Control of complement activation in membranous and membranoproliferative glomerulonephritis

Renal biopsy specimens from 22 membranous (MGN) and 19 membranoproliferative glomerulonephritis (MPGN) patients were examined for the presence of the three regulators of the complement system; C1- inhibitor (C1--INH), C3b inactivator (C3b-INA), and beta 1H. The serum concentrations of these proteins, at the time of biopsy, were also measured. To study the modulation of complement activation by these three control proteins in MGN and MPGN, we examined the relationship between each control protein and the protein whose activity it regulates, in four ways; (a) the concordance between the presence of the control proteins and the components regulated was studied, (b) the correlations in intensity of deposition of the control and complement proteins were measured, (c) the patterns of distribution of the proteins within the glomeruli were compared, and (d) the serum levels of control proteins and components, regulated were examined. C1--INH (23 of 35 biopsies) and beta 1H (34 of 36 biopsies) were frequently deposited in both disease groups. C3b-INA was found only rarely in MPGN (4 of 19 biopsies). This is probably because the former two proteins modulate complement activation stoichiometrically, whereas C3b-INA acts enzymatically. A relationship was demonstrated between C1--INH and C1s and between beta 1H and C3 in both groups, but no such relationship was found between C3bINA and C3. Conclusion. There is no generalized deficiency in modulation of complement activation in MGN or MPGN.