Ciliated cell-derived IL-17D restrains allergic asthma through controlling monocyte recruitment

The airway epithelium plays a crucial role in maintaining lung homeostasis, and its dysregulation is often linked to various lung diseases, including asthma. Ciliated cells, abundantly present in the mammalian airway epithelium, have a critical function in clearing inhaled particles and pathogens. We show here that ciliated cells constitutively express IL-17D, which functions as an immune brake in limiting allergic inflammation in murine models of asthma. Mechanistically, IL-17D functions to prevent influx of classical monocytes into the lung and their subsequent conversion to pathogenic alveolar macrophages, through binding to CD93. Deficiency in Il17d or Cd93 increased the expression of chemokine receptors on classical monocytes, including CCR6, thereby enhancing their recruitment to the lung and type 2 inflammation. Our study thus reveals an unexpected protective role of ciliated cells and IL-17D in lung immune responses and asthma, which can be further explored for treating related diseases.