Collapse and restoration of MHC class-I-dependent immune privilege: exploiting the human hair follicle as a model

Single-cell transcriptome profiling reveals cell type-specific variation and development in HLA expression of human skin

Skin, the largest organ of body, is a highly immunogenic tissue with a diverse collection of immune cells. Highly polymorphic human leukocyte antigen (HLA) molecules have a central role in coordinating immune responses as recognition molecules. Nevertheless, HLA gene expression patterns among diverse cell types within a specific organ, like the skin, have yet to be thoroughly investigated, with stromal cells attracting much less attention than immune cells. To illustrate HLA expression profiles across different cell types in the skin, we performed single-cell RNA sequencing (scRNA-seq) analyses on skin datasets, covering adult and fetal skin, and hair follicles as the skin appendages. We revealed the variation in HLA expression between different skin populations by examining normal adult skin datasets. Moreover, we evaluated the potential immunogenicity of multiple skin populations based on the expression of classical HLA class I genes, which were well represented in all cell types. Furthermore, we generated scRNA-seq data of developing skin from fetuses of 15 post conception weeks (PCW), 17 PCW, and 22 PCW, delineating the dynamic expression of HLA genes with cell type-dependent variation among various cell types during development. Notably, the pseudotime trajectory analysis unraveled the significant variance in HLA genes during the evolution of vascular endothelial cells. Moreover, we uncovered the immune-privileged properties of hair follicles at single-cell resolution. Our study presents a comprehensive single-cell transcriptomic landscape of HLA genes in the skin, which provides new insights into variation in HLA molecules and offers a clue for allogeneic skin transplantation.

Interleukin-15 is a hair follicle immune privilege guardian

The autoimmunity-promoting cytokine, Interleukin-15 (IL-15), is often claimed to be a key pathogenic cytokine in alopecia areata (AA). Yet, rhIL-15 promotes human hair follicle (HF) growth ex vivo. We have asked whether the expression of IL-15 and its receptor (IL-15R) isoforms is altered in human AA and how IL-15 impacts on human HF immune privilege (HF-IP) in the presence/absence of interferon-γ (IFNγ), the well-documented key AA-pathogenic cytokine, as well as on hair regrowth after experimental AA induction in vivo. Quantitative immunohistomorphometry showed the number of perifollicular IL-15+ T cells in AA skin biopsies to be significantly increased compared to healthy control skin, while IL-15, IL-15Rα, and IL-15Rγ protein expression within the hair bulb were significantly down-regulated in AA HFs. In organ-cultured human scalp HFs, rhIL-15 significantly reduced hair bulb expression of MICA, the key "danger" signal in AA pathogenesis, and increased production of the HF-IP guardian, α-MSH. Crucially, ex vivo, rhIL-15 prevented IFNγ-induced HF-IP collapse, restored a collapsed HF-IP by IL-15Rα-dependent signaling (as documented by IL-15Rα-silencing), and protected AA-preventive immunoinhibitory iNKT10 cells from IFNγ-induced apoptosis. rhIL-15 even promoted hair regrowth after experimental AA induction in human scalp skin xenotransplants on SCID/beige mice in vivo. Our data introduce IL-15 as a novel, functionally important HF-IP guardian whose signaling is constitutively defective in scalp HFs of AA patients. Our data suggest that selective stimulation of intrafollicular IL-15Rα signaling could become a novel therapeutic approach in AA management, while blocking it pharmacologically may hinder both HF-IP restoration and hair re-growth and may thus make HFs more vulnerable to AA relapse.

Mechanical epilation exerts complex biological effects on human hair follicles and perifollicular skin: An ex vivo study approach

OBJECTIVE

Electrical epilation of unwanted hair is a widely used hair removal method, but it is largely unknown how this affects the biology of human hair follicles (HF) and perifollicular skin. Here, we have begun to explore how mechanical epilation changes selected key biological read-out parameters ex vivo within and around the pilosebaceous unit.

METHODS

Human full-thickness scalp skin samples were epilated ex vivo using an electro-mechanical device, organ-cultured for up to 6 days in serum-free, supplemented medium, and assessed at different time points by quantitative (immuno-)histomorphometry for selected relevant read-out parameters in epilated and sham-epilated control samples.

RESULTS

Epilation removed most of the hair shafts, often together with fragments of the outer and inner root sheath and hair matrix. This was associated with persistent focal thinning of the HF basal membrane, decreased melanin content of the residual HF epithelium, and increased HF keratinocyte apoptosis, including in the bulge, yet without affecting the number of cytokeratin 15+ HF epithelial stem cells. Sebocyte apoptosis in the peripheral zone was increased, albeit without visibly altering sebum production. Epilation transiently perturbed HF immune privilege, and increased the expression of ICAM-1 in the bulge and bulb mesenchyme, and the number of perifollicular MHC class II+ cells as well as mast cells around the distal epithelium and promoted mast cell degranulation around the suprabulbar and bulbar area. Moreover, compared to controls, several key players of neurogenic skin inflammation, itch, and/or thermosensation (TRPV1, TRPA1, NGF, and NKR1) were differentially expressed in post-epilation skin.

CONCLUSION

These data generated in denervated, organ-cultured human scalp skin demonstrate that epilation-induced mechanical HF trauma elicits surprisingly complex biological responses. These may contribute to the delayed re-growth of thinner and lighter hair shafts post-epilation and temporary post-epilation discomfort. Our findings also provide pointers regarding the development of topically applicable agents that minimize undesirable sequelae of epilation.

Deciphering the molecular mechanisms of stem cell dynamics in hair follicle regeneration

Hair follicles, which are connected to sebaceous glands in the skin, undergo cyclic periods of regeneration, degeneration, and rest throughout adult life in mammals. The crucial function of hair follicle stem cells is to maintain these hair growth cycles. Another vital aspect is the activity of melanocyte stem cells, which differentiate into melanin-producing melanocytes, contributing to skin and hair pigmentation. Sebaceous gland stem cells also have a pivotal role in maintaining the skin barrier by regenerating mature sebocytes. These stem cells are maintained in a specialized microenvironment or niche and are regulated by internal and external signals, determining their dynamic behaviors in homeostasis and hair follicle regeneration. The activity of these stem cells is tightly controlled by various factors secreted by the niche components around the hair follicles, as well as immune-mediated damage signals, aging, metabolic status, and stress. In this study, we review these diverse stem cell regulatory and related molecular mechanisms of hair regeneration and disease conditions. Molecular insights would provide new perspectives on the disease mechanisms as well as hair and skin disorder treatment.

