[Eosinophils, parasites and allergy: from the biological to the clinical]

Eosinophils have been considered for a long time as secondary cells, only able to be attracted by chemotactic factors and recruited from blood to tissues, at the site of inflammation. More recent studies have shown that their functions are not limited to the release of cytotoxic mediators, effector against parasitic targets but deleterious for tissues in allergy, but they can also participate in the regulation of immune response by producing type 1 and type 2 cytokines. Although questionable, animal models indicate a rather beneficial role of eosinophils in parasitic infections but a detrimental one in allergy. The results of clinical trials aiming at increasing or decreasing respectively their effects are discussed.