Abnormal interactions between perifollicular mast cells and CD8+ T-cells may contribute to the pathogenesis of alopecia areata

Epidermal growth factor receptor/mitogen-activated kinase inhibitor treatment induces a distinct inflammatory hair follicle response that includes collapse of immune privilege

BACKGROUND

Inhibitors of epidermal growth factor receptor (EGFRi) or mitogen-activated kinase (MEKi) induce a folliculitis in 75-90% of patients, the pathobiology of which remains insufficiently understood.

OBJECTIVES

To characterize changes in the skin immune status and global transcriptional profile of patients treated with EGFRi; to investigate whether EGFRi affects the hair follicle's (HF) immune privilege (IP); and to identify early proinflammatory signals induced by EGFRi/MEKi in human scalp HFs ex vivo.

METHODS

Scalp biopsies were taken from patients exhibiting folliculitis treated long term with EGFRi ('chronic EGFRi' group, n = 9) vs. healthy scalp skin (n = 9) and patients prior to commencing EGFRi treatment and after 2 weeks of EGFRi therapy ('acute EGFRi' group, n = 5). Healthy organ-cultured scalp HFs were exposed to an EGFRi (erlotinib, n = 5) or a MEKi (cobimetinib, n = 5). Samples were assessed by quantitative immunohistomorphometry, RNA sequencing (RNAseq) and in situ hybridization.

RESULTS

The 'chronic EGFRi' group showed CD8+ T-cell infiltration of the bulge alongside a partial collapse of the HF's IP, evidenced by upregulated major histocompatibility complex (MHC) class I, β2-microglobulin (B2 M) and MHC class II, and decreased transforming growth factor-β1 protein expression. Healthy HFs treated with EGFRi/MEKi ex vivo also showed partial HF IP collapse and increased transcription of human leucocyte antigen (HLA)-A, HLA-DR and B2 M transcripts. RNAseq analysis showed increased transcription of chemokines (CXCL1, CXCL13, CCL18, CCL3, CCL7) and interleukin (IL)-26 in biopsies from the 'chronic EGFRi' cohort, as well as increased IL-33 and decreased IL-37 expression in HF biopsies from the 'acute EGFRi' group and in organ-cultured HFs.

CONCLUSIONS

The data show that EGFRi/MEKi compromise the physiological IP of human scalp HFs and suggest that future clinical management of EGFRi/MEKi-induced folliculitis requires HF IP protection and inhibition of IL-33.

Innovative strategies for the discovery of new drugs against alopecia areata: taking aim at the immune system

INTRODUCTION

The autoimmune hair loss condition alopecia areata (AA) exacts a substantial psychological and socioeconomic toll on patients. Biotechnology companies, dermatology clinics, and research institutions are dedicated to understanding AA pathogenesis and developing new therapeutic approaches. Despite recent efforts, many knowledge gaps persist, and multiple treatment development avenues remain unexplored.

AREAS COVERED

This review summarizes key AA disease mechanisms, current therapeutic methods, and emerging treatments, including Janus Kinase (JAK) inhibitors. The authors determine that innovative drug discovery strategies for AA are still needed due to continued unmet medical needs and the limited efficacy of current and emerging therapeutics. For prospective AA treatment developers, the authors identify the pre-clinical disease models available, their advantages, and limitations. Further, they outline treatment development opportunities that remain largely unmapped.

EXPERT OPINION

While recent advancements in AA therapeutics are promising, challenges remain, including the lack of consistent treatment efficacy, long-term use and safety issues, drug costs, and patient compliance. Future drug development research should focus on patient stratification utilizing robust biomarkers of AA disease activity and improved quantification of treatment response. Investigating superior modes of drug application and developing combination therapies may further improve outcomes. Spirited innovation will be needed to advance more effective treatments for AA.

IL-33-primed human mast cells drive IL-9 production by CD4+ effector T cells in an OX40L-dependent manner

Interleukin-33 (IL-33) is an alarmin released by epithelial cells in response to tissue damage. It activates resident immune sentinel cells, which then produce signals commonly associated with type 2 immune responses, particularly affecting infiltrating antigen-specific T cells. Given that mast cells (MCs) are a primary target of IL-33 and can shape T helper (Th) cell responses, we investigated the effect of IL-33 priming on the ability of MCs to influence Th cell cytokine production. To examine the Th cell/MC interaction, we developed human primary MC/memory CD4+ T-cell coculture systems involving both cognate and non-cognate interactions. Our results demonstrated that IL-33-primed MCs, whether as bystander cells cocultured with activated effector T cells or functioning as antigen-presenting cells, promoted IL-9 and increased IL-13 production in Th cells via an OX40L-dependent mechanism. This indicates that MCs sense IL-33-associated danger, prompting them to direct Th cells to produce the key type 2 effector cytokines IL-9 and IL-13.

Dandruff lesional scalp skin exhibits epidermal T cell infiltration and a weakened hair follicle immune privilege

OBJECTIVE

Dandruff is characterised by the presence of perivascular leukocytes and mild inflammation; however, the immune microenvironment of dandruff-affected scalp skin and the potential changes to the hair follicle's (HF) physiological immune privilege (HF IP) remain unknown. Here, we characterised the HF immune microenvironment and immune privilege status in dandruff-affected scalp skin.

METHODS

We assessed relevant key parameters in healthy versus dandruff-affected human scalp biopsies using quantitative immunohistomorphometry, laser capture microdissection, and RNA sequencing.

