Successful transplantation across major histocompatibility barrier of deoxyguanosine-treated embryonic thymus expressing class II antigens.

Foreign tissues grafted into healthy recipients are usually rejected by the hosts' immune system largely by means of major histocompatibility complex (MHC) products expressed on donor cells. During ontogeny, developing T lymphocytes acquire tolerance to self-MHC antigens and the thymus has been considered as the most likely site for the abrogation of self-reactive clones. We demonstrate here that embryonic thymus lobes, when organ cultured in the presence of deoxyguanosine, which is toxic to proliferating embryonic thymic lymphocytes but does not affect the epithelial framework, when transplanted to the kidney capsule of normal healthy histoincompatible mice, are not rejected despite their continued expression of both class I and class II donor MHC products but do not induce tolerance. This suggests that immunogenicity is not solely a function of MHC antigen expression but is also influenced by the type of cell upon which the antigens are expressed and, if the thymus is involved in the induction of tolerance to self-MHC products, this is a function of a component other than the epithelium, perhaps thymic dendritic cells.