New evidence of circulating immune complexes in Crohn's disease using two sensitive methods.

Circulating immune complexes (AgAb) were studied in 183 serum samples from 119 patients with Crohn's Disease. AgAb were studied by the solid phase C1q binding test in all sera and also by the conglutinin binding assay in 161 sera. A significantly higher prevalence of circulating AgAb was observed in Crohn's disease patients in comparison with the control population. About one half of the sera were AgAb positive when the results of both tests were combined whereas AgAb were found in about one third of the sera by each individual method. Complexes revealed by the C1q-SP appeared to be related to the disease activity and to the occurrence of complications. Such a correlation was not observed as far as conglutinin results are concerned. Data emerging from the present investigation indicate that circulating AgAb may be present in Crohn's disease and suggest that the AgAb material is heterogeneous. They also suggest the possibility that AgAb represent a secondary phenomenon.