Controlling Hair Loss by Regulating Apoptosis in Hair Follicles: A Comprehensive Overview

Apoptosis is a physiological process that occurs in all cell types of the human body, and it profoundly changes the fate of hair by affecting hair follicle cells. This review outlines the cellular changes, intrinsic biochemical characteristics, and mechanisms underlying apoptosis and summarizes the hair follicle life cycle, including development, cycle stages, and corresponding cellular changes. Finally, the relationship between apoptosis and the hair cycle is discussed and the significance of apoptosis in hair loss conditions and drug treatments is highlighted. Apoptosis induces cellular changes and exhibits distinctive properties through intricate signaling pathways. Hair follicles undergo cyclic periods of growth, regression, and dormancy. Apoptosis is closely correlated with the regression phase by triggering hair follicle cell death and shedding. Regulation of apoptosis in hair follicles plays an essential role in hair loss due to maladies and drug treatments. Mitigating apoptosis can enhance hair growth and minimize hair loss. A comprehensive understanding of the correlation between apoptosis and the hair cycle can facilitate the development of novel treatments to prevent hair loss and stimulate hair regeneration.

Alopecia Areata: Current Treatments and New Directions

Alopecia areata is an autoimmune hair loss disease that is non-scarring and is characterized by chronic inflammation at the hair follicle level. Clinically, patients' presentation varies from patchy, circumscribed scalp involvement to total body and scalp hair loss. Current management is guided by the degree of scalp and body involvement, with topical and intralesional steroid injections as primarily first-line for mild cases and broad immunosuppressants as the mainstay for more severe cases. Until recently, the limited number of blinded, randomized, placebo-controlled clinical trials for this disease had made establishing an evidence-based treatment paradigm challenging. However, growing insights into the pathogenesis of alopecia areata through blood and tissue analysis of human lesions have identified several promising targets for therapy. T-helper (Th) 1/interferon skewing has traditionally been described as the driver of disease; however, recent investigations suggest activation of additional immune mediators, including the Th2 pathway, interleukin (IL)-9, IL-23, and IL-32, as contributors to alopecia areata pathogenesis. The landscape of alopecia areata treatment has the potential to be transformed, as several novel targeted drugs are currently undergoing clinical trials. Given the recent US FDA approval of baricitinib and ritlecitinib, Janus kinase (JAK) inhibitors are a promising drug class for treating severe alopecia areata cases. This article will review the efficacy, safety, and tolerability of current treatments for alopecia areata, and will provide an overview of the emerging therapies that are leading the revolution in the management of this challenging disease.

Diagnosis and Management of Alopecia Areata: A Saudi Expert Consensus Statement (2023)

Alopecia areata (AA) is a complex autoimmune disease manifesting as a chronic inflammatory disease characterized by non-scarring patches of hair loss over the face, scalp, and body. Several treatments have been proposed for AA, but none are curative nor achieve a state of remission. The present consensus statement aims to present the evidence- and experience-based recommendations on the diagnosis and management of AA in Saudi Arabia. The Ministry of Health in Saudi Arabia has opted to initiate a meeting of a multidisciplinary group to discuss and concede on this topic. Eight dermatology experts and clinical pharmacists convened in eight consensus meetings. All content presented in this document was agreed upon by this working group, including diagnosis and severity assessment, prognostic indicators, and therapeutic options for AA. Special consideration was given to special patient populations including pediatric patients and patients with less frequent presentations of AA. Updates of the current recommendations will take place as new evidence evolves in the treatment of AA.

Identification of immune microenvironment changes, immune-related pathways and genes in male androgenetic alopecia

BACKGROUND

Although androgenetic alopecia (AGA) is classified as a non-inflammatory alopecia, histological evidence of microinflammation has long been recognized. However, changes in the immune microenvironment, immune-related pathways and the expression of immune-related genes (IRGs) involved in AGA remain unclear.

METHODS

The microarray gene expression data (GSE36169) from patients with male AGA were analyzed. gene set enrichment analysis (GSEA) among statistically changed genes was done. Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analyses among differentially expressed genes were performed. differentially expressed genes were screened to identify IRGs based on the ImmPort database. The cytohubba-MCC plugin of Cytoscape was applied to screen hub immune genes. The infiltration levels of 28 immune cells were quantified adopting single-sample GSEA (ssGSEA) algorithm. The microarray gene expression data (GSE90594) of male AGA was analyzed to validate hub IRGs genes and differential infiltrated immune cells.

RESULTS

The ssGSEA revealed γδT cell, central memory CD8+ T cell, mast cell, immature B cell, activated CD8+ T cell, effector memory CD4+ T cell, eosinophil and neutrophil were significantly increased infiltration in the bald scalp. GSEA showed statistically changed genes were most enriched in immune related pathways, including innate immune system, adaptive immune system, cytokine signaling, interferon-γ signaling, interferon signaling and interleukins signaling. The 4 hub IRGs, including matrix metallopeptidase 9, protein tyrosine phosphatase receptor type C, bone morphogenetic protein 2, and thrombospondin 1, were enriched in the pathways of allograft rejection, coagulation and interferon-γ response.

CONCLUSION

In summary, we proposed that the increase in γδ T cells, central memory CD8+ T cells, activated CD8+ T cell as well as the infiltration of mast cells contributed to immune microenvironment changes in male AGA. The 4 hub IRGs may be involved in the development and progression of hair loss in male AGA through interferon-γ signal pathways.

Recent Advances in Understanding of the Etiopathogenesis, Diagnosis, and Management of Hair Loss Diseases

Hair-loss diseases comprise heterogenous conditions with respective pathophysiology and clinicopathological characteristics. Major breakthroughs in hair follicle biology and immunology have led to the elucidation of etiopathogenesis of non-scarring alopecia (e.g., alopecia areata, AA) and cicatricial alopecia (e.g., lichen planopilaris, LPP). High-throughput genetic analyses revealed molecular mechanism underlying the disease susceptibility of hair loss conditions, such as androgenetic alopecia (AGA) and female pattern hair loss (FPHL). Hair loss attracted public interest during the COVID-19 pandemic. The knowledge of hair loss diseases is robustly expanding and thus requires timely updates. In this review, the diagnostic and measurement methodologies applied to hair loss diseases are updated. Of note, novel criteria and classification/scoring systems published in the last decade are reviewed, highlighting their advantages over conventional ones. Emerging diagnostic techniques are itemized with clinical pearls enabling efficient utilization. Recent advances in understanding the etiopathogenesis and management for representative hair diseases, namely AGA, FPHL, AA, and major primary cicatricial alopecia, including LPP, are comprehensively summarized, focusing on causative factors, genetic predisposition, new disease entity, and novel therapeutic options. Lastly, the association between COVID-19 and hair loss is discussed to delineate telogen effluvium as the predominating pathomechanism accounting for this sequela.

Alopecia and Periodontitis: Exploring the connecting dots

Alopecia areata is a systemic disease with nonscarring hair loss from the scalp, face, or any part of the body. The disease with undetermined etiology and pathogenesis has a considerable impact on the social life of patients which gradually builds up stress and expedites further deterioration of their condition. Interestingly, in such patients, besides stress-relieving exercises and immunomodulators, well-timed dental assessment and prompt treatment have contributed to improving the prognosis of alopecia. This depicts an interrelationship between alopecia and oral foci of infections. Over the past few decades, periodontitis has remained to be one of the predominant forms of oral focus of infection for systemic diseases. The present review throws light on the role of stress and autoimmunity in establishing a possible correlation between alopecia and periodontitis. It is augmented with documented case reports, demanding a complete oral examination in patients with the unexplained origin of alopecia. An interdisciplinary approach is the need of the hour which can prevent the progression of both the diseases as well as other oral infections.

