Project

Discipline

Persistent viral infections; immunopathogenesis; antiviral immunity; autoimmunity; lymphocytic choriomeningitis virus; T cells; Antibodies; negative strand RNA virus reverse genetics; immunoprivilege; central nervous system

Lead
Lay summary
Project goals: This projects aims at investigating basic mechanisms how the body can successfully eliminate persisting viruses, and how “killer T cells” cause disease of the central nervous system. A better understanding of these processes and the governing principles may help in the future design of preventive and therapeutic interventions in viral and autoimmune diseases. Context and significance of the project: In persistent viral infection, interactions between the virus and the infected body (host) are multifaceted, and different levels of balance can establish between the host and its intruder. Accordingly, persisting viruses can cause a broad range of diseases. Examples are: a) In sub-Saharan Africa up to 30% of the human population are infected with human immunodeficiency virus (HIV), the causative agent of the AIDS syndrome. Similarly, an estimated global number of 170 million people are carriers of hepatitis C virus (HCV) that can cause liver cancer and end-stage liver disease. Yet, protective vaccines against HIV or HCV remain unavailable, and we lack a clear understanding how the immune system can prevail in such infections. b) Neurons represent an irreplaceable population of highly differentiated cells in our brain and spinal cord, and therefore viruses preferentially take refuge in these cells. A growing body of evidence suggests that in multiple sclerosis (MS) and other inflammatory diseases of the central nervous system, neurons become a target of “killer T cells”, possibly as a result of viral infection. This process ultimately accounts for long-term disease progression and disability. MS affects up to 0.2% of the human population in high-risk areas, but the therapeutic options in MS remain unsatisfactory. Taken together, viral and autoimmune diseases have a tremendous impact on global health. Therefore a better general understanding of the underlying mechanisms is urgently needed, including better knowledge about successful strategies of defense as well as about mechanisms of disease. Scientific approach, methodology and expected insights: This project applies newly developed gene technology (reverse genetics) to one of the best-characterized animal models for persistent viral infection (lymphocytic choriomeningitis virus). The combination thereof with genetically engineered mice, multi-parameter immune cell characterization (flow cytometry), tissue and gene expression analysis and disease parameters may help shedding light on the complex interactions between virus and host in persistent infection, and on the interactions of “killer T cells” with neurons. Specifically, this project aims to understand how antibodies and “killer T cells” can succeed in controlling persistent viral infection and whether specific qualitative thresholds exist that govern “killer T cell” interactions with neurons in the context of autoimmune disease.

Direct link to Lay Summary

Last update: 21.02.2013

Active participation

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Number	Title	Start	Funding scheme

Background: Persistent viral infections count amongst the grand challenges of contemporary biomedicine. Prominent examples are the global HIV/AIDS pandemic with up to 30% seroprevalence rates in sub-Saharan Africa and an estimated worldwide number of 170 million carriers of hepatitis C virus. Unlike these systemic persistent viruses, others take refuge at immunoprivileged sites, particularly neurons, to escape clearance by the host's T cells. A growing body of evidence suggests that the resulting hide-and-seek of virus and immune system may be involved in the pathogenesis of autoimmune diseases. Amongst them is multiple sclerosis (MS), affecting up to 0.2% of the population in high-risk areas. The available options for prevention and treatment of viral persistence and autoimmune diseases remain unsatisfactory. This explains the need to better understand the mechanisms and parameters dictating virus control in systemic persistent infection and immunopathological tissue damage in the central nervous system.Working hypothesis: I) CD8+ cytotoxic T cells (CTLs) and antiviral antibodies may need to cooperate to control chronic systemic virus infections. Only with the aid of antibodies, a subset of CTL specificities may enter genetic programs and develop effector functions conferring heightened antiviral efficacy. However, antibody "help" to CTL defense may not depend on its virus neutralizing capacity. II) The documented low levels of MHC class I expression on neurons and high protein biosynthesis activity may impose quality thresholds to recognition and attack by CTLs. This threshold may be uniformly applicable in virus-induced as well as autoimmune pathology, and may be explained by two not mutually exclusive mechanisms: 1. Endogenous MHC ligands of high abundance and affinity may outcompete viral peptides of low or intermediate affinity for binding to a limited number of MHC class I molecules. 2. T cell receptors of low or intermediate affinity may fail to recognize a very low number of cognate peptide/MHC complexes on neurons. Experimental models and methods: Lymphocytic choriomeningitis virus (LCMV) represents the prototype small rodent model to study virus-host balance and pathogenesis in persistent infection. This project will exploit two distinct experimental settings: a) overwhelming systemic viremia causing “exhaustion” of CTLs, and b) a novel model for virus-induced immune disease of the central nervous system. We will use cutting-edge reverse genetic techniques to engineer infectious LCM viruses for our experimental demands. Multiplex TaqMan RT-PCR technology, multi-parameter flow cytometry and multi-color cell sorting will be combined with genome-wide cDNA expression analysis i) to identify and characterize antivirally effective CTL populations and ii) to determine the "helper" effect of adoptively transferred antibody on the antiviral efficacy of CTLs. Immunohistochemical analysis and behavioral tests in gene-targeted mice will unveil iii) quality thresholds and mechanisms thereof, which operate at the CTL-neuron synapse in vivo.Specific aims: Regarding CTL-mediated antiviral defense in chronic viral infection we aim to address i) the impact of antiviral antibodies on CTL efficacy, and ii) Functional and transcriptional characteristics of “driver” CTL populations. With respect to quality criteria for CTL-mediated damage of virus-infected neurons in vivo, we aim to investigate i) the role of TCR - MHC/peptide affinity and ii) the contribution of peptide - MHC binding affinity.Significance: The reverse genetic approach to well-defined small rodent models of persistent infection are likely to provide new key insights into basic mechanisms of virus-host balance and pathogenesis. The present proposal is expected to provide fundamental new insights into mechanisms of immune control in chronic viral infection, as well as into rules governing CTL-mediated neuron damage. This may help in the future design of vaccines and immunotherapy aimed at combating persistent viral diseases and autoimmunity.