Circulating IgG complexes in primary biliary cirrhosis. A serial study in forty patients followed for two years

Several antibodies are present in sera of patients with primary biliary cirrhosis (PBC). We have looked for evidence of antigen-antibody complexes in sera of PBC assuming that some of the antibodies may circulate complexed with an antigen. The Raji cell radioimmunoassay, which determines complement-bound immune complexes, was used to determine the levels of such complexes in serial samples of sera from forty patients with PBC followed for 2 years. Twenty-four patients (60%) were found to have significantly elevated levels of circulating complexes. In the majority they were detected from the beginning of the study and the high levels persisted. In seven patients whose sera initially had normal levels of complexes, the levels increased to become abnormal during the following year. These complexes sedimented at greater than or equal to 19S in the majority of patients studied. The mean level of C3 but not C4 was lower in patients with elevated complexes than in those with normal complexes. A significant correlation was observed between the presence of elevated complexes and the severity of the inflammatory cell infiltrate surrounding intrahepatic portal tracts and serum IgG and IgM levels. There was also a significant correlation with titres of antimitochondrial antibody, but not with the histological stage of disease or with the collagen and copper content of the liver. Although the method of detection of immune complexes is indirect and the antigen is unknown, the presence of such high levels of complexes suggests a possible role of immune complexes in the pathogenesis of PBC.