Immunohistochemical study of the membrane attack complex of complement and S-protein in idiopathic and secondary membranous nephropathy.

Twenty-eight renal biopsies from 12 patients with idiopathic membranous nephropathy (MN), eight patients with lupus MN, and eight patients with hepatitis B virus-(HBV) related MN were investigated by immunofluorescence for the presence of C5b-C9 neoantigens of the terminal sequence of complement and for S-protein, which is a regulatory component of the membrane attack complex (MAC). Glomerular MAC was detected in 50% of patients with idiopathic MN, in 75% of patients with lupus MN, and in only 12.5% of the HBsAg carrier with MN. Glomerular adhesions to Bowman's capsule were associated with a high incidence of glomerular MAC deposition only in patients with idiopathic MN. Lupus patients had a high incidence of MAC deposition and patients with HBV-related MN had a low incidence of MAC deposition, in both cases regardless of the presence of glomerular capsular adhesions. It is unlikely that deposition of S-protein could inhibit the glomerular damage in idiopathic or lupus MN because significant glomerular capsular adhesions and MAC deposition were observed despite the concomitant glomerular deposition of S-protein. It was concluded that activation of terminal components of complement may play a role in glomerular injuries in idiopathic and lupus MN. The rare occurrence of glomerular MAC deposition in HBV-related MN could be related to its distinct immunopathogenetic mechanism and its indolent clinical course.