Doctoral Dissertations

Date of Award

5-2001

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Microbiology

Major Professor

Barry T. Rouse

Committee Members

Robert Moore, Philip Bochsler, Pamela Small

Abstract

Herpes simplex virus infection of the ocular tissue induces a blinding immunoinflammatory lesion, Herpetic Stromal Keratitis (HSK). In mice of susceptible strains, a similar lesion can be induced following a primary infection mode. Virus infection induces an acute short lived epithelial keratitis. At this time, an immune cell infiltration of polymorpho nuclear leukocytes, mainly neutrophils are seen in the underlying stroma. The virus is usually cleared by days 5-6 post infection and the cornea assumes a state of normalcy. The chronic phase of the immunoinflammatory process begins around day 7 post infection in the absence of replicating virus. The primary cells mediating the lesion are CD4+ , T cells of the Th1 cytokine producing phenotype. Accordingly, SCID mice or athymic nude mice fail to support HSK lesions unless reconstituted with CD4+ T cell subsets. The absence of inciting virus during the course of clinical phase of the lesion implies that HSK might represent an autoimmune lesion. Several hypotheses have been put forth to explain the nature of the agonists driving the CD4+ T cells in the cornea in HSK lesion. The main ideas include persistence of viral antigens in the cornea, alternatively the role of virus encoded molecular mimic in inducing autoimmune lesion and HSK as a consequence of bystander activation of CD4+ T cells. In the present study, an attempt has been made to understand the role of the three mechanisms in the HSK pathogenesis. Experiments were designed to address the role of virus and viral antigens in lesion development with use of SCID reconstitution and replication defective virus mutants. The role of the immune response in HSK was tested by evaluating cross reactive responses to putative agonists following immunization or tolerization experiments. A number of transgenic and knockout mice were used to obtain mechanistic evidence for many of the hypotheses.

Part I consists of a general introduction and overview of mechanisms involved in viral pathogenesis in general and HSK specifically. Part II is devoted to the analysis of autoantigen and molecular mimicry hypothesis in HSK pathogenesis. The results cast doubts over the role of IgG2a and UL6 as agonists driving the immunoinflammatory reaction. An explanation for the susceptibility of mice lacking B cells or the IgG2a autoantigen to HSK is provided in Part III of the dissertation. These results suggest that in the absence of B cells two mechanisms may contribute to lesion severity: biased Thl response and the spread and persistence of virus to the corneal stroma, which is the site of inflammation. Part IV and V are devoted to the understanding of bystander activation as a model for HSK. In Part IV, bystander activation as an exclusive means of immunopathology is demonstrated in Pigeon Cytochrome C CD4+ TCR transgenic mice. Part V is aimed at understanding the role of bystander activation in HSK in immunocompetent mice. Cytokine knockout TCR transgenic mice were also used in this study to examine the components of the immune system responsible for non specific activation of CD4+ T cells. The results in these sets of experiments suggest that the activating stimuli determine the contribution of bystander activation in the ocular lesion. In the absence of IFN y, activation stimuli for bystander CD4+ T cells are insufficient for lesion induction.

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