LYMPHOCYTE-MEDIATED NITRIC-OXIDE PRODUCTION BY RAT ENDOTHELIAL-CELLS

Lymphocyte migration from the blood to sites of tissue injury is media ted, in part, through the interaction of these cells with endothelial cells lining the vessel walls. The ability of endothelial cells to pro duce nitric oxide may be important in this process. We found that the addition of the nonspecific lymphocyte activators lipopolysaccharide ( LPS) or concanavalin A (Con A) to rat hepatic endothelial cell culture s from control or endotoxemic rats markedly enhanced the ability of th ese cells to produce nitric oxide. In contrast, wheat germ agglutinin (WGA) and phytohemagglutinin (PHA) had no effect on nitric oxide relea se. Coculture of endothelial cells with lymphocyte-rich preparations o f rat thymocytes or splenocytes stimulated endothelial cell nitric oxi de production. This response was enhanced by LPS or Con A and to a les ser extent by WGA or PHA. In contrast to endothelial cells, thymocytes and splenocytes did not produce nitric oxide either in the presence o r absence of lymphocyte mitogens. Increased production of nitric oxide by endothelial cells in response to lymphocytes and lymphocyte mitoge ns was due, at least in part, to increased expression of protein for a n inducible form of nitric oxide synthase, as measured by Western blot ting. Stimulation of endothelial cell nitric oxide production by thymo cytes and splenocytes was inhibitable by the specific nitric oxide syn thase inhibitor N-G-monomethyl-L-arginine and dependent on cell-cell c ontact. Thus, nitric oxide production by endothelial cells was reduced when the lymphocytes were physically separated from the endothelial c ells using cell culture inserts. We hypothesize that nitric oxide rele ased by endothelial cells increases vascular permeability, thereby all owing the extravasation of lymphocytes into the surrounding tissue, a process that may be important in inflammation, tissue injury, and/or w ound healing.