Renal localization of the membrane attack complex in systemic lupus erythematosus nephritis.

Abstract

The membrane attack complex (MAC) of the complement system was localized in glomeruli and peritubular regions of 22 kidneys manifesting systemic lupus erythematosus (SLE) nephritis. A similar distribution was observed for immune complex markers (IgG, complement components C1q and C3) and MAC in glomeruli, although the MAC deposits were more discrete and showed lesser immunofluorescence staining intensity compared with Ig and complement components. Peritubular immune complexes were present in only 7 of 22 kidneys, involved comparatively small clusters of tubules, exhibited weaker immunofluorescence staining than MAC and failed to correlate with interstitial foci of inflammation. Granular or irregular linear aggregates of the MAC were observed at the periphery of larger groups of tubules, contiguous to areas of interstitial inflammation. Comparable amounts of IgG, C1q, C3 and MAC were present in blood vessel walls in areas of fibrinoid necrosis. Thus the MAC may be a direct mediator of tissue injury occurring in renal glomeruli, tubules and blood vessels. The discordance between immune complexes and MAC localized in the peritubular region, but not in glomeruli or blood vessels, raises the possibility that both immune complexes and nonimmune agents, such as bacterial antigens, may activate the classical or alternative complement pathways and thereby play a role in the pathogenesis of tubulointerstitial lesions of SLE nephritis.