Humoral and cellular mechanisms in acute allograft injury.

An intact thymus-competent immune system seems both necessary and sufficient for acute allograft rejection. T-lymphocytes fulfill a form of Kochs postulate in this regard: (1) They are present in rejecting allografts; and (2) rejection is abrogated by depriving the host of T cells but can be recreated by providing such T cell-deficient hosts with purified T cells. However, the dilemma of whether Th or Tc cells actually mediate allograft rejection remains. Although belonging to opposite immunologic "teams," they act on each other in many ways, interactions that are probably just the beginning of the complex cascade of both specific and nonspecific host immunologic events, both cell mediated and humoral, that are stimulated by the presence of allogeneic tissues.