[Investigations on strain-specific differences in the relationship between hemagglutination-inhibition titers and the number and quality of antibody molecules oriented to influenza virus type A strains (author's transl)].

For a series of influenza virus A strains, the number of antibody molecules per ml (A) and their quality in terms of the equilibrium constant K was determined. The relationship between the values of A and K and the HI titers was examined and the following results were obtained: 1. For the majority of strains tested, no significant differences in the number of antibody molecules per HI unit were found. For some strains, significantly differing A/HI values were recorded. However, it cannot be excluded that these differences were artifacts, reflecting different numbers of antigenic sites per virus particle for the strains compared and not different numbers of antibody molecules per HI unit. 2. N2 antineuraminidase (= AN) antibodies were found to influence both the A and HI values in like manner when allowed to react simultaneously in presence of antihemagglutinin antibodies with homologous virus. As a consequence, the A/HI ratios were not measurably influenced by AN antibodies, reflecting antihemagglutinin antibodies, only. 3. For the sera tested, the HI titers were found to depend primarily on the values of A and much less on the values of K. The results are interpreted to suggest that the ratios of HI titers measured against different influenza A strains will in first approximation reflect the ratios of the concentration of antibody molecules.