Description:
<jats:p>Epithelia‐associated dendritic cells (DC) including Langerhans cells in the skin (LC) are precursors of lymph node located interdigitating DC (iDC). CD1a<jats:sup>+</jats:sup> LC are known to be derived from CD34<jats:sup>+</jats:sup> haemopoietic progenitor cells (HPC); however, cells of an intermediate differentiation state that are CD34<jats:sup>−</jats:sup> and CD1a<jats:sup>−</jats:sup> have not been identified. Monitoring the differentiation pathway of HPC in the presence of GM‐CSF + IL‐4, we observed the emergence of a distinct LC precursor population that was CD33<jats:sup>+</jats:sup> CD13<jats:sup>+</jats:sup> CD4<jats:sup>+</jats:sup> CD38<jats:sup>+</jats:sup> CD44<jats:sup>+</jats:sup> CD34<jats:sup>−</jats:sup> CD14<jats:sup>−</jats:sup> CD1a<jats:sup>−</jats:sup>. The cells could be separated by FACS due to a unique CD44/CD38 expression pattern or by CD44 expression in conjunction with the SSC profile. It was found that they were similarly generated in the presence of GM‐CSF alone and were detectable in culture for at least a week. Irrespective of being generated in the presence of GM‐CSF + IL‐4 or GM‐CSF alone, CD44/SSC‐sorted precursor cells matured to MHC class II compartments (MIIC) and Birbeck granules (BG) expressing LC, when subsequently cultured in the presence of GM‐CSF + IL‐4. When IL‐4 was omitted, however, the same cells matured to phagocytically active adherent macrophages (MΦ). These culture conditions were associated with a > 4‐fold increase in the concentration of IL‐6 when compared to those used for LC differentiation. The identification of a distinct oligopotent precursor cell population that can deliberately be induced to give rise to BG<jats:sup>+</jats:sup> MIIC<jats:sup>+</jats:sup> CD1a<jats:sup>+</jats:sup> CD14<jats:sup>−</jats:sup> LC or to adherent CD14<jats:sup>+</jats:sup> MΦ further substantiates the close relationship of monocytes and DC and may help to identify its <jats:italic>in vivo</jats:italic> equivalent.</jats:p>