Working model illustrating the present findings. This work implicates 5-HT_2B receptors at different levels of the myeloid lineage. The absence of 5-HT_2BRs in mutant mice (2B^−/−) leads to a reduction in (↓) platelets and immature endothelial progenitors and lineages but to an increase (↑) in granulocyte precursors and lineages.