Common lymphoid progenitors, early B-lineage precursors, and IL-7: characterizing the trophic and instructive signals underlying early B cell development.

Precursors for B lymphocytes develop from semirestricted lymphoid progenitors in the bone marrow. Here we review current knowledge on the cellular stages underlying early B cell development from multipotent progenitor cells, and discuss the factors implicated in the regulation of this process. In particular, we will focus on the role of cytokine receptor signaling in early lymphocyte ontogeny and lymphoid lineage commitment, with an emphasis on the role of interleukin- 7 (IL-7) in early lymphocyte development within the bone marrow microenvironment. We will also discuss recent evidence that lymphocytes and subsets of dendritic cells develop from a common pathway, speculating that IL-7 may regulate cell fate decisions in multipotent B/dendritic cell precursors by driving these cells to differentiate into B-lineage-committed cells.