Spontaneous immunological activities in the target tissue of vitiligo-prone Smyth and vitiligo-susceptible Brown lines of chicken.

Introduction: Vitiligo is an acquired de-pigmentation disorder characterized by the post-natal loss of epidermal melanocytes (pigment-producing cells) resulting in the appearance of white patches in the skin. The Smyth chicken is the only model for vitiligo that shares all the characteristics of the human condition including: spontaneous post-natal loss of epidermal melanocytes, interactions between genetic, environmental and immunological factors, and associations with other autoimmune diseases. In addition, an avian model for vitiligo has the added benefit of an easily accessible target tissue (a growing feather) that allows for the repeated sampling of an individual and thus the continuous monitoring of local immune responses over time. Methods: Using a combination of flow cytometry and gene expression analyses, we sought to gain a comprehensive understanding of the initiating events leading to expression of vitiligo in growing feathers by monitoring the infiltration of leukocytes and concurrent immunological activities in the target tissue beginning prior to visual onset and continuing throughout disease development. Results: Here, we document a sequence of immunologically significant events, including characteristic rises in infiltrating B and αß T cells as well as evidence of active leukocyte recruitment and cell-mediated immune activities (CCL19, IFNG, GZMA) leading up to visual vitiligo onset. Examination of growing feathers from vitiligo-susceptible Brown line chickens revealed anti-inflammatory immune activities which may be responsible for preventing vitiligo (IL10, CTLA4, FOXP3). Furthermore, we detected positive correlations between infiltrating T cells and changes in their T cell receptor diversity supporting a T cell-specific immune response. Conclusion: Collectively, these results further support the notion of cell-mediated immune destruction of epidermal melanocytes in the pulp of growing feathers and open new avenues of study in the vitiligo-prone Smyth and vitiligo-susceptible Brown line chickens.

Research progress of vitiligo repigmentation: from oxidative stress to autoimmunity.

Vitiligo belongs to a frequent chronic autoimmune skin disease with the features of pigmented plaques on the diseased skin along with potential damage of melanocytes. There are many factors underlying the pathogenesis of vitiligo, among which oxidative stress is extensively regarded to be the critical factor leading to the loss of melanocytes. The changed redox state resulting from oxidative stress, containing ROS overproduction along with the reduced activity of the skin's antioxidant system, makes melanocytes less resistant to exogenous or endogenous stimuli, and ultimately pushes normal defense mechanisms, resulting in the loss of melanocytes. Given the crucial potential of innate together with adaptive immunity in vitiligo, there is growing evidence of a relation between oxidative stress and autoimmunity. Our review offers estimable insights into the possible properties of oxidative stress and autoimmunity in pathogenesis of vitiligo, as well as the potential role of antioxidant-based supportive therapy in vitiligo repigmentation, providing a hopeful value for further research and development of effective treatments.

Pathogenesis of Alopecia Areata and Vitiligo: Commonalities and Differences.

Both alopecia areata (AA) and vitiligo are distinct, heterogenous, and complex disease entities, characterized by nonscarring scalp terminal hair loss and skin pigment loss, respectively. In AA, inflammatory cell infiltrates are in the deep reticular dermis close to the hair bulb (swarm of bees), whereas in vitiligo the inflammatory infiltrates are in the epidermis and papillary dermis. Immune privilege collapse has been extensively investigated in AA pathogenesis, including the suppression of immunomodulatory factors (e.g., transforming growth factor-ß (TGF-ß), programmed death-ligand 1 (PDL1), interleukin-10 (IL-10), α-melanocyte-stimulating hormone (α-MSH), and macrophage migration inhibitory factor (MIF)) and enhanced expression of the major histocompatibility complex (MHC) throughout hair follicles. However, immune privilege collapse in vitiligo remains less explored. Both AA and vitiligo are autoimmune diseases that share commonalities in pathogenesis, including the involvement of plasmacytoid dendritic cells (and interferon-α (IFN- α) signaling pathways) and cytotoxic CD8+ T lymphocytes (and activated IFN-γ signaling pathways). Blood chemokine C-X-C motif ligand 9 (CXCL9) and CXCL10 are elevated in both diseases. Common factors that contribute to AA and vitiligo include oxidative stress, autophagy, type 2 cytokines, and the Wnt/ß-catenin pathway (e.g., dickkopf 1 (DKK1)). Here, we summarize the commonalities and differences between AA and vitiligo, focusing on their pathogenesis.

