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

Abstract

The second component of complement (C′2^hu) in whole human serum has been measured by its specific interaction with a cellular intermediate prepared with guinea pig complement, the EAC′1a^gp, 4^gp cell. In this interaction the conversion of SAC′1a^gp, 4^gp sites to SAC′1a^gp, 4^gp, 2^hu sites is stoichiometrically related to the relative C′2^hu concentration in the reaction mixture; the reciprocal of the serum dilution which produces one SAC′1a^gp, 4^gp, 2^hu site/cell is arbitrarily defined as the number of C′2^hu 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′2^hu. The titration is linear with the sera of patients with hereditary angioneurotic edema even though the C′2^hu 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.