Life before the pre-B cell receptor checkpoint: Specification and commitment of primitive lymphoid progenitors in adult bone marrow

The production of B cells is a complex process determined by well-timed combinations of intrinsic factors and environmental cues that guide the differentiation of primitive progenitors in the bone marrow. Expression of several key transcription factors and receptor–stromal cell ligand interactions are landmarks of the earliest events in B lymphopoiesis in adult bone marrow. We describe this as a gradual loss of options for other blood cell lineages coincident with gain of essential properties. Experimental, stress or infection-related deregulation may change B cell fate specification, commitment or population dynamics, and consequently the production rate of mature populations.