Studies on a systemic xenogeneic graft-versus-host reaction model in newborn mice.

A xenogeneic graft-versus-host reaction model is described, evoked in neonatal mice by injection of rat spleen cells, and registered as splenomegaly at day 7. The following arguments are given as support for the idea that the reaction is indeed a graft-versus-host reaction: only living rat cells can give the reaction; rat cells treated with antilymphocyte serum cannot do so. The reaction is of almost the same strength in mice which have thymus dysplasia and are probably incapable of mounting a host-versus-graft reaction. Pretreatment of the grafted cells with mitomycin C, which abolishes the cells' capacity for DNA synthesis and proliferation, also eliminates their capacity to cause splenomegaly. This is probably because the grafted cell clone, reactive to mouse antigens, is small and has to be expended in order to be effective. Dividing rat cells have been demonstrated by chromosome studies in the enlarged mouse spleens 2--6 days after grafting.