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

Abstract

Bacteroides thetaiotaomicron , a Gram-negative anaerobic rod and a member of the Bacteroides fragilis group (BFG) causes many systemic and local infections in humans, most of which are endogenous and suppurative. The microorganism produces two high-molecular weight, carbohydrate-containing cell-surface antigens, both of which have been implicated as virulence factors for this organism; these consist of lipopolysaccharide (LPS) and capsular polysaccharide (CPS). Adhesion molecules ICAM-1, VCAM-1 and E-selectin can be stimulated to be expressed on the surface of endothelial cells (ECs) by a variety of mediators of inflammation. The aim of this study was to assess the ability of polysaccharide (PS) and lipid (lipid A) components of three B. thetaiotaomicron 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. thetaiotaomicron LPS. ELISA was performed using monoclonal mouse anti-human ICAM-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 endothelial 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 contrast, the PS moiety of LPS extracted from a reference strain B. thetaiotaomicron NCTC 10582 was totally unable to induce the expression of any adhesion molecule under investigation. The lipid A of B. thetaiotaomicron LPS is, therefore, and probably not unexpectedly, involved in the stimulation of adhesion molecules that are expressed on HMEC-1 to a greater extent than the PS moiety. Importantly, however, the PS components of the two LPS preparations tested manifest a weak but, nevertheless, significant activity in this process. It is possible that the PS moiety may modify the immunobiological effects of the complete LPS molecule.