EFFECT OF TGF-BETA ON INTERFERON-GAMMA-INDUCED HLA-DR EXPRESSION IN HUMAN RETINAL-PIGMENT EPITHELIAL-CELLS

Purpose. Retinal pigment epithelial (RPE) cells express human leukocyt e antigen (HLA)-DR (class II) antigens when stimulated with interferon gamma (IFN-gamma) and may be capable of local antigen presentation. T he authors examined the effect of transforming growth factor-beta (TGF -beta), a cytokine normally found in the eye, on the expression of the se immunoregulatory molecules in vitro and attempted to determine the mechanism by which this cytokine acts. Methods. Human RPE cells were c ultured in the presence of IFN-gamma and then stained immunohistochemi cally for HLA-DR antigens. TGF-beta(1) or TGF-beta(2) was added simult aneously with IFN-gamma or after 3 days of IFN-gamma treatment. In par allel experiments, RPE cells were pretreated with 4-phorbol-12 myrista te-13 acetate (PMA), staurosporine, or calphostin C before stimulation with IFN-gamma or TGF-beta. Quantitative analysis was performed by fl uorescence-activated cell sorting. Results. IFN-gamma induced HLA-DR e xpression on RPE cells. Both TGF-beta(1) and TGF-beta(2) were able to inhibit this effect. These inhibitory effects of TGF-beta were augment ed by pretreatment with either PMA or calphostin C. Pretreatment of th e cells with PMA before stimulation with IFN-gamma downregulated HLA-D R expression. Staurosporine pretreatment suppressed HLA-DR expression by IFN-gamma-stimulated RPE cells, but this was not additive with TGF- beta. Conclusions. The authors conclude that TGF-beta(1), and TGF-beta (2) strongly inhibit the IFN-gamma-induced upregulation of class II an tigens on human RPE cells. The modulation of these IFN-gamma and TGF-b eta effects by calphostin C, staurosporine, and PMA treatment suggests involvement of the protein kinase C pathway.