Tuft cell-produced cysteinyl leukotrienes and IL-25 synergistically drive lung type 2 inflammation

Aeroallergen sensing by airway epithelial cells can trigger pathogenic immune responses leading to chronic type 2 inflammation, the hallmark of airway diseases such as asthma. Airway tuft cells are specialized chemosensory epithelial cells and the dominant source of the epithelial cytokine IL-25 in the trachea and of cysteinyl leukotrienes (CysLTs) in the naive murine nasal mucosa. The interaction of IL-25 and CysLTs and the contribution of tuft cell-derived CysLTs to the development of allergen-triggered inflammation in the airways has not been clarified. Here we show that inhalation of LTC4 in combination with a subthreshold dose of IL25 leads to dramatic synergistic induction of type 2 inflammation throughout the lungs, causing rapid eosinophilia, dendritic cell (DC) and inflammatory type 2 innate lymphoid cell (ILC2) expansion, and goblet cell metaplasia. While lung eosinophilia is dominantly mediated through the classical CysLT receptor CysLT1R, type 2 cytokines and activation of innate immune cells require signaling through both CysLT1R and CysLT2R. Tuft cell-specific deletion of the terminal enzyme requisite for CysLT production, Ltc4s, was sufficient to reduce both the innate immune response in the lung: eosinophilia, ILC2 activation and DC recruitment, and the systemic immune response in the draining lymph nodes after inhalation of the mold aeroallergen Alternaria. Our findings identify surprisingly potent synergy of CysLTs and IL-25 downstream of aeroallergen-trigged activation of airway tuft cells leading to a highly polarized type 2 immune response and further implicate airway tuft cells as powerful modulators of type 2 immunity in the lungs.

Co-exposure to lipopolysaccharide and desert dust causes exacerbation of ovalbumin-induced allergic lung inflammation in mice via TLR4/MyD88-dependent and -independent pathways

Background Lipopolysaccharide (LPS) often presents in high concentrations in particulate matter (PM), few studies have reported the enhancing effects of both LPS and PM on airway inflammation in mice and the role of toll-like receptors (TLRs) in this process. Asian sand dust (ASD) is observed most frequently during the spring. This study aimed to clarify the role of TLRs in murine lung eosinophilia exacerbated by ASD and LPS. Methods The effects of LPS and ASD co-treatment on ovalbumin (OVA)-induced lung eosinophilia were investigated using wild-type (WT), TLR2−/−, TLR4−/−, and adaptor protein myeloid differentiation factor 88 (MyD88)−/− BALB/c mice. ASD was heated (H-ASD) to remove the toxic organic substances. WT, TLR2−/−, TLR4−/− and MyD88−/− BALB/c mice were intratracheally instilled with four different combinations of LPS, H-ASD and OVA treatment. Subsequently, the pathological changes in lungs, immune cell profiles in bronchoalveolar lavage fluid (BALF), inflammatory cytokines/chemokines levels in BALF and OVA-specific immunoglobulin (Ig) in serum were analyzed. Results In WT mice, H-ASD + LPS exacerbated OVA-induced lung eosinophilia. This combination of treatments increased the proportion of eosinophils and the levels of IL-5, IL-13, eotaxin in BALF, as well as the production of OVA-specific IgE and IgG1 in serum compared to OVA treatment alone. Although these effects were stronger in TLR2−/− mice than in TLR4−/− mice, the expression levels of IL-5, IL-13, eotaxin were somewhat increased in TLR4−/− mice treated with OVA + H-ASD + LPS. In MyD88−/− mice, this pro-inflammatory mediator-induced airway inflammation was considerably weak and the pathological changes in lungs were negligible. Conclusions These results suggest that LPS and H-ASD activate OVA-induced Th2 response in mice, and exacerbate lung eosinophilia via TLR4/MyD88, TLR4/TRIF and other TLR4-independent pathways.

Club cell TRPV4 as a damage sensor driving lung allergic inflammation

SUMMARYAirway epithelium is the first body surface to contact inhaled irritants and report danger. We studied how epithelial cells recognize and respond to protease, which is a critical component of many allergens that provoke asthma. In a murine model, the aeroallergen alkaline protease 1 (Alp1) of Aspergillus sp. elicited helper T (Th) cell-dependent lung eosinophilia. Bronchiolar club cells responded rapidly to Alp1 by coordinating the accumulation of allergic immune cells in the lung. Alp1 degraded bronchiolar cell junctions, and club cells within the bronchioles propagated this signal via calcium and calcineurin to incite inflammation. In two human cohorts, we linked fungal sensitization and asthma with SNP/protein expression of the mechanosensitive calcium channel, TRPV4. TRPV4 was also necessary and sufficient for club cells to sensitize mice to Alp1. Thus, club cells detect junction damage as mechanical stress, which signals danger via TRPV4, calcium and calcineurin to initiate Th cell sensitization.Graphical Abstract

CD4+CD25+ Regulatory T Cells Decreased CD8+IL-4+Cellsin a Mouse Model of Allergic Asthma

