Graft-versus-host Reaction in F1 Hybrid Mice Injected with Pre-immunized Parental Thymus Cells.

LTHOUGH the thymus has been proved to play an essential role in the development and maintenance of immune reactivity, the mechanisms by which it exerts these functions are still to be elucidated. While significant titers of antibody”2 or plasma cell accumulation3’4 have not been detected in the intact thymus of animals given antigens at distant site, histologic signs indicative of local antibody formation have been observed after direct injection of antigens into the thymus gland.5 The existence of a functional bloodthymic barrier which excludes thymus cells from exposure to circulating antigens has therefore been postulated.5 However, whether the immunologic inadequacy of intact thymus depends on its physiologic sequestration or on the relative incapability of thymus cells to take part by themselves in immune reactions remains in considerable doubt. Parental thymus grafted as solid tissue in F1 hybrids does not produce runt disease,6 but dissociated thymus cells are capable of inducing graft-versus-host reactions, though less effective than other lymphoid cells, when injected into normal6 or irradiated7 F1 recipients as well as into newborn mice of unrelated strains.8’9 However, injection of allogeneic thymus cells in chick embryost#{176} or in newborn rats was found to be ineffective or only slightly active in determining graft-versus-host reaction. The present experiments were designed to study the capacity of thymus cells to initiate a graft-versus-host reaction and particularly to ascertain whether previous sensitization against foreign transplantation antigens would result in a detectable activation of the immunologic potentiality of thymus cells. The Simonsen’s method of spleen assay was used as a sensitive test to evaluate the capability of thymus cells derived from normal or pre-immunized parental donors to initiate a graft-versus-host reaction in young F1 hybrid hosts.