Selective deacylation of the nonhydroxylated fatty acids from S. typhimurium LPS by an acyloxyacyl hydrolase isolated from leukocytes reduces toxic activity of LPS in vivo. We examined the effect of deacylated LPS on neutrophil adherence to human umbilical vein endothelial cells (HUVE). Pretreatment of HUVE with LPS (13 ng/ml for 4 h) produced a marked increase in the adherence of subsequently added neutrophils. In contrast, there was no increase in the adherence of neutrophils to HUVE pretreated with deacylated LPS (up to 260 ng/ml for 4 h). Neutrophil adherence to HUVE pretreated with LPS decreased as the degree of LPS deacylation increased. Deacylated LPS was not only itself inactive, but it inhibited neutrophil-endothelial interactions induced by LPS. Neutrophil adherence to HUVE pretreated with LPS was inhibited by deacylated LPS in a dose-dependent manner. Complete inhibition of adherence was observed at a 20:1 ratio (wt/wt) of deacylated LPS to LPS. Significantly, inhibition of neutrophil adherence to HUVE pretreated with LPS was observed even when deacylated LPS was added to HUVE up to 60 min after LPS. Deacylated LPS, however, did not inhibit neutrophil adherence induced by pretreatment of HUVE with IL-1 or TNF-alpha. We conclude that enzymatic deacylation of the nonhydroxylated fatty acids of LPS abolishes the ability of LPS to induce surface expression of a neutrophil adherence promoting activity in HUVE. Furthermore, deacylated LPS inhibits neutrophil adherence to HUVE induced by LPS, perhaps by preventing the interaction of LPS with a specific cell-surface or intracellular target.

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