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.