Genetic control of antibody responses to PHA in inbred rats

Phytohemagglutinin (PHA-P; Difco) contains four immunogenic components. The antibody response in rats to two of these components is shown to be genetically determined: AS rats are high responders and BN rats are low responders to both antigens. Responsiveness to the two components segregates independently as autosomal, dominant traits in a manner that is compatible with a one-gene hypothesis for both responses. The antibody response to the mitogenic fraction of PHA segregates together with the in vitro mitogenic response to PHA and to other mitogens. These responses are not linked to the major histocompatibility complex (MHC) of the rat. The antibody response to a nonmitogenic fraction from PHA is, however, linked to the MHC.