Beta 2-integrin/intercellular adhesion molecule (ICAM) expression in the normal human intestine

The beta 2-integrin family of adhesion molecules and their ligands, the ICAM molecules, probably have an important role to play in the intestinal immune response. To date, any data published regarding the intestinal expression of beta 2-integrins and ICAMs have mostly described only mucosal expression. The presence in the intestine of alpha d, a newly described beta 2-integrin molecule, has not yet been determined. To understand further the expression of these molecules in all layers of the intestine, a comprehensive study was undertaken in both normal colon and normal small intestine specimens from 15 patients (colon n = 15, and ileum n = 6) who underwent surgical resections. Immunohistochemistry was performed for CD18, CD11a, CD11b, CD11c, alpha d, ICAM-1, ICAM-2, and ICAM-3. The colon and small intestine cases were grouped separately and each of the mucosal, submucosal, muscle and adventitial layers were scored for expression. The beta 2-integrin molecules were expressed by mononuclear cells in all layers of the bowel, predominantly in the mucosa and adventitia. CD11a showed the greatest mucosal expression and CD11b showed the greatest adventitial expression. alpha d exhibited expression in all bowel layers, as well, with most intense expression in the mucosa and adventitia. CD11c exhibited the least expression of all alpha subunit molecules. The expression of these alpha-chains at times appeared to be greater than that seen for CD18 (beta 2), raising the possibility of non-beta 2-containing complexes (i.e. alpha-chains associating with an alternate beta-chain). ICAM-1 was expressed on endothelium, particularly in the mucosa and rarely on mucosal mononuclear cells. ICAM-2 was predominantly on submucosal endothelium and rarely expressed in colon mucosa and never expressed in ileal mucosa. ICAM-3 was expressed by mononuclear cells throughout the bowel wall, but also on adventitial endothelium in selected cases. In summary, we are reporting a comprehensive immunohistochemical study of the differential expression of beta 2-integrins, including the newly described alpha d molecule, and the ICAM molecules in all layers of normal human colon and ileum. We raise the possibility that a second beta 2-integrin beta subunit may exist, and we report that ICAM-3 is expressed on endothelium, particularly in the adventitial layer.