METHOD FOR DETERMINING THE EQUILIBRIUM-CONSTANT AND THE CONCENTRATIONOF INFLUENZA-VIRUS IGG ANTIHAEMAGGLUTININ ANTIBODY MOLECULES BY USE OF EIA TITERS DETERMINED WITH AND WITHOUT GUANIDINE-HYDROCHLORIDE

A novel technique for determining the concentration of influenza virus antihaemagglutinin antibody molecules (A) of the IgG class and their equilibrium constant (K) is described which is based on recording EIA (enzyme-linked immunosorbent assay) guanidine titre ratios R (EIA titr e determined in the absence of guanidine divided by EIA titre determin ed in the presence of 0.25 M guanidine hydrochloride). K is determined by using a regression line relating values of K to values of R. The l ine was established by testing antisera comparatively for K by means o f equilibrium filtration and for R by EIA. The assay of A is based on the finding that the concentration of antibody molecules adsorbed at s erum dilutions yielding an O.D. reading of 0.9 in the EIA test is with in the experimental limits constant. Since K is known, this point of r eference can be used to calculate A. For a panel of 57 influenza antis era, the A and K values determined by equilibrium filtration agreed we ll with the respective values determined by use of the novel technique .