Blood endotyping distinguishes the profile of vitiligo from that of other inflammatory and autoimmune skin diseases

Hair regrowth in alopecia areata and re-pigmentation in vitiligo in response to treatment: Commonalities and differences

Both alopecia areata (AA) and vitiligo share common pathogenesis involving, interferon-γ (IFN-γ) and interleukin-15 (IL-15) signalling pathways that activate cytotoxic CD8+ T lymphocytes. These shared mechanisms may explain why both diseases respond to currently available treatments (e.g. topical/systemic corticosteroid) and emerging treatment modalities. As compared with the speed of re-pigmentation in vitiligo lesions, the regeneration of pigmented terminal hair follicles in AA lesions appears fast in response to treatments targeting the inhibition of the Janus kinases (JAKs) and other kinases. We summarize the commonalities and differences between AA and vitiligo focusing on the treatment modalities, followed by recent findings associated with hair follicle stem cells (HFSC) in hair bulge (HBg) and melanocyte stem cells (McSC) in HBg and hair germ (HGm). We then discuss how HFSC and HGm-McSC are involved in the initiation of anagen phase, followed by pigmented terminal hair regrowth in the recovering AA lesions in association with immunology. We also discuss how HBg-McSC contribute to the migration of fully dendritic mature melanocytes into interfollicular epidermis and the equal distribution of melanin in recovering vitiligo lesions. Finally, we present four hypotheses to elucidate the delayed distribution of melanin by mature melanocytes in depigmented vitiligo lesions from the aspects of stem cell biology, as compared with quick hair recovery in AA: (1) McSC are less abundant than HFSC. (2) McSC require a long travel, whereas HFSC reside close to hair regeneration trigger point. (3) Keratinocyte scaffold to accept melanin is not well preserved, whereas scaffold for hair regrowth is well preserved. (4) Inhibitors targeting JAKs and other kinases have less direct effects on melanocyte proliferation and differentiation in vitiligo than hair regrowth in AA. Our review provides an overview of treatment modalities and bridges the gap between scientific advancement and clinical practice in AA and vitiligo management.

Efficacy and safety of ritlecitinib in vitiligo patients across Fitzpatrick skin types with biomarker analyses

Efficacy and safety of ritlecitinib (an oral JAK3/TEC family kinase inhibitor) were evaluated in patients with nonsegmental vitiligo (NSV) across Fitzpatrick skin types (FSTs). Patients with FST I-III ('light skin'; n = 247) and FST IV-VI ('dark skin'; n = 117) received once-daily ritlecitinib 50 mg (with/without 4-week loading dose), low-dose ritlecitinib or placebo for 24 weeks. At baseline, patients with light skin displayed higher CLM-1 and NCR1 serum levels than patients with dark skin (p < 0.05). At 24 weeks, ritlecitinib 50 mg improved the extent of depigmentation measured by percent change from baseline in facial-vitiligo area scoring index (placebo-adjusted mean difference [90% CI]) in patients with light (-15.2 [-24.7, -5.8]; p = 0.004) and dark (-37.4 [-50.3, -24.4]; p < 0.0001) skin, with continuous re-pigmentation through week 48. Treatment-emergent adverse events were similar across FSTs. At weeks 4 and 24, ritlecitinib 50 mg reduced CXCL11 serum levels (p < 0.001) in patients with light skin, whereas patients with dark skin had increased levels at week 4 (p = 0.05) and no significant change at week 24. Ritlecitinib 50 mg decreased IL-9 and IL-22 expression levels in dark skin compared with light skin (qPCR; p < 0.05). These differences in immune dysregulations may explain why NSV patients with dark skin respond to therapy earlier than patients with light skin.

Heterogeneous IL-9 Production by Circulating Skin-Tropic and Extracutaneous Memory T Cells in Atopic Dermatitis Patients

Interleukin (IL)-9 is present in atopic dermatitis (AD) lesions and is considered to be mainly produced by skin-homing T cells expressing the cutaneous lymphocyte-associated antigen (CLA). However, its induction by AD-associated triggers remains unexplored. Circulating skin-tropic CLA+ and extracutaneous/systemic CLA- memory T cells cocultured with autologous lesional epidermal cells from AD patients were activated with house dust mite (HDM) and staphylococcal enterotoxin B (SEB). Levels of AD-related mediators in response to both stimuli were measured in supernatants, and the cytokine response was associated with different clinical characteristics. Both HDM and SEB triggered heterogeneous IL-9 production by CLA+ and CLA- T cells in a clinically homogenous group of AD patients, which enabled patient stratification into IL-9 producers and non-producers, with the former group exhibiting heightened HDM-specific and total IgE levels. Upon allergen exposure, IL-9 production depended on the contribution of epidermal cells and class II-mediated presentation; it was the greatest cytokine produced and correlated with HDM-specific IgE levels, whereas SEB mildly induced its release. This study demonstrates that both skin-tropic and extracutaneous memory T cells produce IL-9 and suggests that the degree of allergen sensitization reflects the varied IL-9 responses in vitro, which may allow for patient stratification in a clinically homogenous population.

Ritlecitinib, a JAK3/TEC family kinase inhibitor, stabilizes active lesions and repigments stable lesions in vitiligo

The efficacy of ritlecitinib, an oral JAK3/TEC family kinase inhibitor, on active and stable lesions was evaluated in patients with active non-segmental vitiligo in a phase 2b trial (NCT03715829). Patients were randomized to placebo or daily ritlecitinib 50 mg (with or without 4-week 100-mg or 200-mg loading dose), 30 mg, or 10 mg for 24 weeks. Active lesions showed greater baseline expression of inflammatory/immune markers IFNG and CCL5, levels of CD103, and T-cell infiltrates than stable lesions. Patients with more active than stable vitiligo lesions showed higher baseline serum levels of CXCL9 and PD-L1, while patients with more stable than active lesions showed higher baseline serum levels of HO-1. At Week 24, ritlecitinib 50 mg significantly stabilized mean percent change from baseline in depigmentation extent in both active lesions and stable lesions vs. placebo-response, with stable lesions showing greater repigmentation. After 24 weeks of treatment, ritlecitinib 50 mg increased expression of melanocyte markers in stable lesions, while Th1/Th2-related and co-stimulatory molecules decreased significantly in both stable and active lesions. Serum from patients with more active than stable lesions showed decreased levels of ICOS and NK cell activation markers. These data, confirmed at transcription/protein levels, indicate that stable lesion repigmentation occurs early with ritlecitinib, while active lesions require stabilization of inflammation first. ClinicalTrials.gov: NCT03715829.

