Antilipopolysaccharide factor from horseshoe crab, Tachypleus tridentatus, inhibits lipopolysaccharide activation of cultured human endothelial cells

Antilipopolysaccharide (anti-LPS) factor is a basic protein that is purified from the hemocyte lysate of the Japanese and American horseshoe crabs (Tachypleus tridentatus and Limulus polyphemus). Anti-LPS factor has previously been reported to inhibit LPS-mediated activation of limulus factor C, lyse endotoxin-sensitized erythrocytes, and inhibit the growth of some gram-negative bacteria. In this study, we examine the ability of anti-LPS factor purified from T. tridentatus to inhibit the activation of cultured human endothelial cells by LPS. Anti-LPS factor inhibited the stimulation of endothelial adhesiveness for neutrophils by LPS in a dose-dependent manner. Maximum inhibition was achieved when anti-LPS factor was mixed with LPS prior to addition to the endothelial cell monolayers. Anti-LPS factor inhibited endothelial cell activation by LPS derived from Salmonella minnesota Re and Rc mutants as well as from the wild type (smooth), suggesting that it recognizes the lipid A moiety of LPS.