Recognition of nucleic acid and nucleic acid analogs by Toll-like receptors 7, 8 and 9

Plasmacytoid dendritic cells (pDCs) efficiently produce large amounts of type I IFN in response to TLR7 and TLR9 ligands, whereas conventional DCs (cDCs) predominantly secrete high levels of the cytokines IL-10 and IL-12. The molecular basis underlying this distinct phenotype is not well understood. In this study, we identified the MAPK phosphatase Dusp9/MKP-4 by transcriptome analysis as selectively expressed in pDCs, but not cDCs. We confirmed the constitutive expression of Dusp9 at the protein level in pDCs generated in vitro by culture with Flt3 ligand and ex vivo in sorted splenic pDCs. Dusp9 expression was low in B220− bone marrow precursors and was upregulated during pDC differentiation, concomitant with established pDC markers. Higher expression of Dusp9 in pDCs correlated with impaired phosphorylation of the MAPK ERK1/2 upon TLR9 stimulation. Notably, Dusp9 was not expressed at detectable levels in human pDCs, although these displayed similarly impaired activation of ERK1/2 MAPK compared with cDCs. Enforced retroviral expression of Dusp9 in mouse GM-CSF–induced cDCs increased the expression of TLR9-induced IL-12p40 and IFN-β, but not of IL-10. Conditional deletion of Dusp9 in pDCs was effectively achieved in Dusp9flox/flox; CD11c-Cre mice at the mRNA and protein levels. However, the lack of Dusp9 in pDC did not restore ERK1/2 activation after TLR9 stimulation and only weakly affected IFN-β and IL-12p40 production. Taken together, our results suggest that expression of Dusp9 is sufficient to impair ERK1/2 activation and enhance IFN-β expression. However, despite selective expression in pDCs, Dusp9 is not essential for high-level IFN-β production by these cells.

Section: N Innate Immune Cells Recognition Of Microbial Ligands Bymentioning

confidence: 99%

Selective Expression of the MAPK Phosphatase Dusp9/MKP-4 in Mouse Plasmacytoid Dendritic Cells and Regulation of IFN-β Production

Niedzielska

Raffi

Tel

et al. 2015

“…The nucleic acids derived from viruses during cytosolic replication can be transported into endosomes via autophagy. The expression of these TLRs in intracellular compartments prevents the activation of these TLRs by self-derived nucleic acids under physiological conditions because self-nucleic acids from dead cells within damaged tissues are unable to enter the cells and endosomes spontaneously (22,23). However, self-nucleic acid tolerance can be broken under some pathological conditions.…”

mentioning

confidence: 99%

Identification of Thiostrepton as a Novel Inhibitor for Psoriasis-like Inflammation Induced by TLR7–9

Lai

Yeh

et al. 2015

Activation of TLR7–9 has been linked to the pathogenesis of autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus, and psoriasis. Thus, therapeutic applications of antagonists of these TLRs for such disorders are being investigated. Bortezomib (Velcade) is a proteasome inhibitor known to suppress activation of these TLRs. To identify novel TLR7–9 inhibitors, we searched the Gene Expression Omnibus database for gene expression profiles of bortezomib-treated cells. These profiles were then used to screen the Connectivity Map database for chemical compounds with similar functions as bortezomib. A natural antibiotic, thiostrepton, was identified for study. Similar to bortezomib, thiostrepton effectively inhibits TLR7–9 activation in cell-based assays and in dendritic cells. In contrast to bortezomib, thiostrepton does not inhibit NF-κB activation induced by TNF-α, IL-1, and other TLRs, and it is less cytotoxic to dendritic cells. Thiostrepton inhibits TLR9 localization in endosomes for activation via two mechanisms, which distinguish it from currently used TLR7–9 inhibitors. One mechanism is similar to the proteasome inhibitory function of bortezomib, whereas the other is through inhibition of endosomal acidification. Accordingly, in different animal models, thiostrepton attenuated LL37- and imiquimod-induced psoriasis-like inflammation. These results indicated that thiostrepton is a novel TLR7–9 inhibitor, and compared with bortezomib, its inhibitory effect is more specific to these TLRs, suggesting the potential therapeutic applications of thiostrepton on immunologic disorders elicited by inappropriate activation of TLR7–9.

“…TLR7 is localized in the endosomal compartment of PDCs and recognizes single-stranded RNA (ssRNA), genomic RNA, or synthetic nucleoside analogs (2,3). Activation of PDCs via TLR7 results in enhanced IFN-a production, which is supposed to be a crucial protective mechanism to establish and sustain an efficient viral defense (1).…”

mentioning

confidence: 99%

Human Plasmacytoid Dendritic Cells Support Th17 Cell Effector Function in Response to TLR7 Ligation

Peng

Oldenburg

et al. 2009

100

Signals involved in the commitment of Th17 differentiation are of substantial interest for our understanding of antimicrobial defense mechanisms and autoimmune disorders. Various ways in which myeloid dendritic cells modulate Th17 differentiation have been identified. However, although plasmacytoid dendritic cells (PDCs) are regarded as important players in antiviral/antimicrobial host defense and autoimmune diseases, a putative modulatory role of PDCs in Th17 differentiation has not yet been elucidated in detail. We demonstrated that PDCs are capable of promoting Th17 differentiation in response to TLR7 stimulation. Further, both the differentiation of Th17 cells from naive T cells and the amplification of Th17 effector functions of memory T cells are promoted by PDCs after TLR7 activation. Our data are of strong clinical relevance because TLR7 activation in PDCs might represent one of the missing links between innate and adaptive immune mechanisms and contribute to the amplification of Th17-driven autoimmune disorders as well as viral host defense.