Alopecia areata: Animal models illuminate autoimmune pathogenesis and novel immunotherapeutic strategies

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.

Mendelian randomization study highlights hypothyroidism as a causal determinant of alopecia areata

Background

Although observational studies have found an association between hypothyroidism and alopecia areata, the causality of this relationship remains unclear.

Objectives

This study aimed to investigate the genetic variants associated with hypothyroidism and their potential impact on the risk of developing alopecia areata.

Methods

genome-wide association study summary statistics for hypothyroidism (30,155 cases and 379,986 controls) and alopecia areata (289 cases and 211,139 controls) were obtained from the IEU OpenGwas project. The inverse variance-weighted method was used as the primary analysis method to evaluate the causality between hypothyroidism and alopecia areata, supplemented by the weighted median, MR-Egger, simple mode and weighted mode. Furthermore, the function of causal SNPs was evaluated by gene ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, and protein-protein interaction networks.

Result

Utilizing two-sample Mendelian randomization analysis, we found that the single-nucleotide polymorphisms (SNPs) of hypothyroidism (OR = 1.40, 95% CI: 1.12-1.75, p = 3.03×10-3) significantly increased the risk of alopecia areata ( 289 cases and 211,139 controls ). KEGG pathway analysis showed that the candidate genes were mainly enriched in virion-herpesvirus, Th1 and Th2 cell differentiation, Th17 cell differentiation, T-cell receptor signaling pathway, PD-L1/PD-1 checkpoint pathway in cancer and Toll-like receptor signaling pathway. Protein-protein interaction networks results showed that CTLA4, STAT4, IL2RA, TYK2, IRF7, SH2B3, BACH2, TLR3, NOD2, and FLT3.

Conclusion

This study provided compelling genetic evidence supporting a causative association between hypothyroidism and alopecia areata, which could potentially inform the development of more efficacious treatment strategies for patients afflicted by alopecia areata.

A randomized, double-blind, placebo-controlled phase II study to evaluate the efficacy and safety of ivarmacitinib (SHR0302) in adult patients with moderate-to-severe alopecia areata

BACKGROUND

Alopecia areata (AA) is a CD8+ T cell-mediated autoimmune disease characterized by nonscarring hair loss. Ivarmacitinib, which is a selective oral Janus kinase 1 inhibitor, may interrupt certain cytokine signaling implicated in the pathogenesis of AA.

OBJECTIVE

To evaluate the efficacy and safety of ivarmacitinib in adult patients with AA who have ≥25% scalp hair loss.

METHODS

Eligible patients were randomized 1:1:1:1 to receive ivarmacitinib 2, 4, or 8 mg once daily or placebo for 24 weeks. The primary end point was the percentage change from baseline in the Severity of Alopecia Tool score at week 24.

RESULTS

A total of 94 patients were randomized. At week 24, the least squares mean difference in the percentage change from baseline in the Severity of Alopecia Tool score for ivarmacitinib 2, 4, and 8 mg and placebo groups were -30.51% (90% CI, -45.25, -15.76), -56.11% (90% CI, -70.28, -41.95), -51.01% (90% CI, -65.20, -36.82), and -19.87% (90% CI, -33.99, -5.75), respectively. Two serious adverse events-follicular lymphoma and COVID-19 pneumonia-were reported.

LIMITATIONS

A small sample size limits the generalizability of the results.

CONCLUSION

Treatment with ivarmacitinib 4 and 8 mg doses in patients with moderate and severe AA for 24 weeks was efficacious and generally tolerated.

Efficacy and safety of baricitinib in patients with alopecia areata: evidence to date

Alopecia areata (AA) is a chronic, tissue-specific autoimmune disorder, characterized by non-scaring hair loss, with a global prevalence of approximately 2%. Typically, it affects a young population, with initial onset frequently occurring before the age of 30 years. Even though the exact pathogenesis of AA remains unclear, the predominant hypothesis is the breakdown of immune privilege of the hair follicle, resulting in increased self-antigen and major histocompatibility complex expression in the follicular epithelium. The relapsing nature of the disease negatively impacts patients' quality of life and makes them more susceptible to developing psychiatric comorbidities. Although many treatment modalities have been proposed, there are no currently available treatments able to induce and sustain disease remission. Traditional treatment modalities, despite being widely used, present limited results and a high risk of adverse effects. Hence, there exists an unfulfilled requirement for treatments that are both more efficient and safer. The latest understanding of the pathophysiology of AA and its connection to the JAK-STAT pathway has prompted the advancement of JAK inhibitors. These small-molecule agents function by obstructing the JAK-STAT intracellular signalling pathway. Baricitinib an orally administered, selective JAK1 and JAK2 inhibitor is a promising alternative to the available treatments, and is already approved for the treatment of AA.

