Immunoglobulin classes of antibodies produced in the primary and secondary responses in man.

A method, radio-immunoprecipitation, is described which measures the antibody in the different classes in whole sera by its antigen binding capacity. In nineteen of twenty-four individuals immunized with haemocyanin, haemagglutinating antibodies were produced in the primary response, but in only five were amounts significant enough to measure by radio-immunoprecipitation. In these five individuals, the primary response was characterized by an early appearance of IgM and IgA antibodies; IgG antibody was detectable but only in small amounts and not before the 18th day after immunization. All twenty-four individuals responded to a secondary injection. A sharp rise in IgG antibody after the secondary injection is typical of the secondary response. A definite but much lower anamnestic response for IgM and IgA is observed. The difference is so uniform and striking that it may well be characteristic for some primary responses in man.