Purpose: 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.
Methods: 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.
Results: 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.
Conclusions: 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.