Eosinophil granule proteins and bronchial asthma

For over 100 years, the association of eosinophils with bronchial asthma has been known. Over the past 20 years, the proteins comprising the eosinophil granule have been isolated and characterized. Four proteins are recognized and termed the major basic protein (MBP), the eosinophil peroxidase (EPO), the eosinophil-derived neurotoxin (EDN), and the eosinophil cationic protein (ECP). The activities of these proteins are reviewed with emphasis on their abilities to interact with structures in the bronchus and to reproduce features of the pathology of bronchial asthma. In addition, the relationship of these proteins to bronchial hyperreactivity, a major stigma of bronchial asthma, is discussed, and information highlighting the role of MBP is reviewed. Evidence also exists that eosinophil granule proteins may interact with the nervous system, and results showing increased vagal reactivity in an experimental animal model and the role of MBP as an allosteric muscarinic M2 receptor are presented. Finally, the effects of eosinophil granule proteins as cytostimulants on other cells including basophils, mast cells, neutrophils, platelets and alveolar macrophages are reviewed. Overall, these results indicate that eosinophil granule proteins have many abilities to alter lung function in asthma and to reproduce many of the cardinal manifestations of this disease.