Lymphocyte activation. II. Kinetics and specificity of the activation process with phytohaemagglutinin and concanavalin A.

Mouse peripheral blood lymphocytes were cultured with phytohaemagglutinin or Concanavalin A and at various times antiserum to each mitogen was added. Stimulation could be completely blocked for 5–6 hr and partially inhibited for at least 48 hr, and probably longer. The block produced by antiserum was specific and dependent on the relative concentrations of mitogen and antiserum. The gradual release of activation from the requirement for mitogen was not due to the production of a soluble non-specific mediator since the stimulatory activity of culture supernatants of fresh lymphocytes could be completely blocked in turn by antiserum to the original mitogen. Other experiments made the operation of a locally concentrated mediator unlikely. These data support a direct proliferative mechanism of lymphocyte transformation to these mitogens.