Effect of TGF-beta on interferon-gamma-induced HLA-DR expression in human retinal pigment epithelial cells

Retinal pigment epithelial (RPE) cells express human leukocyte antigen (HLA)-DR (class II) antigens when stimulated with interferon gamma (IFN-gamma) and may be capable of local antigen presentation. The authors examined the effect of transforming growth factor-beta (TGF-beta), a cytokine normally found in the eye, on the expression of these immunoregulatory molecules in vitro and attempted to determine the mechanism by which this cytokine acts. Human RPE cells were cultured in the presence of IFN-gamma and then stained immunohistochemically for HLA-DR antigens. TGF-beta 1 or TGF-beta 2 was added simultaneously with IFN-gamma or after 3 days of IFN-gamma treatment. In parallel experiments, RPE cells were pretreated with 4-phorbol-12 myristate-13 acetate (PMA), staurosporine, or calphostin C before stimulation with IFN-gamma or TGF-beta. Quantitative analysis was performed by fluorescence-activated cell sorting. IFN-gamma induced HLA-DR expression on RPE cells. Both TGF-beta 1 and TGF-beta 2 were able to inhibit this effect. These inhibitory effects of TGF-beta were augmented by pretreatment with either PMA or calphostin C. Pretreatment of the cells with PMA before stimulation with IFN-gamma downregulated HLA-DR expression. Staurosporine pretreatment suppressed HLA-DR expression by IFN-gamma-stimulated RPE cells, but this was not additive with TGF-beta. The authors conclude that TGF-beta 1 and TGF-beta 2 strongly inhibit the IFN-gamma-induced upregulation of class II antigens on human RPE cells. The modulation of these IFN-gamma and TGF-beta effects by calphostin C, staurosporine, and PMA treatment suggests involvement of the protein kinase C pathway.