Effect of dosage on the survival of embryonic homotransplants in the leopard frog, Rana pipiens

A widespread conviction is that embryonic primordia may be successfully homotransplanted between amphibian embryos without any subsequent antagonism of an immune nature between host and graft tissues. Presumably the grafting of embryonic rudiments prior to the maturation of the immunological machinery of the host has the effect of prolonging, seemingly indefinitely, the survival time of the graft. It now can be shown, at least in the leopard frog, that an embryonic (neural fold) homograft can induce either immunity or tolerance, the given response being largely governed by the amount of tissue that is transplanted. Tolerance is not at all guaranteed simply by exposing the host to an antigenic stimulus before the functional differentiation of the immune system. Indeed, small quantities of homografted neural fold tissue confer immunity, not tolerance. The host's reactive system can only be suppressed by a large dose of transplanted neural fold material.