Post-thymic T lymphocyte maturation during ontogenesis.

Abstract

Peripheral T lymphocytes from newborn (4-6 days old) mice, isolated from the spleen or lymph nodes, show phenotypic features of immature cortical thymocytes, such as high frequencies of proliferating cells and of peanut lectin-binding cells. These are features of peripheral T cells of recent thymic origin, as shown by in situ labeling of thymocytes and subsequent observation of the migrants to the spleen, which were mainly peanut lectin-binding cells. The function of newborn peripheral T cells was compared, on a per T cell basis, with that of thymocytes and of fully mature peripheral T cells of the adult, using preparations of newborn lympho node cells containing .apprx. 80% of T lymphocytes. They were strikingly (.apprx. 10-fold) less competent than adult T cells in their phytohemagglutinin responsiveness, their capacities to induce a graft vs. host reaction, to proliferate in the mixed lymphocyte reaction and to help B lymphocytes in a humoral response in vivo and in vitro. Newborn T lymphocytes were comparable to those of adults in their capacity to generate cytotoxic T lymphocytes. No suppressive effect of newborn T lymphocytes could be demonstrated in several of these assays. These results argue for an asynchronous maturation of 2 T cell subsets during ontogeny and demonstrate that at least some T lymphocytes leave the thymus as immature T cells resembling cortical thymocytes and further mature at the periphery. Investigation of mice submitted to thymectomy at 5 days of age showed that these incompetent post-thymic T lymphocytes are capable of considerable expansion and maturation in the peripheral lymphoid organs in the absence of a thymic influence.