Thrombin regulates chemokine induction during human retinal pigment epithelial cell/monocyte interaction

Thrombin, an important clotting factor, extravasates at sites of blood-reti na barrier breakdown that is often associated with many retinal diseases. H ere we investigated the effects of thrombin on human retinal pigment epithe lial (HRPE) cells, monocytes, and HRPE cell/monocyte co-cultures. Thrombin induced secretion and mRNA expression of HRPE interleukin (IL)-8 and monocy te chemoattractant protein-1 (MCP-1). Thrombin also enhanced IL-8 and MCP-1 by HRPE cell/monocyte co-cultures, by apparently enhancing cell-cell conta ct mechanisms. The thrombin effects on IL-6 secretion were similar to those on chemokine secretion. Thrombin-induced chemokines by co-cultures were in hibited by anti-tumor necrosis factor-alpha (TNF-alpha) antibody, but not b y anti-IL-1 beta antibody. TNF-alpha was detected in cell lysates of monocy tes detached from HRPE cells after co-culture stimulation with thrombin. HR PE cells mainly produced these chemokines. However, thrombin generally pote ntiated exogenous IL-1 beta- and TNF-alpha -induced chemokine production by HRPE cells, monocytes, and co-cultures. Interferon-gamma potentiated chemo kine secretion by co-cultures with or without thrombin. Our results indicat e that thrombin may cause leukocyte recruit ment by inducing HRPE cell and monocyte chemokine and by enhancing HRPE cell/monocyte interactions, in par t because of monocyte TNF-alpha induction, suggesting important mechanisms for ocular inflammation during blood-retina barrier breakdown and intra-ocu lar hemorrhage.