Distinct Expression and Function of Fc{varepsilon}RII in Human B Cells and Monocytes [ALLERGY AND OTHER HYPERSENSITIVITIES]

FcRII is a multifunctional low-affinity IgER that is involved in the pathogenesis of allergic, inflammatory, and neoplastic diseases. Although discrepancies in FcRII-mediated functions are being increasingly recognized, the consequences of FcRII activation are not completely understood. In this study, we evaluated the expression of FcRII on human blood cells and found that it was primarily expressed on monocytes and B cells. Although IL-4 promoted expression of the FcRIIb isoform on B cells and monocytes, the expression of the FcRIIa isoform was not dependent on IL-4. Furthermore, FcRII predominantly bound allergen–IgE complexes on B cells but not on monocytes. FcRII-mediated allergen–IgE complex uptake by B cells directed Ags to MHC class II–rich compartments. FcRII-bearing monocytes and B cells expressed high levels of the FcRII sheddase a disintegrin and metalloproteinase 10, which implies that they are important sources of soluble FcRII. Moreover, we identified that IgE immune complex stimulation of FcRII activated intracellular tyrosine phosphorylation via Syk in B cells but not in monocytes. Importantly, FcRII-mediated signaling by allergen–IgE immune complexes increased IFN- production in B cells of allergic patients during the build-up phase of allergen-specific immunotherapy. Together, our results demonstrate that FcRII mediates cell type-dependent function in allergic reactions. In addition, the results identify a novel allergen–IgE complex/FcRII/Syk/IFN- pathway in allergic responses and suggest that FcRII may play a role in regulating allergic reactions via modulating IFN- production in B cells.

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