Eosinophils constitute approximately 1-5% of circulating white cells and have a life span of about 8-12 days. They spend from 3-8 hours in the blood before making their way to the tissues.
Eosinophils are differentiated from other leucocytes by Side Fluorescent Light and Forward Scattered Light measurements in the Sysmex XN WDF Channel.
Eosinophils are a similar size to neutrophils but the nucleus is generally bilobed and occasionally has three lobes. They are characterised by many deeply red staining cytoplasmic granules in Romanovsky stained slides.
Eosinophil Function
Eosinophils have less phagocytic and bactericidal activity than neutrophils but play an important role in mediating hypersensitivity reactions, bronchial asthma and skin inflammation. Their granules contain proteases, peroxidases and acid phophatase but primarily they are released to kill microbes extracellularly. Eosinophils play a major role with T helper lymphocytes to kill parasites and proteins released also stimulate basophils to release histamines etc. thus amplifying the inflammatory response.
Causes of a raised eosinophil count (eosinophila):
Parasitic infection - Filaria, schistosomes, hookworm, toxicara.
Allergy - Bronchial asthma, hay fever, food sensitivity.
Drug sensitivity - Ibuprofen, diclofenac.
Metabolic disorders - Uraemia, acidosis, gout, eclampsia.
Haematologic - Hodgkin's disease, myeloproliferative disorders, hypereosinophilic syndrome.
Skin disease - Psoriasis, pemphigus, dermatitis herpetiformis.
Carcinoma
Polyarteritis nodosa
Recovery from acute infection.