A type of white blood cell (leucocyte) that has a granular cytoplasm (see granulocyte) and is found chiefly in tissues, with only small numbers in the circulation. Eosinophils attack antibody-coated parasites by releasing from their granules powerful enzymes and free radicals. When activated they also release mediators such as prostaglandins, cytokines, and leukotrienes, which amplify the inflammatory response. Defective regulation of eosinophil activation, as in certain allergies and hypereosinophilia, can cause serious damage to body tissues.