Airway-Associated Macrophages in Homeostasis and Repair

There is an increasing appreciation for the heterogeneity of myeloid lineages in the lung, but relatively little is known about populations specifically associated with the conducting airways. We use single-cell RNA sequencing, flow cytometry, and immunofluorescence to characterize myeloid cells of the mouse trachea during homeostasis and epithelial injury/repair. We identify submucosal macrophages, similar to lung interstitial macrophages, and intraepithelial macrophages. Following injury, there are early increases in neutrophils and submucosal macrophages, including M2-like macrophages. Intraepithelial macrophages are lost after injury and later restored by CCR2+ monocytes. We show that repair of the tracheal epithelium is impaired in Ccr2-deficient mice. Mast cells and group 2 innate lymphoid cells are sources of interleukin-13 (IL-13) that polarize macrophages and directly influence basal cell behaviors. Their proximity to the airway epithelium establishes these myeloid populations as potential therapeutic targets for airway disease. [Display omitted] •The myeloid compartment composition in the trachea changes upon injury•Monocytes and macrophages promote tracheal epithelial repair in vivo•Monocytes and macrophages support basal cell growth in vitro•Tracheal and lung macrophages are distinct at the transcript and protein level Engler et al. identify molecularly unique populations of monocytes and macrophages associated with the tracheal epithelium. The composition of the tracheal myeloid compartment changes upon injury, and repair is delayed in the absence of Ccr2+ monocytes. Injury-associated myeloid cells and type 2 cytokines directly affect basal cell behaviors.