Involvement of ILC1-like innate lymphocytes in human autoimmunity, lessons from alopecia areata

Here, we have explored the involvement of innate lymphoid cells-type 1 (ILC1) in the pathogenesis of alopecia areata (AA), because we found them to be significantly increased around lesional and non-lesional HFs of AA patients. To further explore these unexpected findings, we first co-cultured autologous circulating ILC1-like cells (ILC1lc) with healthy, but stressed, organ-cultured human scalp hair follicles (HFs). ILClc induced all hallmarks of AA ex vivo: they significantly promoted premature, apoptosis-driven HF regression (catagen), HF cytotoxicity/dystrophy, and most important for AA pathogenesis, the collapse of the HFs physiological immune privilege. NKG2D-blocking or IFNγ-neutralizing antibodies antagonized this. In vivo, intradermal injection of autologous activated, NKG2D+/IFNγ-secreting ILC1lc into healthy human scalp skin xenotransplanted onto SCID/beige mice sufficed to rapidly induce characteristic AA lesions. This provides the first evidence that ILC1lc, which are positive for the ILC1 phenotype and negative for the classical NK markers, suffice to induce AA in previously healthy human HFs ex vivo and in vivo, and further questions the conventional wisdom that AA is always an autoantigen-dependent, CD8 +T cell-driven autoimmune disease.

Lysine 222 in PPAR γ1 functions as the key site of MuRF2-mediated ubiquitination modification

Peroxisome proliferator-activated receptor gamma (PPAR γ) plays key roles in the development, physiology, reproduction, and homeostasis of organisms. Its expression and activity are regulated by various posttranslational modifications. We previously reported that E3 ubiquitin ligase muscle ring finger protein 2 (MuRF2) inhibits cardiac PPAR γ1 protein level and activity, eventually protects heart from diabetic cardiomyopathy; furthermore, by GST-pulldown assay, we found that MuRF2 modifies PPAR γ1 via poly-ubiquitination and accelerates PPAR γ1 proteasomal degradation. However, the key ubiquitination site on PPAR γ that MuRF2 targets for remains unclear. In the present study, we demonstrate that lysine site 222 is the receptor of MuRF2-mediated PPAR γ1 ubiquitination modification, using prediction of computational models, immunoprecipitation, ubiquitination assays, cycloheximide chasing assay and RT-qPCR. Our findings elucidated the underlying details of MuRF2 prevents heart from diabetic cardiomyopathy through the PPAR γ1 regulatory pathway.

Alopecia Areata: Burden of Disease, Approach to Treatment, and Current Unmet Needs

Alopecia areata is an autoimmune hair loss disorder with variations in distribution, duration, and severity. The disease is chronic and often follows an unpredictable course, frequently leading to stress and anxiety for those who suffer from it. Throughout the years more knowledge has been gained regarding pathogenesis, diagnostic tools, impact on quality of life, as well as treatment strategies for alopecia areata. However, challenges in treating and alleviating the burden of disease remain. In this article, we discuss updates regarding the pathogenesis and treatment of alopecia areata and highlight unmet needs of the condition, including a review of limitations of current treatments, accessibility to management strategies, and the need for disease awareness and advocacy.

Alopecia Areata: Case report and review of pathophysiology and treatment with Jak inhibitors

Alopecia Areata (AA) is a T-cell mediated autoimmune attack on hair follicles resulting in rapidly developing areas of hair loss involving the scalp and beard that can progress to total scalp hair loss (alopecia totalis) and loss of eyebrows, eyelashes, and total body hair (alopecia universalis). Affected patients have high rates of psychological disorders and decreased quality of life. There are no FDA approved treatments, and the available treatments have a high failure rate. JAK inhibitors are remarkably effective in many autoimmune diseases including Alopecia Areata. Presented is a case report of successful treatment with tofacitinib, and a literature review of the pathophysiology of alopecia areata, the mechanism of action of JAK inhibitors, and the JAK inhibitors in phase 2 and 3 trials.

Is There a Pathogenetic Relationship Between Alopecia Areata and Familial Mediterranean Fever?

Alopecia areata (AA) is type of autoimmune, T-cell-mediated disease with abnormal expression of MHC Class I, a common reason for non-scarring hair loss. Familial Mediterranean fever (FMF) is a hereditary autoinflammatory disease characterized by periodic fever and serositis. Various diseases and conditions that may be related to FMF have been reported. It has been known that patients with FMF are vulnerable to MHC Class I-related diseases. The co-existence of the two MHC Class I group-associated entities, FMF and AA, has not been reported in the literature. Here, we present three cases with AA and FMF and discuss the possible common pathway in their pathogenesis.

How Our Microbiome Influences the Pathogenesis of Alopecia Areata

Alopecia areata is a multifactorial autoimmune-based disease with a complex pathogenesis. As in all autoimmune diseases, genetic predisposition is key. The collapse of the immune privilege of the hair follicle leading to scalp loss is a major pathogenic event in alopecia areata. The microbiota considered a bacterial ecosystem located in a specific area of the human body could somehow influence the pathogenesis of alopecia areata, as it occurs in other autoimmune diseases. Moreover, the Next Generation Sequencing of the 16S rRNA bacterial gene and the metagenomic methodology have provided an excellent characterization of the microbiota. The aim of this narrative review is to examine the published literature on the cutaneous and intestinal microbiota in alopecia areata to be able to establish a pathogenic link. In this review, we summarize the influence of the microbiota on the development of alopecia areata. We first introduce the general pathogenic mechanisms that cause alopecia areata to understand the influence that the microbiota may exert and then we summarize the studies that have been carried out on what type of gut and skin microbiota is found in patients with this disease.

Hair Follicle Melanocytes Initiate Autoimmunity in Alopecia Areata: a Trigger Point

Alopecia areata (AA) is characterized by common non-scarring alopecia due to autoimmune disorders. To date, the specific pathogenesis underlying AA remains unknown. Thus, AA treatment in the dermatological clinic is still a challenge. Numerous clinical observations and experimental studies have established that melanocytes may be the trigger point that causes hair follicles to be attacked by the immune system. A possible mechanism is that the impaired melanocytes, under oxidative stress, cannot be repaired in time and causes apoptosis. Melanocyte-associated autoantigens are released and presented, inducing CD8⁺ T cell attacks. Thereafter, amplification of the immune responses further spreads to the entire hair follicle (HF). The immune privilege of HF subsequently collapses, leading to AA. Herein, we present a narrative review on the roles of melanocytes in AA pathogenesis, aiming to provide a better understanding of this disease from the melanocyte's perspective.

