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a cell of vertebrates, including man, whose cytoplasm contains rounded granular structures that are stained by acid dyes, in particular by eosin. The eosinophils of the blood originate and mature in the bone marrow. They comprise 3–4 percent of leukocytes in the peripheral blood of a healthy human being. This level is subject to a daily rhythm and is regulated by the system which includes the pituitary body and the adrenal cortex.
In allergic reactions, eosinophils release the inhibitor histamine, which belongs to the prostaglandins E1 and E2. They also serve as phagocytes.
An increase in the percentage of eosinophils in the peripheral blood or an increase in their absolute number is called eosinophilia. As a rule, this condition is reactive in character, regardless of the degree of its severity. The possibility of developing eosinophilic leukemia is still a matter of dispute. Eosinophilia is accompanied by various reactions and diseases, predominantly allergic, including those related to the breaking down of the body’s resistance by parasites or medicinal and food allergens. Aggregations of eosinophils observed in the tissues, as, for example, in the mucosa of the bronchi (and sputum) in bronchial asthma, are called tissue eosinophilia. Eosinophilic infiltrates, large aggregations of eosinophils in the tissues, are occasionally observed in various organs, predominantly the lungs. They may run their course as short-term reactions or result in such severe illnesses as pneumonia, myocarditis, vasculitis, and meningoencephalitis. A number of other diseases are also accompanied by a high eosinophilia. In some cases it is impossible to establish the nature of the disease that is accompanied by a high eosinophilia. The condition may be observed even in people who are otherwise healthy.
Hürtle cells, one of the types of cells of the anterior lobe of the pituitary body, are also called eosinophils.
L. D. GRINSHPUN