Quantitation of the fourth complement component by electrophoresis in agarose gel containing antibodies.

Electrophoresis in agarose gel containing antibodies can be used for quantitation of C4 in serum and plasma. The normal range of the C4 concentration in serum and plasma varied between 40 and 200% of the standard pools. Low C4 values were found in systemic lupus erythematosus, in acquired haemolytic anaemia and in hereditary angioneurotic oedema. Differences in C4 values were found between normal sera and the corresponding EDTA plasma, when tested after dilution in calcium-free and EDTA buffers, respectively. After storage of the samples for 1 day at 20°C or 37°C the C4 values decreased, most markedly in plasma; no further decrease was found on prolongation of storage, and the difference between serum and plasma C4 values disappeared. The plasma C4 levels gradually fell on storage at 4°C, but a clear difference between serum and plasma was still demonstrable after 5 days. The method described is simple and quick and can be used routinely in large scale investigations.