Emerging roles of basophils in protective immunity against parasites.

Basophils, the least common type of granulocyte, have long been considered as minor effector cells in allergic responses because of their ability to release allergy-inducing chemical mediators such as histamine and leukotriene C4. However, it is unlikely that many animal species evolutionarily conserve basophils to only elicit allergic responses without any host-beneficial function. The study of basophils has been hampered by their rarity and difficult identification, as well as the lack of suitable animal models. Recent studies using novel analytical tools, including basophil-depleting antibodies and genetically engineered mice deficient only in basophils, have illuminated the crucial and nonredundant roles for basophils in protective immunity against both ecto- and endoparasites.