LPS, recIL1 and smooth muscle cell-IL1 activate vascular cells by specific mechanisms

Vascular endothelial (EC) or smooth muscle cells (SMC) cultured in vitro respond to cytokines, such as interleukin 1 (IL1), or endotoxin (LPS) by production of IL6 or expression of adhesion molecules. Activation of the cells is mediated by specific recognition mechanisms as shown by inhibition experiments with IL1 receptor antagonists (IL1-Ra) or endotoxin antagonists in this report. IL1Ra reduced the activation of EC and SMC by recombinant IL1, as well as the activation of SMC with vascular cell-derived membrane IL1 in coculture experiments. Radiolabelled IL1 bound specifically to EC and SMC, indicating that both cell types expressed IL1 binding sites. LPS antagonists, such as lipid A precursor Ia or nontoxic LPS of Rhodobacter capsulatus reduced the LPS-stimulated IL6 production of EC and SMC and the adhesion of leukocytes to EC, but not the cytokine-induced activation. The antagonists blocked the LPS-mediated activation of vascular cells both in the presence of fetal calf or human serum. The activation of cells by LPS was dependent on the serum concentration. In contrast, activation of cells by IL1 was not serum dependent. Incubation of EC with CD14 antibodies prior to LPS stimulation in medium containing human serum reduced the activation of the cells. CD18 antibody (IB4) did not reduce activation. S-form LPS and IL1 stimulated IL6 production and adhesion differentially. Compared to IL1 stimulation (100%), S-form LPS induced adhesion to the same degree (96.4 +/- 15.5%; n = 6), however, IL6 production to a lower degree (33.7 +/- 15%; n = 6). These results show that both EC and SMC cultured in vitro respond specifically to both IL1 and LPS and that IL6 production and adhesion are regulated differentially.