by Jason Wasserman MD PhD FRCPC
May 1, 2022


What is an eosinophil?

An eosinophil is a type of white blood cell (WBC) and a part of the body’s immune system. Eosinophils are designed to kill and remove micro-organisms, in particular, parasites from the body. Eosinophils are normally found in the blood and inside tissues. Eosinophils are often found in areas of chronic inflammation. Abnormal activity of eosinophils is associated with allergies and asthma and medications that reduce the activity of eosinophils are used to treat these conditions. Eosinophilia means that the number of eosinophils in the blood is higher than normal. Causes of eosinophilia include allergies, asthma, drug reaction, infection, blood disorders including cancer, and autoimmune diseases. When examined under the microscope, eosinophils are small cells with bright pink cytoplasm. The cytoplasm of the cell is filled with small round granules and the nucleus has two lobes.

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