An overview of JAK/STAT pathways and JAK inhibition in alopecia areata

Alopecia Areata (AA) is a common autoimmune disease characterized by non-scarring hair loss ranging from patches on the scalp to complete hair loss involving the entire body. Disease onset is hypothesized to follow the collapse of immune privilege of the hair follicle, which results in an increase in self-peptide/MHC expression along the follicular epithelium. Hair loss is associated with infiltration of the hair follicle with putatively self-reactive T cells. This process is thought to skew the hair follicle microenvironment away from a typically homeostatic immune state towards one of active inflammation. This imbalance is mediated in part by the dominating presence of specific cytokines. While interferon-γ (IFNγ) has been identified as the key player in AA pathogenesis, many other cytokines have also been shown to play pivotal roles. Mechanistic studies in animal models have highlighted the contribution of common gamma chain (γ_c) cytokines such as IL-2, IL-7, and IL-15 in augmenting disease. IFNγ and γ_c cytokines signal through pathways involving receptor activation of Janus kinases (JAKs) and signal transducers and activators of transcription (STATs). Based on these findings, JAK/STAT pathways have been targeted for the purposes of therapeutic intervention in the clinical setting. Case reports and series have described use of small molecule JAK inhibitors leading to hair regrowth among AA patients. Furthermore, emerging clinical trial results show great promise and position JAK inhibitors as a treatment strategy for patients with severe or recalcitrant disease. Demonstrated efficacy from large-scale clinical trials of the JAK inhibitor baricitinib led to the first-in-disease FDA-approved treatment for AA in June of 2022. This review aims to highlight the JAK/STAT signaling pathways of various cytokines involved in AA and how targeting those pathways may impact disease outcomes in both laboratory and clinical settings.

The impact of perceived stress on the hair follicle: Towards solving a psychoneuroendocrine and neuroimmunological puzzle

While popular belief harbors little doubt that perceived stress can cause hair loss and premature graying, the scientific evidence for this is arguably much thinner. Here, we investigate whether these phenomena are real, and show that the cyclic growth and pigmentation of the hair follicle (HF) provides a tractable model system for dissecting how perceived stress modulates aspects of human physiology. Local production of stress-associated neurohormones and neurotrophins coalesces with neurotransmitters and neuropeptides released from HF-associated sensory and autonomic nerve endings, forming a complex local stress-response system that regulates perifollicular neurogenic inflammation, interacts with the HF microbiome and controls mitochondrial function. This local system integrates into the central stress response systems, allowing the study of systemic stress responses affecting organ function by quantifying stress mediator content of hair. Focusing on selected mediators in this "brain-HF axis" under stress conditions, we distill general principles of HF dysfunction induced by perceived stress.

Immune-mediated alopecias and their mechanobiological aspects

Alopecia is a non-specific term for hair loss clinically diagnosed by the hair loss pattern and histological analysis of patient scalp biopsies. The immune-mediated alopecia subtypes, including alopecia areata, lichen planopilaris, frontal fibrosing alopecia, and central centrifugal cicatricial alopecia, are common, significant forms of alopecia subtypes. For example, alopecia areata is the most common autoimmune disease with a lifetime incidence of approximately 2% of the world's population. In this perspective, we discuss major results from studies of immune-mediated alopecia subtypes. These studies suggest the key event in disease onset as the collapse in immune privilege, which alters the hair follicle microenvironment, e.g., upregulation of major histocompatibility complex molecules and increase of cytokine production, and results in immune cell infiltration, inflammatory responses, and damage of hair follicles. We note that previous studies have established that the hair follicle has a complex mechanical microenvironment, which may regulate the function of not only tissue cells but also immune cell infiltrates. This suggests a potential for mechanobiology to contribute to alopecia research by adding new methods, new approaches, and new ways of thinking, which is missing in the existing literature. To fill this a gap in the alopecia research space, we develop a mechanobiological hypothesis that alterations in the hair follicle microenvironment, specifically in the mechanically responsive tissues and cells, partially due to loss of immune privilege, may be contributors to disease pathology. We further focus our discussion on the potential for applying mechanoimmunology to the study of T cell infiltrates in the hair follicle, as they are considered primary contributors to alopecia pathology. To establish the connection between the mechanoimmunological hypothesis and immune-mediated alopecia subtypes, we discuss what is known about the role of T cells in immune-mediated alopecia subtypes, using the most extensively studied AA as our model.

Frontiers in Lichen Planopilaris and Frontal Fibrosing Alopecia Research: Pathobiology Progress and Translational Horizons

Lichen planopilaris (LPP) and frontal fibrosing alopecia (FFA) are primary, lymphocytic cicatricial hair loss disorders. These model epithelial stem cell (SC) diseases are thought to result from a CD8⁺ T-cell‒dominated immune attack on the hair follicle (HF) SC niche (bulge) after the latter has lost its immune privilege (IP) for as yet unknown reasons. This induces both apoptosis and pathological epithelial‒mesenchymal transition in epithelial SCs, thus depletes the bulge, causes fibrosis, and ultimately abrogates the HFs' capacity to regenerate. In this paper, we synthesize recent progress in LPP and FFA pathobiology research, integrate our limited current understanding of the roles that genetic, hormonal, environmental, and other factors may play, and define major open questions. We propose that LPP and FFA share a common initial pathobiology, which then bifurcates into two distinct clinical phenotypes, with macrophages possibly playing a key role in phenotype determination. As particularly promising translational research avenues toward direly needed progress in the management of these disfiguring, deeply distressful cicatricial alopecia variants, we advocate to focus on the development of bulge IP and epithelial SC protectants such as, for example, topically effective, HF‒penetrating and immunoinhibitory preparations that contain tacrolimus, peroxisome proliferator-activated receptor-γ, and/or CB1 agonists.

Choroidal Thickness In Patients With Alopecia Areata: Is It A Sign For Poor Prognosis?

INTRODUCTION

Alopecia areata (AA) is an autoimmune disease which causes non-scarring type hair loss considered to target the pigmentary system. The hair follicle may not be the only site for involvement of the disease. Iris, the ciliary body, choroid and epithelium of the retinal pigment may also be affected. The aim of the present study was to compare retinal pigment epithelium (RPE) and choroidal thicknesses between patients with AA and healthy controls.

METHODS

The study included 44 patients with alopecia areata, and 44 healthy individuals with similar age and gender distribution. RPE and choroidal thickness measurements were performed through Spectral-domain optical coherence tomography (SD-OCT) (Heidelberg Spectralis® OCT).

RESULTS

There was not any significant difference between patients with AA and healthy individuals for RPE and choroidal thickness (P = 0.751, P = 0.725, respectively). However, the choroidal thickness (422 ± 79 μm) was significantly thinner in patients with poor prognostic criteria than other patients (371 ± 75 μm) (P = 0.039).

CONCLUSION

Monitoring of choroidal thicknesses through optic coherence tomography (OCT) may provide an insight for the disease prognosis in patients with AA.

