Tissue biology perspective on macrophages

Macrophages are essential components of mammalian tissues. Although historically known mainly for their function in host defense and the clearance of apoptotic cells, macrophages are now increasingly recognized as serving many roles in tissue development, homeostasis and repair. In addition, tissue-resident macrophages have many tissue-specific functional characteristics, which are a reflection of distinct gene-expression programs. Here we discuss the emerging views of macrophage biology from evolutionary, developmental and homeostatic perspectives.