The kinetics of the in vivo response to SRBC was studied in mouse spleen at both the B cell and T cell levels. The B cell response was assayed by following the appearance of antibody-secreting cells in the spleen using the hemolytic plaque assay. The T cell response was monitored by following the increase in or "priming" of helper activity in the spleen using a quantitative in vitro assay. The role of cellular proliferation in both responses was established with the inhibitor of mitosis, vinblastine.

The results show that, although the development of T cell activity precedes that of anti-SRBC PFC by as much as 1 day, T cells lag at least 1 day behind B cells in the onset of cellular proliferation.

The evidence suggests either that the helper T cell which proliferates in response to SRBC does so after helping in the initiation of the primary B cell response or that the proliferative T cell response and the initiation of the primary B cell response involve two different subpopulations of T cells.

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