Differentiation and maturation of thy-1 negative bone marrow cells. I. Effects of the thymus and radioresistant helper functions on the maturation of precursor cells specific for heterologous erythrocytes.

The effects of adult thymectomy (ATx) and preimmunization on the differentiation of cells responsible for delayed footpad reaction (DFR), plaque forming cells (PFC) and cell mediated lympholysis (CML) were examined in lethally irradiated and thy-1 negative bone marrow cell reconstituted C57BL/6 recipients. ATx reduced the degrees of immune responses in irradiated and reconstituted mice. When the recipients had been preimmunized, all of DFR, PFC and CML became detectable even in irradiated and reconstituted ATx mice. Preimmunization also evoked early maturation of precursor cells for CML. Therefore, it was suggested that radioresistant helper effects, presumably in the presence of antigens, could promote the differentiation and maturation of T cell precursors in bone marrow in the absence of the thymus. We also demonstrated differences in restoration periods of such responses after lethal irradiation and reconstitution. One or two weeks following irradiation and reconstitution, DFR was first detectable. On the other hand, the generation of PFC was detected later than 2 weeks after bone marrow cell reconstitution, and it took over 4 weeks for thy-1 negative bone marrow cells to raise CML. T cells responsible for DFR may have lower dependency on the thymus than those for PFC and CML.