Antibody response after alloimmunization with heart tissue in the rat. Characterization of the alloantibodies.

The autoantibody component of LEW anti-DA heart homogenate serum was removed by exhaustive absorption with LEW heart, and the remaining alloantibody component assayed on DA heart homogenate target using 125I antirat immunoglobulin binding assays. The alloantibodies could be divided into two components, one present on spleen and presumably directed at major histocompatibility complex (MHC) antigens and the other present on heart but absent from spleen, liver, and kidney, and therefore defining a heart-specific alloantigen. Localization studies on frozen sections showed the antigen to be localized to the membrane and T tubular system of the myocardial cells and also to the membrane of skeletal muscle cells. Backcross studies showed that the locus coding for this heart-specific antigen appeared not to be linked to the MHC, and that the MHC was the only locus of importance for acute rejection of heart grafts in the DA to LEW combination. Thus, it was concluded that the heart-specific alloantigen was not important for acute cardiac rejection at least in the DA to LEW rat strain combination. As regards antibodies to MHC antigens, there appeared to be substantially more of these in LEW anti-DA heart graft serum when compared to LEW anti-DA heart homogenate serum, and both anti-SD (RT1.Aa) and anti-Ia (RT1.Ba) antibodies could be demonstrated in the antiheart graft serum.