Functional differentiation of T-cell precursors. II. Recovery of immunocompetence in lethally irradiated bone marrow reconstituted mice.

The recovery of T-cell immunocompetence in irradiated mice repopulated with syngeneic bone marrow cells has been studied. Both thymocytes and spleen cells from irradiated recipients were tested for Concanavalin A mitogen responsiveness, mixed lymphocyte reactivity, generation of trinitrophenyl-hapten-modified self cytotoxicity and helper cell carrier function. Responsiveness in the thymus reaches peak levels between 3-5 wk after marrow transfer, while splenic reactivity peaks at least 2-3 wk later, presumably a reflection of emigration from the thymus to peripheral lymphoid organs. Most T-cell functions reappeared at approximately the same time, though Con A responsiveness appeared first and helper activity for indirect IgG formation last. Since we have previously demonstrated that helper cell precursors in the marrow can be rendered tolerant, these studies will now allow definition of specificity in other T-cell subsets.