Homocytotropic and heterocytotropic activity of mouse IgG1 antibodies.

Mouse anti-ovalbumin antibodies were isolated by affinity chromatography and fractionated in a column of protein A-Sepharose. Three peaks were obtained: peak I that did not bind to protein A, peak II eluted with 0.5 M NaSCN and peak III eluted with 2.0 M NaSCN. Peak I and peak II contained IgG1 but no detectable IgG2 or IgG3, whereas peak II contained IgG2 and IgG3 but no detectable IgG1. Peak I, but not peak II, showed heat-resistant passive cutaneous anaphylactic (PCA) activity in rats, which was absorbed by anti-IgG1 serum but not by anti-IgE. Both peak I and peak II showed heat-resistant PCA activity in mice, that was absorbed by anti-IgG1. Peak III showed PCA activity in guinea pigs but not in mice or rats. These findings suggest that mouse IgG1 can be divided into 2 populations that differ in physicochemical and biological properties.