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. TLR signaling provides a rapid, robust, burst of reactivity designed to limit pathogens at the site of infection. This burst of reactivity is highlighted by release of cytokines, chemokines and adhesion molecules. Within the retina an uncontrolled inflammatory burst can itself lead to cellular damage. Therefore, it is highly probable that a downregulatory force is also produced to limit immunopathologic damage. We hypothesize that IFN-beta produced by RPE cells primarily by TLR signaling and secondarily by auto-stimulation is a critical component of that limiting force. The general aim of this study is to identify processes by which IFN-beta is produced and to characterize mechanisms by which IFN-beta can protect the retina through its antiviral actions, immunosuppressive actions and anti-proliferative actions. RPE cells treated with Poly I:C or infected with an RNA virus produce IFN-beta. Kinetic studies revealed that IFN-beta levels continue to increase over a 48 h period and this was associated with the up-regulation of IRF-7 gene expression, a known positive feedback molecule for IFN-beta production. 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. We hypothesize that IFN-beta induction during TLR signaling in the retina is an immunosuppressive factor produced to limit immunopathologic damage. Cytokine activation of RPE cells results in the production of the chemokines, CXCL9 and CXCL10 and the adhesion molecule, ICAM-1. Pretreatment of RPE cells with IFN-beta resulted in inhibition of ICAM-1 production and elimination of CXCL9 production. This treatment did not alter CXCL10 production. Anti-IFN-beta antibody blocked the inhibitory action of IFN-beta. Real time PCR analysis revealed that IFN-beta treatment inhibited gene expression of sICAM-1 and CXCL9. The results indicate a critical role for RPE cell derived IFN-beta in the down-regulation of CXCL9 and ICAM-1 expression in the retina and suggest that the inhibition of CXCL9 is an immuno-suppressive mechanism that protects the retina from excessive inflammation.? ? 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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