Eosinophils Defined Share this page: Eosinophils (ee-oh-sin-oh-FILs) are a type of white blood cell that plays an important role in the immune system. White blood cells help protect the body by fighting infections. They are also associated with allergy and asthma. Video: What is Eosinophilic Esophagitis (EoE)? 7/8/2024 Share this page: