CD8αβ+ γδ T Cells: A Novel T Cell Subset with a Potential Role in Inflammatory Bowel Disease.

γδ T cells have been attributed a wide variety of functions, which in some cases may appear as contradictory. To better understand the enigmatic biology of γδ T cells it is crucial to define the constituting subpopulations. γδ T cells have previously been categorized into two subpopulations: CD8αα+ and CD8- cells. In this study we have defined and characterized a novel subset of human γδ T-cells expressing CD8αβ. These CD8αβ+ γδ T cells differed from the previously described γδ T cell subsets in several aspects, including the degree of enrichment within the gut mucosa, the activation status in blood, the type of TCRδ variant used in blood, and small but significant differences in their response to IL-2 stimulation. Furthermore, the novel subset expressed cytotoxic mediators and CD69, and produced IFN-γ and TNF-α. In patients with active inflammatory bowel disease the mucosal frequencies of CD8αβ+ γδ T cells were significantly lower as compared with healthy controls, correlated negatively with the degree of disease activity, and increased to normal levels as a result of anti-TNF-α therapy. In conclusion, our results demonstrate that CD8αβ+ γδ T cells constitute a novel lymphocyte subset, which is strongly enriched within the gut and may play an important role in gut homeostasis and mucosal healing in inflammatory bowel disease.