Circulating autoantibodies against purified colonic mucin in ulcerative colitis

To clarify the role of colonic mucin in the autoimmune process of ulcerative colitis, circulating antibodies against human colonic mucin were investigated. Purified colonic mucin, obtained from human colonic mucosa by gel filtration, using a Bio-Gel A-1.5-m column and CsCl equilibrium density gradient, was divided into soluble mucin (S-mucin) secreted extracellularly and membranous mucin (M-mucin) binding to cell membrane. Sodium dodecylsulfate polyacrylamide gel electrophoresis and Western blotting analysis showed that antibodies in the serum samples of some patients with ulcerative colitis recognized purified S- and M-mucin of >180-kD. By enzyme-linked immunosorbent assay (ELISA), anti-mucin antibodies were detected in 11 of 60 patients with ulcerative colitis (18). In contrast, the antibodies were not detected in 22 patients with Crohn's disease. The titers of anti-mucin antibodies against S-mucin and M-mucin were not different in each patient. By ELISA using mucin in which the sugar chains were destroyed by neuraminidase or NaIO₄ treatment, it was demonstrated that anti-mucin antibodies recognized the epitopes of either the sugar chain or the core protein exposed through destruction of the sugar chains. We then investigated the relationship between anti-mucin antibodies and the patients' clinical features. Anti-mucin antibodies were detected in 6 of 15 patients with chronic continuous type ulcerative colitis (40) and in 5 of 26 patients with relapsing-remitting type (19), but there was no anti-mucin antibody-positive serum in patients who had had only one attack without any relapse. These results suggest that anti-mucin antibodies could be a disease marker for ulcerative colitis and that immunological abnormalities in colonic mucin contribute to the persistence of colonic mucosal inflammation.