Humoral immune system in inflammatory bowel disease: I. Complement levels.

Serum levels of complement components Clq, C4, C3, and Properdin factor B, from the classical and alternative pathways of complement activation, have been estimated in patients with ulcerative colitis and Crohn's disease. C3, factor B, and to some extent C4 concentrations all increased when the disease was active. In remission the levels of these components did not differ from hospital control patients. There was no evidence for the preferential consumption of the proteins of either pathway of activation, even in those patients with evidence of circulating immune complexes.