[Description of a method for the determination of the number and quality of influenza virus antibody molecules by means of equilibrium centrifugation (author's transl)].

The method of equilibrium centrifugation for determining the number of antibody molecules (A) and their equilibrium constant K characterizing the reactivity of antibody with antigen described in this paper is based on the use of virus-coated formaldehyde-treated erythrocytes as immuno-adsorbent. Graded doses of the immuno-adsorbent are mixed with the serum to be tested and the degree of antibody adsorption is measured. By analogy to the formula used in the method of equilibrium filtration, these data can be evaluated in order to determine the concentration of antibody molecules and the equilibrium constant K. Adsorption of virus on formaldehdye-treated erythrocytes results in steric hindrance of a part of the antigenic sites of the virus particles. This was taken into account by measuring sera comparatively both by means of equilibrium centrifugation and by use of equilibrium filtration and establishing correction formulas. Both techniques were found to have the same sensitivity and accuracy. In comparison to equilibrium filtration, equilibrium centrifugation offers the advantage that it can be used with test antigens which are below the minimum size needed in equilibrium filtration.