Animal models unraveling the complexity of vitiligo pathogenesis.

Vitiligo is a chronic skin condition marked by the gradual loss of pigmentation, leading to the emergence of white or depigmented patches on the skin. The exact cause of vitiligo remains not entirely understood, although it is thought to involve a blend of genetic, autoimmune, and environmental factors. While there is currently no definitive cure for vitiligo, diverse treatments exist that may assist in managing the condition and fostering repigmentation in specific instances. Animal models play a pivotal role in comprehending the intricate mechanisms that underlie vitiligo, providing valuable insights into the progression and onset of the disease, as well as potential therapeutic interventions. Although induced experimental models lack the nuanced characteristics observed in natural experimental models, relying solely on a single animal model might not fully capture the intricate pathogenesis of vitiligo. Different animal models simulate specific aspects of human vitiligo pathogenesis to varying degrees. This review extensively explores the array of animal models utilized in vitiligo research, shedding light on their respective advantages, disadvantages, and applications.

Exploring Mast Cell-CD8 T Cell Interactions in Inflammatory Skin Diseases.

The skin is exposed to environmental challenges and contains skin-resident immune cells, including mast cells (MCs) and CD8 T cells that act as sentinels for pathogens and environmental antigens. Human skin MCs and their mediators participate in the maintenance of tissue homeostasis and regulate the recruitment and activity of immune cells involved in the pathogenesis of skin diseases. The cutaneous CD8 T cell compartment is comprised of long-persisting resident memory T cells (TRM) and migratory or recirculating cells; both populations provide durable site immune surveillance. Several lines of evidence indicate that MC-derived products, such as CCL5 and TNF-α, modulate the migration and function of CD8 T cells. Conversely, activated CD8 T cells induce the upregulation of MC costimulatory molecules. Moreover, the close apposition of MCs and CD8 T cells has been recently identified in the skin of several dermatoses, such as alopecia areata. This review outlines the current knowledge about bidirectional interactions between human MCs and CD8 T cells, analyses the alteration of their communication in the context of three common skin disorders in which these cells have been found altered in number or function-psoriasis, atopic dermatitis, and vitiligo-and discusses the current unanswered questions.

Anatomically distinct fibroblast subsets determine skin autoimmune patterns.

The skin serves as a physical barrier and an immunological interface that protects the body from the external environment1-3. Aberrant activation of immune cells can induce common skin autoimmune diseases such as vitiligo, which are often characterized by bilateral symmetric lesions in certain anatomic regions of the body4-6. Understanding what orchestrates the activities of cutaneous immune cells at an organ level is necessary for the treatment of autoimmune diseases. Here we identify subsets of dermal fibroblasts that are responsible for driving patterned autoimmune activity, by using a robust mouse model of vitiligo that is based on the activation of endogenous auto-reactive CD8+ T cells that target epidermal melanocytes. Using a combination of single-cell analysis of skin samples from patients with vitiligo, cell-type-specific genetic knockouts and engraftment experiments, we find that among multiple interferon-γ (IFNγ)-responsive cell types in vitiligo-affected skin, dermal fibroblasts are uniquely required to recruit and activate CD8+ cytotoxic T cells through secreted chemokines. Anatomically distinct human dermal fibroblasts exhibit intrinsic differences in the expression of chemokines in response to IFNγ. In mouse models of vitiligo, regional IFNγ-resistant fibroblasts determine the autoimmune pattern of depigmentation in the skin. Our study identifies anatomically distinct fibroblasts with permissive or repressive IFNγ responses as the key determinant of body-level patterns of lesions in vitiligo, and highlights mesenchymal subpopulations as therapeutic targets for treating autoimmune diseases.

scRNA-seq of human vitiligo reveals complex networks of subclinical immune activation and a role for CCR5 in Treg function.

