Eosinophils in Immunity and Disease
Eosinophils are a type of granulocyte (a subcategory of white blood cells) that play a key role in the immune response against large pathogens and in allergic reactions. An increase in the number of eosinophils in the blood is called eosinophilia.
Role in Parasitic Infections
- Defense Against Parasites: Eosinophils are crucial for defending the body against large parasites, particularly helminths (parasitic worms) such as tapeworms, flukes, and hookworms, which are too big to be ingested by a single phagocytic cell.
- Cytotoxic Action: They contain granules filled with highly toxic proteins (like major basic protein, eosinophil peroxidase, and others) that they release onto the surface of the parasite to try and destroy it.
Role in Allergic Conditions
- Allergic Response: Eosinophils are key inflammatory cells in allergic diseases like asthma, allergic rhinitis (hay fever), and atopic dermatitis (eczema).
- Tissue Damage: They accumulate at the site of allergic inflammation, where they contribute to symptoms and tissue damage by releasing their cytotoxic granule proteins, cytokines, and other mediators.
Summary
The simultaneous elevation of eosinophils in both parasitic infections and allergies reflects their function in the Type 2 immune response, which is a specific pathway evolved to deal with extracellular parasites and, when inappropriately activated, drives allergic inflammation.