Macrophage Dysfunction in Respiratory Disease.

Our understanding of the origin, phenotype, and function of pulmonary macrophages has evolved over recent years. The use of lineage tracing and single-cell RNA sequencing has led to a greater understanding of how these cells regulate homeostasis in the lung. The primary function of alveolar macrophages is to clear any inhaled particles or pathogens and they as well as tissue-resident cells also play a role in the clearance of apoptotic cells and the resolution of inflammation. Lung diseases affect over half a billion people globally and are attributable to 7% of all deaths each year. The common diseases are chronic obstructive pulmonary disease (COPD) and asthma but others that contribute to this statistic include cystic fibrosis and idiopathic pulmonary fibrosis (IPF). Macrophages are aberrant in all these diseases with a reduced phagocytic capacity and a high proinflammatory phenotype with changes to their capacity to resolve inflammation. The pathways leading to these macrophage dysfunctions differ with disease and may relate to the specific lung environment in each condition. However, there are clear changes in metabolic profiles and mitochondrial activity in many of these conditions that contribute to a change in macrophage phenotype towards a more proinflammatory, less homeostatic cell. Understanding the mechanisms that drive these changes will allow for more targeted therapies for the treatment of these long-term and debilitating conditions.