An experimental set up is described in which the degree of optical density during lysis of sensitized sheep erythrocytes by complement (C′) and other hemolytic agents is followed photometrically and recorded automatically.
The time required for 50% reduction in optical density is inversely proportional to the serum dilution and thus can be taken for quantitative measurement of C′-activity. The linear relationship forms the basis for a quantitative comparison of the effect of various inhibitors. A definite advantage of the method is due to the ease with which kinetic studies of whole complement and the intermediate steps of its action can be performed.
Using this method the influence of variations of the quantity of red cells, of antibody concentration, and of temperature are reported.
To demonstrate the usefulness of the method a number of experiments are given, each of which is characteristic for a certain field of application. They include estimation of lytic activity of serum complement, comparison of different C′ inhibitors, action of C′ on tanned erythrocytes in the absence of antibody, estimation of lytic activity of lysolecithin (LL), hemolysis by LL as obtained by activation of C′ in serum and from erythrocytes lysed by C′, inhibition of C′ and of LL by albumin and by lecithin.