BackgroundEsophagitis in infants and children is often characterized by eosinophilic inflammation. The underlying pathophysiologic mechanisms leading to this type of inflammation, and the role of eosinophils in the clinical expression of esophagitis, are unknown. The purpose of this study was to demonstrate the ultrastructural activation state of eosinophils in esophagitis in infants and children.MethodsStandard transmission electron microscopy was used to examine endoscopic esophageal biopsy material from patients with and without esophagitis, as defined by standard histologic criteria.ResultsTwelve esophagitis and three control cases were studied. In patients with esophagitis, electron microscopy revealed numerous eosinophils throughout the mucosa and invariably demonstrated signs of activation, including inversion of coreto-matrix densities and lucency of granule core protein. Eosinophils in an activated state were seen in active diapedesis through vascular endothelium into the mucosa. Eosinophils were sometimes seen in proximity to lymphocytes. Biopsies of control patients did not demonstrate eosinophils.ConclusionsEosinophils present in esophagitis are activated by electron microscopic criteria, and can been seen in an activated state entering into the mucosa. This suggests that eosinophils play an active role in the pathophysiology of this disorder, and that proinflammatory factors are present that selectively recruit and activate eosinophils in esophagitis in children.