mTOR signaling in hair follicle and hair diseases: recent progress

Mammalian target of rapamycin (mTOR) signaling pathway is a major regulator of cell proliferation and metabolism, playing significant roles in proliferation, apoptosis, inflammation, and illness. More and more evidences showed that the mTOR signaling pathway affects hair follicle circulation and maintains the stability of hair follicle stem cells. mTOR signaling may be a critical cog in Vitamin D receptor (VDR) deficiency-mediated hair follicle damage and degeneration and related alopecia disorders. This review examines the function of mTOR signaling in hair follicles and hair diseases, and talks about the underlying molecular mechanisms that mTOR signaling regulates.

Clinical and histopathological investigation of symmetrical alopecia with associated chronic pruritus in tufted capuchin monkeys (Sapajus apella apella)

BACKGROUND

Symmetrical alopecia is a common symptom of endocrine and autoimmune diseases, which are rarely manifested with pruritus. Increased levels of stress in primates have been presented with increased levels of pruritus and alopecia appearance.

METHODS

A pruritic and alopecic disease was investigated in a group of tufted capuchin monkeys (N = 12), but due to ethical reasons, four random animals were further investigated by numerous diagnostic methods. The impact of food and enclosure enrichment was assessed and observed over a 2-year period.

RESULTS

Histopathology of four random tufted capuchin monkeys revealed lymphocytic perifolliculitis, with an appearance of a "swarm of bees" which was suggestive of alopecia areata. Etiological classification of pruritus excluded dermatological, systemic, and neurological causes, making it behavioral. Enclosure and food enrichment had a beneficial impact on pruritus (12/12) and alopecia (10/12).

CONCLUSION

The findings were suggestive of alopecia areata, while the pruritus was considered behavioral in origin. Alopecia and pruritus improved upon enclosure and food enrichment.

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.

Emerging drugs for the treatment of alopecia areata

INTRODUCTION

Alopecia Areata (AA) is the second most common non-scarring hair loss disorder, with a prevalence of 1 in 1000 and a lifetime incidence of 2% worldwide. Data from a recent American study shows that from 68,121 patients with the diagnosis of AA, 37,995 (55.8%) were prescribed treatment for AA within a year of diagnosis, however there are still no therapies able to induce permanent remission, or treatments that guarantee hair regrowth/remissions in 100% of cases, especially in longstanding/severe AA. Recently, oral baricitinib has been approved for AA, being the first drug approved for this specific indication.

AREAS COVERED

The current review will provide a summary of current pharmacological approaches and novel therapeutics in development.

EXPERT OPINION

New and very effective drugs have become available for the treatment of severe AA, and many others are expected soon. However, even new, effective treatments are not effective in all patients and recurrence rates after treatment interruption are high. AA is a systemic disease with important impact on quality of life and should not be considered just as an aesthetic problem. Treatment of the disease should take in account and possibly also address treatment of comorbidities.

Local IL-23 is required for proliferation and retention of skin-resident memory TH17 cells

The cytokine interleukin-23 (IL-23) is critical for development and maintenance of autoimmune inflammation in nonlymphoid tissues; however, the mechanism through which IL-23 supports tissue-specific immunity remains unclear. In mice, we found that circulating memory T cells were dispensable for anamnestic protection from Candida albicans skin infection, and tissue-resident memory (TRM) cell-mediated protection from C. albicans reinfection required IL-23. Administration of anti-IL-23 receptor antibody to mice after resolution of primary C. albicans infection resulted in loss of CD69+ CD103+ tissue-resident memory T helper 17 (TRM17) cells from skin, and clinical anti-IL-23 therapy depleted TRM17 cells from skin of patients with psoriasis. IL-23 receptor blockade impaired TRM17 cell proliferation but did not affect apoptosis susceptibility or tissue egress. IL-23 produced by CD301b+ myeloid cells was required for TRM17 maintenance in skin after C. albicans infection, and CD301b+ cells were necessary for TRM17 expansion during the development of imiquimod dermatitis. This study demonstrates that locally produced IL-23 promotes in situ proliferation of cutaneous TRM17 cells to support their longevity and function and provides mechanistic insight into the durable efficacy of IL-23 blockade in the treatment of psoriasis.

