Enzyme immunoassay analysis of antibody specificities present in the circulating immune complexes of selected pathological sera.

Using immobilized anti-C3 antibody and an enzyme immunoassay, sera from 26 patients (eight with systemic lupus erythematosus (SLE), four with Hashimoto's thyroiditis, eight haemophiliacs and six with post-hepatitis cirrhosis) containing high levels of circulating immune complexes (IC) were selected. The IC were precipitated with 2.5% polyethylene glycol, washed, treated with acid buffer, neutralized and tested using an enzyme immunoassay in parallel with the original sera for antibody activity against a panel of antigens: human myosin and thyroglobulin, mouse actin and tubulin, calf thymus DNA and trinitrophenyl coupled to bovine serum albumin (TNP/BSA). It was found that all the isolated IC may contain IgG, IgA and IgM antibodies reacting with actin tubulin and TNP/BSA and also, depending upon the disease, antibodies reacting with some of the other antigens of the panel. By comparison to the antibodies present in the original sera, higher titers of antibodies were found in the isolated IC while some antibody specificities not detected in a given serum were occasionally noted in the isolated IC. The antibodies present in the IC seem to possess characteristics similar to those of polyreactive human natural autoantibodies. It is concluded that natural autoantibodies participate actively in the formation of IC found in pathological sera.