Interleukin (IL)-4-producing-CD8 (cytotoxic T cells, Tc) contribute to lung eosinophilia and airway hyper-responsiveness (AHR) to an antigen. CD4+CD25+ regulatory T cells (Tregs) attenuate airway inflammation and AHR. This study investigated whether Tregs decrease Tc2frequencies in ovalbumin (OVA)-induced asthma model of mice. Female C57BL/6 mice were sensitized with OVA intraperitoneally and challenged with OVA intranasally to induce allergic asthma model. Tregs were sorted by fluorescence activated cell sorting (FACS) and magnetic activated cell sorting (MACS) microbeads. OVA-sensitized mice were injected with Tregs or phosphate buffer saline (PBS) by tail vein ahead of the first challenge. Airway inflammation and airway hyper-responsiveness (AHR)were evaluated by histological analysis and invasive method, respectively. OVA-specific IgE and cytokine levels were detected by ELISA. Flow cytometry was used to detect the percentages of Tc1 and Tc2. Gata3 and T-bet mRNA was determined by quantitative PCR (qPCR). OVA-sensitized and challenged mice displayed typical asthma features, which included eosinophilic airway inflammation, higher levels of Th2 cytokines and AHR. Gata3 mRNA, Tc2 frequencies and OVA-specific IgE levels were significantly increased in OVA-sensitized and challenged mice. Compared to PBS treatment, Tregs decreased Tc2 frequencies, airway inflammation, Th2 cytokine levels and AHR in OVA-sensitized and challenged mice. IL-13 levels were negatively correlated with Tc1 frequencies and with IFNg levels in experimental mice. Our results demonstrated that Tregs could prevent airway inflammation and AHR by decreasing Tc2 frequencies and cytokine levels in OVA-induced asthma model of mice, supporting Tregmight be as a potent therapeutic target for alleviating airway inflammation and AHR.

Eosinophil-derived IL-13 promotes emphysema

The inflammatory responses in chronic airway diseases leading to emphysema are not fully defined. We hypothesised that lung eosinophilia contributes to airspace enlargement in a mouse model and to emphysema in patients with chronic obstructive pulmonary disease (COPD).A transgenic mouse model of chronic type 2 pulmonary inflammation (I5/hE2) was used to examine eosinophil-dependent mechanisms leading to airspace enlargement. Human sputum samples were collected for translational studies examining eosinophilia and matrix metalloprotease (MMP)-12 levels in patients with chronic airways disease.Airspace enlargement was identified in I5/hE2 mice and was dependent on eosinophils. Examination of I5/hE2 bronchoalveolar lavage identified elevated MMP-12, a mediator of emphysema. We showed, in vitro, that eosinophil-derived interleukin (IL)-13 promoted alveolar macrophage MMP-12 production. Airspace enlargement in I5/hE2 mice was dependent on MMP-12 and eosinophil-derived IL-4/13. Consistent with this, MMP-12 was elevated in patients with sputum eosinophilia and computed tomography evidence of emphysema, and also negatively correlated with forced expiratory volume in 1 s.A mouse model of chronic type 2 pulmonary inflammation exhibited airspace enlargement dependent on MMP-12 and eosinophil-derived IL-4/13. In chronic airways disease patients, lung eosinophilia was associated with elevated MMP-12 levels, which was a predictor of emphysema. These findings suggest an underappreciated mechanism by which eosinophils contribute to the pathologies associated with asthma and COPD.

Lung eosinophilia induced by house dust mites or ovalbumin is modulated by nicotinic receptor α7 and inhibited by cigarette smoke

Eosinophilia (EOS) is an important component of airway inflammation and hyperresponsiveness in allergic reactions including those leading to asthma. Although cigarette smoking (CS) is a significant contributor to long-term adverse outcomes in these lung disorders, there are also the curious reports of its ability to produce acute suppression of inflammatory responses including EOS through poorly understood mechanisms. One possibility is that proinflammatory processes are suppressed by nicotine in CS acting through nicotinic receptor α7 (α7). Here we addressed the role of α7 in modulating EOS with two mouse models of an allergic response: house dust mites (HDM; Dermatophagoides sp.) and ovalbumin (OVA). The influence of α7 on EOS was experimentally resolved in wild-type mice or in mice in which a point mutation of the α7 receptor (α7E260A:G) selectively restricts normal signaling of cellular responses. RNA analysis of alveolar macrophages and the distal lung epithelium indicates that normal α7 function robustly impacts gene expression in the epithelium to HDM and OVA but to different degrees. Notable was allergen-specific α7 modulation of Ccl11 and Ccl24 (eotaxins) expression, which was enhanced in HDM but suppressed in OVA EOS. CS suppressed EOS induced by both OVA and HDM, as well as the inflammatory genes involved, regardless of α7 genotype. These results suggest that EOS in response to HDM or OVA is through signaling pathways that are modulated in a cell-specific manner by α7 and are distinct from CS suppression.