About EOS Diseases What is an Eosinophil? What is an eosinophil? What Are Eosinophils? In a healthy individual, typically one to five per cent 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 pro-inflammatory cell contains around 200 large granules of enzymes and proteins which break open (degranulate) and release their toxic contents when the Eosinophil is activated. They move to 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. post, gestational 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. The Origin of the Eosinophil's Name and Colour Eosinophils get their name from a special dye called eosin. When scientists look at these cells under a microscope, they use this dye to make them easier to see. The eosin dye makes the cells turn a deep pink colour. This pink colour is where eosinophils get their name. It's like a special tag that helps scientists know they're looking at eosinophils. Registered Charity 1198883 Last updated 04/07/23 ©EOS Network 2023 All rights reserved Manage Cookie Preferences