Lethal Graft-versus-host Reaction Induced by Parental Cells in the Clawed Frog, Xenopus Laevis

(J X K)F1 hybrid frogs, Xenopus laevis, were produced by mating between the MHC-homozygous but distinct "J" and "K" group frogs. When the spleen or splenocytes from parental J were transplanted into the F1 frogs, a typical graft-versus-host reaction (GVHR) was induced that included wasting and death, accompanied by a prominent spleen enlargement and other histological changes in skin and lymphoid organs. To induce the reaction, sensitization against F1 cells prior to transfer of spleen was necessary. The reaction was accelerated when the parental donor cells had been sensitized by gamma-irradiated leukocytes from the F1 hybrid. The injection of presensitized triploid J splenocytes into F1 hybrids followed by ploidy analyses revealed that the donor cells constituted the major cell population in host lymphoid organs--such as the spleen, liver, and kidney--but not the thymus. These observations provide the first clear evidence in poikilothermic vertebrates for GVHR caused by parental lymphocytes.