Retinoic acid inhibits dendritic cell differentiation driven by interleukin-4

All-trans-retinoic acid (atRA) appears to affect Th1–Th2 differentiation and its effects on immune responses might also be mediated by dendritic cell (DC). Nonetheless, studies have been showing contradictory results since was observed either induction or inhibition of DC differentiation. Our aim was to investigate atRA action on human monocyte derived DC differentiation. For this purpose we tested pharmacological and physiological doses of atRA with or without cytokines. Cell phenotypes were analyzed by flow cytometry and function was investigated by phagocytosis and respiratory burst. DC, positive control group, was differentiated with GM-CSF and IL-4 and maturated with TNF-α. We demonstrated that atRA effects depend on the dose used as pharmacological doses inhibited expression of all phenotypic markers tested while a physiological dose caused cell differentiation. However, atRA combined or not with cytokines did not promote DC differentiation. In fact, atRA was detrimental on IL-4 property as a DC inductor.