A common pathway for dendritic cell and early B cell development

B cells and dendritic cells (DCs) each develop from poorly described progen itor cells in the bone marrow (BM). Although a subset of DCs has been propo sed to arise from lymphoid progenitors, a common developmental pathway for B cells and BM-derived DCs has not been clearly identified. To address this possibility, we performed a comprehensive analysis of DC differentiative p otential among lymphoid and B lymphoid progenitor populations in adult mous e BM. We found that both the common lymphoid progenitors (CLPs), shown here and elsewhere to give rise exclusively to lymphocytes, and a down-stream e arly B-lineage precursor population devoid of T and NK cell precursor poten tial each give rise to DCs when exposed to the appropriate cytokines. This result contrasts with more mature B-lineage precursors, all of which failed to give rise to detectable numbers of DCs. Significantly, both CLP and ear ly B-lineage-derived DCs acquired several surface markers associated with f unctional DCs, and CLP-derived DCs readily induced proliferation of allogen eic CD4(+) T cells. Surprisingly, however, DC differentiation from both lym phoid-restricted progenitors was accompanied by up-regulation of CD11b expr ession, a cell surface molecule normally restricted to myeloid lineage cell s including putative myeloid DCs. Together, these data demonstrate that los s of DC developmental potential is the final step in B-lineage commitment a nd thus reveals a previously unrecognized link between early B cell and DC ontogeny.