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Published on: May 31, 2018
Toll-like receptor 9 suppression in plasmacytoid dendritic cells after IgE-dependent activation is mediated by
John T Schroeder1, Kristin L Chichester, Anja P Bieneman
1Department of Medicine, Division of Allergy and Clinical Immunology, Johns Hopkins Asthma and Allergy Center, Johns Hopkins University, Baltimore, MD 21224, USA. schray@jhmi.edu
Background:
Functional significance for the alphagamma(2) variant of the high-affinity IgE receptor (FcepsilonRI) reportedly expressed on human dendritic cell subtypes remains poorly understood. Studies show that immature plasmacytoid dendritic cells (pDCs) secrete large quantities of TNF-alpha and IL-6 when directly stimulated with anti-IgE antibody. This mode of activation, however, reduces Toll-like receptor 9 (TLR9) expression in pDCs and their ability to mount an IFN-alpha response when subsequently activated with oligodeoxynucleotide containing CpG.
Objective:
To investigate the mechanisms underlying this IgE-dependent suppression of TLR9 and innate immune responsiveness in pDCs by focusing on autocrine cytokine responses.
Methods:
pDCs were isolated from blood by using blood dendritic cell antigen 4 selection. Cytokine responses to anti-IgE antibody-dependent and/or CpG-dependent stimulation were measured by using ELISA. TLR9 expression was determined by using quantitative RT-PCR and Western blotting.
Results:
The time required for downregulating TLR9 expression in pDCs after anti-IgE stimulation correlated with the induction and duration of TNF-alpha secreted by these cells. Pretreatment of pDCs with recombinant TNF-alpha (but not IL-6 or IL-10) markedly suppressed TLR9 expression. Functional response to CpG (ie, IFN-alpha induction) was also inhibited with TNF-alpha pretreatment (inhibitory concentration(50) = approximately 200 pg/mL). Finally, an antibody that neutralizes TNF-alpha activity completely restored TLR9 expression during anti-IgE stimulation and significantly improved IFN-alpha secretion on subsequent activation with CpG.
Conclusion:
Autocrine TNF-alpha secretion resulting from IgE/FcepsilonRI-dependent activation plays a critical role in suppressing TLR9-dependent responses in pDCs that normally promote T(H)1 activity.
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