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Macrophage
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Macrophage Full Name
Macrophage
Macrophage Introduction
Macrophages are large, specialized phagocytic cells of the innate immune system that populate every tissue in the body. While historically thought to derive solely from circulating blood monocytes, modern fate-mapping studies have revealed that many tissue-resident macrophages (such as microglia in the brain and Kupffer cells in the liver) actually originate from embryonic precursors in the yolk sac or fetal liver and maintain themselves locally. Functionally, macrophages display remarkable plasticity. Depending on the environmental cues, they can polarize into two distinct phenotypes: M1 macrophages (classically activated), which are pro-inflammatory and microbicidal, or M2 macrophages (alternatively activated), which are anti-inflammatory and involved in tissue repair and fibrosis. Their primary role is phagocytosis: the engulfment and digestion of cellular debris, foreign substances, microbes, and apoptotic cells (efferocytosis). Beyond cleaning, they act as professional Antigen-Presenting Cells (APCs), processing foreign proteins and displaying them on MHC Class II molecules to activate T-lymphocytes, thus bridging the innate and adaptive immune systems.
Figure 1. Macrophages in development, homeostasis and disease. (Source: Wynn TA, et al. 2013)
The clinical relevance of macrophages is vast due to their central role in inflammation. In metabolic disease, specifically Atherosclerosis, macrophages accumulate oxidized Low-Density Lipoproteins (oxLDL) within the arterial wall. Unable to process this excess lipid, they transform into "foam cells," which form the core of the atherosclerotic plaque and drive vascular inflammation. In oncology, Tumor-Associated Macrophages (TAMs) are a major component of the tumor microenvironment. Paradoxically, these macrophages are often "educated" by the tumor to adopt an M2-like immunosuppressive phenotype, which promotes tumor growth, angiogenesis (blood vessel formation), and metastasis rather than attacking the cancer cells. Furthermore, in infectious diseases like Tuberculosis, macrophages are the primary host for Mycobacterium tuberculosis; when they fail to eliminate the bacteria, they aggregate to form granulomas, a hallmark of the disease intended to contain the infection.
Alternate Names for Macrophage
Macrophages
Rabbit Macrophage
RAM11
Macrophage
