Suppressive effect of IgG1 antibody on the complement activation of IgG2 antibody of the guinea pig

The effect of interposition of non-hemolytic antibody on the hemolytic activity of the complement-nxing antibody was examined. When mixtures of the hemolytic IgG2 and non-hemolylic IgG1 classes of guinea pig antibody to TNP 3, the total amount being kept constant, were reacted with TNP-SRBC, the average number of complement-induced lesions per cell (Z) varied as a function of (proportion to IgG2)ⁿ. The experimental values for the exponent n fell in a range between 3 and 4. Comparison of the hemolylic activity of IgG2 in the mixture with IgGl (Z_i) with that of the same amount of IgG2 without IgGl (Z₀) gave a relationship: Z_i = Z₀ × (proportion of IgG2)^{n ? m}, where m was obtained from the dose-response curve. Z₀ vs (concentration of IgG2)^m. Since values for m obtained under the conditions used (1?2) were always smaller than those for n, the activity of IgG2 was apparently suppressed by the presence of IgG 1. From the C1-transfer experiments, the C1-binding step was shown to be affected. Results were tested by a simple hypothesis and the mechanism for the suppressive effect of IgG1 antibody was analysed.