Human Thymus Cell Cultures--Evidence for Two Functional Populations.

Abstract

Summary Human thymus cells were cultured in vitro with and without phytohemagglutinin (PHA). At the time of culture, the cells were morphologically heterogeneous with respect to size, and 5–7% took up H³-thymidine (H³T). After longer periods of incubation, the labelling decreased and the cell population was composed almost solely of small cells. In the presence of PHA, large cells appeared and up to 20% of the cell population took up H³T at 72 hours. The data are interpreted to show 2 populations of cells in the human thymus—one synthesizing DNA spontaneously for a short period of time and the other a “resting” population of small cells many of which can be transformed into large cells capable of manufacturing DNA in the presence of PHA.