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Eosinophil granulocytes, commonly referred to as eosinophils (or less commonly as acidophils), are white blood cells that are responsible for combating infection by parasites in the body.
Transparent in vivo, these cells appear brick-red when stained with eosin using the Romanowsky method (and are thus, 'eosin (or acid)-loving' cells, hence the name). The red color is visible as small granules within the cellular cytoplasm. These granules contain histamine and proteins such as eosinophil peroxidase, RNase, DNases, lipase, plasminogen, and Major Basic Protein that are toxic to both parasites and the host's tissues.
Eosinophils persist in the circulation for 6-12 hours, and survive in the tissues for another 2-3 days if they aren't further stimulated.
Eosinophils make up about 2.3% of the all white blood cells, and are about 10-12 micrometers in size.
A key mediator in eosinophil activation is interleukin 5.
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Functions of eosinophils
Eosinophils play a role in fighting viral infections which is evident from the abundance of RNAses they contain within their granules.
Eosinophils are considered the main effector cells in asthma pathogenesis and are associated with disease severity.
Eosinophils fight helminth (worm) colonization and may be slightly elevated in the presence of certain parasites.
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Eosinophilia
An increase in eosinophils, i.e. the presence of more than 500 eosinophils/microlitre of blood is called an eosinophilia, and is typically seen in people with a parasitic infection of the intestines, a collagen vascular disease (such as rheumatoid arthritis), malignant diseases such as Hodgkin's Disease, extensive skin diseases (such as exfoliative dermatitis), Addison's Disease, and with the use of certain drugs such as penicillin. In 1989, contaminated l-tryptophan supplements caused a deadly form of eosinophilia known as eosinophilia-myalgia syndrome.
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Eosinopenia
Eosinopenia is a decrease in eosinophil number, which occurs characteristically when glucocorticoids are administered.
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