Induction of specific transplantation tolerance with blood serum in newborn and adult rats.

Histocompatibility (H) antigens present in the serum of rats induce a relatively high degree of neonatal transplantation tolerance in the absence of cellular chimerism. With the non-H-1 difference, which is relatively strong in the rat strain combination used, skin grafts survive permanently in some animals. With the H-1 plus non-H-1 difference, only some animals show a slight prolongation of skin graft survival, but cytotoxic antibody production is inhibited for long periods of time. In adult animals, at least with the non-H-1 difference, allograft survival is very significantly prolonged after treatment with serum alone, or in combination with hydrocortisone. The nonspecific component(s) of the serum also contributes to a prolongation of graft survival. The data suggest that blood serum is a good source of H antigens which seem to be present in a tolerogenic active form.