RESULTS

The number of epidermal CD4+ and CD8+ T cells was increased in lesional dandruff scalp skin, while the number of MHC class II+/CD1a+ Langerhans cells was decreased in the infundibulum. The number of intrafollicular and perifollicular CD4+ T cells and CD8+ T cells, perifollicular CD68+ macrophages, and tryptase+ mast cells remained unchanged. Interestingly, MHC class Ia and ß2-microglobulin protein expression were significantly increased specifically in the suprabulbar outer root sheath (ORS) compartment of dandruff-associated HFs. RNAseq analysis of laser capture micro-dissected suprabulbar ORS compartment revealed antigen presentation pathway as the top regulated canonical pathway, along with the upregulation of HF-IP genes such as HLA-C, HLA-DP, and TAP1, which are normally down-regulated in healthy HFs. Intrafollicular protein expression of known HF IP guardians (CD200 and α-MSH) and 'danger signals' (MICA and CXCL10) remained unaltered at the IP sites of dandruff lesional HFs compared to non-lesional and healthy HFs. Instead, the expression of macrophage migration inhibiting factor (MIF), another HF IP guardian, was reduced.

CONCLUSION

Together, this work shows that dandruff is associated with epidermal T-cell infiltration and a weakened HF IP in the suprabulbar ORS of HFs in dandruff lesional scalp.

Mast cells: a double-edged sword in inflammation and fibrosis

As one of the key components of the immune system, mast cells are well known for their role in allergic reactions. However, they are also involved in inflammatory and fibrotic processes. Mast cells participate in all the stages of acute inflammatory responses, playing an immunomodulatory role in both innate and adaptive immunity. Mast cell-derived histamine, TNF-α, and IL-6 contribute to the inflammatory processes, while IL-10 mediates the suppression of inflammation. Crosstalk between mast cells and other immune cells is also involved in the development of inflammation. The cell-cell adhesion of mast cells and fibroblasts is crucial for fibrosis. Mast cell mediators, including cytokines and proteases, play contradictory roles in the fibrotic process. Here, we review the double-edged role of mast cells in inflammation and fibrosis.

Commensal microbe regulation of skin cells in disease

Human skin is the host to various commensal microbes that constitute a substantial microbial community. The reciprocal communication between these microbial inhabitants and host cells upholds both the morphological and functional attributes of the skin layers, contributing indispensably to microenvironmental and tissue homeostasis. Thus, disruption of the skin barrier or imbalances in the microbial communities can exert profound effects on the behavior of host cells. This influence, mediated by the microbes themselves or their metabolites, manifests in diverse outcomes. In this review, we examine existing knowledge to provide insight into the nuanced behavior exhibited by the microbiota on skin cells in health and disease states. These interactions provide insight into potential cellular targets for future microbiota-based therapies to prevent and treat skin disease.

Current Protocols: Alopecia Areata Mouse Models for Drug Efficacy and Mechanism Studies

Alopecia areata is the second most common form of hair loss in humans after androgenetic alopecia. Although a variety of animal models for alopecia areata have been described, currently the C3H/HeJ mouse model is the most commonly used and accepted. Spontaneous hair loss occurs in 15%-25% of older mice in which the lesions wax and wane, similar to the human disease, with alopecia being more common and severe in female mice. Full-thickness skin grafts from mice with spontaneous alopecia areata to young, normal-haired, histocompatible mice provide a highly reproducible model with progressive lesions that makes it useful for drug efficacy and mechanism-based studies. As alopecia areata is a cell-mediated autoimmune disease, transfer of cultured lymph node cells from affected mice to unaffected, histocompatible recipients also promotes disease development and provides an alternative, nonsurgical protocol. Protocols are presented to produce these models such that they can be used to study alopecia areata and to develop novel drug therapies. © 2024 The Author(s). Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: Full-thickness skin grafts to reproducibly induce alopecia areata in C3H/HeJ mice Basic Protocol 2: Adoptive transfer of cultured lymphoid cells provides a nonsurgical method to induce alopecia areata in C3H/HeJ mice.

Spatial Distribution and Functional Impact of Human Scalp Hair Follicle Microbiota

Human hair follicles (HFs) constitute a unique microbiota habitat that differs substantially from the skin surface. Traditional HF sampling methods fail to eliminate skin microbiota contaminants or assess the HF microbiota incompletely, and microbiota functions in human HF physiology remain ill explored. Therefore, we used laser-capture microdissection, metagenomic shotgun sequencing, and FISH to characterize the human scalp HF microbiota in defined anatomical compartments. This revealed significant compartment-, tissue lineage-, and donor age-dependent variations in microbiota composition. Greatest abundance variations between HF compartments were observed for viruses, archaea, Staphylococcus epidermidis, Cutibacterium acnes, and Malassezia restricta, with the latter 2 being the most abundant viable HF colonizers (as tested by propidium monoazide assay) and, surprisingly, most abundant in the HF mesenchyme. Transfection of organ-cultured human scalp HFs with S. epidermidis-specific lytic bacteriophages ex vivo downregulated transcription of genes known to regulate HF growth and development, metabolism, and melanogenesis, suggesting that selected microbial products may modulate HF functions. Indeed, HF treatment with butyrate, a metabolite of S. epidermidis and other HF microbiota, delayed catagen and promoted autophagy, mitochondrial activity, and gp100 and dermcidin expression ex vivo. Thus, human HF microbiota show spatial variations in abundance and modulate the physiology of their host, which invites therapeutic targeting.

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.

