Effect of nephritogenic antibody on complement regulation in cultured rat glomerular epithelial cells.
In passive Heymann nephritis, a rat model of membranous nephropathy, antibody (anti-Fx1A) activates C on the surface of the glomerular epithelial cell (GEC), leading to GEC injury and proteinuria. In this study, we examined C activation by anti-Fx1A in cultured rat GEC. In addition to anti-Fx1A IgG, anti-Fx1A F(ab')2 and Fab' led to GEC injury in the presence of rat or human sera as sources of C. Cytotoxicity was Mg2+ and factor B dependent, but Ca2+ independent, indicating that anti-Fx1A activated the C alternative pathway (AP). Furthermore, in the presence of Mg2+ and factor B, anti-Fx1A enhanced 125I-C3b deposition on GEC in the absence of classical pathway activation. AP C3 and C5 convertases formed on GEC (GEC-C3bBbP) were inactivated over time, probably due to binding of GEC C regulatory proteins. This inactivation was prevented when GEC-C3bBbP were incubated with anti-Fx1A IgG. An antibody raised against cultured GEC that binds to GEC in vitro and in vivo had no effect on C3 and C5 convertases, suggesting that stabilization of C3bBbP is unique to anti-Fx1A. Anti-Fx1A Fab' also stabilized GEC-C3bBbP, indicating that cross-linking of membrane Ag was not required. C3bBbP on E were not affected by anti-Fx1A, excluding direct stabilization of convertases by anti-Fx1A. Therefore, anti-Fx1A inhibits C regulation on GEC, which can account for its ability to activate the AP. This represents a potentially powerful mechanism of producing disease in vivo.
Quigg
R J
RJ
Department of Internal Medicine, Medical College of Virginia, Richmond 23298.
Cybulsky
A V
AV
Salant
D J
DJ
D000818:Animals; D001324:Autoantigens / Q000502:physiology*; D003167:Complement Activation / Q000276:immunology*; D050577:Complement C3-C5 Convertases / Q000378:metabolism; D003179:Complement C3b / Q000378:metabolism; D003170:Complement Pathway, Alternative / Q000276:immunology; D003602:Cytotoxicity, Immunologic; D004195:Disease Models, Animal; D004306:Dose-Response Relationship, Immunologic; D005921:Glomerulonephritis / Q000276:immunology*; D026541:Heymann Nephritis Antigenic Complex; D007678:Kidney Glomerulus / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000502:physiology*; D051381:Rats; D013997:Time Factors
D001324:Autoantigens; D026541:Heymann Nephritis Antigenic Complex; D008562:Membrane Glycoproteins; D003179:Complement C3b; D050577:Complement C3-C5 Convertases