Proliferation of human lymphocytes by mitogen stimulated cells

Lymphocytes cultured for three days with PHA or Con A were capable of inducing vigorous proliferation of autologous or allogeneic lymphocytes. Kinetics of the response varied with mitogen dose used for obtaining stimulating cells and with the ratio of stimulating to responder cells. A requirement for viable, mitogen-reactive lymphocytes cultured for at least two days with the mitogen, for their contact with the reacting cells and an absence of significant quantities of mitogen on Con A lymphoblasts examined by electron microscopy demonstrated that a mitogen itself was not responsible for the stimulation. The PHA blast-stimulated lymphocytes were not cytotoxic to PHA blasts nor did they diminish lymphocyte stimulating abilities of PHA blasts in vitro cultures. This indicated that PHA did not induce proliferation of autologous lymphocytes by derivatization of lymphocyte surface.