CXCL8 and gastroesophageal reflux disease: In this study, to explore the production of IL-33 and other inflammatory cytokines in patients with heartburn without mucosal break, we examined mucosal biopsies and evaluated the expression pattern of cytokines including IL-33, IL-6, IL-8, and monocyte chemotactic protein-1 (MCP-1) in patients with heartburn, using DIS as a marker of GER.