Circulating immune complexes in inflammatory bowel disease.

Evidence for circulating immune complexes in sera of patients with ulcerative colitis or Crohn's disease is described. Such sera produced significantly greater inhibition of antibody-induced cytotoxicity mediated by lymphocytes than did sera from normal control subjects. Inhibitory activity of patients' sera showed a positive correlation with severity of disease, the height of the ESR and, in the case of ulcerative colitis, with the severity of inflammation as seen at sigmoidoscopy. Using gel filtration on Sepharose 6B, inhibitory activity was found in fractions of higher molecular weight than monomeric IgG but of lower molecular weight than IgM. These fractions were shown to contain IgG measured by immunodiffusion. Evidence that inhibition is not due to aggregated IgG molecules is provided by the fact that no correlation was found between inhibitory activity and total IgG concentration. A possible role of immune complexes in the pathogenesis of ulcerative colitis and Crohn's disease is proposed.