Circulating conversion products of C3 in liver disease. Evidence for in vivo activation of the complement system.

Circulating conversion products of the third component of human complement (C3) were sought for in different forms of liver disease by the method of antigen–antibody crossed electrophoresis. Immunochemical determinations of C3 and C4 by the single radial immunodiffusion method were performed simultaneously. The conversion product C3b was found in four out of twelve patients with chronic active hepatitis (CAH) and in seven out of nine with primary biliary cirrhosis (PBC). C3b was also seen in a patient with the special form of acute hepatitis characterized by arthritic prodromas and a high titre of hepatitis-associated antigen (HAA) in serum in the acute phase. The group of CAH patients had low serum C3 and C4 regardless of whether C3 breakdown products could be demonstrated or not. In PBC normal serum levels of C3 and C4 were generally found. It is concluded that in some patients with CAH and in a majority of the patients with PBC activation of complement takes place in vivo, possibly on immune complexes deposited in the liver. The serum level of C3 is not a good parameter of immunologic activity in liver disease.