Herpes simplex virus (HSV) expresses an immediate early protein, ICP47, which inhibits presentation of viral antigens to CD8+ T lymphocytes. CD8+ T lymphocytes play important roles in limiting infections by members of the herpesvirus family, as well as other viruses including HIV. The present application includes studies of the molecular mechanisms of action of ICP47, as well as studies of ICP47's effects on viral pathogenesis. ICP47 binds to ATP-dependent TAP transporter proteins which are responsible for translocation of peptide antigens into the endoplasmic reticulum so that these peptides can associate with MHC class I proteins. Thus, by inhibiting TAP-mediated transport, ICP47 inhibits the MHC class I-mediated presentation of viral and cellular peptides to CD8+ T lymphocytes. In addition, ICP47 binds to a novel calcium binding protein, calcyclin, which currently has unknown functions in cells. It is an aim of these studies to characterize the molecular mechanisms by which ICP47 inhibits TAPs, to determine whether there are direct or indirect interactions between ICP47 and TAPs, and whether calcyclin plays a role in ICP47's effects and in antigen presentation. Information learned about the cellular targets of ICP47 should add to our understanding of the MHC class I antigen pathway and further illuminate the process by which HSV evades cellular immune responses. It is also an aim of this application to characterize the effects of ICP47 on antigen presentation in a variety of human and animal cells. At the present time, ICP47's effects have only been demonstrated in human skin fibroblasts. In order to facilitate animal studies of ICP47's effects on viral pathogenesis and to determine whether ICP47 can be used as a mobile immunosuppressive agent, in autoimmune disorders or in tissue transplantation, inhibition of antigen presentation by ICP47 will be studied in other human cell types and in animals cells from a variety of tissues. We have obtained evidence that ICP47 can have pronounced effects on virus pathogenesis in mice. In a mouse model of HSV infection of the cornea, we found that an HSV mutant unable to express ICP47 caused no stromal inflammation and no disease in the periocular skin, whereas wild type HSV caused severe stromal and skin disease. The differences in pathogenesis between the ICP47 mutant and the wild type HSV parent were related to anti-HSV CD8+ T cell responses because mice which were depleted of CD8+ T lymphocytes and infected with the ICP47- mutant developed severe stromal and periocular disease. Therefore, it is my hypothesis that ICP47 allows HSV to escape detection by CD8+ T lymphocytes which normally limit virus spread through tissues or into the nervous system. This hypothesis will be tested further using this eye model and other models of HSV disease to more directly investigate the role of CD8+ T cells in containing infection, causing immunopathology, and limiting HSV spread into the nervous system. ICP47's effects as a mobile immunosuppressive will be investigated using recombinant adenovirus vectors. These studies will add to our understanding of anti-HSV immune responses, virus immune evasion strategies and cellular antigen presentation pathways.
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