Type-2 immunity associated with type-1 related skin inflammatory diseases: friend or foe?

Chronic inflammatory skin diseases are multifactorial diseases that combine genetic predisposition, environmental triggers, and metabolic disturbances associated with abnormal immune responses. From an immunological perspective, the better understanding of their physiopathology has demonstrated a large complex network of immune cell subsets and related cytokines that interact with both epidermal and dermal cells. For example, in type-1-associated diseases such as alopecia areata, vitiligo, and localized scleroderma, recent evidence suggests the presence of a type-2 inflammation that is well known in atopic dermatitis. Whether this type-2 immune response has a protective or detrimental impact on the development and chronicity of these diseases remains to be fully elucidated, highlighting the need to better understand its involvement for the management of patients. This mini-review explores recent insights regarding the potential role of type-2-related immunity in alopecia areata, vitiligo, and localized scleroderma.

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-β (TGF-β), 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/β-catenin pathway (e.g., dickkopf 1 (DKK1)). Here, we summarize the commonalities and differences between AA and vitiligo, focusing on their pathogenesis.

Resident memory T cells in nonlesional skin and healed lesions of patients with chronic inflammatory diseases: Appearances can be deceptive

Tissue-resident memory T (TRM) cells serve as a first line of defense in peripheral tissues to protect the organism against foreign pathogens. However, autoreactive TRM cells are increasingly implicated in autoimmunity, as evidenced in chronic autoimmune and inflammatory skin conditions. This highlights the need to characterize their phenotype and understand their role for the purpose of targeting them specifically without affecting local immunity. To date, the investigation of TRM cells in human skin diseases has focused mainly on lesional tissues of patients. Accumulating evidence suggests that self-reactive TRM cells are still present in clinically healed lesions of patients and play a role in disease flares, but TRM cells also populate skin that is apparently normal. This review discusses the ontogeny of TRM cells in the skin as well as recent insights regarding the presence of self-reactive TRM cells in both clinically healed skin and nonlesional skin of patients with autoimmune and inflammatory skin conditions, with a particular focus on psoriasis, atopic dermatitis, and vitiligo.

The role of aryl hydrocarbon receptor in vitiligo: a review

Vitiligo is an acquired autoimmune dermatosis characterized by patchy skin depigmentation, causing significant psychological distress to the patients. Genetic susceptibility, environmental triggers, oxidative stress, and autoimmunity contribute to melanocyte destruction in vitiligo. Due to the diversity and complexity of pathogenesis, the combination of inhibiting melanocyte destruction and stimulating melanogenesis gives the best results in treating vitiligo. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that can regulate the expression of various downstream genes and play roles in cell differentiation, immune response, and physiological homeostasis maintenance. Recent studies suggested that AhR signaling pathway was downregulated in vitiligo. Activation of AhR pathway helps to activate antioxidant pathways, inhibit abnormal immunity response, and upregulate the melanogenesis gene, thereby protecting melanocytes from oxidative stress damage, controlling disease progression, and promoting lesion repigmentation. Here, we review the relevant literature and summarize the possible roles of the AhR signaling pathway in vitiligo pathogenesis and treatment, to further understand the links between the AhR and vitiligo, and provide new potential therapeutic strategies.

Improvements in immune/melanocyte biomarkers with JAK3/TEC family kinase inhibitor ritlecitinib in vitiligo

BACKGROUND

Vitiligo is an autoimmune depigmenting disorder with no effective and safe treatments. Its pathogenesis is not fully elucidated.

OBJECTIVE

This substudy of a randomized, double-blind, placebo-controlled phase 2b trial (NCT03715829) evaluated effects of ritlecitinib, an oral JAK3/TEC family kinase inhibitor, on skin and blood biomarkers in participants with nonsegmental vitiligo (NSV).

METHODS

Sixty-five adults with NSV participated in the substudy and received daily treatment for 24 weeks with placebo (n = 14) or ritlecitinib with or without a 4-week loading dose: 200 (loading dose)/50 mg (n = 13), 100/50 mg (n = 12), 50 mg (n = 11), 30 mg (n = 8), or 10 mg (n = 6). Skin (lesional and nonlesional) biopsy samples were obtained at baseline and at 4 and 24 weeks. Changes from baseline to weeks 4 and 24 in skin and blood molecular and cellular biomarkers were evaluated by RNA sequencing, quantitative real-time PCR, proteomic analysis, and flow cytometry.

RESULTS

Ritlecitinib-treated groups showed downregulation of immune biomarkers and upregulation of melanocyte-related markers at weeks 4 and 24 compared to baseline and/or placebo. Significant reductions were seen in CD3+/CD8+ T-cell infiltrates, with significant increases in melanocyte markers (tyrosinase; Melan-A) in NSV lesions in the 50 mg ritlecitinib groups (both P < .05). There was significant, dose-dependent downregulation in T-cell activation, NK, cytotoxic, and regulatory markers in lesional skin (IL-2, IL2-RA, IL-15, CCR7, CD5, CRTAM, NCR1, XCL1, KIR3DL1, FASLG, KLRD; P < .05). TH1 and TH2 markers were also downregulated in lesional skin and blood in a dose-dependent manner (P < .05). Changes in immune biomarkers correlated with clinical response.

CONCLUSIONS

Ritlecitinib significantly downregulated proinflammatory biomarkers and increased melanocyte products in skin and blood of participants with NSV, suggesting its potential in treatment. Ritlecitinib-mediated changes positively correlated with clinical response.

