The development of hypersensitive lymphocytes in cell culture.

An in vitro cell-mediated immune response to pokeweed mitogen (PWM) is described. Rat lymphocytes were stimulated by PWM, by phytohemagglutinin (PHA), and by concanavalin A (ConA). In the presence of PWM only a fraction of the lymphocytes underwent blastogenesis. This was in contrast to the apparent total blastogenesis obtained in response to PHA or ConA. When blast cells derived from each of the mitogens were plated on rat fibroblast monolayer in the absence of mitogen they differentiated into a distinct type of lymphocyte termed "secondary lymphocyte." Addition of mitogens to cultures of these lymphocytes resulted in a retransformation to blast cells. The secondary lymphocytes were tested for their ability to effect lysis in the presence of each of the three mitogens. In. the presence of PWM, lysis of fibroblasts produced by PWM-lymphocytes was considerably more efficient than lysis obtained by ConA- or PHA-lymphocytes. No difference in effect on target fibroblasts was obtained when the three types of secondary lymphocytes were tested in the presence of either PHA or ConA. The stimulating action of PWM on lymphocytes was shown to be immunologically specific. No such specificity was found in the case of PHA or ConA. The results are interpreted to indicate that PWM combines with cell membranes and acts on the lymphocytes as a "transplantation antigen." Lymphocytes capable of responding to "PWM-transplantation antigen" transform to blast cells capable of specifically lysing PWM-conjugated fibroblasts. In the absence of the mitogen, PWM-induced blast cells differentiate to lymphocytes hypersensitive to PWM.