Inflammatory bowel disease, in particular ulcerative colitis, is characterized by localization of leukocytes in close proximity to the colonic epithelium, which may be mediated by the expression of intercellular adhesion molecules (ICAM-1; CD 54). We previously reported the presence of an organ-specific M(r) 40K colonic protein that acts as an autoantigen in ulcerative colitis and is present on the surface of colonic epithelial cells and also in DLD-1 colon cancer cells. Using the colon tumor cell line DLD-1 and flow cytometry, ICAM-1 antibody binding by untreated cultured DLD-1 cells was similar to background antibody binding (mean channel number, MCN = 9.77 +/- 2.13). Interferon-gamma (100 U) induced a 1-2 log increase in anti-ICAM-1 antibody binding from as early as 12 hr after exposure up to 72 hr and a moderate increase (up to about 100%) in the binding of anti-M(r) 40K antibody. Additional studies showed that anti-ICAM-1 and anti-M(r) 40K antibodies bound to DLD-1 cells regardless of the presence of the other antibody. Taken together, the present observations suggest that the epitopes of ICAM-1 and M(r) 40K molecules are coexpressed by colonic epithelial cells, regardless of the presence of the other molecule. Furthermore, lymphocytes in the colonic mucosa that are activated to produce interferon-gamma may upregulate the expression of both of these molecules.