Role of neurogenic inflammation in the pathogenesis of alopecia areata

Alopecia areata refers to an autoimmune illness indicated by persistent inflammation. The key requirement for alopecia areata occurrence is the disruption of immune-privileged regions within the hair follicles. Recent research has indicated that neuropeptides play a role in the damage to hair follicles by triggering neurogenic inflammation, stimulating mast cells ambient the follicles, and promoting apoptotic processes in keratinocytes. However, the exact pathogenesis of alopecia areata requires further investigation. Recently, there has been an increasing focus on understanding the mechanisms of immune diseases resulting from the interplay between the nervous and the immune system. Neurogenic inflammation due to neuroimmune disorders of the skin system may disrupt the inflammatory microenvironment of the hair follicle, which plays a crucial part in the progression of alopecia areata.

The mast cell-T lymphocyte axis impacts cancer: Friend or foe?

Crosstalk between mast cells (MCs) and T lymphocytes (TLs) releases specific signals that create an environment conducive to tumor development. Conversely, they can protect against cancer by targeting tumor cells for destruction. Although their role in immunity and cancer is complex, their potential in anticancer strategies is often underestimated. When peripheral MCs are activated, they can affect cancer development. Tumor-infiltrating TLs may malfunction and contribute to aggressive cancer and poor prognoses. One promising approach for cancer patients is TL-based immunotherapies. Recent reports suggest that MCs modulate TL activity in solid tumors and may be a potential therapeutic layer in multitargeting anticancer strategies. Pharmacologically modulating MC activity can enhance the anticancer cytotoxic TL response in tumors. By identifying tumor-specific targets, it has been possible to genetically alter patients' cells into fully humanized anticancer cellular therapies for autologous transplantation, including the engineering of TLs and MCs to target and kill cancer cells. Hence, recent scientific evidence provides a broader understanding of MC-TL activity in cancer.

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.

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.

Identifying immuno-related diagnostic genes and immune infiltration signatures for periodontitis and alopecia areata

BACKGROUND

Although there have been indications that periodontitis (PD) may be susceptible to alopecia areata (AA), the underlying mechanism of its pathogenesis remains poorly understood. The objective of our study is to conduct further research into the occurrence of this complication.

METHODS

The gene expression omnibus (GEO) database was the source of acquisition for both PD and AA datasets. Various methods, including the differentially expressed genes (DEGs) analysis, functional enrichment analysis, protein-protein interaction (PPI) network construction, Cytohubba algorithms, and RandomForest algorithms, were utilized to identify candidate hub immuno-related genes (IRGs) for diagnosing AA with PD. The diagnostic efficacy was assessed by constructing receiver operating characteristic (ROC) curves. To further deepen our understanding, immune cell infiltration, flow cytometry assay, and immunofluorescence techniques were employed to uncover immune cell dysregulation in PD and AA.

RESULTS

899 and 803 DEGs were detected in AA and PD, respectively, with an intersection of 150 common DEGs enriched in immune regulation. Further analysis of the junction of shared DEGs and IRGs was analyzed using the PPI network, Mcode, and Cytohubba algorithms. Three hub genes (CTSS, IL2RG, and ITGAL) were subsequently selected by Cytohubba and RandomForest algorithms and were found to be promising candidate hub genes with high diagnostic values (AUC ranging from 0.776 to 0.909) for diagnosing AA with PD. Additionally, various dysregulated immune cells were observed, with mast cells potentially serving as markers for AA and plasma for PD.

CONCLUSION

Three candidate hub IRGs (CTSS, IL2RG, and ITGAL) were identified with considerable diagnostic values. Besides, mast cells could serve as markers for AA, while plasma may indicate PD. Our research has the potential to identify shared diagnostic candidate genes and immune cells for AA and PD patients.

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.

Psychological Stress-Induced Pathogenesis of Alopecia Areata: Autoimmune and Apoptotic Pathways

Alopecia areata (AA) is an autoimmune dermatological disease with multifactorial etiology and is characterized by reversible hair loss in patches. AA may be closely related to emotional stress and influenced by psychological factors as part of its pathophysiology; however, its etiology remains predominantly unknown. This review aimed to elucidate the association between AA occurrence and the neuropeptide substance P (SP) and corticotropin-releasing hormone (CRH), which are secreted during emotional stress, and have been understood to initiate and advance the etiopathogenesis of AA. Therefore, this review aimed to explain how SP and CRH initiate and contribute to the etiopathogenesis of AA. To assess the etiopathogenesis of AA, we conducted a literature search on PubMed and ClinicalTrials.gov. Overall, several authors described interactions between the hair follicles (HFs) and the stress-associated signaling substances, including SP and CRH, in the etiology of AA; this was attributed to the understanding in that AA can occur without the loss of HFs, similar to that observed in hereditary hair loss with age. Most studies demonstrated that the collapse of "immune privilege" plays a crucial role in the development and exacerbation of the AA; nonetheless, a few studies indicated that substances unrelated to autoimmunity may also cause apoptosis in keratocytes, leading to the development of AA. We investigated both the autoimmune and apoptotic pathways within the etiology of AA and assessed the potential interactions between the key substances of both pathways to evaluate potential therapeutic targets for the treatment of AA. Clinical trials of marketed/unreviewed intervention drugs for AA were also reviewed to determine their corresponding target pathways.

Construction of regulatory network for alopecia areata progression and identification of immune monitoring genes based on multiple machine-learning algorithms

Objectives

Alopecia areata (AA) is an autoimmune-related non-cicatricial alopecia, with complete alopecia (AT) or generalized alopecia (AU) as severe forms of AA. However, there are limitations in early identification of AA, and intervention of AA patients who may progress to severe AA will help to improve the incidence rate and prognosis of severe AA.

