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 are also important for further activation. NOD2 (Nucleotide-binding oligomerization domain-containing protein 2) is an intracellular pattern recognition receptor that plays a key role in the immune system. It recognizes muramyl dipeptide (MDP), a component of bacterial cell walls. The aim of this study is to clarify the role of NOD2 as a key receptor for human eosinophil activation.