Relative importance of C4 binding protein in the modulation of the classical pathway C3 convertase in patients with systemic lupus erythematosus.
Serum concentrations of C1q, C4, C4 binding protein (C4bp), C3 and C2 haemolytic activity have been measured in 110 samples from 20 patients with systemic lupus erythematosus (SLE). Significant reductions in comparison to normal levels were found in the mean serum concentrations of C4, C3 and C4bp as well as C2 haemolytic activities. For patients serum concentrations of C4 correlated with C2 haemolytic activities (r = 0.91) and C4bp (r = 0.79); the C2 haemolytic levels correlated with the concentration of C4b (r = 0.72). It is concluded that serum concentrations of the complement components C4 and C2, which are the constituents of the classical pathway C3 convertase, are regulated by C4bp in vivo. Further metabolic studies are required to determine the causes of decreased serum concentrations of C4bp in patients with SLE.
D002352:Carrier Proteins / Q000032:analysis*; D003166:Complement Activating Enzymes / Q000032:analysis; D015922:Complement C1q; D003175:Complement C2 / Q000032:analysis; D003176:Complement C3 / Q000032:analysis; D050577:Complement C3-C5 Convertases / Q000276:immunology; D003181:Complement C4 / Q000032:analysis; D003171:Complement Pathway, Classical; D006801:Humans; D016167:Integrin alphaXbeta2; D008180:Lupus Erythematosus, Systemic / Q000097:blood / Q000276:immunology*
D002352:Carrier Proteins; D003175:Complement C2; D003176:Complement C3; D003181:Complement C4; D016167:Integrin alphaXbeta2; D015922:Complement C1q; D003166:Complement Activating Enzymes; D050577:Complement C3-C5 Convertases