In vitro differentiation of human marrow cells into T lymphocytes by thymic extracts using the rosette technique.

The manner by which human and calf thymic extracts induce precursor cells of human marrow to differentiate in vitro into T lymphocytes has been studied using as a T-cell marker the spontaneous rosette formation technique of human T lymphocytes with sheep erythrocytes (E rosette). These findings confirm previous observations made in the study of the same process using a different T-cell marker, specific antigenicity recognizable by a heterologous anti-human T-cell serum in a microcytotoxicity test. The number of cells revealing evidence of differentiation demonstrated by the E rosette formation technique is smaller than that obtained with the anti-human T-cell serum, indicating perhaps that a different stage of maturation of T lymphocytes is recognized by the antiserum from the one detected by spontaneous rosette formation. Based on the effects of specific inhibitors of nucleic acids and protein synthesis, it can be concluded that these thymic extracts ultimately act by influences exerted in the cell nucleus and that RNA and protein synthesis are required for the differentiation of precursor cells into T lymphocytes induced by thymic extracts. In addition, continued protein synthesis appears to be required for maintenance of receptors for sheep erythrocytes on the cell surface.