Plasma C3d/C3 quotient as a parameter for in vivo complement activation.
Plasma levels of C3 and C3d in 30 healthy donors and 58 patients with systemic lupus erythematosus were determined by rocket immunoelectrophoresis and Con-A affinoimmunoelectrophoresis. Significantly decreased levels of C3 were found in approximately 50% of the SLE sera. Slight increases of free C3d were found in 55%, and marked increases in 9% of the SLE sera; the remaining SLE sera did not show increased C3d levels. When results were expressed as quotients of plasma C3d/C3, a significant pattern emerged and 70% of the SLE sera clearly fell outside the normal range. 10% of the SLE sera had normal C3d/C3 indices but had markedly depressed C3 levels. We conclude that in cases where total serum C3 is not markedly reduced (less than 60% of normal), the C3d/C3 quotient may be a more sensitive parameter for assessing in vivo complement activation than C3 or C3d determinations alone.
D003176:Complement C3 / Q000032:analysis*; D015933:Complement C3d; D003208:Concanavalin A; D004789:Enzyme Activation; D006801:Humans; D007123:Immunoelectrophoresis, Two-Dimensional / Q000379:methods; D008180:Lupus Erythematosus, Systemic / Q000097:blood; D012016:Reference Values
D003176:Complement C3; D003208:Concanavalin A; D015933:Complement C3d