NKG2D Defines a Subset of Skin Effector Memory CD8 T Cells with Proinflammatory Functions in Vitiligo

Vitiligo is an autoimmune disease that results from the loss of melanocytes, associated with skin infiltration of CD8(+) effector memory T cells with a Tc1 skewed immune response. NKG2D is an activating receptor found on immune cells, in particular natural killer and activated CD8(+) T cells, that are able to produce a high amount of IFN-gamma. Here we found that NKG2D expression was increased in vitiligo skin CD8(+) effector memory T cells and was promoted by IL-15. Phenotypic and functional analyses showed that NKG2D(+) CD8(+) skin effector memory T cells displayed an activated phenotype and produced elevated levels of both IFN-gamma and tumor necrosis factor-alpha. Additional experiments revealed that vitiligo skin dendritic cells expressed the NKG2D ligands MICA-MICB, and in vitro experiments showed that these ligands could be induced on dendritic cells by IFN-alpha. Cultures of IFN-alpha-estimulated dendritic cells with skin NKG2D(+) CD8(+) T cells potentiated the production of type 1 cytokines, which was next inhibited by blocking the NKG2D/MICA-MICB interaction. These data show that NKG2D is a potential marker of pathogenic skin CD8(+) effector memory T cells during vitiligo. Therefore, targeting NKG2D could be an attractive strategy in vitiligo, a disease for which there is a strong need of innovative treatments.