Molecular forms of rabbit antibody synthesized during the primary response to human albumin.

Rabbits were injected intravenously or into the hind footpads with 10 mg alum-precipitated human serum albumin or this antigen in complete Freund's adjuvant. Passive haemagglutination, antigen-binding, precipitation, radio-immunoelectrophoresis and passive cutaneous anaphylactic reactions were applied to the assay of antibodies in sera and in ultracentrifugal, electrophoretic and chromatographic fractions of these sera. The γM and γG antibodies appeared simultaneously in the blood on day 6 after immunization. The γM antibodies were detected most readily by haemagglutination, but also by radio-immunoelectrophoresis. These antibodies were not detected by antigen-binding, by precipitation, or by passive cutaneous anaphylaxis. The small amounts of γG antibody that first appeared on day 6 were detected by antigen-binding and radio-immunoelectrophoresis. On day 8 these γG antibodies were revealed by haemagglutination, precipitation and passive cutaneous anaphylaxis. A third type of antibody with the mobility of a β-globulin was identified by radio-immunoelectrophoresis in concentrated electrophoretic fractions prepared from 10 to 25 ml of day 6 antisera. The data are discussed with regard to the validity of the postulated sequential synthesis of γM and γG antibodies, to the cellular origins of antibodies, and to the methods for demonstrating different classes of antibodies.