Antibody responses after successive injections of related antigens.

The response of serologically mature fowls to antigens having varying degrees of relationship to a previously injected antigen was studied by quantitative precipitin methods and absorption analyses. After successive injections with related antigens three major antibody populations were detected: (1) antibodies reacting only with the second antigen, equivalent in amount to those obtained in a primary response to that antigen; (2) antibodies reacting only with the first antigen, lower in amount than those obtained during a primary response to that antigen; and (3) antibodies reacting with both antigens, in much greater amount than after successive injections with a single antigen. Successive immunization with unrelated antigens did not result in the formation of antibodies capable of reacting with the primary antigen.