High serum thymus and activation-regulated chemokine levels in the lymphocytic variant of the hypereosinophilic syndrome.

The idiopathic hypereosinophilic syndrome is associated with expansion of an IL-5-producing T-cell subset in a subgroup of patients. Identification of such patients is critical to adequate management because there is some evidence that they present an increased risk for development of T-cell lymphoma. Although the T(H)2-like cells often bear an aberrant surface phenotype and can readily be detected with flow cytometry, we now show that lymphocyte phenotyping might be normal in some cases. In contrast, serum thymus and activation-regulated chemokine levels are consistently increased in such patients compared with others with persistent idiopathic hyper-eosinophilia and could therefore represent a useful diagnostic tool.