Polysaccharide and lipid components of Bacteroides thetaiotaomicron lipopolysaccharide as stimulators of endothelial adhesion molecule expression

Bacteroides thetaiotaomicron, a Gram-negative anaerobic rod and a member of the Bacteroides fragilis group (BFG) causes many systemic and local infect ions in humans, most of which are endogenous and suppurative. The microorga nism produces two high-molecular weight, carbohydrate-containing cell-surfa ce antigens, both of which have been implicated as virulence factors for th is organism; these consist of lipopolysaccharide (LPS) and capsular polysac charide (CPS). Adhesion molecules ICAM-1,VCAM-1 and E-selectin can be stimu lated to be expressed on the surface of endothelial cells (ECs) by a variet y of mediators of inflammation. The aim of this study was to assess the abi lity of polysaccharide (PS) and lipid (lipid A) components of three B. thet aiotaomicron LPS preparations to induce adhesion molecule expression on the surface of human vascular endothelial cells. The HMEC-1 cell line has been employed along with ELISA assays to examine the relative activity of B. th etaiotaomicron LPS. ELISA was performed using monoclonal mouse anti-human I CAM-1, VCAM-1 and E-selectin antibodies. The lipid A moieties of the three LPS revealed the ability to stimulate ICAM-1,VCAM-1 and E-selectin on endot helial cells. Their relative activities were similar and stronger than the biological activity of the lipid A-depleted polysaccharide (PS) components of LPS that were, nevertheless, significantly above background levels. In c ontrast, the PS moiety of LPS extracted from a reference strain B. thetaiot aomicron NCTC 10582 was totally unable to induce the expression of any adhe sion molecule under investigation. The lipid A of B, thetaiotaomicron LPS i s, therefore, and probably not unexpectedly, involved in the stimulation of adhesion molecules that are expressed on HMEC-1 to a greater extent than t he PS moiety. Importantly, however, the PS components of the two LPS prepar ations tested manifest a weak but, nevertheless, significant activity in th is process. It is possible that the PS moiety may modify the immunobiologic al effects of the complete LPS molecule.