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.

JAM-A facilitates hair follicle regeneration in Alopecia Areata through functioning as ceRNA to protect VCAN expression in dermal papilla cells

The dermal papilla cells in hair follicles function as critical regulators of hair growth. In particular, alopecia areata (AA) is closely related to the malfunctioning of the human dermal papilla cells (hDPCs). Thus, identifying the regulatory mechanism of hDPCs is important in inducing hair follicle (HF) regeneration in AA patients. Recently, growing evidence has indicated that 3′ untranslated regions (3′ UTR) of key genes may participate in the regulatory circuitry underlying cell differentiation and diseases through a so-called competing endogenous mechanism, but none have been reported in HF regeneration. Here, we demonstrate that the 3′ UTR of junctional adhesion molecule A (JAM-A) could act as an essential competing endogenous RNA to maintain hDPCs function and promote HF regeneration in AA. We showed that the 3′ UTR of JAM-A shares many microRNA (miRNA) response elements, especially miR-221–3p, with versican (VCAN) mRNA, and JAM-A 3′ UTR could directly modulate the miRNA-mediated suppression of VCAN in self-renewing hDPCs. Furthermore, upregulated VCAN can in turn promote the expression level of JAM-A. Overall, we propose that JAM-A 3′ UTR forms a feedback loop with VCAN and miR-221–3p to regulate hDPC maintenance, proliferation, and differentiation, which may lead to developing new therapies for hair loss.

The Emergent Power of Human Cellular vs Mouse Models in Translational Hair Research

Different animal models have been used for hair research and regeneration studies based on the similarities between animal and human skins. Primary knowledge on hair follicle (HF) biology has arisen from research using mouse models baring spontaneous or genetically engineered mutations. These studies have been crucial for the discovery of genes underlying human hair cycle control and hair loss disorders. Yet, researchers have become increasingly aware that there are distinct architectural and cellular features between the mouse and human HFs, which might limit the translation of findings in the mouse models. Thus, it is enticing to reason that the spotlight on mouse models and the unwillingness to adapt to the human archetype have been hampering the emergence of the long-awaited human hair loss cure. Here, we provide an overview of the major limitations of the mainstream mouse models for human hair loss research, and we underpin a future course of action using human cell bioengineered models and the emergent artificial intelligence.

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.

Estimation of CD3, CD4, and CD8 in Iraqi patients with alopecia areata and alopecia universalis

BACKGROUND

Alopecia areata is considered to be an autoimmune disease characterized by T-cell response and production of cytokines around the anagen stage.

AIM OF THE STUDY

The aim of this study was to assess T cells in blood using immune biomarkers (CD3, CD4, and CD8) in patients with AA and AU compared with healthy individuals.

MATERIALS AND METHODS

This study was carried out at private clinic and in the Department of Dermatology in Al Karama Teaching Hospital. The study groups included 58 patients from different geographic areas in Iraq, with ages ranging from 5 to 48 years from the end of August 2019 to the January 2020; AA patient group included 19, AU patient group included, 11 and control group included 30 with no scalp or body lesions in their disease history. All patients were clinically diagnosed to detect clinical types of disease in the scalp, in the body, and any hair-bearing area. Venous blood samples were collected from all participants where CD3 T cell, CD4 T cell, and CD8 T cell in whole blood were estimated by flow cytometry technique.

RESULTS

The present study has found the males are more susceptible to infection than the females in both types of disease. There was no significant difference (p > 0.05) detected for immune biomarkers (CD3, CD4, and CD8) in blood between patient groups in comparison with healthy individuals, but there was a significant decrease (p ≤ 0.05) in immune biomarkers (CD8, CD3) according to stress status in AU and in CD8 T cell between patient groups. CD4/CD8 ratio increased in alopecia patients.

CONCLUSION

In current study, There was no significant difference detected for biomarkers (CD3, CD4, and CD8) in blood between patient groups and healthy control, but significantly decrease in CD8 T cell and CD3T cell according to stress in AU, and in CD8T cell between patient groups according to stress This research may have proven one of the theories. Study of CD markers receptors and B cell receptors these will help for future studies.

