Elicitation of weak immune response in larval and adult Xenopus laevis by allografted pituitary.

ABSTRACT

To test the claim that tolerance to organ-specific self antigens is established during the ontogenic development of the immune system, pituitary anlagen were removed from early tailbud embryos of Xenopus laevis, and the resulting hypophysectomized tadpoles were grafted with pituitaries after the tadpoles had become immunocompetent. The result was that none of the histocompatible or allogeneic pituitary grafts was rejected throughout an observation period of 100 days. Subsequent experiments revealed that hypophysectomy does not affect the development of immune responsiveness. In addition, allogeneic pituitary grafts were usually not rejected by unoperated, normal tadpoles or froglets, although they suffered lymphoid invasion to various degrees. However, a significant number of allogeneic pituitaries was rejected when they were grafted, either after or at the same time as the grafting of skin from the pituitary donors. We conclude that the pituitary of Xenopus possesses weak transplantation antigens or expresses them in ways that make them less accessible to the immune surveillance system of the allogeneic host.