Advances in the immunobiology of eosinophils and their role in disease.

Eosinophils play a protective role in host immunity to infections by parasitic worms and, detrimentally, are involved in the pathophysiology of asthma and other allergic diseases. Airway inflammation is central to the pathology of asthma and is characterized by infiltration of the bronchial mucosa by large numbers of proinflammatory cells, amongst which the eosinophil is prominent despite being a minority constituent of circulating leukocytes. Crucial steps in eosinophilic inflammation include augmented production of eosinophils in the bone marrow, their increased release into the circulation, and their selective accumulation in the conducting airways. The eosinophil has a potent armory of proinflammatory mediators, including cytotoxic granule proteins, cytokines and lipid mediators with considerable potential to initiate and sustain an inflammatory response. Thus there is much interest in the elucidation of the mechanisms responsible for eosinophil accumulation, persistence, activation and ultimate fate. This article reviews our current understanding of the role of the eosinophil in human disease and the immunobiology of this important proinflammatory cell.