Phenotypical and Functional Characterization of Small Intestinal TcRγδ+ T Cells in Coeliac Disease

Abstract

Increased numbers of TcRγδ⁺ T cells are present in the small intestinal epithelium of patients with coeliac disease (CoD). Their function, however, is unknown. In order lo facilitate detailed functional studies, intestinal γα T cells have been isolated from small intestinal biopsies of patients with CoD (n= 18) and controls (n= 14). As expected, increased numbers of Vδ1⁺ TcRγδ⁺ T cells were detected in freshly isolated intraepithelial cell suspensions (IEL) from CoD patients. Also, in the in vitro expanded IEL T-cell populations from CoD patients the numbers of Vδ1⁺ TcRγδ⁺ T cells were increased compared with similar cell cultures from control patients. From IEL cultures derived from six CoD patients, 107 T-cell clones were generated by limiting dilution and analysed. Sixty of these clones were either CD4 or CD8 positive TcRαβ⁺ clones. The remaining 47 clones expressed the TcRγδ. Further phenotypical analysis of the γδ T-cell clones indicated that the TcRγδ⁺ T-cell population in the small intestinal epithelium of CoD patients is heterogeneous: four TcRγδ phenotypes could be detected and, although the majority of the TcRγδ⁺ T cells were CD4^-CD8^-, γδ T-cell clones expressing either a CD8αα homodimer, a CD8αβ⁺ heterodimer or CD4 were also identified. In contrast to the TCRαβ⁺ IEL, most TcRγδ⁺ IEL were CD5 negative. Furthermore, biochemical analysis indicated that the increase in Vδ1⁺γδ T cells in the small intestinal epithelium of CoD patients was not the result of a monoclonal expansion. The small intestinal epithelium-derived γδ T-cell clones were functional in vitro since the majority of these clones were able to lyse target cell lines such as K562, Molt4 and Daudi. These novel findings therefore indicate that the γδ T cells in the small intestine of CoD patients represent a heterogeneous population and that such cells are functional in vitro. The isolation and the in vitro propagation and cloning of these cells may open new avenues for the study of the putative immune mechanisms leading lo coeliac disease.