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) herpesvirus infections of the eye and (5) Toxoplasma gondii infections of the retina. We have established a model system for studying retinal degenerative diseases, experimental coronavirus retinopathy (ECR). 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. Our goal is to determine the pathophysiological mechanisms and to identify genes involved in the retinal degenerative disease. During the past year we have made the following key findings. We demonstrated the importance and critical role of the non-cytolytic retinal antiviral responses. These studies indicate that generation of IFN-g by T cells infiltrating the retina is an essential part of an immune mechanism responsible for noncytolytic clearance of infectious virus from the retina. Moreover, these studies highlight the distinct advantage of IFN-g medicated noncytolytic clearance of virus from cells that are non-renewable. 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 to evaluate antisense treatment strategies. Antisense oligonucleotides specific for treatment of CMV have been developed and target the viral mRNA complementary to the major immediate early transcription unit of CMV. Our studies demonstrate that HRPE cells were significantly more sensitive than fibroblasts to the antiviral actions of ISIS 1st and 2nd generation antisense oligonucleotides. The enhanced potency of these oligonucleotides in HRPE cells may be associated with a delay in viral gene transcription and slow viral replication and spread in these cells. These studies demonstrate the utility of this CMV RPE cell model system to evaluate virus replication and efficacy of antiviral therapy with antisense oligonucleotides. We have developed molecular diagnostic methods using PCR analysis to detect herpesviruses. These assays are being used to distinguish between infectious and immunopathogenic posterior segment intraocular inflammation.
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