The current state of knowledge of the immune ecosystem in alopecia areata

Alopecia areata (AA) is an autoimmune disease that affects approximately 2% of the general population. Patients with AA most commonly present with one or more patches of hair loss on the scalp in defined circular areas. A fraction of patients progress to more severe forms of the disease, in some cases with involvement of all body surfaces. The healthy anagen stage hair follicle is considered an immune privileged site, described as an environment that suppresses inflammatory immune responses. However, in AA, this immune privileged state collapses and marks the hair follicle as a target for the immune system, resulting in peri- and intrafollicular infiltration by lymphocytes. The complexity of the inflammatory ecosystem of the immune response to the hair follicle, and the relationships between the cellular and soluble participants, in AA remains incompletely understood. Many studies have demonstrated the presence of various immune cells around diseased hair follicles; however, often little is known about their respective contributions to AA pathogenesis. Furthering our understanding of the mechanisms of disease in AA is essential for the novel identification of targeted therapeutics that are efficacious and have few unintended effects.

A Hairy Cituation - PADIs in Regeneration and Alopecia

In this Review article, we focus on delineating the expression and function of Peptidyl Arginine Delminases (PADIs) in the hair follicle stem cell lineage and in inflammatory alopecia. We outline our current understanding of cellular processes influenced by protein citrullination, the PADI mediated posttranslational enzymatic conversion of arginine to citrulline, by exploring citrullinomes from normal and inflamed tissues. Drawing from other stem cell lineages, we detail the potential function of PADIs and specific citrullinated protein residues in hair follicle stem cell activation, lineage specification and differentiation. We highlight PADI3 as a mediator of hair shaft differentiation and display why mutations in PADI3 are linked to human alopecia. Furthermore, we propose mechanisms of PADI4 dependent fine-tuning of the hair follicle lineage progression. Finally, we discuss citrullination in the context of inflammatory alopecia. We present how infiltrating neutrophils establish a citrullination-driven self-perpetuating proinflammatory circuitry resulting in T-cell recruitment and activation contributing to hair follicle degeneration. In summary, we aim to provide a comprehensive perspective on how citrullination modulates hair follicle regeneration and contributes to inflammatory alopecia.

Alopecia areata: Current understanding of the pathophysiology and update on therapeutic approaches, featuring the Japanese Dermatological Association guidelines

Alopecia areata (AA) is a relatively common nonscarring hairloss disease characterized by an autoimmune response to anagen hair follicles (HFs). Accumulated evidence suggests that collapse of the HF immune privilege subsequent to triggering events, represented by viral infection, leads to autoimmune response in which autoreactive cytotoxic CD8+NKG2D+ T cells mainly target exposed HF autoantigens. AA had been recognized as type 1 inflammatory disease, but recent investigations have suggested some roles of type 2- and Th17-associated mediators in AA pathogenesis. The significance of psychological stress in AA pathogenesis is less emphasized nowadays, but psychological comorbidities, such as depression and anxiety, attract greater interest in AA management. In this regard, the disease severity may not solely be evaluated by the extent of hair loss. Use of trichoscopy markedly improved the resolution of the diagnosis and evaluation of the phase of AA, which is indispensable for the optimization of treatment. For the standardization of AA management, the establishment of guidelines/expert consensus is pivotal. Indeed, the Japanese Dermatological Association (JDA) and other societies and expert groups have published guidelines/expert consensus reports, which mostly recommend intralesional/topical corticosteroid administration and contact immunotherapy as first-line treatments, depending on the age, disease severity, and activity of AA. The uniqueness of the JDA guidelines can be found in their descriptions of intravenous corticosteroid pulse therapy, antihistamines, and other miscellaneous domestically conducted treatments. Considering the relatively high incidence of spontaneous regression in mild AA and its intractability in severe subsets, the importance of course observation is also noted. Evidenced-based medicine for AA is currently limited, however, novel therapeutic approaches, represented by JAK inhibitors, are on their way for clinical application. In this review, the latest understanding of the etiopathogenesis and pathophysiology, and update on therapeutic approaches with future perspectives are summarized for AA, following the current version of the JDA AA management guidelines.

Hair follicle-derived mesenchymal stem cells decrease alopecia areata mouse hair loss and reduce inflammation around the hair follicle

Background

Alopecia areata (AA) is a common autoimmune hair loss disease with increasing incidence. Corticosteroids are the most widely used for hair loss treatment; however, long-term usage of hormonal drugs is associated with various side effects. Mesenchymal stem cells (MSCs) therapy has been studied extensively to curb autoimmune diseases without affecting immunity against diseases.

Methods

Hair follicle-derived MSCs (HF-MSCs) were harvested from the waste material of hair transplants, isolated and expanded. The therapeutic effect of HF-MSCs for AA treatment was investigated in vitro AA-like hair follicle organ model and in vivo C3H/HeJ AA mice model.

Results

AA-like hair follicle organ in vitro model was successfully established by pre-treatment of mouse vibrissa follicles by interferon-γ (IFN-γ). The AA-like symptoms were relieved when IFN-γ induced AA in vitro model was co-cultured with HF-MSC for 2 days. In addition, when skin grafted C3H/HeJ AA mice models were injected with 10⁶ HF-MSCs once a week for 3 weeks, the transcription profiling and immunofluorescence analysis depicted that HF-MSCs treatment significantly decreased mouse hair loss and reduced inflammation around HF both in vitro and in vivo.

Conclusions

This study provides a new therapeutic approach for alopecia areata based on HF-MSCs toward its future clinical application.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02614-0.

Altered T cell subpopulations and serum anti-TYRP2 and tyrosinase antibodies in the acute and chronic phase of alopecia areata in the C3H/HeJ mouse model

BACKGROUND

C3H/HeJ mouse models progress gradually in hair loss from acute to chronic phase and reflect the symptoms of patients with alopecia areata (AA). However, the underlying pathological characteristics alteration associated with disease progression and autoantigens remain unclear.

OBJECTIVE

We aimed at elucidating the pathological differences between acute and chronic-AA in the C3H/HeJ mouse model.

METHODS

We analyzed populations of PBMCs, skin-draining lymph node (SDLN) cells, and cutaneous cells of AA mice using flow cytometry. The cytokine and chemokine expressions in the serum and skin were determined using multiplex assay and qPCR. The antibody serum levels were determined using ELISA and the antigen-specific T cells were detected using the MHC class I tetramer.

RESULTS

The CD8⁺NKG2D⁺ T and CD8⁺ T_EM cell percentage in the chronic-AA SDLNs or among the unaffected and acute-AA mice PBMCs increased. The Th1 and CD4⁺ T_EM cell percentage in the SDLNs and among PBMCs increased in the unaffected and AA mice. The percentage of CD8⁺ T_EM/T_RM cells and MHC class I expression increased in the lesions of acute-AA or the non-lesions and lesions of chronic-AA. The Th1 cells, dendritic cell-related cytokines, CD11c⁺ cells and MHC class II expression increased in the skin of AA mice. The antibody levels and TYRP2 and tyrosinase-specific CD8⁺ T cell percentages were upregulated in AA mice.

