[Antibody titer to Bacteroides fragilis is increased in Crohn disease patients with fistula development]

We compared antibody levels to Bacteroides fragilis in patients with different stages of Crohn's disease and ulcerative colitis to normal controls using an ELISA. IgM-titers were low in patients with Crohn's disease who had undergone surgery of small or large bowel but normal in all other groups of patients. Similarly, IgG-titers were similar to control values in all patients with uncomplicated Crohn's disease but elevated in patients with complicating fistula, colonic Crohn's disease and resected small or large bowel. IgM- and IgG-titers were elevated in patients with ulcerative colitis. However, only sera from patients with fistula inhibited increased the binding of a monoclonal antibody specific for B. fragilis thus demonstrating their specificity for B. fragilis. This findings could point to an involvement of B. fragilis in the formation of fistula in patients with Crohn's disease.