Activated eosinophils are a major cell type involved in allergic diseases. IL-5 primarily activates eosinophils and prolongs their survival. However, interactions between these cells and microorganisms, including fungi, are also important for further activation. Aspergillus fumigatus is a common indoor allergen for patients with allergic disorders who are often sensitized to it. The aim of this study is to clarify the role of this fungus as a direct activator of human eosinophils.