[Effect of pH on the physico-chemical and immunologic properties of rabbit antibodies]

The effects of an incubation at low pH (during 20 h at 37 degrees) on the antibody activity and anticomplementary activity of rabbit IgG have been studied. Modifications have also been examined by physicochemical methods. The properties of rabbit anti-sheep red cell IgG are not modified by incubation at pH values between 7.4 and 4.0 during 20 h at 37 degrees. Below pH 4 a decrease of hemolytic activity is apparent concomitant with an important increase of the agglutinating activity. This phenomenon is due to the formation of polymers from native IgG. At pH values below 3.8 the anticomplementary activity of a nonspecific IgG decreases rapidly. One observes an increase of optical rotation, a finding which is compatible with the appearance of heavier compounds with sedimentation coefficients of 9.5 and 11.5 S, probably dimers of native IgG. The increase of optical rotation is partially reversible when the pH is readjusted to 7.4. The use of starch-gel and immunoelectrophoresis has shown the appearance of compounds with higher mobility which are closely related to a peptide (PEP III') which was isolated from a peptic hydrolysate of rabbit IgG. The decrease of anticomplementary activity of nonspecific IgG seems to be closely related to the liberation of PEP III'.