Blood vessel-resident macrophages safeguard blood and vessel integrity in zebrafish

Their function is influenced by their microenvironment and origin. While tissue-resident macrophages originate from yolk sac progenitors and persist in some adult tissues through self-renewal, no dedicated macrophage population is known to function within the vast network of blood vessels, despite the importance of maintaining a healthy vascular and blood system.

Here, using high spatiotemporal live imaging of zebrafish embryos, we identified a distinctive population of macrophages residing within blood vessels, which we term blood vessel-resident macrophages (bMs). bMs actively survey the bloodstream, clearing foreign particles and unfit cells, and are the first responders to endothelial damage. bMs emerge directly from axial vessels through an atypical endothelial-to-macrophage transition (EMacT), independent of Runx1 and Csf1r, both essential for hematopoiesis and myelopoiesis, respectively.