Figure 1.

Ontogeny of tissue resident macrophages. Most organs contain a heterogeneous mix of bone marrow derived macrophages and macrophages deriving from embryonic progenitors; however, in the brain, the resident macrophage population (microglia) derives solely from the proliferation of progenitors seeded in the embryo. Of note, the two first embryonic waves are represented together in this figure, for simplicity. Within the intestine, the large majority of macrophages derive from the bone marrow, however, a small population of macrophages derives from embryonic progenitors and is able to self-maintain in adulthood. These self-maintaining macrophage populations colonise specific niches in close proximity to the vasculature in the submucosa and enteric neurons. Other macrophage populations, located in the villi and surrounding the mucosal vascular network, derive entirely from precursors that originate in the bone marrow. Adapted from Ginhoux and Guilliams, 2016.¹³