About EOS Diseases What is an Eosinophil? What is an eosinophil? What are eosinophils? In a healthy individual typically 1 to 5% of white blood cells are eosinophils (pronounced ee-oh-sin-oh-fills), which far from being an enemy play an important role in your immune system. Produced in the bone marrow they circulate through your blood vessels for 8-12 hours around the body before migrating into a tissue, where they remain for 1-2 weeks. What do eosinophils do? This proinflammatory cell contains around 200 large granules of enzymes and proteins which break open (degranulate) and release their toxic contents when the Eosinophil is activated. Their function is to move to the inflamed areas, trapping substances and killing cells. This process can occur when fighting bacteria, parasites, allergic reactions and other inflammatory responses. Friend or foe? The eosinophil has many varied roles some of which are yet to be discovered. Current research shows that they can be both helpful and harmful, they may even be part of organ formation (e. g. postgestational mammary gland development). However, when a person has abnormally elevated numbers of eosinophils in their digestive system, tissues, organs, and/or bloodstream, without a known cause, he or she may have an eosinophil-associated disease. It is from the eosin staining of the cells under a microscope and them becoming a deep pink that they get their name eosinophil. Registered Charity 1198883 Last updated 2/5/23 ©EOS Network 2023 All rights reserved Manage Cookie Preferences