Enteric microflora contribute to constitutive ICAM-1 expression on vascular endothelial cells

Quantitative estimates of endothelial cell adhesion molecule expression hav e revealed that some adhesion molecules [e.g., intercellular adhesion molec ule-1 (ICAM-1)] are abundantly expressed in different vascular beds under n ormal conditions. The objective of this study was to determine whether the enteric microflora contribute to the constitutive expression of ICAM-1 and other endothelial cell adhesion molecules in the gastrointestinal tract and other regional vascular beds. The dual radiolabeled monoclonal antibody te chnique was used to measure endothelial expression of ICAM-1, ICAM-2, vascu lar cell adhesion molecule-1 (VCAM-1), and E-selectin in conventional, germ free mice and germ-free mice receiving the cecal contents of conventional m ice to reestablish the enteric microflora (total association). Constitutive ICAM-1 expression was significantly lower in the splanchnic organs (pancre as, stomach, small and large intestine, mesentery, and liver), kidneys, ske letal muscle, and skin of germ-free mice compared with their conventional c ounterparts. These differences were abolished after total association of ge rm-free mice with the indigenous gastrointestinal flora. The expression of ICAM-2, VCAM-1, and E-selectin in the various tissues studied did not diffe r between conventional and germ-free mice. These findings indicate that the indigenous gastrointestinal microflora are responsible for a significant p roportion of the basal ICAM-1 expression detected in both intestinal and ex traintestinal tissues.