Cell-mediated autoimmunity has been suggested to be involved in the melanocyte apoptosis that occurs in vitiligo. We investigated the cytotoxicity to autologous melanocytes of CD8+ T cells from the perilesional margins and peripheral blood samples of vitiligo patients. CD8+ T cells isolated from skin biopsied from the edges of depigmented skin patches of vitiligo patients or from peripheral blood samples of the same donors were proliferated in culture medium. The primary cultures of CD8+ T cells and autologous melanocytes were mixed at ratios of 1:1, 1:2 or 1:5 and incubated for 3 days. The apoptosis of the melanocytes was analyzed by flow cytometry. Secreted cytokines in selected samples were measured by cytokine arrays. The results show that the CD8+ T cells were successfully isolated from the vitiligo perilesional margins. This cell population showed a significantly higher percentage of CD69 expression (56.13±3.55 versus 29.93±2.35%, p<0.01) and CD137 expression (41.74±1.06 versus 25.97±1.63%, p<0.01) compared with CD8+ T cells in peripheral blood from the same donors. The co-culturing of CD8+ T cells from lesional skin with autologous melanocytes induced apoptosis in the melanocytes (16.63±1.21, 16.71±0.63 and 18.32±1.60% for CD8+ T cells and autologous melanocytes at ratios of 1:1, 1:2 and 1:5, respectively). IL-6 levels were much higher in the co-culture (3.01-fold higher than in a melanocyte monoculture and 17.32-fold higher than in a CD8+ T-cell monoculture). The CD8+ T cells were also demonstrated to secrete more IL-13. Taken together, our data demonstrate that the infiltration of active CD8+ T cells takes place in the vitiligo perilesional margins. Those CD8+ T cells present significantly higher activation levels and higher cytotoxicity to autologous melanocytes than their counterparts from peripheral blood samples. These data suggest that CD8+ T cells are likely to be involved in the pathogenesis of vitiligo.

The paucity of vitiligo animal models limits the understanding of vitiligo pathogenesis and the development of therapies for the skin disorder. In this study, we developed a new mouse model of vitiligo by topically applying the skin‐depigmenting agent monobenzone on mice. We demonstrated that monobenzone‐induced skin depigmentation on the non‐exposed sites and that the severity of lesions depended on drug dosage. The result of the histological examination of the depigmented skin indicated loss of epidermal melanocytes and perilesional accumulation of CD8⁺ T cells. Furthermore, the monobenzone‐induced depigmentation of the Rag1 gene knockout did not appear on the non‐exposed sites, supporting the involvement of infiltrating CD8⁺ T cells in melanocyte destruction. Resemblance in histological characteristics and pathogenesis between monobenzone‐induced depigmentation and active human vitiligo suggests good potential of our mouse model for use in vitiligo research.

Interferon-γ (IFN-γ) plays an important role in the proceedings of vitiligo through recruiting lymphocytes to the lesional skin. However, the potential effects of IFN-γ on skin melanocytes and the subsequent contribution to the vitiligo pathogenesis are still unclear. To investigate the effects of IFN-γ on viability and cellular functions of melanocytes. Primary human melanocytes were treated with IFN-γ. Cell viability, apoptosis, cell cycle melanin content and intracellular reactive oxygen species (ROS) level were measured. mRNA expression was examined by real-time PCR. The release of interleukin 6 (IL-6) and heat shock protein 70 (HSP-70) was monitored by ELISA. β-galactosidase staining was utilized to evaluate melanocyte senescence. Persistent IFN-γ treatment induced viability loss, apoptosis, cell cycle arrest and senescence in melanocytes. Melanocyte senescence was characterized as the changes in pigmentation and morphology, as well as the increase of β-galactosidase activity. Increase of p21^Cip1/Waf1 protein was evident in melanocytes after IFN-γ treatment. IFN-γ induction of senescence was attenuated by siRNAs against p21, Janus kinase 2 (JAK2) or signal transducer and activator of transcription 1 (STAT1), but not by JAK1 siRNA nor by p53 inhibitor pifithrin-α. IFN-γ treatment increased the accumulation of intracellular ROS in melanocytes, while ROS scavenger N-acetyl cysteine (NAC) effectively inhibited IFN-γ induced p21 expression and melanocyte senescence. IL-6 and HSP-70 release was significantly induced by IFN-γ treatment, which was largely inhibited by NAC. The increase of IL-6 and HSP-70 release could also be observed in senescent melanocytes. IFN-γ can induce senescence in melanocytes and consequently enhance their immuno-competency, leading to a vitiligo-prone milieu.