Evidence for eosinophil activation in eosinophilic cystitis.

Eosinophilic cystitis (EC) is a rare condition. Recent studies have shown that activated eosinophils release cytotoxic cationic proteins which can induce tissue damage. Moreover, in vitro studies have shown that interleukin-5 (IL-5) is a cytokine able to attract and activate eosinophils. The goal of this study was to detect a possible activation of eosinophils in EC using electron microscopy, in situ hybridization with an IL-5 RNA probe and immunochemistry with a specific anti-IL-5 antibody. Using these combined methods in a typical case of EC, we found numerous activated eosinophils synthesizing and secreting IL-5 protein. IL-5 could enhance the activation of eosinophils and their cytotoxic potential in bladder tissues. This mechanism might explain the chronicity of the lesions in EC.