Characteristics of specific unresponsiveness toward kidney and skin allografts in adult rats inoculated at birth with allogenic bone marrow or kidney cells across a strong H-1 barrier.

Specific unresponsiveness inducible in newborn Lewis (Le) rats by injection of bone marrow or kidney cells from (Bu x Le)F1 hybrids was tested in adults by allografting of skin or kidneys from strongly incompatible Buffalo (Bu) strain donors. High doses of bone marrow cells (10(7) or more) proved quite effective in procuring indefinite survival of subsequent Bu kidney allografts, but not Bu skin allografts. Kidney allografts remained fully functional without modulation of their inherent immunogenicity regardless whether skin allografts were acutely rejected before or after kidney grafting on bone marrow-tolerant recipients. Lower doses of bone marrow cells were either near threshold for induction of specific Bu kidney allograft tolerance (5 x 10(6)) or, conversely, led to increased immunity(1-5 x 106). A strikingly different pattern of reactivity was found in adult Le recipients of Bu skin allografts as shown by only a moderate, but stepwise increase in survival times as a function of increasing allogeneic cell dosage at birth. Allogeneic kidney cells at all doses were surprisingly ineffective in inducing tolerance of either kidney or skin allografts, so the existence of kidney-specific transplantation antigens remains problematical. Lymphocytes from kidney allograft-tolerant recipients showed much reduced but still significant antidonor activity in several tests of cell-mediated immunity in vitro and in vivo. Blocking antibody activity was also demonstrable in these animals. Acquired tolerance (i.e., essential nonreactivity) may not only exist in degrees in either T or B cell pathways but may coexist with specific immunoblocking reactions in a dynamic equilibrium. Instead of tolerance versus enhancement, a new concept of selective specific immunoregulation emerges.