The radioresistant portion of the thymus dictates the H-2 self specificity spectrum of T cells and the peripheral lymphoreticular cells' H-2 type determines which of the thymically selected specificities for H-2 are to be expressed by antigen specific effector T cells; these contentions derive from experiments with irradiation bone marrow and thymus chimeras. These phenomena cannot be readily explained by suppression as shown in mixture experiments. Furthermore, specificity for thymic self-H-2 is exquisite, since lymphocytes from C57BL/6 (Kb) → Hz170 (Kba) mutant mice chimeras do not cross-react on Kb. These findings have great theoretical and practical implications with respect to reconstitution of immunocompetence, Ir-gene phenomena and our understanding of T cell recognition.

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