Abstract
Abstract: :
Purpose: CD99 is a ubiquitous 32 kDa transmembrane protein expressed in many types of cells, including T cells and endothelial cells. Although no clear biological function is known, engagement of CD99 with agonistic antibody has been reported to induce cellular proliferation, apoptosis, aggregation, and up–regulation of many transmembrane molecules. The aims of this study were to investigate the expression of CD99 in human retinal pigment epithelial cells, and to evaluate the effects of agonistic antibody in these cells. Methods: Human retinal pigment epithelial cells were cultured, and Jurkat cells were used as a control. mRNA expression of CD99 was determined by RT–PCR. Cell surface expression of CD99 was measured by flow cytometry. Immunoblotting and immunohistochemistry were used to determine the CD99 immunoreactivity of cultured cells and normal RPE cells in situ. Light microscopic examination and WST–1 assay were used to evaluate the effects of CD99 signals induced by the anti–CD99 antibody. Results: Expression of two isoforms of CD99 was detected in cultured human retinal pigment epithelial cells. CD99 protein was expressed on the cell surface, and the protein levels were increased in proliferating cells compared with density–arrested cells. Low level of immunoreactivity was detected in normal RPE cells in situ. Antibody–induced CD99 signals induced no cellular responses, such as aggregation, proliferation, and cellular death. Conclusions: Human retinal pigment epithelial cells express CD99 molecules on the cell surface. Further experiments are needed to find out biological roles of CD99 in these cells.
Keywords: retinal pigment epithelium • gene/expression • cell death/apoptosis