Screening test for complement activation by counterimmunoelectrophoresis.

This report describes the use of counterimmunoelectrophoresis (CIE) as a method of detecting activation of the complement system. With this technic small amounts of C3 split products (C3c/d) can be detected in plasma samples by specific precipitation with antiserum in less than two hours. The CIE technic is a highly sensitive, rapid method for detecting activation of the complement system in the presence of normal concentrations of C3 measured hemolytically or by radial immunodiffusion (RID) in human disease. A clinical investigation was carried out in 40 patients with systemic rheumatic diseases and 116 normal healthy individuals. The following observations were made: (1) plasmas and sera from normal individuals had normal total complement hemolytic activity (CH50), hemolytic active C4 (C4H50) and C3 (C3H50); (2) in 30% of the serum samples it was possible to identify the presence of C3 split products, in contrast to only 2.5% of the plasma samples obtained simultaneously; (3) in the specimens from patients who had rheumatic disease activity, C3 split products were identified by CIE in all cases except one in the presence of normal C3 protein measured by RID.