Lymphocytes as inducers of mitoses of human morphologically identifiable progenitor cells. Phase contrast observations.

Phase contrast time lapse observations of human bone marrow cells demonstrate the induction of progenitor cell mitoses or amitoses by the touch of locomotive lymphocytes on the cell surface. Interkinetic progenitor cells as well as precursor cells before mitosis were very rarely touched by lymphocytes. We suppose this cell-cell interaction is essential in the T-cell participation in hematopoietic stem cell proliferation.