Vitiligo is an autoimmune skin disease characterized by the targeted destruction of melanocytes by T cells. Cytokine signaling between keratinocytes and T cells results in CD8+ T cell infiltration of vitiligo lesions, but the full scope of signals required to coordinate autoimmune responses is not completely understood. We performed single-cell RNA sequencing on affected and unaffected skin from patients with vitiligo, as well as healthy controls, to define the role of each cell type in coordinating autoimmunity during disease progression. We confirmed that type 1 cytokine signaling occupied a central role in disease, but we also found that this pathway was used by regulatory T cells (Tregs) to restrain disease progression in nonlesional skin. We determined that CCL5-CCR5 signaling served as a chemokine circuit between effector CD8+ T cells and Tregs, and mechanistic studies in a mouse model of vitiligo revealed that CCR5 expression on Tregs was required to suppress disease in vivo but not in vitro. CCR5 was not required for Treg recruitment to skin but appeared to facilitate Treg function by properly positioning these cells within the skin. Our data provide critical insights into the pathogenesis of vitiligo and uncover potential opportunities for therapeutic interventions.

Tissue-Resident Memory T Cells in Skin Diseases: A Systematic Review.

In health, the non-recirculating nature and long-term persistence of tissue-resident memory T cells (TRMs) in tissues protects against invading pathogens. In disease, pathogenic TRMs contribute to the recurring traits of many skin diseases. We aimed to conduct a systematic literature review on the current understanding of the role of TRMs in skin diseases and identify gaps as well as future research paths. EMBASE, PubMed, SCOPUS, Web of Science, Clinicaltrials.gov and WHO Trials Registry were searched systematically for relevant studies from their inception to October 2020. Included studies were reviewed independently by two authors. This study was conducted in accordance with the PRISMA-S guidelines. This protocol was registered with the PROSPERO database (ref: CRD42020206416). We identified 96 studies meeting the inclusion criteria. TRMs have mostly been investigated in murine skin and in relation to infectious skin diseases. Pathogenic TRMs have been characterized in various skin diseases including psoriasis, vitiligo and cutaneous T-cell lymphoma. Studies are needed to discover biomarkers that may delineate TRMs poised for pathogenic activity in skin diseases and establish to which extent TRMs are contingent on the local skin microenvironment. Additionally, future studies may investigate the effects of current treatments on the persistence of pathogenic TRMs in human skin.

Clinical Features, Immunopathogenesis, and Therapeutic Strategies in Vitiligo.

Vitiligo is an autoimmune disease of the skin characterized by epidermal melanocyte loss resulting in white patches, with an approximate prevalence of 0.5-2% worldwide. Several precipitating factors by chemical exposure and skin injury present commonly in patients with vitiligo. Although the diagnosis appears to be straightforward for the distinct clinical phenotype and specific histological features, vitiligo provides many challenges including chronicity, treatment resistance, frequent relapse, associated profound psychosocial effect, and negative impact on quality of life. Multiple mechanisms are involved in melanocyte disappearance, including genetics, environmental factors, and immune-mediated inflammation. Compelling evidence supports the melanocyte intrinsic abnormalities with poor adaptation to stressors leading to instability and release of danger signals, which will activate dendritic cells, natural killer cells, and innate lymphoid cells to initiate innate immunity, ultimately resulting in T-cell mediated adaptive immune response and melanocyte destruction. Importantly, the cross- talk between keratinocytes, melanocytes, and immune cells, such as interferon (IFN)-γ signaling pathway, builds inflammatory loops that give rise to the disease deterioration. Improved understanding of the immune pathogenesis of vitiligo has led to the development of new therapeutic options including Janus kinase (JAK) inhibitors targeting IFN-γ signaling pathways, which can effectively reverse depigmentation. Furthermore, definition of treatment goals and integration of comorbid diseases into vitiligo management have revolutionized the way vitiligo is treated. In this review, we highlight recent developments in vitiligo clinical aspects and immune pathogenesis. Our key objective is to raise awareness of the complexity of this disease, the potential of prospective therapy strategies, and the need for early and comprehensive management.