CONCLUSION

These results suggest that the CD8⁺ and CD4⁺ T cell subpopulations, cytokine and chemokine expressions differ between the disease phases. Moreover, TYRP2 and tyrosinase are potential autoreactive targets in the AA mouse model.

A folliculocentric perspective of dandruff pathogenesis: Could a troublesome condition be caused by changes to a natural secretory mechanism?

Dandruff is a common scalp condition, which frequently causes psychological distress in those affected. Dandruff is considered to be caused by an interplay of several factors. However, the pathogenesis of dandruff remains under-investigated, especially with respect to the contribution of the hair follicle. As the hair follicle exhibits unique immune-modulatory properties, including the creation of an immunoinhibitory, immune-privileged milieu, we propose a novel hypothesis taking into account the role of the hair follicle. We hypothesize that the changes and imbalance of yeast and bacterial species, along with increasing proinflammatory sebum by-products, leads to the activation of immune response and inflammation. Hair follicle keratinocytes may then detect these changes in scalp microbiota resulting in the recruitment of leukocytes to the inflammation site. These changes in the scalp skin immune-microenvironment may impact hair follicle immune privilege status, which opens new avenues into exploring the role of the hair follicle in dandruff pathogenesis. Also see the video abstract here: https://youtu.be/mEZEznCYtNs.

Resident human dermal γδT-cells operate as stress-sentinels: Lessons from the hair follicle

Murine γδT-cells have stress-surveillance functions and are implicated in autoimmunity. Yet, whether human γδT-cells are also stress sentinels and directly promote autoimmune responses in the skin is unknown. Using a novel (mini-)organ assay, we tested if human dermis resident γδT-cells can recognize stressed human scalp hair follicles (HFs) to promote an alopecia areata (AA)-like autoimmune response. Accordingly, we show that γδT-cells from healthy human scalp skin are activated (CD69⁺), up-regulate the expression of NKG2D and IFN-γ, and become cytotoxic when co-cultured with autologous stressed HFs ex vivo. These autologous γδT-cells induce HF immune privilege collapse, dystrophy, and premature catagen, i.e. three hallmarks of the human autoimmune HF disorder, AA. This is mediated by CXCL12, MICA, and in part by IFN-γ and CD1d. In conclusion, human dermal γδT-cells exert physiological stress-sentinel functions in human skin, where their excessive activity can promote autoimmunity towards stressed HFs that overexpress CD1d, CXCL12, and/or MICA.

Alopecia Areata: An Autoimmune Disease of Multiple Players

Alopecia areata (AA) is an autoimmune disease of the hair follicles. It is characterized by a well-defined non-scarring alopecic patch or patches that may extend to the entire scalp or lead to total body hair loss. Due to its unpredictable clinical course, AA causes substantial psychological harm. Despite the high prevalence of this disease and extensive research, its exact pathomechanism is unclear, and current treatments have a high relapse rate that has deemed AA incurable. Over the past few decades, researchers have investigated multiple potential factors that may help alleviate its pathogenesis and provide effective treatment. Given its complex immunopathogenesis, AA is considered an autoimmune disease with multiple factors. This review gathers current evidence that emphasizes molecular mechanisms, possible causative etiologies, and targeted immunotherapies for AA. Understanding its underlying mechanisms may shed light on new strategies to effectively manage AA in the future.

Hair follicle stem cells promote cutaneous wound healing through the SDF-1α/CXCR4 axis: an animal model

OBJECTIVE

An appropriate source of adult stem cells for therapeutic use is stem cells deriving from the hair follicle bulge. Following injury, ischaemic tissues produce a variety of cytokines and growth factors that are essential for tissue repair. This study sought to investigate the temporal effects of hair follicle bulge stem cells (HFSCs) on cutaneous wound healing in rats using the SDF-1α/CXCR4 axis.

METHOD

HFSCs obtained from rat vibrissa, labeled with DiI and then special markers, were detected using flow cytometry. The animals were divided into five groups: control (non-treated, n=18), sham (PBS, n=18), AMD (treated with AMD3100, n=18), HFSC + AMD (treated with HFSCs + AMD3100, n=18) and HFSC (treated with HFSCs, n=18). A full-thickness excisional wound model was created and DiI-labeled HFSCs were injected around the wound bed. Wound healing was recorded with digital photographs. The animals were sacrificed 3, 7 and 14 days after the surgery and were used for histological (H&E, Masson's trichrome staining) and molecular (ELISA and q-PCR) assays.

RESULTS

The flow cytometry results demonstrated that HFSCs were CD34-positive, nestin-positive, but Kr15-negative. The morphological analysis of the HFSC-treated wounds showed accelerated wound closure. The histological analysis of the photomicrographs exhibited more re-epithelialisation and dermal structural regeneration in the HFSC-treated wounds compared with the control group. In the HFSC + AMD group, the histological parameters improved on the same days, but showed a significant decrease compared with the HFSC group in all the days assayed. In the AMD group, there was a significant reduction in the noted parameters. qRT-PCR and ELISA showed a high expression level of SDF-1α, CXCR4 and VEGFR-2 in the HFSC-treated wounded skin tissue, but the expression of CXCR4 and VEGFR-2 showed a significant reduction in the HFSC + AMD group compared with the HFSC group.

CONCLUSIONS

Based on the findings of this study, HFSC transplantation affects wound closure parameters and the expression of SDF-1α and CXCR4. As the SDF-1α expression level increases in the injured area, the HFSCs contribute to wound repair through the SDF-1α/CXCR4 axis. This result is extremely valuable because it raises the possibility of wounds healed by isolating autologous HFSCs from the patient.

A Cell Membrane-Level Approach to Cicatricial Alopecia Management: Is Caveolin-1 a Viable Therapeutic Target in Frontal Fibrosing Alopecia?

Irreversible destruction of the hair follicle (HF) in primary cicatricial alopecia and its most common variant, frontal fibrosing alopecia (FFA), results from apoptosis and pathological epithelial-mesenchymal transition (EMT) of epithelial HF stem cells (eHFSCs), in conjunction with the collapse of bulge immune privilege (IP) and interferon-gamma-mediated chronic inflammation. The scaffolding protein caveolin-1 (Cav1) is a key component of specialized cell membrane microdomains (caveolae) that regulates multiple signaling events, and even though Cav1 is most prominently expressed in the bulge area of human scalp HFs, it has not been investigated in any cicatricial alopecia context. Interestingly, in mice, Cav1 is involved in the regulation of (1) key HF IP guardians (TGF-β and α-MSH signaling), (2) IP collapse inducers/markers (IFNγ, substance P and MICA), and (3) EMT. Therefore, we hypothesize that Cav1 may be an unrecognized, important player in the pathobiology of cicatricial alopecias, and particularly, in FFA, which is currently considered as the most common type of primary lymphocytic scarring alopecia in the world. We envision that localized therapeutic inhibition of Cav1 in management of FFA (by cholesterol depleting agents, i.e., cyclodextrins/statins), could inhibit and potentially reverse bulge IP collapse and pathological EMT. Moreover, manipulation of HF Cav1 expression/localization would not only be relevant for management of cicatricial alopecia, but FFA could also serve as a model disease for elucidating the role of Cav1 in other stem cell- and/or IP collapse-related pathologies.

