Two biologically different mouse IgG1 antibodies.

Isolated mouse antibodies were submitted to affinity chromatography with protein A. 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 III 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 antiserum but not by anti-IgE. Both peak I and peak II showed heat-resistant PCA activity in mice, that was absorbed by anti-IgG1 serum. 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 their affinity for protein A and in their PCA activity.