Alveolar Macrophage Polarization and Its Role in Common Lung Diseases

Pulmonary macrophages are a crucial component of the lung immune system. They exhibit high heterogeneity and plasticity: the heterogeneity of pulmonary macrophages is reflected in their diverse origins, which consist of multiple subpopulations identified by surface marker expression, location, and origin[1]: alveoli, interstitium, and recruited (monocyte-derived). Pulmonary macrophages can polarize into various phenotypes to respond to the local microenvironment. After sensing changes in the local tissue microenvironment, macrophages are regulated by multiple intracellular signaling molecules and pathways, leading to polarization into different phenotypes, and even mutual conversion between different phenotypes[2]. They are associated with the pathophysiology of various lung diseases, including acute lung injury (ALI), chronic obstructive pulmonary disease (COPD), and asthma. This article reviews the origin and phenotype of pulmonary macrophages, pulmonary macrophage polarization, and the role of macrophage polarization in lung diseases.