An in vivo study of the ontogeny of alloreactivity in the frog, Xenopus laevis.

Pre- and perimetamorphic larval and post-metamorphic juvenile frogs (Xenopus laevis) from a single family were grafted with skin from either of their patents (who differed from the hosts by one major histocompatibility complex (MHC) haplotype and multiple minor H loci) or from an unrelated adult (to provide a greater immunogenetic disparity). The fate of such skin grafts transplanted to hosts of various developmental stages indicated that a net destructive alloimmunity in this amphibian species develops gradually during ontogeny. In contrast to the uniform rejection of grafts on animals transplanted as postmetamorphic froglets, many recipients of grafts transplanted during larval life became tolerant. The incidence of tolerance depended on the recipients' developmental stage at the time of grafting and on the particular MHC haplotype barriers involved. In general, larvae grafted at an early developmental stage became tolerant, whereas recipients transplanted at older larval stages rejected grafts from the same donor. Even when larvae rejected their grafts, the reaction was often more chronic than that mounted by postmetamorphic froglet controls.