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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]
The activation of T H 1 and M1 macrophage is a positive feedback loop, with IFN-γ from T H 1 cells upregulating CD40 expression on macrophages; the interaction between CD40 on the macrophages and CD40L on T cells activate macrophages to secrete IL-12; and IL-12 promotes more IFN-γ secretion from T H 1 cells.
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.
Macrophages are diffusely scattered in the connective tissue and in liver (Kupffer cells), spleen and lymph nodes (sinus histiocytes), lungs (alveolar macrophages), and central nervous system (microglia). The half-life of blood monocytes is about 1 day, whereas the life span of tissue macrophages is several months or years.
[2] [9] Lipid-laden alveolar macrophages have been reported in cases of vaping-associated pulmonary injury. [10] [1] [11] The lipid-laden macrophage index (LLMI) can be calculated by counting 100 macrophages in a BAL specimen treated with a lipid stain and scoring each macrophage from 0 to 4 based on the amount of lipids present in the cell.
Microglia are a type of glial cell located throughout the brain and spinal cord of the central nervous system (CNS). [1] Microglia account for about 10–15% of cells found within the brain. [2] As the resident macrophage cells, they act as the first and main form of active immune defense in the CNS. [3]
Phagocytic cells (of the mononuclear phagocyte system) called macrophages engulf (phagocytose) the hemoglobin to degrade it, producing hemosiderin and biliverdin. Excessive systemic accumulations of hemosiderin may occur in macrophages in the liver, lungs, spleen, kidneys, lymph nodes, and bone marrow.
Production of CSF-1 by brain tumors called glioblastomas causes microglia (brain-resident macrophages) to exhibit immunosuppressive, tumor-permissive phenotypes. [16] CSF1R inhibition in mouse glioblastoma models is beneficial and improves survival by inhibiting tumor-promoting functions of microglia.