Identification of Colon Antigen Recognized by Tissue Bound IgG of Ulcerative Colitis and Clinical Significance of Quantitation of Corresponding Antibody in Sera

Ulcerative colitis is a chronic nonspecific inflammatory bowel disease whose etiology is still uncertain. Recently, it was reported that mucosal tissues of ulcerative colitis contained a significant amount of immunoglobulin G (colitis colon associated IgG, CCA-IgG) but not those taken from normal colon or Crohn's disease colon. The nature of this tissue bound IgG has not been well elucidated up to the present. In the present study, the identification of antigen in the colonic mucosa recognized by CCA-IgG and the clinical significance of the quantitation of the corresponding antibody in sera of patients with ulcerative colitis were investigated. The results obtained were as follows; (1) A protein with a molecular weight of 40,000 daltons (40-kD protein), which was specifically bound by 125I-labeled CCA-IgG, was identified in the extracts of human colonic mucosa by an SDS/PAGE-immunotransblotting-autoradiography procedure. This 40-kD protein was not detected in the tissue extracts from mucosa of stomach, duodenum, jejunum and ileum and from liver. (2) By a discontinuous KCl gradient of DE 52 ion exchange chromatography, the 40-kD protein was enriched in the fraction eluted by 0.35 M KCl. This fraction was used for the solid phase antigen of enzymelinked immunosorbent assay (ELISA) procedure for the quantitation of serum antibody which reacted with the 40-kD protein. (3) A high titer for the 40-kD protein was observed specifically in the sera during the active stage of ulcerative colitis. There was no significant increase of serum titers in patients with remission of ulcerative colitis or patients with Crohn's disease and other diarrheal conditions. (4) The quantitation of circulating antibody for the 40-kD protein is helpful for monitoring the disease stage and for evaluating the effect of proctocolectomy in patients with ulcerative colitis. These results suggest that the 40-kD protein in colonic mucosa is a target molecule for CCA-IgG and ?the quantitation of the corresponding antibody in sera of patients with ulcerative colitis is important for the diagnosis and the evaluation of disease activity of ulcerative colitis