Eosinophils and urticaria.

Previously believed to have an exclusive role in the release of cytotoxic mediators in the defense against helminthic infections, eosinophils are now considered key players in inflammatory reaction and regulation of immune response. Through activation of a large variety of membrane receptors and production of various pharmacologically active mediators, eosinophils may exert a detrimental role in tissues in which they have been recruited and may contribute to the perennization of inflammatory processes. The crucial role of eosinophils has been documented in several eosinophilic skin diseases, such as hypereosinophilic syndrome and bullous pemphigoid, and the literature provides strong evidence for their role in urticaria. The aim of this article is to discuss the mechanisms of specific tissue recruitment of eosinophils, the factors of eosinophil activation, and the contribution of these cells to inflammation and immunoregulation in urticaria. Recent advances in the knowledge of eosinophils will certainly help toward developing new strategies for the management of antihistamines resistant to urticaria.