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Pulmonary and thoracic macrophage subpopulations and clearance of particles from the lung
1Cellular and Molecular Biology Group, Life Sciences Division, Los Alamos National Laboratory, NM 87545.
Abstract:
Pulmonary macrophages consist of several subpopulations that can be defined by their anatomical locations as well as by other criteria. In addition to the well-known alveolar macrophages that reside on the alveolar surface, pulmonary macrophages also occur in the conducting airways, in various pulmonary interstitial regions, and, in some mammalian species, in the lung's intravascular compartment. Other thoracic macrophages of relevance to pulmonary defense and some lung disease processes are the pleural macrophages resident in the pleural space and macrophages present in regional lymph nodes that receive lymphatic drainage from the lung. Of the above subpopulations of pulmonary and thoracic macrophages, the alveolar macrophages have received the most experimental attention in the context of the pulmonary clearance and retention of deposited particles. Accordingly, less information is currently available regarding the roles other pulmonary and thoracic populations of macrophages may play in the removal of particles from the lower respiratory tract and associated tissue compartments. This report provides an overview of the various subpopulations of pulmonary and thoracic macrophages, as defined by their anatomical locations. The known and postulated roles of macrophages in the pulmonary clearance and retention of particles are reviewed, with particular emphasis on macrophage-associated processes involved in the pulmonary clearance of relatively insoluble particles.
Insights
Pulmonary macrophages, including alveolar and airway populations, play key roles in clearing inhaled particles from the lungs. This review details their locations and functions in particle clearance, especially for insoluble particles.
Area of Science:
- Pulmonary immunology
- Cell biology
- Respiratory medicine
Background:
- Pulmonary macrophages are diverse, residing in alveoli, airways, interstitium, and pleural space.
- Alveolar macrophages are well-studied for particle clearance, but other populations' roles are less understood.
- Thoracic macrophages, including pleural and lymph node macrophages, are relevant to lung defense and disease.
Purpose of the Study:
- To provide an overview of pulmonary and thoracic macrophage subpopulations based on anatomical location.
- To review known and proposed functions of these macrophages in particle clearance from the respiratory tract.
- To emphasize macrophage roles in clearing relatively insoluble particles.
Main Methods:
- Literature review of anatomical locations of pulmonary and thoracic macrophages.
- Synthesis of existing research on macrophage functions in particle clearance.
- Focus on macrophage-associated mechanisms for removing insoluble particles.
Main Results:
- Identification of multiple pulmonary macrophage locations: alveolar, airway, interstitial, and intravascular.
- Recognition of pleural and lymph node macrophages as relevant thoracic populations.
- Highlighting the knowledge gap regarding non-alveolar macrophage roles in particle clearance.
Conclusions:
- Understanding diverse pulmonary macrophage locations is crucial for assessing particle clearance.
- Further research is needed to elucidate the specific contributions of various macrophage subpopulations.
- Macrophage-associated processes are central to the lung's defense against inhaled particles, particularly insoluble ones.