Abnormal expression pattern of Tac and T9 antigens on in vitro activation of leukemic T cells.

Mitogen-induced T-lymphocyte proliferation is dependent on the presence of both interleukin 2 (IL-2) and transferrin, even though resting lymphocytes do not have receptors for either. Recently, it has been reported that IL-2 stimulates T-lymphocyte proliferation via IL-2 receptor by induction of transferrin receptor on these cells. Using leukemic T cells as a model of the monoclonal mature T cell, we examined those sequential steps of T-cell activation. Our studies revealed that transferrin receptors do not always appear after IL-2 receptor expression, IL-2 up-regulates the expression of IL-2 receptor but not of transferrin receptor, and IL-2 can initiate DNA synthesis without altering transferrin receptor expression. Thus, the sequential activation steps reported for normal T cells were not observed in the present study on leukemic T cells. These data suggest that there are other pathways to DNA synthesis in leukemic T cells and even in normal T cells.