Development and clinical application of electroimmunoassays for the direct quantification of the complement C3 split products C3c and C3d.

The present report describes the development of electroimmunoassays for the direct quantification of C3d and C3c, split products of the third complement factor (C3). Both methods were developed as rocket immunoelectrophoreses, using two antibody preparations with specificities against the C and D epitopes on C3. A stable calibrator preparation for C3c and C3d was produced by autolytic cleavage of C3. Investigations of patients with anaphylactic reactions or chronic immunological disorders showed that quantification of C3c and C3d in plasma by these methods reflected the degree and rate of complement activation. C3d determination was found to be the most sensitive and reliable indicator of C activation, both during acute and chronic activation since C3c is eliminated considerably faster from the circulation than C3d (estimated half lives of 2 h and 4 h, respectively). Treatment of rheumatoid arthritis patients with prednisolone caused a prompt decrease of plasma C3d values, indicating that the clinical effect may be due to inhibition of complement activation.