VIRUS INFECTIONS IN THE EYE

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Our studies of various virologic and immunopathologic processes that occur when viruses and parasites replicate in the ocular microenvironment comprise five areas: (1) virus induced retinal degenerative processes; (2) the possible roles of viruses in human diseases; (3) molecular diagnosis and pathogenesis of cytomegalovirus (CMV) infections in man; (4) Varicella - zoster virus (VZV) infections of the retina and (5) Toxoplasma gondii infections of the retina. We have established that murine coronavirus can induce ocular disease and may be used as a model system for studying retinal degenerative diseases. This model has many unique features. The virus is capable of inducing an acute infection in the presence of mild retinal vascular inflammation. Initial retinal damage is followed by clearance of infectious virus and progressive retinal degeneration. This is the first retinal model to demonstrate a virus induced degeneration, viral persistence, a genetic predisposition to virus induced tissue damage and a virus triggered autoimmune response. During the past year we have evaluated the role of apoptosis in this retinal disease. The number of apoptotic cells was significantly elevated in infected eyes, reaching a maximum at days 6 to 10. Double-labeled immunostaining demonstrated that apoptotic events within the retina were associated with viral antigen and CD8+ T cells. RT- PCR analysis identified the upregulation of Fas ligand (FasL) and granzyme B mRNAs within the infected retinas. The development of apoptosis, regulative gene expression and viral clearance were similar, in both, retinal degeneration susceptible (BALB/c) and resistant (CD-1) mice. Thus, apoptosis was associated with retinal inflammation and a decrease of infectious virus. In vitro studies demonstrated that JHM virus did not directly induce apoptosis in infected cells. These findings indicated that retinal apoptosis was triggered by virus-host interactions which then may contribute to limit the retinal infection. Human CMV is a herpesvirus that is a major cause of blindness in children born with congenital infections and in immunocompromised individuals. It is difficult to study CMV latency in man. Therefore cell culture models of CMV replication and latency may provide insight into a rationale for alternative treatment modalities. In order to understand the retinal tissue tropism for CMV, we have extended our original studies of CMV replication in HRPE . The data indicate that regulation of HCMV infection of HRPE cells differed from that of human fibroblasts at both the levels of virus entry and transcription of the viral genome. Moreover, the data demonstrate that HCMV uses heparin sulfate binding and the gH ?gL glycoprotein complex as a means of cell entry. These differences in CMV - host cell interactions in HRPE cells which may be instrumental in CMV activation, replication and spread within the eye. In a separate series of studies we have evaluated methods of diagnosis and treatment of CMV infections. These studies demonstrate the utility of this CMV RPE cell model system to evaluate virus replication and efficacy of antiviral therapy with antisense oligonucleotides. CMV infection and associated diseases continue to be a major complication encountered in bone marrow transplant patients. We found that flow cytometric identification of CMV antigenemia correlates with virus isolation in transplant patients and may be a predictive test for the rapid detection of CMV in the blood. Human VZV infections of the eye can result in keratitis, uveitis, acute retinal necrosis or progressive outer retinal necrosis in AIDS patients. However, a small animal model that replicates these diseases does not yet exist. We have shown that intravitreal inoculation of guinea pigs with VZV results in a chronic uveitis consisting of a mononuclear cell infiltrate in the posterior segment of the eye. Using a recombinant VZV that expresses beta-galactosidase, we detected expression of the enzyme in the eye for up to four months after intraocular inoculation. During the past year we have utilized this model to evaluate VZV vaccines. We found that immunization with VZV gE and gI recombinant proteins induced potent humoral and cellular responses that accelerated the clearance of VZV DNA and may neutralize virus within the eye.