Single-cell transcriptomics reveals peripheral immune responses in non-segmental vitiligo

Background

Vitiligo is a common autoimmune depigmented dermatology due to destruction of melanocytes. Much evidence suggests that vitiligo is associated with systemic immune activation. Previous studies have focused on immune cell infiltration in and around lesion areas, but few studies have investigated the cell types and function of circulating immune cells in peripheral blood. Here, single cell RNA-sequencing (scRNA-seq) was used to investigate the mechanisms of peripheral immune responses in vitiligo patients.

Methods

Peripheral blood was collected from five patients with progressive non-segmental vitiligo and three healthy controls. Peripheral blood mononuclear cells (PBMCs) were obtained by Ficoll-Paque density gradient centrifugation, and scRNA-seq was performed on isolated cell populations to obtain single cell transcriptomes and characterize important genes and intracellular signaling pathways. The key findings were validated with qPCR and flow cytometry assays.

Results

We identified 10 major cell types by scRNA-seq. Among these cell types, neutrophils were specifically observed in our scRNA-seq data from PBMCs. Peripheral blood effector CD8+ T cells from vitiligo patients did not show significant differences at the transcriptome level compared with healthy controls, whereas regulatory T cells showed pro-inflammatory TH1-like properties. Innate immune cells, including natural killer cells and dendritic cells, showed increased antigen processing and presentation as well as upregulated interferon responses. B cells, monocytes, and neutrophils all showed activation. B cells, especially memory B cells, had upregulated expression of genes related to humoral immunity. Monocytes showed production of proinflammatory cytokines and chemokines. Neutrophils showed strong chemokine ligand-receptor (L-R) pair (CXCR8-CXCR2) autocrine signaling pathway.

Conclusion

This study revealed the genetic profile and signaling pathway characteristics of peripheral blood immune cells in vitiligo patients, providing new insights into its pathogenesis, which may facilitate identification of potential therapeutic targets.

Baseline Levels of Circulating Inflammatory Biomarkers Stratify Patients with Vitiligo Who Significantly Repigment after Treatment with Ruxolitinib Cream

BACKGROUND

Efficacy of ruxolitinib cream, a topical Jak1/Jak2 inhibitor, was demonstrated in a phase 2 trial in patients with vitiligo.

OBJECTIVE

This study aimed to characterize circulating inflammatory biomarker profiles in patients who demonstrated ≥50% improvement in facial Vitiligo Area Scoring Index scores by week 24 (group 1) and those who did not (group 2).

DESIGN

This was a posthoc analysis of a multicenter, randomized, double-blind, vehicle-controlled, phase 2 study in which screening was conducted between June 7, 2017 and March 21, 2018.

POPULATION

Patients aged between 18 and 75 years with vitiligo, including depigmentation affecting ≥0.5% of body surface area on the face and ≥3% of body surface area on nonfacial areas, were eligible.

INTERVENTION

Patients applied 1.5% ruxolitinib cream to lesions once or twice daily for 52 weeks.

MAIN OUTCOMES AND MEASURES

Patients were grouped by achievement of ≥50% improvement in facial Vitiligo Area Scoring Index at week 24. Proteomic analysis was performed on baseline serum samples.

RESULTS

Mean ± standard error facial Vitiligo Area Scoring Index in group 1 (n = 30) versus group 2 (n = 27) improved by 79.9 ± 4.0% versus 1.1 ± 7.3% and 91.9 ± 1.5% versus 25.1 ± 13.4% at weeks 24 and 52, respectively. Broad proteomic analysis revealed 76 proteins (of 1,104 tested) that were differentially expressed between groups 1 and 2 at baseline (P < 0.05). Ten distinct proteins were upregulated in group 1; 64 were elevated in group 2.

CONCLUSION

This analysis identified potential differences between patients who achieved ≥50% improvement in facial Vitiligo Area Scoring Index at 24 weeks and those who did not that require deeper scientific interrogation and may be important in stratifying therapeutic benefit for patients with vitiligo.

TRIAL REGISTRATION

The original study was registered at ClinicalTrials.gov, NCT03099304.

Tralokinumab therapy for moderate-to-severe atopic dermatitis: Clinical outcomes with targeted IL-13 inhibition

Atopic dermatitis (AD) is a chronic, inflammatory, intensely pruritic skin disorder associated with significant patient burden. Interleukin (IL)-13 is a cytokine that acts as a driver of immune dysregulation, skin-barrier dysfunction, and microbiome dysbiosis that characterizes AD, and is consistently overexpressed in AD skin. Tralokinumab is a fully human immunoglobulin (Ig) G4 monoclonal antibody that binds specifically to IL-13 with high affinity, thereby inhibiting subsequent downstream IL-13 signaling. Three pivotal phase 3 clinical trials demonstrated that tralokinumab 300 mg every other week, as monotherapy or in combination with topical corticosteroids as needed, provides significant improvements in signs and symptoms of moderate-to-severe AD, as measured by Investigator's Global Assessment 0/1 (clear/almost clear) and Eczema Area and Severity Index-75 at Week 16. Improvements were observed soon after tralokinumab initiation and were maintained over 52 weeks of therapy. Tralokinumab significantly improved patient-reported outcomes such as itch and sleep, and demonstrated a safety profile comparable with placebo; conjunctivitis during tralokinumab therapy was generally mild. Similar results were observed in a phase 3 adolescent trial. The role of IL-13 in the pathophysiology of AD justifies a targeted approach and a wealth of clinical data supports tralokinumab as a new therapeutic option for people with moderate-to-severe AD.

Cytokine-Mediated Crosstalk Between Keratinocytes and T Cells in Atopic Dermatitis

Atopic dermatitis (AD) is a chronic inflammatory skin disease characterized by barrier dysfunction, dysregulated immune response, and dysbiosis with increased Staphylococcus aureus colonization. Infiltration of various T helper cell subsets into lesional skin and subsequent cytokine release are a hallmark of AD. Release of cytokines by both T cells and keratinocytes plays a key role in skin inflammation and drives many AD features. This review aims to discuss cytokine-mediated crosstalk between T cells and keratinocytes in AD pathogenesis and the potential impact of virulence factors produced by Staphylococcus aureus on these interactions.