Identification of TYR, TYRP1, DCT and LARP7 as related biomarkers and immune infiltration characteristics of vitiligo via comprehensive strategies.

This study aims to explore biomarkers associated with vitiligo and analyze the pathological role of immune cell infiltration in the disease. We used the robust rank aggregation (RRA) method to integrate three vitiligo data sets downloaded from gene expression omnibus database, identify the differentially expressed genes (DEGs) and analyze the functional correlation. Then, the comprehensive strategy of combined weighted gene coexpression network analysis (WGCNA) and logical regression of the selection operator (LASSO), support vector machine recursive feature elimination (SVM-RFE), and random forest (RF) machine learning algorithm are employed to screen and biomarkers associated with vitiligo. Finally, the immune cell infiltration of vitiligo was evaluated by CIBERSORT, and the correlation between biomarkers and infiltrating immune cells was analyzed. Herein, we identified 131 robust DEGs, and enrichment analysis results showed that robust DEGs and melanogenesis were closely associated with vitiligo development and progression. TYR, TYRP1, DCT and LARP7 were identified as vitiligo-related biomarkers. Immune infiltration analysis demonstrated that CD4 T Cell, CD8 T Cell, Tregs, NK cells, dendritic cells, and macrophages were involved in vitiligo's pathogenesis. In summary, we adopted a comprehensive strategy to screen biomarkers related to vitiligo and explore the critical role of immune cell infiltration in vitiligo.Abbreviations: TYR, Tyrosinase; TYRP1, Tyrosinase-related protein-1; DCT, dopachrome tautomerase; LARP7, La ribonucleoprotein domain family, member-7; RRA, robust rank aggregation; DEGs, differentially expressed genes; WGCNA, weighted gene coexpression network analysis; LASSO, logical regression of the selection operator; SVM-RFE, support vector machine recursive feature elimination; RF, random forest; GWAS, Genome-wide association study; FasL, Fas-Fas ligand; Tregs, T-regulatory cells; NK, natural killer; GEPCs, gene expression profiling chips; GO, gene ontology; GSEA, gene set enrichment analysis; FDR, false discovery rate; AUC, area under the curve; ROC, receiver-operating characteristic; BP, biological process; CC, cellular component; MF, molecular function.

Does autoimmune vitiligo protect against COVID-19 disease?

The SARS-CoV-2 pandemic has evolved to a global health problem with a dramatic morbidity and mortality rate impacting our daily life and those of many patients. While there is evidence that some diseases are associated with an increased risk for development of a more severe course of COVID-19, little is known on protective conditions. Importantly, clearance of viral infection and protection against disease manifestation crucially depends on functional innate and adaptive immunity and the interferon signalling axis. Here, we hypothesize that patients with non-segmental vitiligo (NSV), an autoimmune skin (and mucosal) disorder, may clear SARS-CoV-2 infection more efficiently and have a lower risk of COVID-19 development. Conversely, in case of COVID-19 development, vitiligo autoimmunity may influence the cytokine storm-related disease burden. In addition, immune activation during SARS-CoV-2 infection or COVID-19 disease might increase vitiligo disease activity. Our hypothesis is based on the shift of the immune system in NSV towards adaptive type 1 (IFNγ and CD8 T cells) and innate immune responses. Identified susceptibility genes of NSV patients may further confer increased antiviral activity. To validate our hypothesis, we suggest an international consortium to perform a retrospective data registry and patient-reported study on a large number of NSV patients worldwide during the COVID-19 pandemic.