Methods

We obtained two AA-related datasets from the gene expression omnibus database, identified the differentially expressed genes (DEGs), and identified the module genes most related to severe AA through weighted gene co-expression network analysis. Functional enrichment analysis, construction of a protein-protein interaction network and competing endogenous RNA network, and immune cell infiltration analysis were performed to clarify the underlying biological mechanisms of severe AA. Subsequently, pivotal immune monitoring genes (IMGs) were screened through multiple machine-learning algorithms, and the diagnostic effectiveness of the pivotal IMGs was validated by receiver operating characteristic.

Results

A total of 150 severe AA-related DEGs were identified; the upregulated DEGs were mainly enriched in immune response, while the downregulated DEGs were mainly enriched in pathways related to hair cycle and skin development. Four IMGs (LGR5, SHISA2, HOXC13, and S100A3) with good diagnostic efficiency were obtained. As an important gene of hair follicle stem cells stemness, we verified in vivo that LGR5 downregulation may be an important link leading to severe AA.

Conclusion

Our findings provide a comprehensive understanding of the pathogenesis and underlying biological processes in patients with AA, and identification of four potential IMGs, which is helpful for the early diagnosis of severe AA.

Nivolumab-Induced Lichen Planopilaris: Case Report and Literature Review of Hair Disorders Associated with Targeted Oncological Therapies

Immune checkpoint inhibitors (ICIs) have revolutionized cancer therapies. Their mechanism promotes a cytotoxic T-cell activation against the tumor cells, but as a consequence, immune-mediated toxicities are increasingly being identified. Cutaneous immune-mediated adverse events (AE) occur in 32% of patients, with possible higher grade AEs seen with anti-programmed cell death protein 1, such as nivolumab. A 67-year-old woman with metastatic melanoma, previously treated for 2 years on dual ICI (ipilimumab and nivolumab), had her treatment interrupted due to grade-3 hepatitis. She was subsequently recommenced on single-agent nivolumab with good response, before discontinuation due to remission. She reported worsening scalp pruritus with associated erythema, scaling, and global hair thinning. On examination, she had significant erythema throughout the scalp with perifollicular scaling and evidence of scarring. She reported severe distress from her symptoms. Her scalp biopsy demonstrated features of scarring alopecia with infundibular and isthmic inflammation and interface change in keeping with lichen planopilaris. Follicular toxicities are rarely reported, possibly due to imprecise AE phenotyping or underreporting. However, growing evidence suggests that patients can develop follicular pigmentary changes and nonscarring alopecia. To our knowledge, this is the first case of scarring alopecia reported with nivolumab. Current treatments for ICI-induced toxicities are limited.

Allergen desensitization reduces the severity of relapsed alopecia areata in dust-mite allergic patients

Atopy may be a facilitating factor in some alopecia areata (AA) patients with early disease onset and more severe/extensive AA. The underlying immune mechanisms are unknown, but allergen responses may support a pro-inflammatory environment that indirectly promotes AA. To investigate the long-term effect of allergen immunotherapy (AIT) against house dust mite (HDM) allergy on disease severity and prognosis for AA patients. An observational comparative effectiveness study was conducted on 69 AA patients with HDM allergy. 34 patients received conventional/traditional AA treatment (TrAA) plus AIT (AIT-TrAA), and 35 patients received TrAA alone. Serum total immunoglobulin E (tIgE), HDM specific IgE (sIgE), HDM specific IgG4 (sIgG4) and cytokines (IL-4, IL-5, IL-10, IL-12, IL-13, IL-33, IFNγ) were quantified in these patients, together with 58 non-allergic AA patients and 40 healthy controls. At the end of the 3-year desensitization course, the AIT-TrAA group presented with lower SALT scores than the TrAA group, especially in non-alopecia totalis/universalis (AT/U) patients and pre-adolescent AT/U patients (age ≤ 14). In patients with elevated tIgE levels before AIT, a decrease in tIgE was correlated to reduced extent of AA on completion of the AIT course. After desensitization, elevation of IL-5 and decrease of IL-33 were observed in HDM allergic-AA patients. Desensitization to HDM in allergic AA patients reduces the severity of relapse-related hair loss over the 3-year AIT treatment course, possibly via opposing Th2 dominance. This adjunctive treatment may help reduce disease severity and curtail the disease process in allergic patients with AA.

Diverse Role of OX40 on T Cells as a Therapeutic Target for Skin Diseases

OX40 is an important costimulatory molecule for T-cell expansion and survival. Because OX40 is expressed on most T-cell subsets, it is an attractive therapeutic target for a variety of T-cell‒mediated diseases. Clinical trials are already underway for some skin inflammatory diseases. In this review, we present various observations that improve our understanding of how OX40-targeted therapy can be applied for skin inflammatory diseases, such as atopic dermatitis and psoriasis, T helper (Th)2- and Th17-mediated diseases, respectively. The important OX40/OX40L-mediated interaction between T cells and other immune cells is also discussed in terms of skin autoimmune diseases, such as alopecia areata and pemphigus. Regulatory T cells (Tregs) highly express OX40, and the skin harbors a large Treg population; thus, understanding how OX40-targeted treatment acts on Tregs is vital for the development of therapeutic strategies for various skin diseases.

