1. Figure 2 Embryonic origins of tissue-resident macrophages
Figure 2 | Embryonic origins of tissue-resident macrophages. The majority of tissue-resident macrophages are seeded during embryonic development. Yolk-sac macrophages arise first from primitive haematopoiesis and seed embryonic tissues, including the brain, as early as day E9.0. A wave of yolk-sac-derived erythromyeloid progenitors (EMPs) seeds the fetal liver, where definitive haematopoiesis is established on E11.0. The fetal liver is the main site of haematopoiesis until birth. On E12.5, fetal-liver-derived monocytes populate the embryo and dilute the yolk-sac-derived populations. However, yolk-sac macrophages remain the sole source of microglia, the brain's resident macrophages, probably because of the establishment of the blood–brain barrier. In the epidermis and pancreas, macrophages seem to have a hybrid origin, arriving in both yolk-sac and fetal-liver waves. In other tissues, resident macrophages are exclusively derived from fetal-liver monocytes. The fate mapping of tissue-resident synovial macrophages has not yet been done.
Udalova, I. A. et al. (2016) Macrophage heterogeneity in the context of rheumatoid arthritis
Nat. Rev. Rheumatol. doi: /nrrheum