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Micrograph showing hemosiderin-laden alveolar macrophages, as seen in a pulmonary hemorrhage. H&E stain. An alveolar macrophage, pulmonary macrophage, (or dust cell) is a type of macrophage, a professional phagocyte, found in the airways and at the level of the alveoli in the lungs, but separated from their walls. [1]
Mucociliary clearance (MCC), mucociliary transport, or the mucociliary escalator describes the self-clearing mechanism of the airways in the respiratory system. [1] It is one of the two protective processes for the lungs in removing inhaled particles including pathogens before they can reach the delicate tissue of the lungs.
The cells are primarily monocytes and macrophages, and they accumulate in lymph nodes and the spleen. The Kupffer cells of the liver and tissue histiocytes are also part of the MPS. The mononuclear phagocyte system and the monocyte macrophage system refer to two different entities, often mistakenly understood as one.
They are also called pulmonary macrophages, and dust cells. Alveolar macrophages also play a crucial role in immune responses against viral pathogens in the lungs. [25] They secrete cytokines and chemokines, which recruit and activate other immune cells, initiate type I interferon signaling, and inhibit the nuclear export of viral genomes. [25]
A siderophage is a hemosiderin-containing macrophage. Heart failure cells are siderophages generated in the alveoli of the lungs of people with left heart failure or chronic pulmonary edema, when the high pulmonary blood pressure causes red blood cells to pass through the vascular wall. [1] Siderophages are not specific of heart failure.
The short-term exposure attracts macrophages and neutrophils to the lung with a 4-fold increase in cellularity. [ 4 ] [ 2 ] Short duration also biases polarization towards M1 phenotype. The number of immune cells however will be normalized in 6 months, demonstrating the shift in signaling direction.
Rupture of congested capillaries leads to release of hemosiderin from damaged red blood cells. When alveolar macrophages engulf hemosiderin they are called heart failure cells. Death of heart failure cells in their journey back to lung tissue with subsequent hemosiderin release leads to lung fibrosis. [1] [2] [3]
The cells in the respiratory epithelium are of five main types: a) ciliated cells, b) goblet cells, c) brush cells, d) airway basal cells, and e) small granule cells (NDES) [6] Goblet cells become increasingly fewer further down the respiratory tree until they are absent in the terminal bronchioles; club cells take over their role to some extent here. [7]