Eosinophils: role in asthma, allergy and parasite immunity

The distinct features of the eosinophil include their content of large crystalloid granules which contain a number of unique basic proteins, and their capacity to selectively generate the SRS-A, sulphidopeptide leukotrienes. Eosinophil-derived products probably play an important role in the destruction of helminthic larvae but in some situations, for instance, chronic bronchial asthma and the hypereosinophilic syndrome, the cell might be responsible for considerable tissue damage. Eosinophils can be activated, in vitro, by a variety of agents which include factors associated with eosinophil maturation, mast cell products and other substances released during allergic tissue reactions and other inflammatory processes. At the present time there is growing interest in the fact that in many conditions associated with eosinophilia there is a population of light density "activated" cells which, in a variety of biological systems, respond more vigorously than normal ("normodense") eosinophils. Knowledge of eosinophils and eosinophil-associated events is growing rapidly and there is a need to modify continuously our views on the precise role(s) of the eosinophil in the light of these new findings.