Studies Of The Bioregulatory Aspects Of The Retinal Pigment Epithelial Cell

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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 identified that IFN-beta produced by RPE cells primarily by TLR signaling and secondarily by auto-stimulation is a critical component of that limiting force. 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. Recently we identified that IFN-beta can significantly down-regulate CXCL9 gene expression and protein production in a variety of cells, such as, endothelial cells, macrophages, epithelial cell, neuroblastoma and glial cells. Interestingly, this down-regulatory effect occurs for CXCL9 but not for CXCL10 or CXCL11. In order to explore the potential in vivo effects of IFN-beta treatment on CXCL9 and sICAM-1 production, we studied the animal model system of experimental cerebral malaria. CXCL9 and ICAM-1 are know to be key components in the pathogenesis of this disease. We found that IFN-beta treatment resulted in an increase in survival of mice from death following infection with Plasmodium bergie ANKA. This increase in survival was associated with a decrease in the protein expression of CXCL9 and ICAM-1 on brain endothelial cells. Moreover, gene expression of CXCL9 and ICAM-1 in the brain was also significantly inhibited by IFN-beta treatment. These studies clearly demonstrate that IFN-beta treatment in vivo results in significant immuno-suppression associated with inhibition of CXCL9 and ICAM-1. We are now evaluating retinal changes in these animals and evaluating other ocular diseases.