Antigen-initiated B lymphocyte differentiation. XIV. Nonspecific effects of antigen stimulation cause proliferation in the "pre-progenitor" subset of primary B cells.

The effect of specific and nonspecific stimuli on the cycle status of subsets of primary B lymphocytes was assessed by preinjecting donor CBA mice 1 to 2 days previously with various substances, and then incubating the isolated spleen cells with high specific activity 3H-TdR before assay. AFC-progenitor activity was assessed as a response to NIP-POL antigen, either by adoptive transfer to irradiated recipients or by cell culture. Previous studies showed these assays reflected the activity of different subsets of B cells, termed "pre-progenitors" (adoptive assay) and "direct progenitors" (culture assay). Most functional primary B cells, whether assayed in culture or by adoptive transfer, were not initially in rapid cell cycle in normal adult mice. However, nonspecific stimulation for 1 day caused NIP-specific adoptive transfer IgM AFC-progenitors to enter rapid cell cycle. This effect was independent of T cells and not related to the antigenicity of the stimulus: particulate peritoneal irritants were the most effective stimulants. In contrast to adoptive transfer results. AFC-progenitors assayed in cell culture were unaffected by nonspecific stimuli, but were activated into cell cycle by specific antigen.