Metamorphosis-dependent recognition of larval skin as non-self by inbred adult frogs (Xenopus laevis).

Larval cells in tissues of the anuran tadpole are replaced by adult cells in the corresponding tissue of the frog during metamorphosis. As an extreme example of such replacement, tissues of the tail, which have no counterpart in the adult, are completely eliminated during metamorphosis. We postulated that some immunological recognition mechanism might be involved in this specific elimination of the tail tissue. Our working hypothesis was tested by applying the skin transplantation technique to individuals of the inbred J strain of Xenopus laevis, which accept homografts. We demonstrated that young adults reject skin grafts from larvae. This rejection was immunological in nature because the secondary response of rejection was observed. There was a clear difference in graft rejection between grafts from the tail and those from the body. Grafts of tail skin were rejected irrespective of the metamorphic stages of donors. By contrast, grafts of body skin became acceptable as donors metamorphosed. The mean survival time of the larval skin was much longer than that of major histocompatibility complex (MHC)-disparate skin grafts reported by other investigators, suggesting that the rejection described in the present study is due to disparity in minor histocompatible (minor-H) antigens. We propose the involvement of the immunological recognition mechanism in the process of specific detection and elimination of larval cells in the tail.