C1q PRECIPITINS IN THE SERA OF PATIENTS WITH SYSTEMIC LUPUS ERYTHEMATOSUS AND OTHER HYPOCOMPLEMENTEMIC STATES: CHARACTERIZATION OF HIGH AND LOW MOLECULAR WEIGHT TYPES

TLDR

C1q precipitin reactions in gel diffusion detect unknown gamma‑globulin complexes in the sera of patients with systemic lupus erythematosus. Low‑molecular‑weight C1q reactants and circulating complexes are present in SLE and other diseases, correlate with disease activity, complement depression, cryoprecipitation, nephritis, and involve rheumatoid factors that localize to cryoprecipitates and renal deposits.

Abstract

Precipitin reactions of C1q in gel diffusion proved useful in detecting unknown complexes containing gamma-globulin in the sera of patients with SLE. Using this method low molecular weight C1q reactants also have been detected in a number of sera from patients with SLE as well as other diseases. Both the circulating complexes and the unidentified low molecular weight reactants are associated with disease activity and in vivo complement depression. In some sera from patients with SLE, circulating complexes as detectable by C1q precipitation were closely associated with cryoprecipitins and an active nephritic process. Evidence is presented that both rheumatoid factors and C1q interact with circulating complexes in these patients and that the interaction is related to cryoprecipitation. The demonstration of the same rheumatoid factors in the cryoprecipitates and in the renal glomerular deposits suggests that rheumatoid factors have a special significance in the presence of circulating complexes.