Oxidative stress drives CD8+ T-cell skin trafficking in patients with vitiligo through CXCL16 upregulation by activating the unfolded protein response in keratinocytes

Background: In patients with vitiligo, an increased reactive oxygen species (ROS) level has been proved to be a key player during disease initiation and progression in melanocytes. Nevertheless, little is known about the effects of ROS on other cells involved in the aberrant microenvironment, such as keratinocytes and the following immune events. CXCL16 is constitutively expressed in keratinocytes and was recently found to mediate homing of CD8(+) T cells in human skin. Objective: We sought to explicate the effect of oxidative stress on human keratinocytes and its capacity to drive CD8(+) T-cell trafficking through CXCL16 regulation. Methods: We first detected putative T-cell skin-homing chemokines and ROS in serum and lesions of patients with vitiligo. The production of candidate chemokines was detected by using quantitative real-time PCR and ELISA in keratinocytes exposed to H2O2. Furthermore, the involved mediators were analyzed by using quantitative real-time PCR, Western blotting, ELISA, and immunofluorescence. Next, we tested the chemotactic migration of CD8(+) T cells from patients with vitiligo mediated by the CXCL16-CXCR6 pair using the transwell assay. Results: CXCL16 expression increased and showed a positive correlation with oxidative stress levels in serum and lesions of patients with vitiligo. The H2O2-induced CXCL16 expression was due to the activation of 2 unfolded protein response pathways: kinase RNA (PKR)-like ER kinase-eukaryotic initiation factor 2 alpha and inositol-requiring enzyme 1 alpha-X-box binding protein 1. CXCL16 produced by stressed keratinocytes induced migration of CXCR6+ CD8+ T cells derived from patients with vitiligo. CXCR6+ CD8+ T-cell skin infiltration is accompanied by melanocyte loss in lesions of patients with vitiligo. Conclusion: Our study demonstrated that CXCL16-CXCR6 mediates CD8+ T-cell skin trafficking under oxidative stress in patients with vitiligo. The CXCL16 expression in human keratinocytes induced by ROS is, at least in part, caused by unfolded protein response activation.