Human C1q: rapid isolation and quantitative determination by immunodiffusion

A simple and rapid 2-step procedure for isolating C1q from human plasma at high yields (about 50%) is described. The purification involves diaminopropane precipitation followed by chromatography on IgG-Sepharose. The final product (obtained at a concentration of about 1.5 mg/ml) was electrophoretically and immunochemically pure and stable at -70 degrees C for long periods. The Mancini technique for the quantitative determination of C1q was reinvestigated and the use of gels containing high salt concentrations (1.0 M NaCl) was found to be absolutely necessary. A value of 0.076 mg/ml C1q in pooled human plasma was obtained.