Thrombin activates endothelial PAR1 resulting in release of IL-6 and MCP-1. Confluent monolayers of hBOECs were cultured with the indicated concentrations of thrombin for 24 hours. Flow cytometric analysis was used to evaluate surface expression of (A) uncleaved PAR1 and (B) ICAM-1. Values represent the fold increase in mean fluorescence relative to untreated cells and are expressed as a mean, with vertical bars indicating standard deviation from the mean. Experiments were repeated at least 3 times. Culture media from confluent BOECs exposed to various amounts of thrombin or LPS was isolated and assayed for (C) IL-6 and (D) MCP-1 by ELISA. Values represent the mean of 3 experiments with vertical bars indicating the standard deviation.