Syngeneic or parental strain T cells adoptively transferred into hybrid rats tolerant of third party alloantigens (L/DA tolerant of BN), in numbers insufficient to abolish tolerance, induce instead an active resistance to tolerance abolition with larger, usually effective dosages of donor cells. Of particular interest is the finding that immunization with T cells from one parental strain donor (e.g., DA) inhibited the tolerance-abolishing alloreactivity (anti-BN) of subsequently transferred T cells from the same (DA) and the other (L) parental strain donor. We conclude that anti-MHC receptors on T cells from different genetic backgrounds reactive to the same third party alloantigens share the same conserved immunogenic specificity-associated markers (SAM). The nonpolymorphism of anti-MHC receptors shown here in the transplantation tolerance model is a confirmation of the same conclusion drawn from earlier studies with the GVHD-resistance model, and it therefore suggests that these two models of T cell MHC interactions involve very similar mechanisms of T cell idiotypic regulation.

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