Complement activation by antibodies to Sm in systemic lupus erythematosus.
An enzyme linked immunosorbent assay was developed to quantitate antibodies to Sm (anti-Sm) and to measure complement activation by anti-Sm in vitro. Anti-Sm in plasma of patients with systemic lupus erythematosus (SLE) were bound to purified Sm bound to polyvinyl chloride microtitre plates and assayed for bound IgG or IgM using enzyme linked anti-gamma or anti-mu. The activation of C4 by anti-Sm was measured by adding diluted normal human serum (complement) to the wells and quantitating the amount of C4 bound to the well surface using (Fab')2 goat anti-C4 followed by enzyme linked rabbit anti-goat IgG. The plasmas of 12 of 36 patients with SLE contained anti-Sm and all 12 activated complement (complement activating anti-Sm). Twenty-eight plasmas containing anti-Sm from 12 patients with SLE were studied. Ten of the 12 patients had anti-Sm of the IgG class whereas two had anti-Sm of both IgG and IgM classes. The amount of C4 activating anti-Sm correlated significantly with the in vivo activation of C4 measured by rocket immunoelectrophoresis for C4d and C4, suggesting that complement activation by anti-Sm is important in vivo.
D000974:Antibodies, Antinuclear / Q000276:immunology*; D000918:Antibody Specificity; D000941:Antigens / Q000276:immunology*; D001324:Autoantigens; D003167:Complement Activation; D003181:Complement C4 / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D008180:Lupus Erythematosus, Systemic / Q000276:immunology*; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins
D000974:Antibodies, Antinuclear; D000941:Antigens; D001324:Autoantigens; D003181:Complement C4; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins