Self-pituitary grafts are not rejected by frogs deprived of their pituitary anlagen as embryos.

In the present study, we have adopted the model of Triplett to reinvestigate the timing of development of immunological tolerance to self-organ-specific antigens. We have removed pituitary or eye analgen from embryos before development of the immune system and returned them at a later time as differentiated organ implants to their now immunocompetent larval or adult original owners. If immunological tolerance to these putative organ-specific self-antigens occurs at an early and fixed time period, than organ-deprived hosts, lacking the opportunity to become tolerant, would be expected to reject such implants. Our results show that self-implants were never rejected whereas control allogeneic implants were usually rejected by larval hosts and were always rejected by adult hosts. These data, which contrast with those reported by Triplett, suggest that frogs, and perhaps other higher vertebrates, can become tolerant to self-organ-specific antigens throughout life.