Regarding the duodenal subpopulations evaluated, the most important differences between healthy controls and patients with GERD were found in the lamina propria compartment; this consisted of profound differences in the CD4/CD8 balance, with a significant decrease in CD4+ T cells and an increase in CD8+ T cells in patients with GERD compared with those in controls. Here, CD4 is linked to gastroesophageal reflux disease.