Effect of thrombin on IL-8 and MCP-1 secretion by HRPE cell/monocyte co-cultures. A and B: Thrombin enhanced IL-8 (A) and MCP-1 (B) secretion by HRPE cell/monocyte co-cultures. Various concentrations of thrombin (0 to 10 U/ml) or thrombin (10 U/ml) and hirudin (20 U/ml) were added to HRPE cell/monocyte co-cultures (HRPE + Mo). After 24 hours, supernatants were collected and IL-8 and MCP-1 protein levels in supernatants were measured by ELISA. *, P < 0.05; **, P < 0.01, compared with chemokine secretion from HRPE cell/monocyte co-cultures without thrombin (n = 3). HRPE, HRPE cells; Mo, monocytes. C and D: Thrombin-induced IL-8 (C) and MCP-1 (D) secretion was time-dependent. HRPE cells were incubated with (black bars) or without (gray bars) thrombin (10 U/ml) for different times and IL-8 and MCP-1 protein levels in supernatants were measured (n = 3).