[Niche signals regulate differentiation and functions of tissue resident macrophages]

Emerging evidence has revealed that tissue-resident macrophages (TRMs) are differentiated from fetal precursors, including yolk sac macrophages, and late erythro-myeloid progenitors (EMPs) derived from fetal monocytes. Furthermore, TRMs can locally undergo self-renewal independent of circulating bone marrow-derived monocytes. Recent data has indicated the existence of a TRM niche that controls TRM differentiation, maintenance, and diversification. Niche availability and accessibility for different TRM precursors determine the cell origin of each TRM. Furthermore, the TRM niche in each organ induces epigenetic and gene expression programing to develop the specific functions of each TRM, which are critical for homeostasis maintenance in the corresponding organs. In this review article, we discuss the recent findings concerning TRM differentiation and maintenance from the perspective of TRM niche function.