Determination of serum 25-hydroxyvitamin D levels in patients with alopecia areata and their comparison with levels in healthy controls: A cross-sectional study

Background

Alopecia areata (AA) has been postulated to be an autoimmune disease affecting the hair follicles. Because vitamin D receptors are present in the immune system and hair follicles, vitamin D has been hypothesized to affect the disease.

Objective

The aim of this study was to determine serum 25-hydroxyvitamin D levels and the percentage of vitamin D deficiency in AA patients and compare them with those in healthy controls in a Philippine tertiary hospital.

Methods

This cross-sectional study included 29 AA patients and 29 healthy controls. The serum 25-hydroxyvitamin D levels were determined using the chemiluminescent immunoassay method.

Results

There was no significant difference in the mean vitamin D levels between AA patients (24.41 ± 6.87 ng/mL) and healthy controls (24.68 ± 6.68 ng/mL) (P = .88). The percentage of patients with vitamin D deficiency, defined as <20 ng/mL, trended to higher among AA patients (34.4%) than among healthy controls (17.2%), with an odds ratio of 2.53 (95% CI 0.73-8.65), though this was not statsitically significant.

Limitations

This study involved a limited number of patients in an urbanized area in the Philippines, and majority of the AA cases seen had mild AA.

Conclusion

The trend toward the increased percentage of vitamin D-deficient individuals among AA patients seen in this study may provide insight into the association of vitamin D with AA.

Natural Killer T (NKT) Cells and Periodontitis: Potential Regulatory Role of NKT10 Cells

Natural killer T (NKT) cells constitute a unique subset of T lymphocytes characterized by specifically interacting with antigenic glycolipids conjugated to the CD1d receptor on antigen-presenting cells. Functionally, NKT cells are capable of performing either effector or suppressor immune responses, depending on their production of proinflammatory or anti-inflammatory cytokines, respectively. Effector NKT cells are subdivided into three subsets, termed NKT1, NKT2, and NKT17, based on the cytokines they produce and their similarity to the cytokine profile produced by Th1, Th2, and Th17 lymphocytes, respectively. Recently, a new subgroup of NKT cells termed NKT10 has been described, which cooperates and interacts with other immune cells to promote immunoregulatory responses. Although the tissue-specific functions of NKT cells have not been fully elucidated, their activity has been associated with the pathogenesis of different inflammatory diseases with immunopathogenic similarities to periodontitis, including osteolytic pathologies such as rheumatoid arthritis and osteoporosis. In the present review, we revise and discuss the pathogenic characteristics of NKT cells in these diseases and their role in the pathogenesis of periodontitis; particularly, we analyze the potential regulatory role of the IL-10-producing NKT10 cells.

The hair follicle-psoriasis axis: Shared regulatory mechanisms and therapeutic targets

It has long been known that there is a special affinity of psoriasis for the scalp: Here, it occurs most frequently, lesions terminate sharply in frontal skin beyond the hair line and are difficult to treat. Yet, surprisingly, scalp psoriasis only rarely causes alopecia, even though the pilosebaceous unit clearly is affected. Here, we systematically explore the peculiar, insufficiently investigated connection between psoriasis and growing (anagen) terminal scalp hair follicles (HFs), with emphasis on shared regulatory mechanism and therapeutic targets. Interestingly, several drugs and stressors that can trigger/aggravate psoriasis can inhibit hair growth (e.g. beta-blockers, chloroquine, carbamazepine, interferon-alpha, perceived stress). Instead, several anti-psoriatic agents can stimulate hair growth (e.g. cyclosporine, glucocorticoids, dithranol, UV irradiation), while skin/HF trauma (Köbner phenomenon/depilation) favours the development of psoriatic lesions and induces anagen in "quiescent" (telogen) HFs. On this basis, we propose two interconnected working models: (a) the existence of a bidirectional "hair follicle-psoriasis axis," along which keratinocytes of anagen scalp HFs secrete signals that favour the development and maintenance of psoriatic scalp lesions and respond to signals from these lesions, and (b) that anagen induction and psoriatic lesions share molecular "switch-on" mechanisms, which invite pharmacological targeting, once identified. Therefore, we advocate a novel, cross-fertilizing and integrative approach to psoriasis and hair research that systematically characterizes the "HF-psoriasis axis," focused on identification and therapeutic targeting of selected, shared signalling pathways in the future management of both, psoriasis and hair growth disorders.