AIRE Deficiency Leads to the Development of Alopecia Areata‒Like Lesions in Mice

Alopecia areata (AA) is an autoimmune hair loss disorder with no cure. Patients with sequence variation in AIRE are 15 times more likely to develop AA than the general population, yet the roles of AIRE in AA pathogenesis are unknown. In this study, we report that 62% of C57BL/6J female Aire^‒/‒ mice spontaneously developed persistent AA-like lesions that displayed several hallmarks of human AA. Lesional Aire^‒/‒ skin exhibited hair follicle (HF) dystrophy as determined by a reduced number of anagen HFs, decreased anagen HF proliferation, hair pigmentary changes, and decreased hair width and length. Inflammatory infiltrate comprising CD8⁺ T cells, CD4⁺ T cells, CD68⁺ macrophages, and mast cells was prominent in lesional Aire^‒/‒ HFs. From gene expression analyses, we found lesional Aire^‒/‒ skin to have significantly increased expression of human AA signature genes, including H2-Ab1, Ifnγ, IFN-γ‒induced chemokines (Ccl5, Cxcl9‒11), γ_c family cytokine receptor Il2RA, and JAK‒signal transducer and activator of transcription (STAT) signaling components (Stat1, Stat2, Stat4). By immunostaining, lesional Aire^‒/‒ HFs also show upregulated major histocompatibility complex class I and downregulated α-melanocyte-stimulating hormone, signifying immune privilege collapse, and increased STAT1 activation in HF keratinocytes. Our study highlights a role for AIRE in HF biology and shows that Aire^‒/‒ mice may serve as a valuable model system to study AA pathogenesis.

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.

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

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

Topical SCD-153, a 4-methyl itaconate prodrug, for the treatment of alopecia areata

Alopecia areata is a chronic hair loss disorder that involves autoimmune disruption of hair follicles by CD8⁺  T cells. Most patients present with patchy hair loss on the scalp that improves spontaneously or with topical and intralesional steroids, topical minoxidil, or topical immunotherapy. However, recurrence of hair loss is common, and patients with extensive disease may require treatment with oral corticosteroids or oral Janus kinase (JAK) inhibitors, both of which may cause systemic toxicities with long-term use. Itaconate is an endogenous molecule synthesized in macrophages that exerts anti-inflammatory effects. To investigate the use of itaconate derivatives for treating alopecia areata, we designed a prodrug of 4-methyl itaconate (4-MI), termed SCD-153, with increased lipophilicity compared to 4-MI (CLogP 1.159 vs. 0.1442) to enhance skin and cell penetration. Topical SCD-153 formed 4-MI upon penetrating the stratum corneum in C57BL/6 mice and showed low systemic absorption. When added to human epidermal keratinocytes stimulated with polyinosinic-polycytidylic acid (poly I:C) or interferon (IFN)γ, SCD-153 significantly attenuated poly I:C-induced interleukin (IL)-6, Toll-like receptor 3, IL-1β, and IFNβ expression, as well as IFNγ-induced IL-6 expression. Topical application of SCD-153 to C57BL/6 mice in the resting (telogen) phase of the hair cycle induced significant hair growth that was statistically superior to vehicle (dimethyl sulfoxide), the less cell-permeable itaconate analogues 4-MI and dimethyl itaconate, and the JAK inhibitor tofacitinib. Our results suggest that SCD-153 is a promising topical candidate for treating alopecia areata.

Prevalence, comorbidities, and treatment patterns of Japanese patients with alopecia areata: A descriptive study using Japan medical data center claims database

Real-world data on alopecia areata (AA) demographics, comorbidities, and treatment patterns are sparse, not only in Japan but worldwide. This cross-sectional study assessed the current prevalence of AA in Japan, including analysis of severe subsets, frequency of comorbidities, and unmet medical needs surrounding treatment. Patients registered in the Japan Medical Data Center claims database (January 2012 to December 2019) and diagnosed with AA were included. Prevalence was calculated yearly, with the most common comorbidities evaluated, and treatments described in the Japanese Dermatological Association AA management guidelines and approved in Japan were included in the analysis. In total, 61 899 patients were diagnosed with AA. Among them, 1497 were diagnosed with severe subtypes. AA prevalence in Japan has been gradually increasing (from 0.16% in 2012 to 0.27% in 2019). The most common comorbidities are allergic rhinitis, atopic dermatitis, and asthma. Depression and anxiety are frequent in these patients, as are autoimmune diseases, e.g., vitiligo, thyroid diseases, and rheumatoid arthritis. Intriguingly, the analysis found Down syndrome to be a comorbidity associated with severe AA in children. The principal treatments were topical corticosteroids, followed by carpronium chloride and cepharanthine. The use of systemic corticosteroids and antihistamines is increased in severe disease. The Japanese Dermatological Association guidelines do not support the use of oral corticosteroids in children; however, in the database, this has been prescribed in up to 2.5% and 9.8% of all pediatric and severe pediatric AA cases, respectively. Despite the limitations of using a claims database, the current study demonstrates that AA prevalence in Japan has gradually increased in recent years, with allergic diseases being the most common comorbidities. The data also imply that there is a need for effective and safe therapies, especially for severe and pediatric cases.

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.

