Precipitin reactions of the C1q component of complement with aggregated gamma-globulin and immune complexes in gel diffusion.

A gel diffusion method for demonstrating precipitin reactions of C1q with aggregated γ-globulin and immune complexes is described. Optimal precipitin lines were found to occur with 0.6 per cent agarose in 0.01 M EDTA at pH 7.2 and ionic strength 0.1. Reduction and alkylation of γ-globulin aggregates destroyed the precipitability with C1q. Precipitation occurred only with aggregates greater than 19S and with soluble immune complexes formed in two to twenty times antigen excess. γ-Globulin complexes were detected by this procedure in hypocomplementaemic sera from patients with systemic lupus erythematosus and hypocomplementaemic joint fluids from patients with rheumatoid arthritis. The relevance of this in vitro system to in vivo complement consumption in various disease states is discussed.