Characterization of antigen moiety of HBsAg in the complement fixing immune complexes of hepatitis B virus positive chronic active hepatitis.

Circulating immune complexes (CIC) are frequently found in hepatitis B virus-induced chronic active hepatitis. Since antigen and antibody moieties of complexes are critical in determining many of its pathogenic factors, the constituents of these complexes were investigated with particular attention to the quantity and nature of the HBs antigen moiety of the complexes. Complement fixing immune complexes were isolated from sera of 14 patients with chronic active hepatitis by utilizing conglutinin's unique property to bind C3-fixed complexes. Low pH (2.6) was used to dissociate the complexes. Components of dissociated complexes were separated into antigen and antibody fractions using immobilized Protein A. Both fractions were analysed by electrophoresis in polyacrylamide gel with SDS. The antibody fractions showed heavy and light chains of IgG and IgM. The antigen fractions demonstrated six to 10 protein bands with mol. wt ranging between 17,000 and 120,000 daltons. To define precisely the polypeptide antigen moiety involved in the immune complex formation, a transfer blotting technique was used employing human anti-HBs globulin as probe. Polypeptides with mol. wt 97,000 and 49,000 reacted as antigen moieties of HBsAg. In addition, the levels of HBsAg in the antigen fractions were significantly greater (P less than 0.005) compared to sera from patients with acute hepatitis. Implications of these findings are discussed.