Eosinophils, sometimes called eosinophiles or, less commonly, acidophils, are a variety of white blood cells and one of the immune system components responsible for combating multicellular parasites and certain infections in vertebrates. Along with mast cells and basophils, they also control mechanisms associated with allergy and asthma. They are granulocytes that develop during hematopoiesis in the bone marrow before migrating into blood, after which they are terminally differentiated and do not multiply.
Also Known as: Eosin, Eosino, Eosinophils, Acidophils
Cells Panel: Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils
Key Features
- Size: 12–17 µm
- Shape: Bi-lobed nucleus + bright orange granules
- Lifespan: 8h in blood → Days in tissues
Microscopy
- Staining: Wright-Giemsa highlights refractile red granules
- Key Identifier: Charcot-Leyden crystals (eosinophil debris)
Clinical Ranges
| Parameter | Normal Value |
|---|---|
| % of WBCs | 1–6% |
| Absolute Count | <0.5 × 10⁹/L |
Abnormalities
- Eosinophilia (↑): Allergies, parasites, EGPA
- Eosinopenia (↓): Steroid use, acute infections
Structure of Eosinophils:
- Eosinophils are also 10–12 µm in diameter
- Neucleus: Bilobed, Clumped Chromatin
- Cytoplasm: Coarse GrimsonRed Granules
- The granules of eosinophils stain best with an acidic stain known as eosin.
- The nucleus of the eosinophil will typically have two to three lobes and, if stained properly, the granules will have a distinct red to orange color.
Functions of Eosinophils:
These cells are born in the bone marrow, and migrate from the peripheral blood system after a few hours, into loose connective tissue in the respiratory and gastointestinal tracts. They phagocytose antigen-antibody complexes. They also produce histaminase, and aryl suphatase B, two enzymes that inactivate two inflammatory agents released by mast cells. A high eosinophil blood count may indicate an allergic reaction.
Eosinophils are also important in killing parasitic worms.
Eosinophils increased in:
- Allergy.
- Parasitic infestation.
- Skin disorders.
- Neoplastic diseases like Hodgkin’s lymphoma.
- Collagen vascular diseases.
Eosinophil Decreased in:
- Cushing’s syndrome.
- Stress.
