Alveolar macrophage
Macrophagocytus alveolaris
Also known as: dust cell, heart failure cell
Resident phagocytes on the alveolar surface ("dust cells") that ingest inhaled particles, microbes and spent surfactant — the main defence of the gas-exchange region.
Overview
Alveolar macrophages arise mainly from fetal monocytes that seed the lung around birth and self-renew locally; blood monocytes add to the pool during inflammation. They wander over the alveolar surface within the lining fluid and through the interstitium, engulfing particles too small to be caught by the mucociliary escalator, bacteria and apoptotic cells. Laden macrophages either migrate up to the bronchioles, where they join the mucociliary escalator and are coughed up or swallowed, or pass into lymphatics to hilar nodes.
They also catabolise surfactant (a GM-CSF-dependent function), present antigen and orchestrate inflammation by releasing cytokines (TNF-α, IL-1, IL-8) and proteases. Normally they keep the alveolus "quiet", avoiding inflammation in response to harmless inhaled antigens.
- Location
On the alveolar epithelial surface and in the interalveolar septa.
Anatomy
- Histology
Large cells with abundant cytoplasm often containing phagocytosed carbon (dust cells) or haemosiderin (heart failure cells).
Function
- Phagocytose inhaled particles and microbes.
- Clear and recycle surfactant.
- Initiate and resolve inflammation; antigen presentation.
Clinical significance
Heart failure cells
In chronic pulmonary venous congestion (left heart failure, mitral stenosis) red cells leak into alveoli and macrophages fill with haemosiderin, staining with Prussian blue.
Pneumoconioses and TB
Silica kills macrophages, releasing fibrogenic mediators (silicosis; increased TB risk). Asbestos fibres coated with iron in macrophages form "asbestos bodies". M. tuberculosis survives within alveolar macrophages by blocking phagolysosome fusion.
Pulmonary alveolar proteinosis
Autoantibodies against GM-CSF impair macrophage surfactant clearance, so alveoli fill with lipoproteinaceous material; treated by whole-lung lavage or inhaled GM-CSF.
Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.