The complement system is activated in primary biliary cirrhosis (PBC) and this activated state may be medicated by immunoreactive IgM. To identify and further characterize the relationship between the complement (Clq) and IgM in PBC sera, we developed an anti-Clq ELISA method which allowed detection of Clq-containing circulating immune-like complexes. Utilizing this technique, sera from 3 out of 5 patients with PBC revealed circulating immune-like complexes. Moreover, when serum samples were specifically examined for the presence of IgM containing Clq complexes, four of four samples examined were positive. Additional experiments indicated that these immune-like complexes could be removed from PBC sera by means of an anti-Clq immunoadsorbent. Upon subsequent isolation and characterization, these immune-like complexes demonstrated polypeptide chains corresponding to both human Clq and human IgM. Our experimental studies establish that Clq-containing IgM-like complexes can occur in the serum of patients with PBC, and provide additional support for the proposal that immunoreactive IgM can contribute to the activated complement system observed in PBC.
Antigen-Antibody Complex Complement Activating Enzymes