The genetic control of the antibody response to the Pa antigen in the rat.

The antibody response to the pregnancy-associated (Pa) antigen in the pregnant female segregated with the major histocompatibility complex (MHC) when the female progeny in the (PVG x WF)F1 x PVG testcross, in which the PVG strain is a low responder to Pa and the WF strain is a high responder, were mated to DA male rats. These results show that non-MHC immune response genes do not play a role, or at least any significant role, in the immune response to the paternal component of the placental antigens: the response approximates a unigenic trait with simple Mendelian segregation. Serological analysis showed that the antibodies formed by both the high responder (GMT 15, titer 1:32,768) and low responder (GMT 3, titer 1:8) female rats were directed against the Pa antigen. These findings show that the genetic control mechanism and the specificity of the antibody elicited by the placental antigen Pa are different from those in the responses to organ grafts and to soluble antigens.