Characterization of antibody responses against rectal mucosa-associated bacterial flora in patients with ulcerative colitis

Background: Previous reports on faecal microflora have demonstrated that the total number of aerobes and coliforms was increased in patients with ulcerative colitis (UC). Based on the hypothesis that the pathogenesis of UC may be closely associated with the mucosal microflora, we investigated alterations in the mucosa-associated microflora of UC patients. Methods and Results: The bacterial counts for both aerobes and anaerobes increased in UC patients. In particular, we detected the highest bacterial counts of Bacteroides vulgatus and these bacteria were isolated most frequently. In addition, we also investigated the serum antibody responses against the bacteria isolated from the affected mucosa by serum bacterial agglutination tests and immunoblotting. A high agglutination titre against B. vulgatus, Bacteroides fragilis, and Clostridium ramosum was detected in most UC patients, and the percentage of positive immunoreactivity was much higher in UC patients than in healthy controls. From the results of the immunoblotting, a unique antigenic determinant of B. vulgatus (BV43-26), a 26-kDa protein from the outer membrane, was discovered. The serum immunoreactivity (immunoglobulin (Ig) G) against this 26-kDa protein was much higher in UC patients (53.8%) than in the control sera (9.1%). The serum immunoreactivity (IgG) against a 50-kDa protein isolated from the whole cell protein of Escherichia coli (EC48-1) was also higher in UC patients (29.2%) than in normal controls (6.3%). Conclusions: These results suggest that B. vulgatus and a specific antibody response directed against it may play an important role in the pathogenesis of UC. (C) 2000 Blackwell Science Asia Pty Ltd.