Airway-associated macrophages in homeostasis and repair

Summary

There is an increasing appreciation for the heterogeneity of myeloid lineages in the respiratory system, but whether distinct populations associate with the conducting airways remains unknown. 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 that are similar to lung interstitial macrophages and intraepithelial macrophages, and find that repair of the tracheal epithelium is impaired in Ccr2-deficient mice. Following injury there are early increases in neutrophils and submucosal macrophages, including M2-like macrophages. Unexpectedly, intraepithelial macrophages are initially lost but later replaced from CCR2⁺ monocytes. Mast cells and group 2 innate lymphoid cells are sources of IL13 that polarizes macrophages and directly influences basal cell behaviors. Their proximity to the airway epithelium establishes these myeloid populations as potential therapeutic targets for airway disease.