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. They also have a rather diverse array of other functions, impacting multiple areas of immunology including allergy and asthma.

Eosinophils persist in the circulation for 6-12 hours, and can survive in tissue for an additional 2-3 days in the absence of stimulation. Eosinophils make up about 1-5% of the all white blood cells, and are about 10-12 micrometers in size.

Eosinophils are found naturally in the thymus (cortico-medullary junction and medulla), lower gastrointestinal track, ovary during phases of the cycle, uterus, spleen, and lymph nodes. They are not found naturally in the lung, skin, or other organs. The presence of eosinohils in the lung, skin, esophogus, or internal organs is associated with a disease process.

BMK-13

• can serve as a useful pan-eosinophil marker in tissue sections since it appears to stain most eosinophils. PMID: 1373987

CD9

• involved in the adhesion of eosinophils to fibronectin. PMID: 10704064
• seem to detect activated eosinophils in the circulation. PMID: 8904997

CD44 and CD69

• represent different types of cell-surface activation markers for human eosinophils. PMID: 9618391

CD69

• a useful marker for activated eosinophils at inflammatory sites. PMID: 1500624

ECP (Eosinophil Cationic Protein, EG1/EG2)

• released by eosinophils, is a marker of eosinophil activity. PMID: 17203813
• a marker of eosinophilic activity and degranulation that correlates with the severity of bronchial asthma. PMID: 15719624
• a serological marker of disease activity in childhood bronchial asthma. PMID: 11338688
• a marker of eosinophilic inflammation in asthma. PMID: 9515598

EDN (eosinophil derived neurotoxin)

• a catalytically proficient member of the pancreatic ribonuclease superfamily secreted along with other eosinophil granule proteins during innate host defense responses and various eosinophil-related inflammatory and allergic diseases. PMID: 16401072
• one of the four basic proteins stored in specific eosinophil granules, can also be detected at the surface of granulocytes. PMID: 12606041
• a rapidly evolving secretory protein derived from eosinophilic leukocytes. PMID: 9826755

Eosinophil Peroxidase (EPO)

• a simple specific marker for detecting eosinophils in bronchoalveolar lavage fluid. PMID: 8437132
• a unique component of eosinophils, is a useful marker for the identification of eosinophils in sputum and bronchoalveolar lavage fluid. PMID: 11978925

Eosinophil Protein-X (EPX)

• Eosinophil activation marker. PMID: 8721862
• one of the cationic proteins found in the granules of the human eosinophilic granulocytes. PMID: 1865126

IL-5

• eosinophil activation marker. PMID: 10714084

LA Antigen

• a differentiation marker on human eosinophils. PMID: 6992887

MBP1/MBP2 (major basic protein)

• MBP1 is more abundant than MBP2 in lysates of eosinophils and their granules, as judged by immunoassay and Western blotting. By immunofluorescence, MBP1 is present in eosinophils, basophils, and a human mast cell line (HMC1), whereas MBP2 is only detected in eosinophils. Neither MBP1 nor MBP2 could be detected in any other peripheral blood leukocyte. MBP2 is present only in eosinophils and that it may be a useful biomarker for eosinophil-associated diseases. PMID: 17082653

Other Eosinophil Markers

• A photoreactive fluorescent marker for identifying eosinophils and their cytoplasmic granules in tissues. PMID: 12533534
• Systemic activation of basophils and eosinophils: markers and consequences. PMID: 11080745
• Surface markers of human eosinophils. PMID: 974267
• 3-Bromotyrosine and 3,5-dibromotyrosine are major products of protein oxidation by eosinophil peroxidase: potential markers for eosinophil-dependent tissue injury in vivo. PMID: 10090740
• Eosinophil granule proteins (MBP, ECP, EPX/EDN, EPO)--a possible process of eosinophil activation and degranulation. PMID: 8492433