IDIOPATHIC EOSINOPHILIA

Peripheral and tissue eosinophilia are associated with a wide variety of inflammatory syndromes. These include both multisystem and limited diseases with vasculitis or nonvasculitic tissue damage and variable e xpression of end-stage-fibrosis. The idiopathic hypereosinophilic synd rome (IHS) represents a multisystem disorder defined by sustained eosi nophilia of an undetectable cause with significant organ system dysfun ction. Although not specified as such in the criteria for the diagnosi s of IHS, there are idiopathic eosinophilic syndromes that are clinica lly distinct from IHS by virtue of the fact that the eosinophilic infl ammation is limited to specific-tissues (such as the skin) with an ove rall good prognosis. The pathogenic role of the eosinophilic granulocy te in these conditions is attested by evidence of eosinophil activatio n and degranulation at sites of tissue injury. The recruitment and loc alization of eosinophils to specific sites of tissue inflammation invo lves cytokines with haematopoetic growth factor activity, adhesion mol ecules expressed both by the vascular endothelium and eosinophils,and chemoattractants that stimulate eosinophil migration. Recently, overex pression of IL-5 in transgenic mice was shown to lead to both peripher al blood eosinophilia and tissue eosinophilia. With the advances in ou r understanding of cytokine-dependent regulatory mechanisms that contr ol the peripheral eosinophil number as well as the recruitment and sur vivability of eosinophils at sites of inflammation, more targeted ways of manipulating the eosinophil reaction can be expected in the future .