Equine Antibodies to Human γG-Globulin: III. Immunochemical Behavior and Specificity of γ₂- and γ₁-Antibody Fractions Isolated from Equine Antisera to Human γG-Globulin¹

Several antisera to human γG-globulin obtained from a single horse and isolated γ₁- and γ₂-antibody fractions prepared from these antisera were compared in complement fixation studies. C′-fixing ability of each successive bleeding progressively increased, paralleling an apparent increase in the proportion of γ₂-antibody in the whole serum. Isolated γ₂-antibody fractions fixed complement when tested at a level of 1 µg antibody N and greater. There were no significant differences in complement-fixing ability on an antibody N weight basis among γ₂ fractions from the same or different bleedings. Isolated γ₁-antibody fractions possessed no complement-fixing ability but could inhibit fixation by the γ₂-antibody.

Both γ₂ and γ₁ preparations exhibited similar end points (0.04 µg antibody N) when employed as anti-globulin reagents in the Coombs test. In comparison, the γ₁-antibody fractions gave a prozone in the antibody excess region, whereas no prozone was noted with the γ₂ fractions. The specificity of antisera and antibody fractions from successive bleedings for antigenic determinants on the human γ-globulin molecule was established by reacting these preparations with several antigens related to the heavy and light chains of human γ-globulin.