抄録
Upon activation with antigens or lectins, a transient expression of mature T lymphocytes cell surface molecules specifically binding to interleukin-2 (IL-2), one of the growth factors, is induced (2, 5, 20, 23). The molecules are designated as interleukin-2 receptors (IL-2R). Interaction of the receptor with IL-2 provides an universal signal for T cell proliferation, resulting in clonal expansion of the activated T cells. In the physiological condition without specific antigen stimulation, proliferation of lymphocytes is prominent in the thymus, particularly in the embryonic thymus, in which we have previously found IL-2R expression of immature lymphocytes (4, 10, 22). Is the IL-2R expressing lymphocytes responsible for the cell proliferation in the thymus as is for the peripheral T lymphocytes? Based on the finding that during the period of gestation, the proportion of IL-2R positive (IL-2R+) cells in the thymus decreases but the cell number of IL-2R+ cells moderately increases, one may postulate that the IL-2R+ cells may be slow growing lymphocytes. Alternatively, it may be postulated that the IL-2R+ cells die in the thymus (27) and that the IL-2R expression of newly arrived lymphocytes, which is induced immediately after their migration into the thymus, contributes to the increase in the number of IL-2R+ cells in vivo. In this paper, proliferation of IL-2R+ cells within the embryonic thymus was examined in the organ culture system in which the mouse embryonic thymus lobes were cultured on a floating membrane to prevent cell migration from extrathymic sites.
