A reducing microenvironment leads to the generation of FcepsilonRIhigh inflammatory dendritic epidermal cells (IDEC)

Inflammatory dendritic epidermal cells present in skin lesions of the atopic eczema/dermatitis syndrome display the highest expression of the high-affinity receptor for IgE (FcepsilonRI), ever detected on human antigen-presenting cells. Owing to the instability of the FcepsilonRI (alphagammagamma) complex and fast cleavage from the cell surface during the interleukin-4/granulocyte-macrophage colony-stimulating factor driven in vitro differentiation of monocytes, a method to generate inflammatory dendritic epidermal cells was not at our disposal in the past and the amount of ex vivo isolated inflammatory dendritic epidermal cells available for functional assays was limited. Therefore, information about the role of inflammatory dendritic epidermal cells and FcepsilonRI on this dendritic cell subtype in atopic and inflammatory skin diseases is completely missing. In this study, we were able to: (i) increase the expression of a functional FcepsilonRI complex on the cell surface of immature monocyte-derived dendritic cells from atopic donors by creating a reducing microenvironment; (ii) enhance significantly the intracellular pool of the FcepsilonRIgamma chains, which is the limiting parameter for the FcepsilonRI surface expression; and (iii) generate monocyte-derived dendritic cells displaying the phenotypical characteristics of inflammatory dendritic epidermal cells, producing high amounts of proinflammatory cytokines and chemokines similar to the cytokines found in lesional skin of the atopic eczema/dermatitis syndrome. Altogether the high expression of functional FcepsilonRI on these cells enables us for the first time to study inflammatory dendritic epidermal cells and FcepsilonRI-mediated mechanisms of inflammatory dendritic epidermal cells in vitro, in order to shed light on the putative role of this important cell type in the atopic eczema/dermatitis syndrome.