[Eosinophilic granulocytes: on the way to knowledge of their functional significance]

Although the eosinophilic granulocyte has been recognized as a blood cell type for more than 100 years, its functional significance has long remained an enigma. The introduction of successful isolation procedures resulted in rapidly progressive research efforts, but the concept of the functional role of this cell type made a full about turn between the 1970s and 1980s. In the 1970s, the role of the eosinophil was thought to be a homeostatic one, with its main task being to repair mast-cell-dependent tissue damage in parasitic and allergic disease. Further structural analysis and improved biological and clinical integration of such knowledge led to the completely revised concept of the 1980s: the eosinophil is now seen as the main culprit in the damage that accompanies allergic disease, as a result of mistaken identity between the parasite (where cytotoxic power against the aggressor is desirable) and the allergen (where the eosinophil's cytotoxic power results in self-damage). The latest research news about cytokine-dependent regulatory mechanisms governing the eosinophilic reaction supports our hope that by specific blocking of tissue hormones, such as the lymphocyte-derived IL-5, elegant ways of manipulating hypereosinophilic reactions will be found in the near future.