The RPE cell plays a basic role in maintaining the structural and physiological integrity of the neural retina. Alterations in its structural and functional actions can result in loss of photoreceptors and vision. We have studied the RPE cell extensively as an important immunoregulatory cell within the posterior pole of the eye. Our research activities on RPE cells can be subdivided into three categories: normal cell function studies, cytokine interactions and infectious processes. This project has concentrated on studying the ways in which cytokines interact with cells of the immune system and with cells in the ocular microenvironment. These studies indicate that cytokine-mediated activation of RPE cells may be a basic component of ocular immunity and an important aspect of RPE cell transplantation. During the past year, we have studied the Toll-Like receptors (TLR) in RPE cells and possible biological markers associated with patients with retinal vasculitis. TLRs are crucial components of innate immunity that participate in host defense against microbial pathogens. We evaluated the expression and function of TLRs in human retinal pigment epithelial (RPE) cells. Real time PCR analysis revealed gene expression for TLR 1 to 7, 9 and 10 in RPE cells. TLR 1 and 3 were the most highly expressed TLRs. TLR 3 is the receptor for dsRNA, an intermediate of virus replication. Since RPE cells express TLR 3 and are frequently the site of virus replication within the retina, we evaluated TLR 3 signaling and found that IFN-beta is one of the key molecules produced. The presence of TLRs on RPE cells and the resultant TLR signaling in RPE cells suggest that these molecules may play an important role in innate and adaptive immune responses within the retina. Since IFN-beta is produced by the RPE cell we have initiated studies to evaluate the effects of IFN-b on the various functions of the RPE cell. Microarray analysis revealed that in IFN-beta treated cells, 480 genes out of 22,283 genes were up or down regulated by greater than 2 fold and 39 genes with greater than 4 fold changes.? ? Retinal vasculitis is a major component of ocular inflammation that plays a role in retinal tissue damage in patients with idiopathic uveitis and Behcets disease. We found that levels of selected soluble adhesion molecules and cytokines were altered in the serum of patients with retinal vasculitis. Type 1 IFN, IFN-alpha and IFN-beta were not detectable in normal individuals but were detected in up to 39% of the serum from Behcets patients and 47% of uveitis patients. Our in vitro findings further demonstrated that the retinal vascular endothelial cell could be activated throuth TLR3 to produce sE-selectin, sICAM-1 and IFN-beta. Further analysis of innate immune signaling may prove to be a novel target for future studies on pathogenic mechanisms and therapeutic approaches in retinal vasculitis.
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