Alopecia totalis following hand-foot-and-mouth disease

We present a case of a 13-month-old male patient with alopecia totalis that began two months after an episode of hand-foot-and-mouth disease. It is hypothesized that the viral infection triggered an autoimmune response, which lead to production of lymphocytes targeting an antigen present in the hair bulb. Future research is necessary to determine whether and how the pathophysiology of alopecia totalis may be triggered by viral infection.

Exploring the human hair follicle microbiome

Human hair follicles (HFs) carry complex microbial communities that differ from the skin surface microbiota. This likely reflects that the HF epithelium differs from the epidermal barrier in that it provides a moist, less acidic, and relatively ultraviolet light-protected environment, part of which is immune-privileged, thus facilitating microbial survival. Here we review the current understanding of the human HF microbiome and its potential physiological and pathological functions, including in folliculitis, acne vulgaris, hidradenitis suppurativa, alopecia areata and cicatricial alopecias. While reviewing the main human HF bacteria (such as Propionibacteria, Corynebacteria, Staphylococci and Streptococci), viruses, fungi and parasites as human HF microbiome constituents, we advocate a broad view of the HF as an integral part of the human holobiont. Specifically, we explore how the human HF may manage its microbiome via the regulated production of antimicrobial peptides (such as cathelicidin, psoriasin, RNAse7 and dermcidin) by HF keratinocytes, how the microbiome may impact on cytokine and chemokine release from the HF, and examine hair growth-modulatory effects of antibiotics, and ask whether the microbiome affects hair growth in turn. We highlight major open questions and potential novel approaches to the management of hair diseases by targeting the HF microbiome.

Mesenchymal Stem Cells Antagonize IFN-Induced Proinflammatory Changes and Growth Inhibition Effects via Wnt/β-Catenin and JAK/STAT Pathway in Human Outer Root Sheath Cells and Hair Follicles

Mesenchymal stem cell therapy (MSCT) has been shown to be a new therapeutic option for treating alopecia areata (AA). Outer root sheath cells (ORSCs) play key roles in maintaining the hair follicle structure and supporting the bulge area. In human ORSCs (hORSCs), the mechanism for this process has not been extensively studied. In this study, we aimed to examine the influence of human hematopoietic mesenchymal stem cells (hHMSCs) in the hORSCs in vitro model of AA and determine the mechanisms controlling efficacy. Interferon-gamma (IFN-γ) pretreatment was used to induce an in vitro model of AA in hORSCs. The effect of MSCT on the viability and migration of hORSCs was examined using co-cultures, the MTT assay, and migration assays. We investigated the expression of molecules related to the Wnt/β-catenin pathway, JAK/STAT pathway, and growth factors in hHMSC-treated hORSCs by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses. hHMSCs increased hORSC viability and migration when they were co-cultured. hHMSCs reverted IFN-γ-induced expression-including NLRP3, ASC, caspase-1, CXCL-9 through 11, IL-1β, and IL-15-and upregulated several growth factors and hair stem cell markers. hHMSCs activated several molecules in the Wnt/β-catenin signaling pathway, such as in the Wnt families, β-catenin, phosphorylated GSK-3β and cyclin D1, and suppressed the expression of DKK1 induced by IFN-γ in hORSCs. hHMSCs suppressed the phosphorylation of JAK1 to 3, STAT1, and STAT3 compared to the controls and IFN-γ-pretreated hORSCs. These results demonstrate that hHMSCs increased hORSC viability and migration in the in vitro AA model. Additionally, MSCT definitely stimulated anagen survival and hair growth in an HF organ culture model. MSCT appeared to be associated with the Wnt/β-catenin and JAK/STAT pathways in hORSCs.

Immunological Properties of Atopic Dermatitis-Associated Alopecia Areata

Alopecia areata (AA) is regarded as a tissue-specific and cell-mediated autoimmune disorder. Regarding the cytokine balance, AA has been considered a type 1 inflammatory disease. On the other hand, AA often complicates atopic dermatitis (AD) and AD is regarded as type 2 inflammatory disease. However, the immunological aspects of AA in relation to AD are still poorly understood. Therefore, we aim to clarify the immunological properties of AD-associated AA. In this study, we performed comparative analysis of the expression of intracytoplasmic cytokines (IFN-γ, IL-4, and IL-13), chemokine receptors (CXCR3 and CCR4) in peripheral blood which were taken from healthy controls, non-atopic AA patients, AA patients with extrinsic AD, and AA patients with intrinsic AD by flowcytometric analysis. We also compared the scalp skin samples taken from AA patients with extrinsic AD before and after treatment with dupilumab. In non-atopic AA patients, the ratios of CD4+IFN-γ+ cells to CD4⁺IL-4⁺ cells and CD4⁺IFN-γ⁺ cells to CD4⁺IL-13⁺ cells were higher than those in AA patients with extrinsic AD. Meanwhile, the ratio of CD8⁺IFN-γ⁺ cells to CD8+IL-13+ cells was significantly higher in the non-atopic AA than in the healthy controls. In AA patients with extrinsic AD, the skin AA lesion showed dense infiltration of not only CXCR3+ cells but also CCR4⁺ cells around hair bulb before dupilumab treatment. However, after the treatment, the number of CXCR3⁺ cells had no remarkable change while the number of CCR4⁺ cells significantly decreased. These results indicate that the immunological condition of AA may be different between atopic and non-atopic patients and between extrinsic and intrinsic AD patients. Our study provides an important notion that type 2 immunity may participate in the development of AA in extrinsic AD patients. It may be considered that the immunological state of non-atopic AA is different from that of atopic AA.

The Potential Relevance of the Microbiome to Hair Physiology and Regeneration: The Emerging Role of Metagenomics

Human skin and hair follicles are recognized sites of microbial colonization. These microbiota help regulate host immune mechanisms via an interplay between microbes and immune cells, influencing homeostasis and inflammation. Bacteria affect immune responses by controlling the local inflammatory milieu, the breakdown of which can result in chronic inflammatory disorders. Follicular microbiome shifts described in some inflammatory cutaneous diseases suggest a link between their development or perpetuation and dysbiosis. Though the hair follicle infundibulum is an area of intense immunological interactions, bulb and bulge regions represent immune-privileged niches. Immune privilege maintenance seems essential for hair growth and regeneration, as collapse and inflammation characterize inflammatory hair disorders like alopecia areata and primary cicatricial alopecia. Current research largely focuses on immunological aberrations. However, studies suggest that external stimuli and interactions across the follicular epithelium can have profound effects on the local immune system, homeostasis, and cycling. Herein, we review hair follicle bacterial colonization, its possible effects on the underlying tissue, and links to the pathogenesis of alopecia, beyond the pure investigation of specific species abundance. As skin microbiology enters the metagenomics era, multi-dimensional approaches will enable a new level of investigations on the effects of microorganisms and metabolism on host tissue.