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.

NLRP3 inflammasome activation contributes to development of alopecia areata in C3H/HeJ mice

Alopecia areata (AA) is an autoimmune non‐scarring hair loss disease. Recently, several reports have suggested that innate immune systems such as interferon‐α (IFN‐α)‐producing plasmacytoid dendritic cells and NOD‐like receptor family pyrin domain‐containing protein 3 (NLRP3) inflammasomes play a role in the pathogenesis of AA. However, critical studies about their involvement in the initiation of AA have not yet been reported. Therefore, we investigated the expression of innate immune cytokines in serum and skin, and examined the effect of a selective NLRP3 inhibitor, MCC950, on AA in C3H/HeJ mice, induced by transferring cultured skin‐draining lymph node cells. IFN‐α production was upregulated in lesions of AA‐affected mice, and interleukin‐1β in serum and skin was highly expressed before onset as well as postonset. Furthermore, MCC950 treatment prevented AA development and promoted hair growth in AA mouse models by reducing NLRP3 signalling and Th1/Tc1 chemokines and cytokines in the skin. These results suggest that NLRP3 inflammasome contributes to AA onset and chronicity, and NLRP3 inhibitor may be a potential therapeutic agent for AA.

Janus kinase inhibitors in dermatology: Part II. A comprehensive review

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) intracellular signaling pathway is implicated in the pathogenesis of a number of inflammatory dermatoses. Clinical trials and other studies have demonstrated the efficacy of JAK inhibitors in the treatment of a variety of dermatologic conditions. Here we review JAK inhibitors currently under investigation for the treatment of alopecia areata, vitiligo, sarcoidosis, necrobiosis lipoidica, granuloma annulare, and systemic lupus erythematosus with a special emphasis on safety and the implications of JAK inhibitors during the novel coronavirus 2019 pandemic.

Induction of alopecia areata in C3H/HeJ mice using cryopreserved lymphocytes

BACKGROUND

Alopecia areata (AA) is an autoimmune disease resulting in non-scarring hair loss. Animal models are useful means to identify candidates for therapeutic agents. The C3H/HeJ mouse AA model induced via transferring cultured lymphoid cells isolated from AA-affected mice is widely used for AA research. However, this conventional method requires the continuous breeding of AA mice.

OBJECTIVE

We aimed to establish a new method to generate AA model using the transfer of cryopreserved cells, which allows the rapid induction of a large number of AA mice when needed.

METHODS

We cryopreserved lymph node cells soon after isolation from AA-affected mice and injected thawed-cultured cells into recipient mice. H&E staining, immunohistochemical staining, quantitative real-time PCR and ELISA were conducted to identify pathological characteristics. Flow cytometry was performed to reveal the profile of transferred cells.

RESULTS

More than 90 % of recipient mice developed AA-like hair loss and showed inflammatory cell infiltration around anagen hair follicles, markedly increased mRNA expressions of interferon-γ, CXCL11, and granzyme B, and elevated interferon-α protein levels in the skin compared with naïve mice. Higher percentages of effector memory T cells and dendritic cells in transferred cells resulted in a higher incidence of AA.

CONCLUSION

This is the first report to establish a method for generating AA mice using cryopreserved lymphocytes. These AA mice have similar pathological characteristics to AA mice generated with the conventional method and AA patients. This convenient and reproducible method is expected to be valuable for AA study.

Current insight into the functions of microRNAs in common human hair loss disorders: a mini review

Alopecia areata (AA) and Androgenic alopecia (AGA) are the most common multifactorial hair loss disorders that have a serious psychological impact on the affected individuals, while frontal fibrosing alopecia (FFA) is comparatively less common. However, due to the unknown etiology and the effect of many adverse factors, the prognosis of these conditions is challenging to predict. Moreover, no approved therapy has been available to date to prevent or treat these disorders. MicroRNAs (miRNAs) are a group of evolutionary conserved small non-coding RNA molecules with significant roles in the posttranscriptional gene regulation either through mRNA degradation or translational repression. A number of biological processes are controlled by these molecules, including cell growth and differentiation, proliferation, inflammation, immune responses, and apoptosis. Recently, a handful of studies have demonstrated the impact of miRNAs on common hair loss-related disorders; however, the exhaustive molecular mechanisms are still unclear. In this review, we discussed the functional implications of miRNAs in common hair loss-related disorders and addressed their efficacy to be used for theranostic purposes shortly.

