eosinophil
Meaning of eosinophil: Its weapons cut both ways: the granule proteins that damage parasites also injure airway and skin tissue in allergic disease.
Definition of eosinophil
An eosinophil is a white blood cell of the granulocyte family, named for the coarse granules in its cytoplasm that soak up the red dye eosin. Those granules hold enzymes and toxic proteins the cell releases when activated. Eosinophils make up a small fraction of circulating white cells and act mainly against parasites and in allergic inflammation.
What does an eosinophil actually do?
It works by release rather than by swallowing. Where a neutrophil engulfs a bacterium, an eosinophil attaches to a target far too large to engulf, such as a parasitic worm, and empties its granules onto the surface. Those granules carry major basic protein, eosinophil cationic protein, eosinophil peroxidase and a neurotoxin, all of which damage cell membranes. The same chemistry accounts for the collateral damage in allergic disease: the proteins do not distinguish between a worm cuticle and the lining of an airway. Eosinophils also release signaling molecules that recruit other cells and prolong inflammation, which is why they feature in the persistent, smoldering phase of asthma rather than in the sudden wheeze.
How does it compare with the other granulocytes?
| Cell | Granules stain | Main role |
|---|---|---|
| Neutrophil | Pale, taking up neither dye strongly | Bacteria and fungi; the most numerous white cell |
| Eosinophil | Red-orange with the acidic dye eosin | Parasites, allergic and asthmatic inflammation |
| Basophil | Dark blue-purple with basic dyes | Releases histamine in the immediate allergic response |
What makes the count go up?
Most eosinophils do not live in the blood at all. They spend their working life in tissue, especially the gut lining, lung and skin, and pass through the circulation only in transit, so a blood cell count samples a small travelling minority. The count rises when a signal called interleukin-5 drives production and release from the bone marrow, which happens in allergic disease, asthma, eczema, some drug reactions and infection with tissue-invading worms. It falls under corticosteroid treatment and during acute bacterial infection or major physical stress, so a normal count in an unwell person does not by itself exclude an allergic or parasitic process.
Used in a sentence
The blood count revealed an increased eosinophil count in the setting of the patient's asthma exacerbation.
Good to know
A raised eosinophil count is most often linked to allergic disease, asthma or parasitic infection, though a markedly raised count also prompts evaluation for less common causes.
Word origin
Where “eosinophil” comes from
Formed from eosin, from Greek eos, meaning dawn, referring to a reddish dye the cell's granules readily absorb, and -phil, from Greek philos, meaning loving or having an affinity for.