Toll-like Receptor 9-Dependent Interferon Production Prevents Group 2 Innate Lymphoid Cell-Driven Airway Hyperreactivity.

Background: Group 2 innate lymphoid cells (ILC2s) are important mediators of allergic asthma. Bacterial components, such as unmethylated CpG DNA, a Toll-like receptor (TLR) 9 agonist, are known to possess beneficial immunomodulatory effects in patients with T cell mediated chronic asthma. However, their roles in regulating ILC2s remain unclear. Objective: We sought to determine the role of TLR9 activation in regulating ILC2 function and to evaluate the therapeutic utility of an immunomodulatory microparticle containing natural TLR9 ligand (MIS416). Methods: We evaluated the immunomodulatory effects of CpG A in IL-33 induced airway hyperreactivity (AHR) and airway inflammation. The roles of interferons were examined in vivo and in vitro by using signal transducer and activator of transcription 1 (Stat1)(-/-) mice and neutralizing antibodies against IFN-gamma and IFN-alpha/beta receptor subunit 1, and their cellular sources were identified. The therapeutic utility of MIS416 was investigated in the Alternaria alternata model of allergic asthma and in humanized NSG mice. Results: We show that TLR9 activation by CpG A suppresses IL-33-mediated AHR and airway inflammation through inhibition of ILC2s. Activation of TLR9 leads to production of IFN-alpha, which drives IFN-gamma production by natural killer cells. Importantly, IFN-gamma is essential for TLR9-driven suppression, and IFN-alpha cannot compensate for impaired IFN-gamma signaling. We further show that IFN-gamma directly inhibits ILC2 function through a STAT1-dependent mechanism. Finally, we demonstrate the therapeutic potential of MIS416 in A alternata-induced airway inflammation and validated these findings in human subjects. Conclusion: TLR9 activation alleviates ILC2-driven AHR and airway inflammation through direct suppression of cell function. Microparticle-based delivery of TLR9 ligands might serve as a therapeutic strategy for asthma treatment.