Objective--The purpose of this study was to investigate the receptor requirements for enhanced IL-1-induced secretion of nitric oxide (NO) by endothelial cells (ECs) in the presence of fibrinogen.

Methods and Results--ECs were exposed to IL-1 with or without fibrinogen and NO was measured as nitrite. NO production by EC exposed to fibrinogen (0.3±0.1 µmol/L) was comparable concentration to control (0.2±0.1 µmol/L), but IL-1 significantly increased NO production (0.8±0.1 µmol/L), and the combination of both fibrinogen and IL-1 resulted in a further increase to 2.2±0.2 µmol/L (P<0.002). 7E3 or LM609, antibodies to _v3, inhibited NO production stimulated by fibrinogen-bound IL-1 to 0.2±0.1 µmol/L (P<0.001) or 0.2±0.03 µmol/L (P<0.0001), respectively. These levels were comparable to control and significantly less than with IL-1 (P<0.002). EC or fibroblasts exposed to both fibrinogen and IL-1, but not vitronectin and IL-1, demonstrated positive Western blotting for _V3 after immunopurification with anti- IL-1R, indicating specific association between _v3 and IL-1R. Dual immunofluorescence also revealed colocalization of _v3 and IL-1R only when the cells were exposed to both fibrinogen and IL-1.

Conclusion--The enhanced NO production by ECs in the presence of fibrinogen-bound IL-1 requires the coordinated effects of colocalized _V3 and IL-1R.