Macrophages as tissue scavengers, builders, and sensors

The cellular biology of macrophages underpins the multitude of roles that these cells undertake under homeostatic and inflammatory conditions. Macrophages populate all tissues where they contribute to organ physiology while acting as sensors of health and triggering inflammation in response to organ dysfunction, trauma, and infection. Sharing key characteristics such as a highly developed endocytic compartment, secretion of growth factors and cytokines, motility and antigen presentation, macrophages undergo specific adaptations in each niche guided by environmental clues that result in diverse phenotypes that support tissue-specific roles such as iron recycling, synaptic pruning, bone reabsorption, and processing of lung surfactant. This review will provide an overview of macrophage biology and heterogeneity that underpin their contribution to homeostasis and inflammation to illustrate their importance as therapeutic targets in a wide range of inflammatory diseases.