The expanding impact of T-regs in the skin

As the interface between the body and the environment, the skin functions as the physical barrier against external pathogens and toxic agents. In addition, the skin is an immunologically active organ with a plethora of resident adaptive and innate immune cells, as well as effector molecules that provide another layer of protection in the form of an immune barrier. A major subpopulation of these immune cells are the Foxp3 expressing CD4 T cells or regulatory T cells (T-regs). The canonical function of T-regs is to keep other immune cells in check during homeostasis or to dissipate a robust inflammatory response following pathogen clearance or wound healing. Interestingly, recent data has uncovered unconventional roles that vary between different tissues and we will highlight the emerging non-lymphoid functions of cutaneous T-regs. In light of the novel functions of other immune cells that are routinely being discovered in the skin, their regulation by T-regs implies that T-regs have executive control over a broad swath of biological activities in both homeostasis and disease. The blossoming list of non-inflammatory functions, whether direct or indirect, suggests that the role of T-regs in a regenerative organ such as the skin will be a field ripe for discovery for decades to come.

Intermediate Hair Follicles from Patients with Female Pattern Hair Loss Are Associated with Nutrient Insufficiency and a Quiescent Metabolic Phenotype

Female pattern hair loss (FPHL) is a non-scarring alopecia resulting from the progressive conversion of the terminal (t) scalp hair follicles (HFs) into intermediate/miniaturized (i/m) HFs. Although data supporting nutrient deficiency in FPHL HFs are lacking, therapeutic strategies are often associated with nutritional supplementation. Here, we show by metabolic analysis that selected nutrients important for hair growth such as essential amino acids and vitamins are indeed decreased in affected iHFs compared to tHFs in FPHL scalp skin, confirming nutrient insufficiency. iHFs also displayed a more quiescent metabolic phenotype, as indicated by altered metabolite abundance in freshly collected HFs and release/consumption during organ culture of products/substrates of TCA cycle, aerobic glycolysis, and glutaminolysis. Yet, as assessed by exogenous nutrient supplementation ex vivo, nutrient uptake mechanisms are not impaired in affected FPHL iHFs. Moreover, blood vessel density is not diminished in iHFs versus tHFs, despite differences in tHFs from different FPHL scalp locations or versus healthy scalp or changes in the expression of angiogenesis-associated growth factors. Thus, our data reveal that affected iHFs in FPHL display a relative nutrient insufficiency and dormant metabolism, but are still capable of absorbing nutrients, supporting the potential of nutritional supplementation as an adjunct therapy for FPHL.

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.

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.

Lesson to Learn From Cellular infiltrate in Scalp Biopsy of Alopecia Areata

BACKGROUND

Alopecia areata (AA) is a common cause of hair loss. It is mediated by T lymphocytes. Scalp biopsy findings in AA differ according to the disease phase and activity.

OBJECTIVES

To study the cellular infiltrate in the transverse section of scalp biopsy of AA at different disease stages and in relation to disease activity.

METHODS

The study was performed on 40 subjects with AA. A 4-mm punch biopsy was obtained from an AA scalp lesion. Biopsies were sectioned horizontally; 2 anatomical levels were studied (mid dermal and deep dermal levels).

RESULTS

Ninety-five percent of AA showed noncicatrical alopecia. A significant relation was found between the course of AA and the terminal:vellus ratio. Peribulbar lymphocytic infiltration was seen in 70% of cases. Mast cells were observed in 87.5% of cases, including fibrous tract and around the arrector pili muscles. Eosinophils were detected in the scalp biopsy of 22.5% of cases. Course and activity of AA were significantly related to the peribulbar lymphocytic cell infiltration but not to mast cells and eosinophils.

CONCLUSION

Although a peribulbar lymphocytic infiltrate is the classical finding of AA, it is absent in the chronic phase. Mast cells are commonly found in the scalp biopsy of AA and could explain the potential therapeutic effect of antihistamines.

An integrated scalp and blood biomarker approach suggests the systemic nature of alopecia areata

BACKGROUND

Alopecia areata (AA) is characterized by immune dysregulation in both scalp and blood, but a large-scale approach establishing biomarkers of AA incorporating both scalp tissue and serum compartments is lacking. We aimed to characterize the transcriptomic signature of AA lesional and nonlesional scalp compared to healthy scalp and determine its relationship with the blood proteome in the same individuals, with comparative correlations to clinical AA disease severity.

METHODS

We evaluated lesional and nonlesional scalp tissues and serum from patients with moderate-to-severe AA (n = 18) and healthy individuals (n = 8). We assessed 33,118 genes in AA scalp tissue using RNAseq transcriptomic evaluation and 340 inflammatory proteins in serum using OLINK high-throughput proteomics. Univariate and multivariate approaches were used to correlate disease biomarkers with Severity of Alopecia Tool (SALT).

RESULTS

A total of 608 inflammatory genes were differentially expressed in lesional AA scalp (fold change/FCH>1.5, false discovery rate/FDR<0.05) including Th1 (IFNG/IL12B/CXCL11), Th2 (IL13/CCL18), and T-cell activation-related (ICOS) products. Th1/Th2-related markers were significantly correlated with AA clinical severity in lesional/nonlesional tissue, while keratins (KRT35/KRT83/KRT81) were significantly downregulated in lesional compared to healthy scalp (p < .05). Expression of cardiovascular/atherosclerosis-related markers (MMP9/CCL2/IL1RL1/IL33R/ST2/AGER) in lesional scalp correlated with their corresponding serum expression (p < .05). AA scalp demonstrated significantly greater biomarker dysregulation compared to blood. An integrated multivariate approach combining scalp and serum biomarkers improved correlations with disease severity/SALT.

CONCLUSION

This study contributes a unique understanding of the phenotype of moderate-to-severe AA with an integrated scalp and serum biomarker model suggesting the systemic nature of the disease, advocating for the need for immune-based systemic treatment.

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.

