Respective involvement of TGF-β and IL-4 in the development of Langerhans cells and non-Langerhans dendritic cells from CD34+ progenitors

In vivo, dendritic cells (DC) form a network comprising different populations. III particular, Langerhans cells (LC) appear as a unique population of cells dependent on transforming growth factor beta (TGF-beta) for its development. In this study, we show that endogenous TGF-beta is required for the development of both LC and non-LC DC front CD34(+) hematopoietic progenitor cells (HPC) through induction of DC progenitor proliferation and of CD1a(+) and CD14(+) DC precursor differentiation. We further demonstrate that addition of exogenous TGF-beta polarized the differentiation of CD34(+) HPC toward LC through induction of differentiation of CD14(+) DC precursors into E-cadherin(+), Lag(+)CD68(-), and Factor XIIIa(-)LC, displaying typical Birbeck granules. LC generated front CD34(+) HPC in the presence of exogenous TGF-beta displayed overlapping functions with CD1a(+) precursor-derived DC. In particular, unlike CD14(+)-derived DC obtained in the absence of TGF-beta, they neither secreted interleukin-10 (IL-10) on CD40 triggering nor stimulated the differentiation of CD40-activated naive B cells. Finally, IL-4, when combined with granulocyte-macrophage colony-stimulating factor (GM-CSF), induced TGF-beta-independent development of non-LC DC front CD34(+) HPC, Similarly, the development of DC front monocytes with GM-CSF and IL-4 was TGF-beta independent. Collectively these results show that TGF-beta polarized CD34(+) HPC differentiation toward LC, whereas IL-4 induced non-LC DC development independently of TGF-beta.