Three step purification of C1q by DNA precipitation, ion exchange and lectin affinity chromatography.

The difficulties associated with the isolation of pure C1q in sufficient amounts are reflected by the substantial number of isolation procedures, which are being published. The two major problems are a low yield and contaminating immunoglobulins. In addition, some isolation protocols appear to produce C1q contaminated with an inhibitor (C1q-INH). The present isolation protocol involves precipitation of C1q by DNA, chromatography using Sephadex QAE A 50 followed by Con A affinity chromatography. By this combination of purification steps maximal advantage was taken of the cationic properties and high carbohydrate content of the C1q molecule. The yield was 1-2 mg C1q per 100 ml serum. The isolated C1q was free of any demonstrable contaminants as demonstrated by Ouchterlony double diffusion and polyacrylamide gel electrophoresis.