Hypercomplementemia in adult patients with IgA nephropathy.

IgA nephropathy (IgAN) is the most common form of chronic glomerulonephritis. Although glomerular deposition of complement components is well known, the evidence of serological complement activation in IgAN is inconclusive. We hypothesized that serum levels of complement components and regulatory proteins in patients with IgAN are correlated with its pathogenesis. In the present study we measured complement components in 50 patients with IgAN and 50 healthy volunteers. C5, C1 inhibitor, factor B, C4 binding protein, factor H, and factor I were measured with the use of single radial immunodiffusion. Mannose-binding lectin (MBL) and properdin (P) were measured by enzyme-linked immunosorbent assay (ELISA). The correlations among complements in the sera of patients with clinical gradings for IgAN (i.e., the good prognosis group, relatively good prognosis group, relatively poor prognosis group, and poor prognosis group) were evaluated. CH50, C4, factor B, P, factor I, and factor H were significantly higher in IgAN patients than in healthy controls. There were significant correlations between C5 and C4 binding protein, between C3 and C5, or between C4 and factor B in patients with IgAN. In the poor prognosis group, C4 binding protein was significantly higher than in the other groups of IgAN patients. hypercomplementemia occurs in IgAN and is associated with an increase in complement regulatory protein (CRP). C4 binding protein analyses can be used to predict disease prognosis.