Alopecia Areata: an Update on Etiopathogenesis, Diagnosis, and Management

Alopecia areata (AA) is a common chronic tissue-specific autoimmune disease, resulting in hair loss, that affects up to 2% of the general population. The exact pathobiology of AA has still remained elusive, while the common theory is the collapse of the immune privilege of the hair follicle caused by immunological mechanism. Multiple genetic and environment factors contribute to the pathogenesis of AA. There are several clinical treatments for AA, varying from one or multiple well-defined patches to more diffuse or total hair loss of the scalp (alopecia totalis) or hair loss of the entire body (alopecia universalis). The available treatments for AA, such as corticosteroids and other immunomodulators, minoxidil, and contact immunotherapy, are of limited efficacy with a high risk of adverse effects and high recurrence rates, especially for patients with severe AA. Recent insights into the pathogenesis of AA have led to the development of new treatment strategies, such as Janus kinase (JAK) inhibitors, biologics, and several small molecular agents. In addition, modern therapies for AA, including antihistamines, platelet-rich plasma (PRP) injection, and other novel therapies have been well explored. In this review, we discussed the recent advances in the pathogenesis, diagnosis, and treatment of AA.

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.

Data assimilation of synthetic data as a novel strategy for predicting disease progression in alopecia areata

The goal of patient-specific treatment of diseases requires a connection between clinical observations with models that are able to accurately predict the disease progression. Even when realistic models are available, it is very difficult to parameterize them and often parameter estimates that are made using early time course data prove to be highly inaccurate. Inaccuracies can cause different predictions, especially when the progression depends sensitively on the parameters. In this study, we apply a Bayesian data assimilation method, where the data are incorporated sequentially, to a model of the autoimmune disease alopecia areata that is characterized by distinct spatial patterns of hair loss. Using synthetic data as simulated clinical observations, we show that our method is relatively robust with respect to variations in parameter estimates. Moreover, we compare convergence rates for parameters with different sensitivities, varying observational times and varying levels of noise. We find that this method works better for sparse observations, sensitive parameters and noisy observations. Taken together, we find that our data assimilation, in conjunction with our biologically inspired model, provides directions for individualized diagnosis and treatments.

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.

Use of H-1 Antihistamine in Dermatology: More than Itch and Urticaria Control: A Systematic Review

H-1 antihistamines are commonly used in dermatological practice for itch and urticaria control. The widespread expression of H-1 receptor on different cells in the skin and various biologic functions of H-1 antihistamines indicate the possible treatment potentials of H-1 antihistamines in dermatology. A literature search was performed on PubMed and Embase, targeting articles reporting use of antihistamine for purposes other than itch and urticaria control in dermatological practice. Several off-label usages of antihistamines were identified, including alopecia, acne, Darier disease, eosinophilic dermatoses, paraneoplastic dermatoses, psoriasis, lichen nitidus, radiation dermatitis, skin dysesthesia, and cutaneous malignancies. Additional benefits were observed when H-1 antihistamines were used either alone or in combination with other therapeutic modalities. Although various novel uses of H-1 antihistamines have been uncovered, the evidence level of most included studies is weak. Further randomized control trials are warranted to better evaluate the efficacy and dosage of H-1 antihistamine for dermatological disorders.

Stress and Nasal Allergy: Corticotropin-Releasing Hormone Stimulates Mast Cell Degranulation and Proliferation in Human Nasal Mucosa

Psychological stress exacerbates mast cell (MC)-dependent inflammation, including nasal allergy, but the underlying mechanisms are not thoroughly understood. Because the key stress-mediating neurohormone, corticotropin-releasing hormone (CRH), induces human skin MC degranulation, we hypothesized that CRH may be a key player in stress-aggravated nasal allergy. In the current study, we probed this hypothesis in human nasal mucosa MCs (hM-MCs) in situ using nasal polyp organ culture and tested whether CRH is required for murine M-MC activation by perceived stress in vivo. CRH stimulation significantly increased the number of hM-MCs, stimulated both their degranulation and proliferation ex vivo, and increased stem cell factor (SCF) expression in human nasal mucosa epithelium. CRH also sensitized hM-MCs to further CRH stimulation and promoted a pro-inflammatory hM-MC phenotype. The CRH-induced increase in hM-MCs was mitigated by co-administration of CRH receptor type 1 (CRH-R1)-specific antagonist antalarmin, CRH-R1 small interfering RNA (siRNA), or SCF-neutralizing antibody. In vivo, restraint stress significantly increased the number and degranulation of murine M-MCs compared with sham-stressed mice. This effect was mitigated by intranasal antalarmin. Our data suggest that CRH is a major activator of hM-MC in nasal mucosa, in part via promoting SCF production, and that CRH-R1 antagonists such as antalarmin are promising candidate therapeutics for nasal mucosa neuroinflammation induced by perceived stress.

Compartmentalised metabolic programmes in human anagen hair follicles: New targets to modulate epithelial stem cell behaviour, keratinocyte proliferation and hair follicle immune status?

