Eosinophil !

Cell

Eosinophils are granulocytes with bright red granules that fight parasitic worms and drive much of the damage in allergic asthma.

Updated 2026-11-01

What it is

Eosinophils are granulocytes with a two-lobed nucleus and large orange-red granules full of toxic proteins. They are made in the bone marrow under the control of IL-5 and move into tissues, especially the gut, airways and skin. They help defend against helminths too big to be eaten, and in allergic disease the same granule proteins injure the airway.

Key facts

Origin: myeloid progenitor in the bone marrow.
A small share of blood white cells; most eosinophils live in tissues.
They kill large parasites mainly by releasing granules onto the parasite's surface after it is coated with antibody.

Function

Defense against helminths (worms) that tissues cannot engulf.
Late-phase allergic inflammation in airways, skin and gut.
Release of lipid mediators and cytokines that sustain Th2 inflammation.

Markers

IL-5 receptor
Major basic protein
Charcot-Leyden crystals in sputum

Clinical notes

Eosinophilia in Colombia and the region: think first of intestinal and tissue helminths (Ascaris, hookworm, Strongyloides, Toxocara).
Strongyloides can cause fatal hyperinfection when a carrier receives glucocorticoids; screening matters in endemic areas.
Eosinophilic asthma and eosinophilic esophagitis are driven by Th2 inflammation.
Drug reaction with eosinophilia and systemic symptoms (DRESS) is a severe drug hypersensitivity.
Biologics that block IL-5 are used in severe eosinophilic asthma.

In the lab

Absolute eosinophil count in the complete blood count with differential.
Stool examination for ova and parasites; serology for some tissue helminths.
Sputum may show Charcot-Leyden crystals (from eosinophil proteins) in asthma.

Test yourself

Think of the answer, then tap the question to see it.

Which cytokine controls eosinophil production and survival?

IL-5.

What are two main causes of eosinophilia?

Allergic diseases such as asthma, and helminth infections; drug reactions and adrenal insufficiency are others.

Why is Strongyloides important before glucocorticoid treatment?

Glucocorticoids can trigger hyperinfection and disseminated, often fatal, disease in carriers.

Which toxic granule protein is classic for the eosinophil?

Major basic protein (others: eosinophil cationic protein, eosinophil peroxidase).

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← All of immunology

Educational content on the immune system; not a treatment or individual vaccination guide and no substitute for a health professional's advice. No doses are given.

Sources: Eosinophils (British Society for Immunology, 2024); 18.4 Leukocytes and Platelets (OpenStax, Rice University (Anatomy and Physiology 2e), 2022); Eosinophil count - absolute (MedlinePlus, U.S. National Library of Medicine, 2024).

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Representative model, for educational purposes only.