Advances in Atopic Dermatitis in 2019-2020: Endotypes from skin barrier, ethnicity, properties of antigen, cytokine profiles, microbiome, and engagement of immune cells

Key research advances in atopic dermatitis (AD) suggest the complexity of its endotypes. A comprehensive serum biomarker panel revealed at least four types of AD. Some represent classic TH2-dominant AD with filaggrin mutations commonly reported in Europeans, a simultaneously activated multipolar axes of cytokines often reported in Asians, and an intrinsic type characterized by TH2-inferiority. Innate lymphoid cells, including NK cells, NKT cells, and fibroblasts, play a role in AD development and heterogeneity. Here, we discuss the endotypes of AD from the perspective of antigen types (hapten vs. protein antigens), barrier function, and a novel set of immune cells. Endotypic stratification of AD may lead to the development of customized therapeutic strategies in the future.

Vitiligo skin T cells are prone to produce type 1- and type 2-cytokines to induce melanocyte dysfunction and epidermal inflammatory response through JAK signaling

Vitiligo is a T cell-mediated inflammatory skin disorder characterized by the loss of epidermal melanocytes. However, the contribution of melanocytes to the physiopathology of the disease in response to the T cell microenvironment remains unclear. Here, using NanoString technology and multiplex ELISA, we show that active vitiligo perilesional skin is characterized by prominent type 1 and 2 associated immune responses. The vitiligo skin T cell secretome downregulated melanocyte function and adhesion, while increasing melanocyte mitochondrial metabolism and expression of inflammatory cytokines and chemokines by epidermal cells. The JAK1/2 inhibitor ruxolitinib strongly inhibited such effects on epidermal cells. Our data highlight that vitiligo is more complex than previously thought with prominent combined activities of both Th1- and Th2-related cytokines inducing inflammatory responses of epidermal cells. Melanocytes do not appear only to be a target of T cells in vitiligo but could actively contribute to perpetuate inflammation. JAK inhibitors could prevent the impact of T cells on epidermal cells and pigmentation, highlighting their potential clinical benefit in vitiligo.

High-dimensional analysis defines multicytokine T-cell subsets and supports a role for IL-21 in atopic dermatitis

BACKGROUND

Flow cytometry is a well-accepted approach for immune profiling; however, its value is restricted by the limited number of markers that can be analyzed simultaneously. Mass cytometry/CyTOF offers broad-scale immune characterization integrating large number of parameters. While partial blood phenotyping was reported in atopic dermatitis (AD), patients' comprehensive profiling, critical for leveraging new targeted treatments, is not available. IL-21 may be involved in inflammatory skin diseases but its role in AD is not well established.

METHODS

We studied T-cell polarization in the blood of 20 moderate-to-severe AD and 15 controls. Using CyTOF and an unsupervised analysis, we measured the frequencies and mean metal intensities of activated polar CD4⁺ /CD8⁺ T-cell subsets. Immunohistochemistry, immunofluorescence, and qRT-PCR were used to analyze skin samples.

RESULTS

Examining 24 surface, intracellular markers, and transcription factors, we identified six CD4⁺ and five CD8⁺ T-cell metaclusters. A CD4⁺ skin-homing IL-13⁺ monocytokine and a novel IL-13⁺ IL-21⁺ multicytokine metaclusters were increased in AD vs. controls (p < .01). While IL-13 signature characterized both clusters, levels were significantly higher in the IL-21⁺ group. Both clusters correlated with AD severity (r = 0.49, p = .029). Manual gating corroborated these results and identified additional multicytokine subsets in AD. Immunohistochemistry and immunofluorescence, validated by mRNA expression, displayed significantly increasedIL-21 counts and colocalization with IL-13/IL-4R in AD skin.

CONCLUSION

A multicytokine signature characterizes moderate-to-severe AD, possibly explaining partial therapeutic responses to one cytokine targeting, particularly in severe patients. Prominent IL-21 signature in blood and skin hints for a potential pathogenic role of IL-21 in AD.

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.

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 Translational Relevance of Human Circulating Memory Cutaneous Lymphocyte-Associated Antigen Positive T Cells in Inflammatory Skin Disorders

Circulating memory T cells are heterogeneous in their tissue tropism. The skin-seeking T cell subset expresses the cutaneous lymphocyte-associated antigen (CLA) on their surface. CLA⁺ memory T cells not only migrate from blood to skin but also recirculate between blood and skin. Studying CLA⁺ memory T cells in cutaneous diseases has allowed a better understanding of immune-inflammatory mechanisms that take place. The analysis of the phenotypical features of these cells, their antigen specificity, cytokine production profile, and changes in relationship to clinical status and therapies among other characteristics have led to the concept that they constitute peripheral cellular biomarkers in T cell-mediated cutaneous conditions. CLA⁺ memory T cells are of relevance in the pathogenesis of several cutaneous diseases, such as psoriasis (PSO), atopic dermatitis, vitiligo, and drug-induced allergic reactions, to name a few. The interaction of circulating CLA⁺ T cells with skin-resident cells has been investigated in different ex vivo coculture models made out of clinical samples. Interestingly, microbes that are present in the skin or related with human skin diseases are preferentially recognized by CLA⁺ T cells. Thus, the interaction of Streptococcus pyogenes with CLA⁺ T cells in PSO is providing novel concepts that help to understand disease immunopathogenesis. The goal of this review is to present latest results in the field of CLA⁺ T cells in T cell-mediated inflammatory skin diseases and their translational relevance for human immunodermatology.

