Frequency of B lymphocytes responsive to anti-immunoglobulin.

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Abstract
The frequency of murine B lymphocytes that respond to antibodies directed against membrane IgM was measured. These anti-.mu. antibodies induced all, or almost all, resting B cells to enlarge over the first 24 h of stimulation. This probably represents the transition from the resting state (G0) to active transit through the cell cycle. Only a fraction of these cells, .apprx. 60% for BDF1 mice, continued through the cell cycle into S phase. There apparently were some types of B cells that did not proliferate in response to anti-.mu.. Many, perhaps all, of these nonresponding B cells, both from normal mice and from mice with the xid defect, actually do respond to the presence of anti-.mu. by going through early parts of the cell cycle. These cells appear to become blocked at some point before the beginning of S phase, perhaps requiring a signal from a T cell or a macrophage to continue through the cell cycle. Thus, the role of antigen may be to prepare all B cells for proliferation. Different subpopulations of B cells may then require different regulatory signals before actually proliferating or before differentiating into antibody-secreting cells.