Sustained mast cell-mediated inflammation may explain why earlier trials of IL-5 blockers mepolizumab and reslizumab reduced eosinophil counts in the esophagus, but did not induce histologic remission or significant improvement in symptoms, and would also be consistent with reports of EoE-like disease without tissue eosinophilia, but with mast cell infiltration67, and with the description of a subset of EoE patients who have epithelium-restricted mast cell infiltration, despite resolution of epithelial eosinophilia68. The gene discussed is IL5; the disease is eosinophilic esophagitis.