Pre-B cell differentiation in the bone marrow: a proliferative pathway parallels the post-mitotic maturation of early B cells.

Considerable heterogeneity was found in bone marrow B cell progenitors as functionally defined, size-separated populations were analyzed for their density of membrane IgM receptors, their adherence potential to nylon wool fibers and their susceptibility to lipopolysaccharide-induced differentiation to IgM secretion. The investigation of their cycling status with tritiated thymidine further permitted definition of resting and actively proliferating populations. Heterogeneity was found in the fraction of resting small cells as expected for early B cells progressing through postmitotic maturation. However, the data suggest that part of the pre-B cell progeny can also mature during a proliferative phase.