Multiomics Analysis and Systems Biology Integration Identifies the Roles of IL-9 in Keratinocyte Metabolic Reprogramming

IL-9‒producing T cells are present in healthy skin as well as in the cutaneous lesions of inflammatory diseases and cancers. However, the roles of IL-9 in human skin during homeostasis and in the pathogenesis of inflammatory disorders remain obscure. In this study, we examined the roles of IL-9 in metabolic reprogramming of human primary keratinocytes (KCs). High-throughput quantitative proteomics revealed that IL-9 signaling in human primary KCs disrupts the electron transport chain by downregulating multiple electron transport chain proteins. Nuclear magnetic resonance-based metabolomics showed that IL-9 also reduced the production of tricarboxylic acid cycle intermediates in human primary KCs. An integration of multiomics data with systems-level analysis using the constraint-based MitoCore model predicted marked IL-9-dependent effects on central carbohydrate metabolism, particularly in relation to the glycolytic switch. Stable isotope metabolomics and biochemical assays confirmed increased glucose consumption and redirection of metabolic flux toward lactate by IL-9. Functionally, IL-9 inhibited ROS production by IFN-γ and promoted human primary KC survival by inhibiting apoptosis. In conclusion, our data reveal IL-9 as a master regulator of KC metabolic reprogramming and survival.

Mechanisms of melanocyte death in vitiligo

Vitiligo is an autoimmune depigment disease results from extensive melanocytes destruction. The destruction of melanocyte is thought to be of multifactorial causation. Genome-wide associated studies have identified single-nucleotide polymorphisms in a panel of susceptible loci as risk factors in melanocyte death. But vitiligo onset can't be solely attributed to a susceptive genetic background. Oxidative stress triggered by elevated levels of reactive oxygen species accounts for melanocytic molecular and organelle dysfunction, a minority of melanocyte demise, and melanocyte-specific antigens exposure. Of note, the self-responsive immune function directly contributes to the bulk of melanocyte deaths in vitiligo. The aberrantly heightened innate immunity, type-1-skewed T helper, and incompetent regulatory T cells tip the balance toward autoreaction and CD8+ cytotoxic T lymphocytes finally execute the killing of melanocytes, possibly alarmed by resident memory T cells. In addition to the well-established apoptosis and necrosis, we discuss several death modalities like oxeiptosis, ferroptosis, and necroptosis that are probably employed in melanocyte destruction. This review focuses on the various mechanisms of melanocytic death in vitiligo pathogenesis to demonstrate a panorama of that. We hope to provide new insights into vitiligo pathogenesis and treatment strategies by the review.

Efficacy and Safety of Lebrikizumab, a High-Affinity Interleukin 13 Inhibitor, in Adults With Moderate to Severe Atopic Dermatitis: A Phase 2b Randomized Clinical Trial

Question

Is lebrikizumab, a novel, high-affinity, monoclonal antibody targeting interleukin 13 that selectively inhibits interleukin 13 signaling, efficacious and safe in adults with moderate to severe atopic dermatitis?

Findings

Among 280 patients with moderate to severe atopic dermatitis in this phase 2b, placebo-controlled randomized clinical trial, lebrikizumab statistically significantly improved measures of clinical manifestations of atopic dermatitis, pruritus, and quality of life in a dose-dependent manner vs placebo during 16 weeks of treatment.

Meaning

Lebrikizumab was efficacious for adults with moderate to severe atopic dermatitis, was generally well tolerated, and had a favorable safety profile consistent with previous lebrikizumab studies; these data support the central role of interleukin 13 in the pathophysiology of atopic dermatitis.

Importance

Interleukin 13 (IL-13) is a central pathogenic mediator driving multiple features of atopic dermatitis (AD) pathophysiology.

Objective

To evaluate the efficacy and safety of lebrikizumab, a novel, high-affinity, monoclonal antibody targeting IL-13 that selectively prevents formation of the IL-13Rα1/IL-4Rα heterodimer receptor signaling complex, in adults with moderate to severe AD.

Design, Setting, and Participants

A phase 2b, double-blind, placebo-controlled, dose-ranging randomized clinical trial of lebrikizumab injections every 4 weeks or every 2 weeks was conducted from January 23, 2018, to May 23, 2019, at 57 US centers. Participants were adults 18 years or older with moderate to severe AD.

Interventions

Patients were randomized 2:3:3:3 to placebo every 2 weeks or to subcutaneous injections of lebrikizumab at the following doses: 125 mg every 4 weeks (250-mg loading dose [LD]), 250 mg every 4 weeks (500-mg LD), or 250 mg every 2 weeks (500-mg LD at baseline and week 2).

Main Outcomes and Measures

The primary end point was percentage change in the Eczema Area and Severity Index (EASI) (baseline to week 16). Secondary end points for week 16 included proportion of patients achieving Investigator’s Global Assessment score of 0 or 1 (IGA 0/1); EASI improvement of at least 50%, 75%, or 90% from baseline; percentage change in the pruritus numeric rating scale (NRS) score; and pruritus NRS score improvement of at least 4 points. Safety assessments included treatment-emergent adverse events.

Results

A total of 280 patients (mean [SD] age, 39.3 [17.5] years; 166 [59.3%] female) were randomized to placebo (n = 52) or to lebrikizumab at doses of 125 mg every 4 weeks (n = 73), 250 mg every 4 weeks (n = 80), or 250 mg every 2 weeks (n = 75). Compared with placebo (EASI least squares mean [SD] percentage change, −41.1% [56.5%]), lebrikizumab groups showed dose-dependent, statistically significant improvement in the primary end point vs placebo at week 16: 125 mg every 4 weeks (−62.3% [37.3%], P = .02), 250 mg every 4 weeks (−69.2% [38.3%], P = .002), and 250 mg every 2 weeks (−72.1% [37.2%], P < .001). Differences vs placebo-treated patients (2 of 44 [4.5%]) in pruritus NRS improvement of at least 4 points were seen as early as day 2 in the high-dose lebrikizumab group (9 of 59 [15.3%]). Treatment-emergent adverse events were reported in 24 of 52 placebo patients (46.2%) and in lebrikizumab patients as follows: 42 of 73 (57.5%) for 125 mg every 4 weeks, 39 of 80 (48.8%) for 250 mg every 4 weeks, and 46 of 75 (61.3%) for 250 mg every 2 weeks; most were mild to moderate and did not lead to discontinuation. Low rates of injection-site reactions (1 of 52 [1.9%] in the placebo group vs 13 of 228 [5.7%] in all lebrikizumab groups), herpesvirus infections (2 [3.8%] vs 8 [3.5%]), and conjunctivitis (0% vs 6 [2.6%]) were reported.