Successful Treatment of Vitiligo with Cold Atmospheric Plasma‒Activated Hydrogel.

Vitiligo shows insufficient response to current therapies largely owing to T-lymphocyte dysfunction, abnormal inflammatory activation, and excessive oxidative stress in lesions. Cold atmospheric plasma (CAP) possesses pleiotropic antioxidant and anti-inflammatory properties and may offer an improvement to current treatment options. In this study, the efficacy and safety of CAP were investigated in a mouse model of vitiligo and a randomized and controlled trial of patients with active focal vitiligo. Skin biopsies showed that topical treatment of vitiligo-like lesions on mouse dorsal skin by CAP restored the distribution of melanin. In addition, CAP treatment reduced the infiltration of CD11c+ dendritic cells, CD3+ T cells, and CD8+ T cells; inhibited the release of CXCL10 and cytokine IFN-γ; and enhanced cellular resistance to oxidative stress and excessive immune response by enhancing the expression of the transcription factor NRF2 and attenuating the activity of inducible nitric oxide synthase. In a randomized and controlled trial, CAP treatment achieved partial and complete repigmentation in 80% and 20% of vitiligo lesions, respectively, without hyperpigmentation in surrounding areas or other adverse events during the treatment period and its follow-up period. In conclusion, CAP offers a promising option for the management of vitiligo.

CD8+ T cell self-tolerance permits responsiveness but limits tissue damage.

Self-specific CD8+T cells can escape clonal deletion, but the properties and capabilities of such cells in a physiological setting are unclear. We characterized polyclonal CD8+ T cells specific for the melanocyte antigen tyrosinase-related protein 2 (Trp2) in mice expressing or lacking this enzyme (due to deficiency in Dct, which encodes Trp2). Phenotypic and gene expression profiles of pre-immune Trp2/Kb-specific cells were similar; the size of this population was only slightly reduced in wild-type (WT) compared to Dct-deficient (Dct-/-) mice. Despite comparable initial responses to Trp2 immunization, WT Trp2/Kb-specific cells showed blunted expansion and less readily differentiated into a CD25+proliferative population. Functional self-tolerance clearly emerged when assessing immunopathology: adoptively transferred WT Trp2/Kb-specific cells mediated vitiligo much less efficiently. Hence, CD8+ T cell self-specificity is poorly predicted by precursor frequency, phenotype, or even initial responsiveness, while deficient activation-induced CD25 expression and other gene expression characteristics may help to identify functionally tolerant cells.

Presence and the roles of IL-9/Th9 axis in vitiligo.

Immune dysregulation is critical in vitiligo pathogenesis. Although the presence and roles of numerous CD4+ T-cell subsets have been described, the presence of Th9 cells and more importantly, roles of IL-9 on melanocyte functions are not explored yet. Here, we quantified the T helper cell subsets including Th9 cells in vitiligo patients by multicolor flowcytometry. There was an increased frequency of skin-homing (CLA+ ) and systemic (CLA- ) Th9 cells in vitiligo patients compared to healthy donors. However, there was no difference in Th9 cell frequency in vitiligo patients with early and chronic disease. There was negligible IL-9 receptor (IL-9R) expression on human primary melanocytes (HPMs); however, IFNγ upregulated IL-9R expression on HPMs. Functionally, IL-9/IL-9R signaling reduced the production of IFNγ-induced toxic reactive oxygen species (ROS) in HPMs. There was no effect of IL-9 on expression of genes responsible for melanosome formation (MART1, TYRP1, and DCT), melanin synthesis (TYR), and melanocyte-inducing transcription factor (MITF) in HPMs. In conclusion, this study identifies the presence of Th9 cells in vitiligo and their roles in reducing the oxidative stress of melanocytes, which might be useful in designing effective therapeutics.

The Role of the NKG2D in Vitiligo.