Immunopathogenesis of alopecia areata

Alopecia areata (AA) is an autoimmune disorder resulting in hair loss. It has numerous variants or patterns, including diffuse type, patchy type, AA totalis, AA universalis, and more. In this graphical review, we provide an overview of AA immunopathogenesis, highlighting loss of immune privilege in the hair follicle as well as key immune cell types, cytokines and chemokines that drive autoimmune attack of the hair follicle. We also summarize recent literature identifying agents that block these pathways that could serve as new immunomodulatory treatments for AA.

Alopecia areata: a review on diagnosis, immunological etiopathogenesis and treatment options

Patients suffering from alopecia areata (AA) can lose hair in focal regions, the complete scalp, including eyelashes and eyebrows, or even the entire body. The exact pathology is not yet known, but the most described theory is a collapse of the immune privilege system, which can be found in some specific regions of the body. Different treatment options, local and systemic, are available, but none of them have been proven to be effective in the long term as well for every treatment there should be considered for the possible side effects. In many cases, treated or non-treated, relapse often occurs. The prognosis is uncertain and is negatively influenced by the subtypes alopecia totalis and alopecia universalis and characteristics such as associated nail lesions, hair loss for more than 10 years and a positive familial history. The unpredictable course of the disease also makes it a mental struggle and AA patients are more often associated with depression and anxiety compared to the healthy population. Research into immunology and genetics, more particularly in the field of dendritic cells (DC), is recommended for AA as there is evidence of the possible role of DC in the treatment of other autoimmune diseases such as multiple Sclerosis and cancer. Promising therapies for the future treatment of AA are JAK-STAT inhibitors and PRP.

Assessment of treatment efficacy of diphenylcyclopropenone (DPCP) for alopecia areata

Background/aim

Alopecia areata (AA) is an inflammatory disease with a genetic and autoimmune basis. Herein, it was aimed to study the efficacy and safety of an immunomodulatory therapeutic agent, diphenylcyclopropenone, while manifesting its association with histopathological features, prognostic factors, and side effects.

Materials and methods

In this retrospective study, 98 patients (60 males, 38 females) with alopecia, who were referred to the Hair Disease Polyclinic at the Department of Dermatology, between 2011 and 2015, were included. Together with medical histories and dermatological examinations, a skin biopsy for histopathological examination was conducted for all of the patients prior to therapy. Therapeutic success was evaluated on the basis of the hair regrowth percentage.

Results

Regarding the overall treatment success, 33 (34%) patients had complete response, 16 (16%) had partial response (between 50% and 99%), 27 (28%) had minimal response (between 1% and 49%), and 22 (22%) were nonresponders. Both sexs were equally represented in the outcome.

Conclusions

There was a significant relation between the severity of alopecia and the treatment outcome (P = 0.038). Patients with AA had significantly better response when compared to those with alopecia totalis and universalis. There was no statistically significant relation with other parameters, such as disease duration, age, sex, atopy history, age of onset, and histopathological features.

Immune privilege of skin stem cells: What do we know and what can we learn?

The skin forms a barrier that prevents dehydration and keeps us safe from pathogens. To ensure proper function, the skin possesses a myriad of stem cell populations that are essential for maintenance and repair upon damage. In order to protect, the skin is also an active immunological site, with abundant resident immune cells and strong recruitment of even more immune cells during wounding or infection. Such active and strong immunity makes the skin susceptible to a diverse spectrum of autoimmune diseases, such as vitiligo and alopecia areata. Conversely, despite constant immune surveillance, the skin is also a tissue where frequent malignancies occur, which suggests that immune evasion must also take place. Skin stem cells play a crucial role during both regeneration and tumorigenesis. How immune cells, and in particular T cells, interact with skin stem cells and the implications this crosstalk has in skin disease (both autoimmunity and cancer) is not fully understood. Uncovering the mechanisms governing immune-stem cells interactions in the skin is critical for the development of new therapeutic strategies to safeguard susceptible cells during autoimmunity and, conversely, to improve cancer immunotherapy. Here, I will discuss how distinct skin stem cell populations are attacked by, or conversely, cloaked from immune cells, and the implications their differences have in autoimmunity and cancer.

Digital immunohistological dissection of immune privilege collapse in syringotropic autoimmune diseases: Implication for the pathogenesis

BACKGROUND

Syringotropic cell infiltration is a histological hallmark of some autoimmune diseases. However, its underlying mechanism remains unclear.

OBJECTIVES

To assess the immune privilege (IP) of the human sweat gland (SwG) in homeostasis and in syringotropic autoimmune diseases.

METHODS

We combined quantitative digital image microdissection with immunohistochemisty to analyze IP molecule expression in SwG of normal and diseased skin. The human skin organ culture model was used to examine the influence of proinflammatory conditions on IP in SwG.

RESULTS

In the normal subjects (n = 10), major histocompatibility complex (MHC) class І expression was significantly reduced in SwGs compared to the epidermis. In contrast, IP-guardians, macrophage migration inhibitory factor (MIF) and alpha-melanocyte stimulating hormone (α-MSH) were upregulated in SwGs. MHC class І was upregulated in whole SwGs in lupus erythematosus (LE; n = 7) and scleroderma/morphea (Scl; n = 9), whereas differential expression was noted only in the secretory portion in Sjögren's syndrome (SjS) (n = 4). MIF expression level inversely correlated with that of MHC class I in all samples tested, and downregulation of α-MSH was detected in LE SwGs alone. The severity of inflammatory changes and MIF and ⍺-MSH expression were inversely correlated in LE. CD200 expression was decreased exclusively in atrophic stage of Scl. In a human skin organ culture model, intratissue injection of interferon-gamma up-regulated MHC class I and downregulated MIF and α-MSH.

CONCLUSIONS

These findings indicate that SwGs enjoy IP. Dysregulated IP molecule expression may lead to SwG IP collapse and contribute to distinct inflammatory cell distribution in syringotropic autoimmune disorders.

Immunology of alopecia areata

Alopecia areata is a condition that affects hair follicles and leads to hair loss ranging from small well-defined patches to complete loss of all body hair. Despite its high incidence, the pathobiology is not fully understood, and no single concept could be universally accepted.

Alopecia areata is mostly considered to be an autoimmune disease, in which the collapse of hair follicle immune privilege plays a key role. Higher incidence rate in the female population and increased overall risk of other autoimmune disorders militate in favor of autoimmune hypothesis. Antibodies against multiple components of hair follicles almost exclusively attack in anagen phase, where melanogenesis takes place. It suggests involvement of melanogenesis-associated autoantigens as a target epitope.

Some investigators believed that alopecia areata is not a truly autoimmune disease but is only ‘consistent with’ autoimmune mechanisms. High frequency of a positive family history up to 42% may reflects the contribution of heredity factors. In addition, no specific target autoantigen has been identified so far, and autoantibodies to hair follicle-associated antigens are detectable in normal individuals.