Abstract
Circulating complement breakdown products, C 4 d, iC 3 b and Bb, in plasma from patients with various rheumatic diseases were determined by ELISA kits using monoclonal antibodies. Plasma C 4 d, iC 3 b and Bb, especially Bb, were elevated in systemic lupus erythematosus (SLE) with hypocomplementemia, and also in rheumatoid arthritis (RA), aortitis syndrome and Behcet's disease with hypercomplementemia. Among plasma levels of C 4 d, iC 3 b and Bb, there was no significant correlation in SLE, mixed connective tissue disease, polymyositis, progressive systemic sclerosis or RA. In aortitis syndrome and Behcet's disease, there was a positive correlation between C 4 d and iC 3 b. In SLE, C 4 d showed significant correlations with circulating immune complex (CIC) (r=0.633, P<0.001) and with CH 50 (r=-0.346, P<0.01). iC 3 b and Bb showed no significant correlation with CIC or CH 50. These data suggested that both pathways of the complement system were activated in patients with SLE and other rheumatic diseases, CIC activated the classical pathway resulting in plasma C 4 d elevation, and other factor activated the alternative pathway resulting in plasma Bb elevation.
