Activated eosinophils and interleukin 5 expression in early recurrence of Crohn's disease

Endoscopic recurrences after radical surgery for Crohn's disease are useful for studying the pathogenesis of initial lesions of Crohn's disease. Factors predisposing to recurrence are poorly understood, but it has been shown that eosinophilic infiltration of the neoileum may occur within a few weeks of resection. The aim of this study was to compare, in nine patients having an ileocolectomy, the infiltration of eosinophils and their activation state in normal and diseased areas of the neoileum, three months after surgery. Tissue eosinophils were studied by histochemical methods and electron microscopy. Mucosal expression of interleukin 5 (IL 5), an important eosinophil activating factor was studied using in situ hybridisation. Sixty per cent of patients had endoscopic recurrence at three months. Eosinophil infiltration was more pronounced in diseased than in endoscopically normal areas and was associated with a high expression of IL 5 mRNA. Ultrastructural analysis showed features of eosinophil activation, but no cytotoxic lesions of surrounding inflammatory or epithelial cells. This study suggests that local synthesis of IL 5 associated with eosinophil activation in the tissues could participate in early mucosal damage in Crohn's disease.