[Eosinophilic granulocytes and their significance in allergic diseases]

Eosinophils are found in the blood and tissues of patients with allergic diseases such as asthma, allergic rhinitis and also atopic dermatitis. The number of eosinophils in the diseased tissue generally correlates with the expression of clinical symptoms. Originally, the eosinophil was regarded as having an exclusively protective role, for example in host defense against parasites. More recently, the eosinophil is recognized as being a pro-inflammatory cell that can mediate allergic disease. The eosinophil is active in inflammation through the release of granule proteins and the synthesis and release of inflammatory mediators. The important eosinophil granule proteins are major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil derived neurotoxin (EDN) and eosinophil peroxidase (EPO). These proteins have toxic effects on the surrounding tissue. Of additional importance for the allergic inflammatory reactions are membrane-derived mediators such as leukotriene C4 (LTC4), platelet activating factor (PAF) and Charcot-Leyden crystals. These mediators are synthesized and released after eosinophil activation, and act toxic on surrounding cells. Eosinophils are active in asthma, and increased numbers and eosinophil-derived mediator concentrations have been documented in bronchial biopsies, BAL and sputum. In addition, eosinophil granule proteins and inflammatory mediators are found in nasal secretions in allergic rhinitis. In atopic dermatitis one finds activated eosinophils and depositions of eosinophil granule proteins in skin biopsies. Eosinophils are not only active in mediating allergic inflammation, but interact in cellular networks with antigen presenting cells (APC), mast cells, and T lymphocytes. These other cells influence eosinophil maturation, mobilization, tissue localization and activation.