Role of histocompatibility in graft rejection.

Several modes of graft rejection are possible; to these can be added hyperacute rejection of kidney and skin grafts by cell-mediated mechanisms, which has been demonstrated in several different models. The complexity of the MHC in the mouse has been emphasized, with the description of possibly 12 H loci within this complex, including the new H gene, H-21J. The use of H-2 mutants in studying the H genes within the MHC has been emphasized, and by the use of such mutants five or six new gene loci have been defined, including a new region, H-2L; also, new complexities in the structure of the H-2K and H-2D genes have been recognized. The importance of the MHC is further emphasized in the finding that serum Ia measurements in the mouse may reflect the state of T cell activation, since the Ia levels rise prior to graft rejection and are suppressed in tumor-bearing mice.