Abstract
Marked eosinophilia and the accumulation of eosinophils in diseased tissues occur with various disorders and physiologic conditions, such as allergic diseases, bronchial asthma, parasitic infection, hypereosinophilic syndrome, and cancer. In normal individuals, the level of blood eosinophils is tightly regulated and eosinophil localization is limited primarily to the gastrointestinal tracts. However, after the onset of disease, eosinophils increase in the blood and infiltrate into various organs in the body, such as lungs and skin. Importantly, selective tissue eosinophilia can be observed even in the absence of marked blood eosinophilia. For example, in patients with bronchial asthma, eosinophils, but not neutrophils, infiltrate into the airway tissues, release various inflammatory mediators, and cause damage to the airway mucosa. Eosinophilia may be harmful because of the proinflammatory effects of the eosinophils, but it may also be beneficial because of the anti-parasitic effects of these cells. This article focuses on the recent advances in our understanding of the mechanisms of eosinophilia and tissue accumulation of eosinophils as well as the roles of these cell types in various human diseases. We hope that this article will help to better understand the biology of eosinophils and the pathologic mechanisms of eosinophilic disorders, and may lead to the development of new therapeutic approaches for patients.
