Role of Macrophages in Air Pollution Exposure Related Asthma

Abstract

Asthma is a chronic inflammatory airway disease characterized by variable airflow obstruction, bronchial hyper-responsiveness, and airway inflammation. The chronic inflammation of the airway is mediated by many cell types, cytokines, chemokines, and inflammatory mediators. Research suggests that exposure to air pollution has a negative impact on asthma outcomes in adult and pediatric populations. Air pollution is one of the greatest environmental risks to health, and it impacts the lungs' innate and adaptive defense systems. A major pollutant in the air is particulate matter (PM), a complex component composed of elemental carbon and heavy metals. According to the WHO, 99% of people live in air pollution where air quality levels are lower than the WHO air quality guidelines. This suggests that the effect of air pollution exposure on asthma is a crucial health issue worldwide. Macrophages are essential in recognizing and processing any inhaled foreign material, such as PM. Alveolar macrophages are one of the predominant cell types that process and remove inhaled PM by secreting proinflammatory mediators from the lung. This review focuses on macrophages and their role in orchestrating the inflammatory responses induced by exposure to air pollutants in asthma.

Keywords: air pollution; asthma; heavy metals; macrophages; particulate matter.

Figure 1

Alteration of macrophage function after air pollutant exposure. After particulate matter exposure (red arrow), the macrophages in the bronchial alveolar lavage fluid increased with PM2.5 exposure in OVA asthma models. However, their functions, including phagocytic activity and autophagy, were decreased, and cell apoptosis increased. After exposure to heavy metals (blue arrow), the macrophages differentiated into M2 macrophage profiles. The functions of macrophages, including phagocytic activity, chemotaxis, and adhesion ability, also decreased, and cell autophagy and apoptosis increased. ^(A) indicates experimental results from animal models and ^(C) indicates experimental results from cell models. The figure was partly generated using Servier Medical Art, provided by Servier, licensed under a Creative Commons Attribution 3.0 unported license.