RETINAL-PIGMENT EPITHELIUM-CELLS PROMOTE THE MATURATION OF MONOCYTES TO MACROPHAGES IN-VITRO

Proliferative vitreoretinopathy is characterized by excessive cell pro liferation within the eye; retinal pigment epithelial (RPE) cells form the majority of proliferating cells and interact with infiltrating le ukocytes including monocytes. The purpose of this study was to determi ne the effect of RPE cells on the maturation of monocytes to macrophag es, The enriched monocyte fraction of peripheral blood mononuclear cel ls was either cultured with or without RPE cells. The expression of th e maturation-associated antigen CD16 on monocytes was assessed by flow cytometry, and the concentration of bioactive transforming growth fac tor-beta (TGF-beta) in the culture supernatant measured by mink lung e pithelial cell (Mv1Lu) bioassay. The cellular density of CD16 in terms of mean fluorescence intensity was significantly higher on monocytes in coculture with RPE cells (p = 0.0153) than on monocytes in monocult ure. The CD16 expression was significantly (p = 0.0093) reduced when a ntibodies to TGF-beta were added to the culture medium. RPE cells did not express CD16. Supernatants from cocultures also contained active T GF-beta (76.7 +/- 23.8 pg/ml), while in those of cell monocultures TGF -beta was close to the detection limit. We conclude that RPE cells sti mulate and modulate the differentiation of monocytes to macrophages. B ioactive TGF-beta generated in the coculture was in part responsible f or this effect. It seems likely that RPE cells or interactions between RPE cells and monocytes could be an important factor in inflammatory/ immune processes and wound healing in the eye, which are probably invo lved in proliferative vitreoretinopathy.