Light and electron microscopic immunolocalization of endothelial leucocyte adhesion molecule-1 in inflammatory bowel disease - Morphological evidence of active synthesis and secretion into vascular lumen

Endothelial leucocyte adhesion molecule-1 (ELAM-1) is a rapidly inducible adhesion molecule for neutrophils in vascular endothelial cells. We investigated its immunohistochemical localization in 17 cases of inflammatory bowel disease. ELAM-1 was preferentially expressed in venules in actively inflamed mucosa and granulation tissue. Most capillaries were negative for ELAM-1. In areas with mild inflammation its expression diminished markedly and in normal mucosa of the colon and small intestine its expression was sparse. Electron microscopically, venules in active inflammation had swollen endothelial cells with well-developed rough endoplasmic reticulum. Immunoelectron microscopy revealed ELAM-1 localization along the luminal plasma membrane and in rough endoplasmic reticulum and round granules, findings suggestive of active production in endothelial cells. Furthermore, exocytosis of immuno-reactive substance into the lumen was confirmed. Our study suggests that venules in actively inflamed area play an important role in eliciting and/or maintaining acute inflammatory processes by active permeation of neutrophils from the blood stream into the tissue, and that ELAM-1 may be a secretory protein as well as a transmembrane receptor protein.