Regulation of the high affinity receptor for IgE on human epidermal Langerhans cells.

Human epidermal Langerhans cells (LC) express variable amounts of the high affinity receptor for IgE (Fc epsilonRI); the strongest expression is characteristic of atopic dermatitis. The receptor is suggested to take part in the pathophysiology of this disease by acting as a link between aeroallergens and Ag-specific T cells in an IgE-mediated, delayed-type hypersensitivity reaction. In the present study we show that even in the absence of surface expression, normal LC maintain an intracellular pool of the alpha-chain of Fc epsilonRI (Fc epsilonRIalpha) of the same m.w. as the surface-bound Fc epsilonRIalpha that is able to bind significant amounts of IgE. The lack of surface expression is linked to the absence or very low expression of the gamma-chain (Fc epsilonRIgamma). Moreover, the amount of Fc epsilonRIalpha expressed at the cell surface significantly correlates with the amount of Fc epsilonRIgamma. LC differentiation toward lymphoid dendritic cells is accompanied by the disappearance of transcripts for Fc epsilonRIalpha, but not for Fc epsilonRIgamma. This leads to a rapid decrease in the intracellular and surface levels of Fc epsilonRIalpha, which cannot be influenced by IL-4, IgE, or other agents. Overall, our findings suggest that these mechanisms enable LC to be highly versatile APCs by rapidly adapting the surface level of Fc epsilonRI to distinct inflammatory environments.