The effects of specific and nonspecific stimuli on the cell cycle status of secondary B cells responding in either an adoptive immune assay or in tissue culture were investigated with a “cell suicide” procedure. Spleen cells from unstimulated or recently stimulated long-term hapten-primed “memory” mice were exposed to high specific activity 3H-TdR before AFC-progenitor assay; in all experiments, AFC-progenitor activity was assessed as a response to NIP-POL antigen.

Secondary adoptive transfer or cell culture AFC-progenitors from animals not receiving immediate prestimulation were not in a state of rapid cell cycle. Secondary AFC-progenitors detected in adoptive immune assays were activated into rapid cell cycle by nonspecific stimuli. Secondary AFC-progenitors responding in cell cultures were not activated by the same nonspecific stimuli, but showed a proliferative response to specific antigen. These results are analogous to those presented in the preceding paper for primary B cells. They suggest that, like primary B cells, secondary B cells contain distinct adoptive transfer AFC-progenitor (termed “preprogenitor”) and culture AFC-progenitor (termed “direct progenitor”) subsets. These various primary and secondary B cell subsets are incorporated into a model of B cell development.

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