Conclusions and Relevance

During 16 weeks of treatment, lebrikizumab provided rapid, dose-dependent efficacy across a broad range of clinical manifestations in adult patients with moderate to severe AD and demonstrated a favorable safety profile. These data support the central role of IL-13 in AD pathophysiology. If these findings replicate in phase 3 studies, lebrikizumab may meaningfully advance the standard of care for moderate to severe AD.

Trial Registration

ClinicalTrials.gov Identifier: NCT03443024

Reciprocal regulation of interleukin-17A and interleukin-22 secretion through aryl hydrocarbon receptor activation in CD4+ T cells of patients with vitiligo

Previous studies have shown the participation of the cytokines interleukin (IL) 17A and IL22 in the development of vitiligo. The aryl hydrocarbon receptor (AhR) functions in the pathogenesis of vitiligo and can modulate cytokine production. The aim of the present study was to determine the relationship between AhR activation and the secretion of IL17A and IL22 in CD4⁺ T cells in vitiligo. A total of 20 newly diagnosed patients with progressive, unstable vitiligo and 20 healthy controls were recruited. CD4⁺ T cells and skin samples were collected. Immunohistochemistry, ELISA, reverse transcription-quantitative PCR, western blotting and RNA interference experiments were performed. The expression of AhR was significantly lower in the CD4⁺ T cells and skin, both lesional and nonlesional, of patients with vitiligo compared with healthy subjects. AhR expression was markedly lower in nonlesional compared with lesional skin of patients with vitiligo. The expression levels of IL17A and IL22 were significantly higher in patients with vitiligo compared with healthy subjects. Knockdown of AhR significantly increased the production of IL17A and markedly decreased IL22 levels in the CD4⁺ T cells of patients with vitiligo. Ginkgo biloba extract EGb 761 activated AhR, inhibited IL17A secretion and enhanced IL22 release in the CD4⁺ T cells of patients with vitiligo. In conclusion, reduced AhR expression is associated with progressive, unstable vitiligo. Activation of AhR with G. biloba extract EGb 761 may have therapeutic potential for decreasing IL17A levels and increasing IL22 levels in patients with vitiligo.

Gut Microbial Dysbiosis and Plasma Metabolic Profile in Individuals With Vitiligo

Autoimmune diseases are increasingly linked to aberrant gut microbiome and relevant metabolites. However, the association between vitiligo and the gut microbiome remains to be elucidated. Thus, we conducted a case-control study through 16S rRNA sequencing and serum untargeted-metabolomic profiling based on 30 vitiligo patients and 30 matched healthy controls. In vitiligo patients, the microbial composition was distinct from that of healthy controls according to the analysis on α- and β-diversity (P < 0.05), with a characteristic decreased Bacteroidetes: Firmicutes ratio. Meanwhile, the levels of 23 serum metabolites (including taurochenodeoxycholate and L-NG-monomethyl-arginine) in the vitiligo patients were different from those in the healthy individuals and showed significant correlations with some microbial markers. We found that Corynebacterium 1, Ruminococcus 2, Jeotgalibaca and Psychrobacter were correlated significantly with disease duration and serum IL-1β level in vitiligo patients. And Psychrobacter was identified as the most predictive features for vitiligo by machine learning analysis ("importance" = 0.0236). Finally, combining multi-omics data and joint prediction models with accuracies up to 0.929 were established with dominant contribution of Corynebacterium 1 and Psychrobacter. Our findings replenished the previously unknown relationship between gut dysbiosis and vitiligo circulating metabolome and enrolled the gut-skin axis into the understanding of vitiligo pathogenesis.

Epigenetic alterations in skin homing CD4+CLA+ T cells of atopic dermatitis patients

T cells expressing the cutaneous lymphocyte antigen (CLA) mediate pathogenic inflammation in atopic dermatitis (AD). The molecular alterations contributing to their dysregulation remain unclear. With the aim to elucidate putative altered pathways in AD we profiled DNA methylation levels and miRNA expression in sorted T cell populations (CD4⁺, CD4⁺CD45RA⁺ naïve, CD4⁺CLA⁺, and CD8⁺) from adult AD patients and healthy controls (HC). Skin homing CD4⁺CLA⁺ T cells from AD patients showed significant differences in DNA methylation in 40 genes compared to HC (p < 0.05). Reduced DNA methylation levels in the upstream region of the interleukin-13 gene (IL13) in CD4⁺CLA⁺ T cells from AD patients correlated with increased IL13 mRNA expression in these cells. Sixteen miRNAs showed differential expression in CD4⁺CLA⁺ T cells from AD patients targeting genes in 202 biological processes (p < 0.05). An integrated network analysis of miRNAs and CpG sites identified two communities of strongly interconnected regulatory elements with strong antagonistic behaviours that recapitulated the differences between AD patients and HC. Functional analysis of the genes linked to these communities revealed their association with key cytokine signaling pathways, MAP kinase signaling and protein ubiquitination. Our findings support that epigenetic mechanisms play a role in the pathogenesis of AD by affecting inflammatory signaling molecules in skin homing CD4⁺CLA⁺ T cells and uncover putative molecules participating in AD pathways.

