All-trans retinoic acid (ATRA) and retinoid derivatives are essential agents for multiple biological processes. Numerous immune system dysfunctions can occur in the case of retinoid deficiency. Because of the central role of dendritic cells (DCs) in controlling immunity and the wide effects of retinoids on the immune system homeostasis, we investigated the ability of ATRA to influence the differentiation of DCs from circulating peripheral blood monocytes. Human peripheral blood monocytes were cultured with granulocyte-macrophage colony-stimulating factor (GM-CSF) and various concentrations of ATRA. Differentiated cells were assayed for their morphology, phenotype, antigen uptake, allostimulatory capacity and cytokine secretion profile. ATRA (10(-12) mol/l) and GM-CSF drove the differentiation of monocytes into dendritic-like cells (ATRA-DC). ATRA-DCs exhibited DC morphology, had a phenotype of immature DCs, with the expression of CD1a, and upregulation of adhesion and co-stimulatory molecules. ATRA-DCs could induce a proliferative response in naive CD4+ T cells. Although ATRA-DCs retained their antigen-capture capacity, they secreted interleukin (IL)-12p70 without the need for any maturation agent. In addition, ATRA-DCs could drive T cells towards an IL-12-dependent T-helper cell type 1 response with secretion of interferon-gamma. DCs appear to be potential targets for ATRA, giving new insights into the immunomodulatory function of retinoids, with implications potentially related to immunotherapy.
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