Human scalp hair follicles (HF) preferentially engage in glycolysis followed by lactate production in the presence of oxygen (i.e. the Warburg effect). Through the spatiotemporally controlled expression of key metabolic proteins, we hypothesise that the Warburg effect and other HF metabolic programmes are compartmentalised by region in order to regulate regional cell fate and phenotypes, such as epithelial stem cell quiescence in the bulge or keratinocyte proliferation in the hair matrix. We further propose that metabolic conditions in the HF are organised in accordance with the lactate shuttle, hypothesised to occur in other tissue systems and tumours, but never before described in the HF. Specifically, we argue that lactate is produced and exported by glycolytic GLUT1+ lower outer root sheath (ORS) keratinocytes. We further propose that lactate is then utilised by neighbouring highly proliferative matrix keratinocytes to fuel oxidative metabolism via MCT1-mediated uptake. Furthermore, as lactate has been described to be immunomodulatory, its production and accumulation could enhance immune tolerance in the HF bulb. Here we delineate how to experimentally probe this hypothesis, define major open questions and present preliminary immunohistological evidence in support of metabolic compartmentalisation and lactate shuttling. Overall, we argue that basic and translational hair research needs to rediscover the importance of lactate in human HF biology, well beyond its recognised role in murine HF epithelial stem cells, and should explore how HF metabolism can be therapeutically targeted to modulate hair growth and the immunological HF microenvironment as a novel strategy for managing hair loss disorders.

Infiltration of Mast Cells in Scalp Biopsies of Patients with Alopcia Areata or Androgenic Alopecia Versus Healthy Individuals: A Case Control Study

BACKGROUND

Alopecia areata (AA) and androgenic alopecia (AGA) are of the most common types of alopecias. Recently, the role of mastcells in inflammatory diseases has become the focus of many studies. However, few studies have been conducted on their role in AA and AGA. Therefore, our study aimed to quantitatively evaluate the presence of mastcells in the AA and AGA specimens.

MATERIALS AND METHODS

Three groups of AA, AGA, and healthy control were studied (each group with 20 subjects). Patients were randomly selected from those referred to the dermatology clinics of Shahid Beheshti University. Specimens were obtained from the scalp, and perifollicular and perivascular areas were investigated.

RESULTS

Significantly higher perifollicular and perivascular mastcell counts were seen in both AGA and AA groups as compared to healthy control (P<0.001 for both). Moreover, AA patients had more frequent perivascular mastcells than the AGA group (P=0.042). Among patients aged <40 years, perifollicular and perivascular mastcell counts were not significantly different among three groups; however, subjects over 40 years of age in both groups had significantly more perifollicular and perivascular mastcells than healthy participants. There was a significant positive correlation between disease severity and mast cell counts in both perifollicular and perivascular areas in AA patients (P=0.001 for both).

CONCLUSION

There is a significantly increased infiltration of mastcells in AA and AGA patients, and this increase is age and severity dependent. Moreover, the increase in mastcell proliferation is more dominant in AA patients.

Pro-inflammatory Vδ1+T-cells infiltrates are present in and around the hair bulbs of non-lesional and lesional alopecia areata hair follicles

BACKGROUND

It is widely accepted that NKG2D⁺cells are critically involved in alopecia areata (AA) pathogenesis. However, besides being expressed in CD8⁺T-cells and NK cells, NKG2D is also found in human γδT-cells. AA lesional hair follicles (HFs) overexpress NKG2D and γδTCR activating ligands, e.g. MICA and CD1d, and chemoattractants for γδT-cells, such as CXCL10.

OBJECTIVE

To investigate whether abnormal activities of γδT-cells may be involved in AA pathogenesis.

METHODS

We analyzed the number and activation status of γδT-cells in human healthy, lesional and non-lesional AA scalp biopsies by FACS and/or quantitative (immuno-)histomorphometry.

RESULTS

In healthy human scalp skin, the few skin-resident γδT-cells were found to be mostly Vδ1⁺, non-activated (CD69^-NKG2D^dim) and positive for CXCL10, and CXCL12 receptors. These Vδ1⁺T-cells predominantly localized in/around the HF infundibulum. In striking contrast, the number of Vδ1⁺T-cells was significantly higher around and even inside the proximal (suprabulbar and bulbar) epithelium of lesional AA HFs. These cells also showed a pro-inflammatory phenotype, i.e. higher NKG2D, and IFN-γ and lower CD200R expression. Importantly, more pro-inflammatory Vδ1⁺T-cells were seen also around non-lesional AA HFs. Lesional AA HFs also showed significantly higher expression of CXCL12.

CONCLUSION

Our pilot study introduces skin-resident γδT-cells as a previously overlooked, but potentially important, mostly (auto-)antigen-independent, new innate immunity protagonist in AA pathobiology. The HF infiltration of these activated, IFN-γ-releasing cells already around non-lesional AA HFs suggest that Vδ1⁺T-cells are involved in the early stages of human AA pathobiology, and may thus deserve therapeutic targeting for optimal AA management.

The Mast Cell-SCF-CB1 Interaction Is a Key Player in Seborrheic Keratosis

Mast cell (MC) is an important player in the development of skin diseases, including atopic dermatitis, psoriasis, and urticaria. It is reported that MC infiltration and activation are observed around various types of tumors and speculated that MCs play key roles in their pathogenesis. As MCs in human seborrheic keratosis (SK) have not been well investigated, here we focused on the MCs in SK. The number of c-Kit and tryptase-positive MCs was significantly increased around the SK compared with the marginal lesion. Degranulated MCs were also increased around the tumors. Furthermore, MC growth factor, stem cell factor (SCF), expression within the SK was significantly upregulated compared with the marginal lesion. Interestingly, one of the cognitive regulators of SCF expression, cannabinoid receptor type 1 (CB1) immunoreactivity was downregulated within the SK. Our results suggest that MCs play important roles in the pathogenesis of SK and that SCF can be also deeply involved in the development of SKs. Our current results highlight the CB1-SCF-MC interaction as a novel mechanism of SK development and this also will be utilized for developing a novel treatment.