Tuft cells produce LTC 4 and IL-25, which cooperate to promote allergen-driven airway inflammation.

integrating single-cell RNA sequencing and immunolocalization we define distinct markers of olfactory neuroepithelial cells, showing that Muc2 uniquely identifies sustentacular cells and Ncam1 is a robust mouse and human marker for OSNs. The enigmatic, transcriptionally uncharacterized subsets of olfactory microvillous cells (MVCs) correspond to nasal tuft cells and ionocytes in both mice and humans. Next we identify three morphologically, molecularly, and spatially distinct subsets of tuft cells: Nrgn+ MVC, Dclk1+ glandular and Gnat3+ respiratory tuft cells. While distinct, these subsets of tuft cells share a core machinery for allergen recognition and generation of the eicosanoid mediators cysteinyl leukotrienes. Single-cell analysis of the response to inhaled allergens revealed robust induction of olfactory stem cell proliferation, which is abolished by tuft cell-specific deletion of Ltc4s, required for cysteinyl leukotriene generation. Together our data provide high resolution characterization of epithelial cell diversity in the nose, uncovering a novel mechanism by which the mucosal response to allergens, specifically tuft cell-derived eicosanoids, regulates stem cell proliferation in the olfactory neuroepithelium.

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.