An Expansion of CD3+CD8+CD28-NKG2A+ T-Cells Occurs in Individuals With Active Celiac Disease

Abstract

Background: Celiac disease (CD), characterized by small intestinal enteropathy, occurs in genetically susceptible individuals intolerant to gluten. Activation of the innate and adaptive immune system occurs locally in the small bowel mucosa. However, recent studies have also described the presence of Gliadin specific T-cells in the peripheral blood of individuals with CD. An oligoclonal expansion of CD8+ T-cells bearing the inhibitory NK-cell receptor NKG2A has been shown to be a marker of antigen experienced cytolytic T-cells in small bowel mucosa and the peripheral blood. Thus, In this study, we characterized the phenotype of circulating T-cells in CD patients during different disease phases, in comparison to normal individuals, to discern disease specific alterations. Methods: Peripheral blood samples were taken at the time of endoscopy from patients in each disease phase (active celiac disease ACD, gluten free diet GFD), as well as normal individuals. The frequency ofCD4+and CD8+ T-cells expressing the NK-cell activating (NKG2D) and inhibitory (NKG2A) receptors was evaluated in conjunction with CD28 expression by flow cytometry of peripheral blood mononuclear cells (PMBC). Results: A total of 15 peripheral blood samples from age and gender matched individuals with ACD (n=5), those on GFD (n=5), and normal controls (n=5) were analyzed. The mean age of the subjects was 35.4yrs and 80% were female. All phases of CD were associated with an increased percentage ofCD8+CD28T-cells compared to age matched controls (P=0.038 -for ACD compared to controls, and 0.082 for GFD compared to controls). Further characterization for NKG2A and NKG2D expression revealed an expansion of NKG2A+ CD28T-cells in ACD compared to controls (p=0.014). The percentage of this subset decreased to control levels in individuals on GFD (p=0.427). No significant differences in CD4+NKG2A+CD28or NKG2D+CD28T-cell subsets was observed between CD patients and controls. CD8 as well as CD4 T-cells from patients with ACD, but not those on GFD, exhibited spontaneous proliferation In Vitro. This proliferating response can further amplified by addition of IL-15 and/or Gliadin. Conclusion: Our findings suggest changes in subsets of circulating CD8+ T-cells in ACD patients that might be of functional importance. It is presently unclear whether the expansion of CD8+CD28-NKG2A + T-cells represents a Gliadin-specific population with effector cytotoxic or regulatory potential. It is conceivable that NKG2A up-regulation on T-cells represents a homeostatic response to dampen the immune response to offending antigens. Further studies evaluating the antigen specificity and cytokine profiles of this subset will shed more light on the systemic immune response in individuals with untreated celiac disease.