The Measurement of Second Component of Human Complement (C′2hu) by Its Interaction with EAC′1agp, 4gp Cells

Abstract

Summary The second component of complement (C′2hu) in whole human serum has been measured by its specific interaction with a cellular intermediate prepared with guinea pig complement, the EAC′1agp, 4gp cell. In this interaction the conversion of SAC′1agp, 4gp sites to SAC′1agp, 4gp, 2hu sites is stoichiometrically related to the relative C′2hu concentration in the reaction mixture; the reciprocal of the serum dilution which produces one SAC′1agp, 4gp, 2hu site/cell is arbitrarily defined as the number of C′2hu units/ml of serum. Although there are deficiencies in the understanding of certain aspects of this titration, it does afford a sensitive and reproducible measurement of C′2hu. The titration is linear with the sera of patients with hereditary angioneurotic edema even though the C′2hu titer may be only 1 to 2% of normal. Because the steps in the assay can be separated, the influence of unusual factors in pathologic sera on the titration can be ascertained.