Two differentiation pathways generate large peritoneal macrophages with one replenishing mesothelial border...

Peritoneal cavity fluid and mesothelial surfaces host distinct resident macrophage populations, among which include the well-described Gata6⁺ large cavity macrophages (LCMs) in peritoneal fluid. Here, we reveal that LCMs arise from two separable differentiation pathways. In the quantitatively minor pathway, monocytes gave rise to LYVE1⁺ LCMs but few Gata6⁺ LCMs. This pathway did not require the transcription factor Gata6 but was severely impaired in mice bearing three mutations in the -165 kb Zeb2 enhancer (Zeb2^TM) with impaired monocyte development. The second, dominant pathway supported Gata6-dependent LCMs and was intact in Zeb2^TM mice, even when turnover was enforced by irradiation, and was supported by adoptive transfer of a specialized LCM intermediate expressing Gata6 before the residency marker TIMD4. Functionally, the quantitatively minor LCM pathway distinctly surveilled the mesothelium, replenishing mesothelial border macrophages upon encountering an open niche. Thus, beyond embryonic versus adult hematopoietic paradigms, LCMs with overlapping and distinct phenotypes arise from two pathways linked to divergent fates.