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Diseases of eosinophils: causes, symptoms, diagnosis, treatment
Last reviewed: 07.07.2025
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Eosinophils are granulocytes and are derived from the same precursor as monocyte-macrophages, neutrophils, and basophils. The precise function of eosinophils is unknown. As phagocytes, eosinophils are less effective than neutrophils in killing intracellular bacteria. There is no direct evidence that eosinophils kill parasites in vivo, but they are toxic to helminths in vitro, and eosinophilia commonly accompanies helminth infections. Eosinophils are able to modulate immediate hypersensitivity reactions by degrading or inactivating mast cell-released mediators such as histamine, leukotrienes (which can cause vasoconstriction and bronchospasm), lysophospholipids, and heparin. Long-term eosinophilia may lead to tissue injury through mechanisms that are not yet fully understood.
Eosinophil granules contain major basic protein and eosinophil cationic protein, which are toxic to a number of parasites and mammalian cells. These proteins bind heparin and neutralize its anticoagulant activity. Eosinophil neurotoxin can cause severe damage to the myelin sheath of neurons. Eosinophil peroxidase, which differs significantly from the peroxidase of other granulocytes, generates oxidative radicals in the presence of hydrogen peroxide and halogen compounds. Charcot-Leyden crystals, consisting mainly of phospholipase B, are localized in sputum, tissues, and feces in diseases accompanied by eosinophilia (e.g., asthma, eosinophilic pneumonia).
Normally, the blood eosinophil count is less than 350/μl, with daily fluctuations inversely proportional to the plasma cortisol level; the highest level occurs at night, the lowest in the morning. The half-life of eosinophils in circulation is from 6 to 12 hours, most of these cells are located in tissues (e.g., upper respiratory tract, gastrointestinal tract, skin, uterus).
Eosinophil production is probably regulated by T cells through the secretion of hematopoietic growth factors such as granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin 3 (IL-3), and interleukin 5 (IL-5). GM-CSF and IL-3 also increase production of other myeloid cells, while IL-5 stimulates production of eosinophils only.
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