Vitiligo, From Physiopathology to Emerging Treatments: A Review

Vitiligo is a chronic inflammatory skin disease leading to the loss of epidermal melanocytes. To date, treatment options for vitiligo patients are limited, lack sustained efficacy, and are mainly based on off-label use of immunosuppressive agents, such as systemic or topical steroids or topical calcineurin inhibitors, in association with the use of ultraviolet light. However, recent insights into the understanding of the immune pathogenesis of the disease have led to the identification of several therapeutic targets and the development of targeted therapies that are now being tested in clinical trials. In this review, based on the physiopathology of the disease, we summarize emerging targets that could be developed for the treatment of vitiligo and discuss recent and ongoing developments of drugs for the management of the disease.

Phenotype and function of circulating memory T cells in human vitiligo

BACKGROUND

Vitiligo is a chronic inflammatory skin disorder characterized by the loss of melanocytes. While a T helper cell (Th)1/cytotoxic T cell (Tc)1-skewed immune response is now well demonstrated in vitiligo, recent data suggest that the T-cell component could be more complex, involving different combinatorial T-cell subsets.

OBJECTIVES

To analyse the phenotype and function of circulating CD4⁺ and CD8⁺ memory T-cell subsets in patients with stable and active vitiligo, in comparison with patients with psoriasis and healthy controls.

METHODS

This is a monocentric, prospective, descriptive and exploratory study. Multiparametric flow cytometry analyses were performed to evaluate the surface expression of homing and T-cell-subset markers together with intracellular cytokine production in peripheral blood mononuclear cells from 60 patients with vitiligo, 25 patients with psoriasis and 28 healthy donors.

RESULTS

Vitiligo peripheral blood circulating effector and central memory T cells expressed similar proportions of skin-homing markers. Decrease in the frequencies of circulating CD4⁺ and CD8⁺ Th1/Tc1, Th17/Tc17, and Th1/Th17 or Tc1/Tc17 effector memory T-cell subsets were observed in patients with vitiligo compared with healthy donors. Similar observations were made in psoriasis. In contrast, vitiligo circulating T cells showed a similar capacity for proinflammatory cytokine production compared with those in psoriasis and healthy controls.

CONCLUSIONS

The decreased frequencies of circulating Th1/Tc1, Th17/Tc17 and Th1/Th17-Tc1/Tc17 cells suggest a possible migration of these T-cell subsets into the skin of patients with vitiligo. These could be targeted to prevent flares of the disease. What is already known about this topic? Vitiligo is a chronic inflammatory skin disorder associated with the loss of melanocytes. Vitiligo is characterized by a T helper cell (Th)1/cytotoxic T cell (Tc)1-skewed immune response in the skin. What does this study add? A thorough analysis of the phenotype and function of circulating memory T cells suggests the migration of Th1/Tc1, Th17/Tc17 and Th1/Th17-Tc1/Tc17 cell subsets in the skin. What is the translational message? A better understanding of the different immune T-cell subsets involved in vitiligo could lead to better therapeutic options. Linked Comment: Matos. Br J Dermatol 2020; 183:803.

The Th9 Axis Reduces the Oxidative Stress and Promotes the Survival of Malignant T Cells in Cutaneous T-Cell Lymphoma Patients

Immune dysfunction is critical in pathogenesis of cutaneous T-cell lymphoma (CTCL). Few studies have reported abnormal cytokine profile and dysregulated T-cell functions during the onset and progression of certain types of lymphoma. However, the presence of IL9-producing Th9 cells and their role in tumor cell metabolism and survival remain unexplored. With this clinical study, we performed multidimensional blood endotyping of CTCL patients before and after standard photo/chemotherapy and revealed distinct immune hallmarks of the disease. Importantly, there was a higher frequency of "skin homing" Th9 cells in CTCL patients with early (T1 and T2) and advanced-stage disease (T3 and T4). However, advanced-stage CTCL patients had severely impaired frequency of skin-homing Th1 and Th17 cells, indicating attenuated immunity. Treatment of CTCL patients with standard photo/chemotherapy decreased the skin-homing Th9 cells and increased the Th1 and Th17 cells. Interestingly, T cells of CTCL patients express IL9 receptor (IL9R), and there was negligible IL9R expression on T cells of healthy donors. Mechanistically, IL9/IL9R interaction on CD3⁺ T cells of CTCL patients and Jurkat cells reduced oxidative stress, lactic acidosis, and apoptosis and ultimately increased their survival. In conclusion, coexpression of IL9 and IL9R on T cells in CTCL patients indicates the autocrine-positive feedback loop of Th9 axis in promoting the survival of malignant T cells by reducing the oxidative stress. IMPLICATIONS: The critical role of Th9 axis in CTCL pathogenesis indicates that strategies targeting Th9 cells might harbor significant potential in developing robust CTCL therapy.

Targeting the cutaneous lymphocyte antigen (CLA) in inflammatory and neoplastic skin conditions

Introduction: The cutaneous lymphocyte antigen interacts with E-selectin on endothelial cells and is expressed on 15% of circulating T-cells. Skin-homing T-cells express the cutaneous lymphocyte antigen and play a role in local cutaneous immunity in inflammatory reactions and neoplastic conditions.Areas covered: Lymphocyte extravasation is the essential para-physiological mechanism enabling immune surveillance of tissues for tumors as well as effector cell recruitment to inflammatory sites.The authors focused on skin inflammatory disorders, on cutaneous lymphoproliferative disease, and on other skin malignancies.Expert opinion: Interfering with leukocyte extravasation has been regarded as an attractive strategy in skin disorders, in the past for inflammatory conditions and more recently for cutaneous T-cell lymphomas. Therapeutic blocking of skin-homing interactions has been attempted in psoriasis and atopic dermatitis and has been achieved in the treatment of cutaneous T-cell lymphomas. Cutaneous lymphocyte antigen is a potential molecular target for both systemic and skin-directed therapy for cutaneous T-cell lymphomas.

Activated NLR family pyrin domain containing 3 (NLRP3) inflammasome in keratinocytes promotes cutaneous T-cell response in patients with vitiligo

BACKGROUND

Keratinocytes can function as innate immune cells under oxidative stress and aggravate the cutaneous T-cell response that undermines melanocytes in the setting of vitiligo. The NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome is a regulator of innate immunity that exists in keratinocytes. However, the role of the NLRP3 inflammasome in the pathogenesis of vitiligo has not been investigated.

