EXPRESSION OF ICAM-I ON M-CELLS COVERING ISOLATED LYMPHOID FOLLICLES OF THE HUMAN COLON

To clarify the immunological function of 'M' (microfold or membranous) cells in the large intestine, we examined the expression of intercell ular adhesion molecule-1 (ICAM-1) and HLA-class II antigens immunohist ochemically in M cells and follicle-associated epithelia (FAE) coverin g isolated lymphoid follicles of the human colon in comparison with th eir expression in Peyer's patches of the small intestine. In Peyer's p atches of the small intestine, ICAM-1 was not expressed on the epithel ial cells covering the lymphoid follicles, but their cell surfaces wer e stained positively for HLA-DR. In contrast, colonic M cells expresse d ICAM-1 on their cell surfaces but were negative far HLA class II ant igens. By immunoelectron microscopy, ICAM-1 was seen to be distributed on the surface of microfolds, on the membranes of apical vesicles and on part of the basolateral plasma membranes of M cells, but was not e xpressed on adjacent FAE. These findings imply that the M cells in the colon and in Peyer's patches have different immunological roles. In a ddition, identification of ICAM-1 expression on the colonic M cells sh ould help elucidate the pathogenesis of some inflammatory colonic dise ases which appear to start in the lymphoid follicles of the colonic mu cosa.