Sensing of metabolic signals via GPR183 promotes occupation of lung macrophage niches by monocytes.

Monocytes populate tissues when local niches are depleted of tissue-resident macrophages, yet the tissue-derived signals controlling monocyte-to-macrophage differentiation are largely undefined. Here, we discovered that the oxysterol receptor GPR183 positions monocytes to sense niche signals that induce lung macrophage differentiation. We found that interstitial macrophages that continuously turn over express the oxysterol receptor GPR183, whereas alveolar macrophages that derive from embryonic progenitors and slowly turn over did not. Models of conditional tissue-resident macrophage depletion showed that newcomer monocyte-derived macrophages expressed GPR183 along their differentiation trajectory. Recruited GPR183+ monocytes interacted with fibroblasts and lack of GPR183 caused defective lung macrophage differentiation. Single-cell RNA analysis over time identified lung fibroblasts as the source of the GPR183 ligand 7α,25-dihydroxycholesterol in the empty niche. Our findings identify oxysterols as instructive signals for tissue-resident macrophage development from monocytes.