Vitiligo is an acquired multifactorial disease that affects melanocytes and results in skin depigmentation. In this review, we examine the role of cells stress and self-reactive T cells responses. Given the canonical and non-canonical functions of NKG2D, such as authenticating stressed target and enhance TCR signaling, we examine how melanocyte stress leads to the expression of ligands that are recognized by the activating receptor NKG2D, and how its signaling results in the turning of T cells against self (melanocyte suicide by proxy). We also discuss how this initiation phase is followed by T cell perpetuation, as NKG2D signaling results in self-sustained long-lasting T cells, with improved cytolytic properties.

Vitiligo: Translational research and effective therapeutic strategies.

This is an exciting phase of vitiligo research with the current understanding of vitiligo pathogenesis and its translation to successful treatment. The pathogenetic origin of vitiligo revolves around autoimmunity with supporting role from many other factors like oxidative stress, inherent melanocyte defects, or defective keratinocytes and fibroblasts. Vitiligo can be classified into segmental or non-segmental depending upon the clinical presentation, or it can be classified as progressing or stable based on the activity of the disease. Vitiligo treatments need to be stratified depending upon which type of vitiligo we are treating and at which phase the vitiligo patient presents to us. There are two different aims of treatment of vitiligo. The first involves rescuing the melanocytes from the damage to arrest the depigmentation. The second strategy focuses on replenishing the melanocytes so that successful repigmentation is achieved. It is also important to maintain the disease in a stable phase or prevent relapse. As stability in non-segmental vitiligo is a dynamic process, maintenance of the stability of repigmentation is also an important consideration in the management of vitiligo. In this review, we shall briefly discuss the current options and future insight into the management of vitiligo.

Translational Research in Vitiligo.

Vitiligo is a disease of the skin characterized by the appearance of white spots. Significant progress has been made in understanding vitiligo pathogenesis over the past 30 years, but only through perseverance, collaboration, and open-minded discussion. Early hypotheses considered roles for innervation, microvascular anomalies, oxidative stress, defects in melanocyte adhesion, autoimmunity, somatic mosaicism, and genetics. Because theories about pathogenesis drive experimental design, focus, and even therapeutic approach, it is important to consider their impact on our current understanding about vitiligo. Animal models allow researchers to perform mechanistic studies, and the development of improved patient sample collection methods provides a platform for translational studies in vitiligo that can also be applied to understand other autoimmune diseases that are more difficult to study in human samples. Here we discuss the history of vitiligo translational research, recent advances, and their implications for new treatment approaches.

Analysis of Matched Skin and Gut Microbiome of Patients with Vitiligo Reveals Deep Skin Dysbiosis: Link with Mitochondrial and Immune Changes.

Vitiligo is an autoimmune disease characterized by patchy, white skin owing to melanocyte loss. Commensal cutaneous or gut dysbiosis has been linked to various dermatological disorders. In this study, we studied the skin and gut microbiota of patients with vitiligo compared with those of healthy controls. We obtained swabs and biopsies from both lesional and nonlesional skin as well as stool and blood samples from each individual. We detected reduced richness and diversity of microbiota in the stools of subjects with vitiligo compared with the stools of the controls (P < 0.01). Skin swabs had greater α-diversity than biopsies (P < 0.001); swabs from lesional sites were primarily depleted of Staphylococcus compared with those from nonlesional sites (P < 0.02). Sampling deeper layers from the same patients showed differences in both α- and ß-diversity between samples with decreased richness and distribution of species (P < 0.01) in the lesional site. Biopsy microbiota from the lesional skin had distinct microbiota composition, which was depleted of protective Bifidobacterium and Bacteroides but was enriched in Proteobacteria, Streptococcus, Mycoplasma, and mtDNA (P < 0.001); the latter increased in the same patients with heightened innate immunity and stress markers in their blood (P < 0.05). These data describe vitiligo-specific cutaneous and gut microbiota and a link between skin dysbiosis, mitochondrial damage, and immunity in patients with vitiligo.