CELL-MEDIATED IMMUNITY AND MHC See APPENDIX (10) INBREEDING; (11) MIXED LYMPHOCYTE REACTION (MLR) Graft rejection is a manifestation of CELL-MEDIATED IMMUNITY

Graft rejection is a manifestation of CELL-MEDIATED IMMUNITY (CMI), as can be demonstrated by adoptive transfer experiments; antibodies generally contribute little to the rejection of grafted tissues. Simple rules predict the acceptance or rejection of alloografts between inbred mice. Although these specific rules are not valid in humans (or other outbred populations), a common fundamental principle holds, namely, that a graft will be rejected if the host's immune system recognizes a foreign antigen on the graft. The most important antigens contributing to graft rejection in vertebrates are those encoded by the MAJOR HISTOCOMPATIBILITY COMPLEX (MHC), a cluster of genes known as H-2 in mice and HLA in humans; within this complex are encoded several CLASS I and CLASS II molecules, with distinct structures and biological functions. The basic rules of immune recognition and reactivity are illustrated by an analysis of GRAFT-VERSUS HOST (GvH) reactions.