FOXP3 expression in duodenal mucosa: Unique role in pathogenesis and differential diagnosis of celiac disease

Forkhead box protein P3 (FOXP3) positive regulatory T lymphocytes are indispensable in the inflammatory homeostasis of the gastrointestinal tract and represent a significant subset of regulatory cells in inflammatory, autoimmune, and neoplastic conditions. This study aimed to elucidate the potential of FOXP3 expression in diagnosing and pathogenesis of celiac disease (CD) by comparing duodenal biopsies of CD cases with non-CD ones, some of which had increased intraepithelial lymphocytes (IELs). Two hundred sixty-one duodenal tissues of patients who applied to adult gastroenterology were reevaluated for immunohistochemical analysis. After excluding patients on a gluten-free diet (n = 44), the CD (n = 97) and non-CD (n = 120) groups were divided based on clinical complaints that could be associated with CD (intestinal or extraintestinal), serologic and histologic findings. The specific threshold was determined by receiver operating characteristic (ROC) analysis, and its relationship with CD diagnosis and clinicopathological data was evaluated. ROC analysis offered a ">14" cutoff value for diagnosing CD, for which AUC (Area Under The Curve): 0.968, p < 0.0001, sensitivity: 92.8, specificity: 91.7, positive and negative predictive values were 90 % and 94 %, respectively. High FOXP3 expression was associated with higher IEL, diagnosis of CD, more severe histologic (higher Marsh score) and endoscopic (scalloping) findings, and higher anti-tissue transglutaminase and anti-endomysium IgA titers (p < 0.001). It also correlates with IEL in CD patients and is unaffected by the increase in IEL and the presence of gastric Helicobacter Pylori in the non-CD group. FOXP3 is a sensitive and specific marker for diagnosing CD despite inflammatory conditions resulting from non-CD causes.