

HCMV disease and treatment in the immunocompromised..................................... 7

Congenital and perinatal HCMV disease ............................................................. 10

C. CMV and the T cell response .......................................................................... 12

Antigen presentation and T cell activation ............................................................ 13

Acute T cell response to MCMV............................................................................. 16

Development of memory T cells and the memory response to MCMV ................. 20

D. Programmed cell death pathways and T cells .................................................. 26

E. Figures 1.1-1.3 .................................................................................................. 29

F. Tables 1.1-1.2 ................................................................................................... 32

Chapter 2: Antiviral T cell response triggers cytomegalovirus hepatitis in mice

A. Abstract............................................................................................................ 35

B. Introduction...................................................................................................... 36

C. Materials and Methods..................................................................................... 40

D. Results.............................................................................................................. 45

E. Discussion......................................................................................................... 55

F. Figures 2.1-2.6................................................................................................... 61

G. Table 2.1........................................................................................................... 71

Chapter 3: Remarkably intact CD8 T cell immunity in the absence of extrinsic apoptosis and programmed necrosis

A. Abstract............................................................................................................. 73

B. Introduction...................................................................................................... 74

C. Materials and Methods..................................................................................... 77

D. Results and Discussion..................................................................................... 80

E. Figures 3.1-3.3 and 3.S1-3.S2............................................................................ 88

Chapter 4: RIP3 contributes to host defense against murine cytomegalovirus infection

A. Introduction...................................................................................................... 95

B. Materials and Methods..................................................................................... 98

C. Results............................................................................................................ 100

D. Discussion...................................................................................................... 105

E. Figures 4.1-4.7................................................................................................. 108

F. Table 4.1.......................................................................................................... 117

Chapter 5: Discussion and Future Directions........................................................ 118

Figure 5.1............................................................................................................. 127

References................................................................................................................... 129

About this Dissertation

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School	Laney Graduate School
Department	Biological and Biomedical Sciences
Degree	PhD
Submission	Dissertation
Language	English
Research Field	Health Sciences, Immunology Biology, Virology
Keyword	RIP3 Cell death Hepatitis Caspase 8
Committee Chair / Thesis Advisor	Mocarski, Edward S, Emory University
Committee Members	Weiss, David S, Emory University Williams, Ifor, Emory University Speck, Sam, Emory University Ford, Mandy L, Emory University

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