[Effect of vinblastine on the blast population of the thymus subcapsular zone in the mouse].

It is well admitted that blast cells of the thymic subcapsular zone play an important role in murine leukemogenesis. Previous ultrastructural investigations have revealed the morphological heterogeneity of this population which is formed by lymphoblasts, X cells and ring shaped nucleolus cells. These aspects could correspond to different positions in the cell cycle of an unique cell type. After administration of vinblastine, a drug blocking mitosis in metaphasis, the percentage of lymphoblasts decreases whereas the percentage of X cells increases. There is no modification of the number of ring-shaped nucleolus cells. This suggests that at least a part of lymphoblasts gives rise to x cells.