Functions of dendritic-cell-bound IgE in allergy

Immunoglobulin E (IgE) functions as an Fc-receptor-bound antigen sensor for mast cells and basophils, the classical effector cells of allergy. A cell-bound IgE pool is formed when monomeric IgE binds to FcɛRI, the high affinity IgE Fc receptor on these cells, and minor amounts of antigen are sufficient to trigger the pro-allergic innate IgE effector axis. Additionally, FcɛRI is constitutively expressed on human dendritic cells (DCs), and thus the latter cell type also receives signals via cell-bound IgE. Notably, steady-state expression of FcɛRI on DCs is absent in SPF-housed mice. How DCs integrate IgE/FcɛRI-derived signals into their sentinel functions as gatekeepers of immunity was therefore only recently studied with transgenic mice that phenocopy human FcɛRI expression. In this review, we summarize advances in our understanding of the functions of DC-bound IgE which demonstrate that IgE-mediated activation of DCs in allergic Th2-type inflammation appears to be immune regulatory rather than pro-inflammatory.