Subcellular localization of intercellular adhesion molecule-1 in colonic mucosa in ulcerative colitis.

Intercellular adhesion molecule-1 (ICAM-1) mediates the firm adhesion of leukocytes to endothelial cells. In ulcerative colitis (UC), ICAM-1 is suggested also to be involved in the further migration of leukocytes toward the epithelial lining, and in colonic tissue it has been reported to be expressed by cell types other than endothelial cells. This study aimed at determining the ultrastructural localization of ICAM-1 on cells belonging to the colonic mucosa from patients with UC. Colonic biopsies from 3 UC patients and 3 control subjects were examined ultrastructurally by immunogold labeling of ICAM-1. ICAM-1 was expressed on the luminal cell membranes of endothelial cells in both controls and inflamed and noninflamed UC colon, although the density was significantly increased in UC (p < .0001). Labeling was observed on the basal endothelial cell membranes and on macrophages and plasma cells in inflamed UC colon only. Epithelial cells did not express ICAM-1. ICAM-1 appears to be constitutively upregulated on the luminal endothelial membrane in UC, and the expression on basal endothelial membranes in active UC only suggests that ICAM-1 is more extensively involved in the leukocyte migration than previously acknowledged.