Bacteroides ovatus as the Predominant Commensal Intestinal Microbe Causing a Systemic Antibody Response in Inflammatory Bowel Disease

To clarify what bacterial species of commensal intestinal microbes are recognized as the antigens that induce a serum antibody response in patients with inflammatory bowel disease (IBD), 72 subjects consisting of 12 Crohn’s disease patients, 30 ulcerative colitis patients, and 30 healthy volunteers were examined for their titers of serum antibody to these intestinal bacteria. In IBD patients, as a result, significant elevations of both the immunoglobulin G (IgG) and IgA titers to Bacteroides ovatus were found. Immunoblotting showed that a definite 19.5-kDa band of B. ovatus was bound to the serum antibody raised in IBD patients. It was thus concluded that B. ovatus causes serum antibody responses in IBD patients, and a 19.5-kDa molecule of this bacterium appears to be the responsible antigen, although the role of this event in pathogenesis remains unclear. An increasing number of both clinical and laboratory find-ings support the importance of luminal bacteria in the patho-genesis of inflammatory bowel disease (IBD) (17). Actually, the anatomic sites of the intestine in which bacteria colonize with a high density, such as the distal ileum and colon, are sites that are frequently affected by inflammation in IBD patients. In addition, the use of antibiotics or a diversion of the feca