Identification of HBsAg determinants in immune complexes from hepatitis B virus-associated vasculitis

Circulating immune complexes were characterized from 25 sera obtained from five patients with polyarteritis nodosa and three with cutaneous venulitis associated with hepatitis B virus infection. Complexes were isolated by polyethylene glycol and conglutinin-anticonglutinin precipitation methods and were analyzed for HBsAg and anti-HBsAg. Low pH was used to dissociate the complexes, and components were separated into antigen and antibody fractions by using immobilized protein A. In this study, three observations were significant: 1) complexes were frequent and quantitatively more in cutaneous venulitis than in polyarteritis; 2) the levels of HBsAg in the antigen fractions of polyarteritis were greater and correlated with the clinical improvement of the disease; the serum levels of HbsAg remained the same throughout the course of the disease; and 3) complexes from polyarteritis were not completely dissociable at pH 2.6 compared with those from patients with cutaneous venulitis and chronic active hepatitis. The antigen fractions electrophoresed in polyacrylamide gel with SDS demonstrated 6 to 10 protein bands with m.w. ranging between 17,000 and 120,000 daltons. To precisely define the polypeptide antigen moiety involved in the immune complex formation, a transfer blotting technique was used employing human anti-HBsAg globulin as probe. Polypeptides with m.w. 97,000, 49,000, and 23,000 were found to form complexes in both groups of patients.