Patients with systemic lupus erythematosus are deficient in complement-dependent prevention of immune precipitation

Objective. A functional deficiency of complement has been implicated but not conclusively demonstrated in the pathogenesis of systemic lupus erythematosus (SLE). To test this, we studied several aspects of complement in 44 patients with SLE, 46 patients with rheumatoid arthritis and 102 blood donors. Methods. Prevention of immune precipitation (PIP) was measured by an enzyme immunoassay, levels of C1q, C4 and C3 by rocket immunoelectrophoresis, C4A, C4B and C3d by enzyme-linked immunosorbent assay (ELISA), complement haemolysis (CH50) by standard methods and C4 allotypes by high-voltage agarose electrophoresis and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Results. PIP was significantly reduced in SLE (P