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

Abstract

Aeroallergen sensing by airway epithelial cells triggers pathogenic immune responses leading to type 2 inflammation, the hallmark of chronic airway diseases such as asthma. Tuft cells are rare epithelial cells and the dominant source of interleukin-25 (IL-25), an epithelial cytokine, and cysteinyl leukotrienes (CysLTs), lipid mediators of vascular permeability and chemotaxis. How these two mediators derived from the same cell might cooperatively promote type 2 inflammation in the airways has not been clarified. Here, we showed that inhalation of the parent leukotriene C₄ (LTC₄) in combination with a subthreshold dose of IL-25 led to activation of two innate immune cells: inflammatory type 2 innate lymphoid cell (ILC2) for proliferation and cytokine production, and dendritic cells (DCs). This cooperative effect led to a much greater recruitment of eosinophils and CD4⁺ T cell expansion indicative of synergy. Whereas lung eosinophilia was dominantly mediated through the classical CysLT receptor CysLT₁R, type 2 cytokines and activation of innate immune cells required signaling through CysLT₁R and partially CysLT₂R. Tuft cell–specific deletion of <i>Ltc4s</i>, the terminal enzyme required for CysLT production, reduced lung inflammation and the systemic immune response after inhalation of the mold aeroallergen <i>Alternaria</i>; this effect was further enhanced by concomitant blockade of IL-25. Our findings identified a 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.