Counterregulation between the FcepsilonRI pathway and antiviral responses in human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) play essential roles in directing immune responses. These cells may be particularly important in determining the nature of immune responses to viral infections in patients with allergic asthma as well those with other atopic diseases. The purposes of this study were 1) to compare the functional capacity of pDCs in patients with one type of allergic disorder, allergic asthma, and controls; 2) to determine whether IgE cross-linking affects antiviral responses of influenza-exposed pDCs; and 3) to determine whether evidence of counterregulation of FcepsilonRIalpha and IFN-alpha pathways exists in these cells. pDC function was assessed in a subset of asthma patients and in controls by measuring IFN-alpha production after exposure of purified pDCs to influenza viruses. FcepsilonRIalpha expression on pDCs was determined by flow cytometry in blood samples from patients with allergic asthma and controls. pDCs from patients with asthma secreted significantly less IFN-alpha upon exposure to influenza A (572 versus 2815; p = 0.03), and secretion was inversely correlated with serum IgE levels. Moreover, IgE cross-linking prior to viral challenge resulted in 1) abrogation of the influenza-induced pDC IFN-alpha response; 2) diminished influenza and gardiquimod-induced TLR-7 upregulation in pDCs; and 3) interruption of influenza-induced upregulation of pDC maturation/costimulatory molecules. In addition, exposure to influenza and gardiquimod resulted in upregulation of TLR-7, with concomitant downregulation of FcepsilonRIalpha expression in pDCs. These data suggest that counterregulation of FcepsilonRI and TLR-7 pathways exists in pDCs, and that IgE cross-linking impairs pDC antiviral responses.