TLR7 Stimulation of APCs Results in Inhibition of IL-5 through Type I IFN and Notch Signaling Pathways in Human Peripheral Blood Mononuclear Cells

Abstract

TLR7 agonists modulate Th2 immune responses through mechanisms that have not been fully elucidated. Suppression of IL-5 production from Ag- or phytohemagglutinin-stimulated human PBMCs by the TLR7 antedrug AZ12441970 was mediated via type I IFN–dependent and type I IFN–independent mechanisms through TLR7 activation of plasmacytoid dendritic cells, B cells, and monocytes. The type I IFN–dependent inhibition of T cell–derived IL-5 was mediated by IFN-α acting directly on activated T cells. IL-10 was shown not to be involved in the type I IFN–independent inhibition of IL-5 and the mechanism of inhibition required cell–cell interaction. Notch signaling was implicated in the inhibition of IL-5, because addition of a γ-secretase inhibitor blocked the type I IFN–independent suppression of IL-5. Accordingly, AZ12441970 induced high levels of the notch ligands Dll1 and Dll4 mRNA, whereas immobilized DLL4 resulted in the suppression of IL-5 production. Therefore, we have elucidated two mechanisms whereby TLR7 agonists can modulate IL-5 production in human T cells. The suppression of Th2 cytokines, including IL-5, would be of benefit in diseases such as atopic asthma, so we assessed TLR7 function in PBMC from asthmatics and showed equivalent activity compared with healthy volunteers. Demonstrating this function is intact in asthmatics and knowing it links to suppression of Th2 cytokines support the case for developing such compounds for the treatment of allergic disease.

Toll-like receptor 7 governs interferon and inflammatory responses to rhinovirus and is suppressed by IL-5-induced lung eosinophilia

“…28 Our results suggest a reciprocal regulation between IL-5-induced eosinophilia and TLR7 expression that affects antiviral IFN responses to RV (summary illustrated in figure 5). In the absence of virus, it has been shown that TLR7 stimulation with synthetic agonists in vitro resulted in inhibition of IL-5 through IFNγ and Notch signalling pathways in antigenpresenting cells 29 and upregulation of IFNγ production by memory CD4+ T cells 30 and natural killer cells. 31 Consistent with these findings, we show impaired IFNγ release in the absence of TLR7 promotes T H 2 immune responses, which can be rescued by type I and III IFN therapy or adoptive transfer of TLR7-sufficient pDCs.…”

Emerging roles of the γ-secretase-notch axis in inflammation

“…The presenilin/γ-secretase (PS/γS) proteolysis of CD46 generates immunoprecipitable cytoplasmic tail peptides (cyt1/2) in response to Neisseria infection (Weyand et al, 2010). However, blocking Notch signaling by γ-secretase inhibitors has been found to reduce the type I IFN-independent suppression of IL-5 in human peripheral blood mononuclear cells, indicating that Notch signaling can inhibit IL-5 (Edwards et al, 2013).…”

Tolerability in man following inhalation dosing of the selective TLR7 agonist, AZD8848

“…TLR7 agonists suppress Th2 responses [9][10][11][12][13][14][15][16] and as atopic asthma is associated with an enhanced Th2 biological drive, TLR7 agonists could be developed as a new treatment paradigm for this disease. However, the generation of 'influenza-like' symptoms resulting from either systemic TLR7 activation or elevated systemic levels of TLR7-induced mediators has been reported in TLR7 clinical programmes.…”

“…18 Peripheral blood mononuclear cell (PBMC) preparation and IL-5 inhibition assays are as described in Edwards et al's study. 15 IFNα was determined following a 24 h incubation of PBMC with compound. In vitro plasma stability determinations were performed by methodologies described in Biffen et al's study.…”

“…7 Ten distinct TLRs have been identified 8 and of these stimulation of either TLR7 or TLR9 in mouse disease models modulates many of the end points associated with allergy including suppression of goblet cell hyperplasia, reduction in Th2 cytokines, lung eosinophilia, lung inflammation and antigenspecific IgE. [9][10][11][12][13][14][15][16][17] TLR7 agonists modulate Th2 responses in vitro through the action of interferon α (IFNα) on T cells as well as through the upregulation of the costimulatory ligand DLL-4, 15 18 and via the downregulation of the Th2 transcription factor, GATA-3, by IFNα. 19 In vivo, the importance of the role of type I IFNs, such as INFα, in TLR7-mediated immunomodulation of…”