Clones of antibody‐forming cells in pokeweed mitogen stimulated microcultures. II. Estimation of the frequency of precursor cells and the average clone size

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Abstract
In allogeneically complemented microcultures of nude spleen cells, the frequency of B precursor cells engaged in the anti‐SRC response is considerably higher in the presence of pokeweed mitogen (PWM) (3 × 10−5 – 1 × 10−4) than in the absence of PWM (1.1 × 10−5 – 5 × 10−5). These precursor cells, in the absence of PWM, give rise to clones of plaque‐forming cells (PFC) with an average clone size of 30–70 at the peak of the response. The addition of PWM results in a smaller average clone size (20–40 PFC/clone) as well as an early decline of the response. It is proposed that in this system at least, PWM does not act mainly as a mitogen but rather as an agent that in the presence of T cells, induces the maturation of B cells.