Age-Related Variation of Intraepithelial Lymphocytes Subsets in Normal Human Duodenal Mucosa

The enumeration of intestinal intraepithelial lymphocytes (IELs), and the phenotyping of CD3⁺CD103⁺ (TcRαβ, TcRγδ) and CD3⁻CD103⁺ IEL subsets constitute useful diagnostic tools for the correct interpretation of the mucosal histology of duodenal/jejunal biopsies in many pathological conditions of the small intestine, particularly celiac disease (CD). This work evaluates the ranges of duodenal IEL counts by flow cytometry in healthy mucosa from pediatric and adult controls, establishing normal reference values for CD3⁺ TcRγδ and CD3⁻ subsets and their variation with age. Seventy-four pediatric controls and 36 adult controls were identified on the basis of their normal histology from more than 1,000 duodenal diagnostic biopsies performed in Caucasian subjects. Total IEL counts and IEL subsets (“IEL lymphogram”) were analyzed by four-color flow cytometry (FCM). IEL represent 7.7%±0.4 (mean±SE) and 8.5%±0.5 of the cells isolated from the epithelium in the pediatric and adult series, respectively. The upper normal range, considered as the 97 percentile, is 14% in pediatrics and 15% in adults. No significant difference was observed between TcRγδIEL percentages in children (6.9%±0.5 of the total IELs) and adults (6.6%±0.8). However, the density of CD3⁻ IELs is significantly higher (p < 0.001) in the mucosa from controls under 3 years (50.2%±2.6) than in adults (25.5%±2.1). IEL lymphogram by flow cytometry is an easy, quick and reliable analysis performed in one of the biopsy specimens obtained during a diagnostic endoscopy, and confers specificity to the histopathological findings. IEL counts below 14% in children and 15% in adults should be considered within a normal range in the evaluation of duodenal mucosa by FCM. No differences with age were observed with respect to TcRγδIEL, while the CD3⁻ IEL fraction was significantly higher on children under 3 years, with a trend to increase again in the elderly.