Toll-like receptor 9 suppression in plasmacytoid dendritic cells after IgE-dependent activation is mediated by autocrine TNF-alpha.
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.


CONCLUSIONS
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.
Schroeder
John T
JT
Department of Medicine, Division of Allergy and Clinical Immunology, Johns Hopkins Asthma and Allergy Center, Johns Hopkins University, Baltimore, MD 21224, USA. schray@jhmi.edu
Chichester
Kristin L
KL
Bieneman
Anja P
AP
D000328:Adult; D019898:Autocrine Communication / Q000502:physiology*; D002478:Cells, Cultured; D018899:CpG Islands; D016207:Cytokines / Q000378:metabolism; D003713:Dendritic Cells / Q000378:metabolism*; D015536:Down-Regulation; D006801:Humans; D007108:Immune Tolerance; D007113:Immunity, Innate; D007073:Immunoglobulin E / Q000378:metabolism*; D007700:Kinetics; D011994:Recombinant Proteins / Q000494:pharmacology; D013997:Time Factors; D051217:Toll-Like Receptor 9 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism* / Q000494:pharmacology
D016207:Cytokines; D011994:Recombinant Proteins; C495371:TLR9 protein, human; D051217:Toll-Like Receptor 9; D014409:Tumor Necrosis Factor-alpha; D007073:Immunoglobulin E