OBJECTIVE

We sought to explicate the contribution of the activated NLRP3 inflammasome in keratinocytes to the autoimmune response in patients with vitiligo.

METHODS

Perilesional and serum samples from patients with vitiligo were collected to examine the status of the NLRP3 inflammasome in the setting of vitiligo. Cultured keratinocytes were treated with H₂O₂ to investigate the mechanism for NLRP3 inflammasome activation under oxidative stress. Peripheral blood T cells were extracted from patients with vitiligo to explore the influence of the NLRP3 inflammasome on the T-cell response in patients with vitiligo.

RESULTS

Expressions of NLRP3 and downstream cytokine IL-1β were consistently increased in perilesional keratinocytes of patients with vitiligo. Notably, serum IL-1β levels were increased in patients with vitiligo, correlated with disease activity and severity, and decreased after effective therapy. Furthermore, oxidative stress promoted NLRP3 inflammasome activation in keratinocytes through transient receptor potential cation channel subfamily M member 2 (TRPM2), a redox-sensitive cation channel, which was dependent on TRPM2-mediated calcium influx. More importantly, blocking TRPM2-induced NLRP3 inflammasome activation in keratinocytes impaired chemotaxis for CD8⁺ T cells and inhibited the production of cytokines in T cells in patients with vitiligo.

CONCLUSION

Oxidative stress-induced NLRP3 inflammasome activation in keratinocytes promotes the cutaneous T-cell response, which could be targeted for the treatment of vitiligo.

Evolution of pathologic T-cell subsets in patients with atopic dermatitis from infancy to adulthood

BACKGROUND

The circulating immune phenotype was defined in adults and young children with early atopic dermatitis (AD), but chronologic changes in the blood of infants and children with AD through adolescence have not been explored.

OBJECTIVE

We sought to compare immune activation and cytokine polarization in the blood of 0- to 5-year-old (n = 39), 6- to 11-year-old (n = 26), 12- to 17-year-old (n = 21) and 18-year-old or older (n = 43) patients with AD versus age-matched control subjects.

METHODS

Flow cytometry was used to measure IFN-γ, IL-9, IL-13, IL-17, and IL-22 cytokine levels in CD4⁺/CD8⁺ T cells, with inducible costimulator molecule and HLA-DR defining midterm and long-term T-cell activation, respectively, within skin-homing/cutaneous lymphocyte antigen (CLA)⁺ versus systemic/CLA^- T cells. Unsupervised clustering differentiated patients based on their blood biomarker frequencies.

RESULTS

Although CLA⁺ T_H1 frequencies were significantly lower in infants with AD versus all older patients (P < .01), frequencies of CLA⁺ T_H2 T cells were similarly expanded across all AD age groups compared with control subjects (P < .05). After infancy, CLA^- T_H2 frequencies were increased in patients with AD in all age groups, suggesting systemic immune activation with disease chronicity. IL-22 frequencies serially increased from normal levels in infants to highly significant levels in adolescents and adults compared with levels in respective control subjects (P < .01). Unsupervised clustering aligned the AD profiles along an age-related spectrum from infancy to adulthood (eg, inducible costimulator molecule and IL-22).

CONCLUSIONS

The adult AD phenotype is achieved only in adulthood. Unique cytokine signatures characterizing individual pediatric endotypes might require age-specific therapies. Future longitudinal studies, comparing the profile of patients with cleared versus persistent pediatric AD, might define age-specific changes that predict AD clearance.

Frontiers in alopecia areata pathobiology research

This current review explores selected and as yet insufficiently investigated frontiers in current alopecia areata (AA) pathobiology research, with an emphasis on potential "new" players in AA pathobiology that deserve more systematic exploration and therapeutic targeting. Indeed, new evidence suggests that CD8⁺ T cells, which have long been thought to be the central players in AA pathobiology, are not the only drivers of disease. Instead, subsets of natural killer (NK) and so-called "unconventional" T cells (invariant NK T cells, γδ T cells, classic NK cells, and type 1 innate lymphoid cells), all of which can produce large amounts of IFN-γ, might also drive AA pathobiology independent of classical, autoantigen-dependent CD8⁺ T-cell functions. Another important new frontier is the role of regulatory lymphocyte subsets, such as regulatory T cells, γδ regulatory T cells, NKT10 cells, and perifollicular mast cells, in maintaining physiologic hair follicle immune privilege (IP); the extent to which these functions are defective in patients with AA; and how this IP-protective role could be restored therapeutically in patients with established AA. Broadening our AA research horizon along the lines suggested above promises not only to open the door to innovative and even more effective immunotherapy strategies for AA but will also likely be relevant for other autoimmune disorders in which pathobiology, ectopic MHC class I expression, and IP collapse play an important role.

Contribution of fibroblasts to tunnel formation and inflammation in hidradenitis suppurativa/ acne inversa

The precise pathogenic mechanisms in the development, persistence and worsening of hidradenitis suppurativa (HS) remain ill-defined. This chronic inflammatory dermatosis displays a strong Th1 and Th17 inflammatory signature with elevated levels of TNF-α, IL-1β, IL-17 and IFNγ in lesional and perilesional tissue. HS significantly differs to other chronic inflammatory dermatoses due to the development of hypertrophic scarring and dermal tunnels. The development of scarring and tunnels suggests that fibroblastic stromal cells (including myofibroblasts, fibroblasts, pericytes etc) may be involved in the development and progression of disease. Heterogeneous populations of fibroblasts have been identified in other inflammatory disorders and malignancy which contribute to inflammation and present novel therapeutic targets for fibrotic disorders. Findings in HS are consistent with these fibroblast subpopulations and may contribute to tunnel formation, aggressive squamous cell carcinoma and the phenotypic presentation of familial HS variants. We describe the existing knowledge regarding these mechanistic pathways and methods to confirm their involvement in the pathogenesis of HS.