Overview
Eosinophils are granulocytes with a bilobed nucleus, blue cytoplasm and orange to red cytoplasmic granules.
The major physiologic role of eosinophils is to identify and mount an immune response against parasites, however they also play a key pathogenic role in allergic reactions.
Eosinophilia
Eosinophilia refers to an increase in circulating eosinophils.
Causes of Eosinophilia
- Allergy - asthma, allergic rhinitis, chronic sinusitis, atopic dermatitis, drug allergy, eosinophilic oesophagitis, allergic bronchopulmonary aspergillosis (ABPA), chronic eosinophilic pneumonia
- Parasites - helminths (especially Strongyloides), protozoa
- Autoimmune - eosinophilic granulomatosis with polyangiitis (Churg-Strauss), other autoimmune diseases (rarely)
- Malignancy - chronic eosinophilic leukaemia, lymphoma, certain solid organ malignancies
- Primary eosinophilia
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