Increased HLA-DR and decreased CD3 on human intestinal intraepithelial lymphocytes: evidence of activation?

BACKGROUND Activation of circulating T lymphocytes results in expression of HLA-DR, interleukin-2 receptor (IL-2R), transferrin receptor (TrR), and decreased amounts of surface CD3. AIM To examine the activation status of human intestinal intraepithelial lymphocytes (IELs) by flow cytometry. PATIENTS AND METHODS Duodenal biopsy specimens from 12 patients provided a source of intestinal lymphocytes. Dual colour analysis was used to compare activation marker expression by IELs with peripheral blood (PB) T lymphocytes from the same patients. RESULTS All human IEL populations express HLA-DR and their density of expression is lower than on the small population of HLA-DR+ resting PB T lymphocytes (mean fluorescence intensity (MFI) 52.9, range 19.8-94.8 v 152.6 range, 49.1-320.3; p < 0.01). The density of CD3 was significantly reduced on IELs (MFI 465.8, range 228.7-660), compared with PB T lymphocytes (756.3, range 444.5-1573.7; p < 0.009). IL-2R was not detected on IELs; nor were the activation markers, TrR, M21 C5, or M2 B3. CONCLUSION HLA-DR expression on IELs together with decreased CD3 expression suggest previous stimulation. However, the absence of additional markers of T cell activation may reflect a unique pathway of activation.