Mast cells play a key role in the disease process in allergies: As a reaction towards an allergen - for example pollen or dust mites - they release big amounts of substances that initiate an inflammatory process. Study leader Hideaki Morita and his team discovered that mast cells are not only "bad guys", but also have a "good side" (see figure): They release the substance interleukin-2 that induces the production of certain immune cells called T-regulatory (Treg) cells. Treg cells can suppress the allergic inflammatory process in the airways induced by interleukin-10.