Nonsurgical Induction of Alopecia Areata in C3H/HeJ Mice via Adoptive Transfer of Cultured Lymphoid Cells

Surgical induction of alopecia areata (AA) via full-thickness grafting of spontaneous AA-affected C3H/HeJ mouse skin to naïve recipients has been a primary method of transferring the AA disease model phenotype. However, this method is associated with the need to perform an invasive procedure that could negatively impact animal wellbeing. Therefore, a rodent model that rapidly develops AA at a predictable rate and without the need to perform invasive surgical procedures on the mice is essential for studying the pathogenesis of AA. Here we describe a cell injection technique using cultured skin-draining lymph node cells (LNCs) injected intradermally into naïve recipients to induce rapid AA development. The cultured LNCs can reach ~ten fold expansion after 6 days with specific cytokine stimulation. The LNCs derived from a single AA affected mouse donor can induce AA development in more than 80 naïve mice within 2-18 weeks. For comparative control studies, mice receiving cultured LNCs from normal donors remain normally haired. The method enables the production of large numbers of AA mice for use in research and treatment development studies while avoiding the use of surgical procedures. We anticipate that the protocol can also be adapted for use in other mouse autoimmune disease models.

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.

Serum level of interleukin-15 in active alopecia areata patients and its relation to age, sex, and disease severity

Introduction

Autoimmune mechanisms with evident genetic background are the main components of alopecia areata (AA) pathogenesis. Interleukin 15 (IL-15) is considered as an important signalling cytokine. Its disordered expression has been linked to inflammatory autoimmune disorders.

Aim

The present study aimed to evaluate serum IL-15 in active AA patients and to assess its association with patients' sex, age, and disease severity.

Material and methods

IL-15 serum level was measured in 40 patients with active alopecia areata and 20 healthy controls using the ELISA technique. The severity of hair loss was assessed in accordance with the Severity of Alopecia Tool (SALT).

Results

A significantly higher serum level of IL-15 in AA patients than in controls was detected (p < 0.001). A significant positive correlation was detected between the SALT score and IL-15 serum level (r_s = 0.433, p = 0.005). No significant correlation between age of the patients and the serum level of IL-15 was observed (r_s = 0.224, p = 0.164). No significant difference in IL-15 serum level regarding patients' sex, history of disease recurrence, or family history of AA was noted.

Conclusions

The elevated serum level of IL-15 in active AA patients might reflect its role in disease pathogenesis as a key signalling cytokine. Its level is correlated with disease severity. However, IL-15 is not influenced by patients' gender or age.

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.

Cumulative Life Course Impairment of Alopecia Areata

Alopecia areata (AA), an unpredictable, nonscarring hair loss, is commonly perceived as a cosmetic, rather than medical, concern. However, substantial evidence exists describing the negative impact on quality of life, as the disease affects patients personally, socially, financially, and physically. Over time, the cumulative disability may perpetuate poor confidence, social disconnection, negative coping strategies, and failure to achieve a full life potential. Here, we describe the cumulative life course impairment (CLCI) of AA by examining the complex interaction of (1) stigmatization, (2) physical and psychiatric comorbidities, and (3) coping strategies. The model aggregates existing cross-sectional data, which have previously captured disease burden only as snapshots in time. Thus, by examining cumulative effects, the CLCI model serves as a proxy for longitudinal data to better describe life course epidemiology of the disease.

Mouse Models of Alopecia Areata: C3H/HeJ Mice Versus the Humanized AA Mouse Model

The C3H/HeJ model has long dominated basic alopecia areata (AA) in vivo research and has been used as proof-of-principle that Jak inhibitors are suitable agents for AA management in vivo. However, its histologic features are not typical of human AA, and it is questionable whether it is sufficiently clinically predictive for evaluating the therapeutic effects of candidate AA agents. Instead, the humanized mouse model of AA has been used to functionally demonstrate the role of key immune cells in AA pathogenesis and to discover human-specific pharmacologic targets in AA management. Therefore, we advocate the use of both models in future preclinical AA research.

The biology of human hair greying

Hair greying (canities) is one of the earliest, most visible ageing-associated phenomena, whose modulation by genetic, psychoemotional, oxidative, senescence-associated, metabolic and nutritional factors has long attracted skin biologists, dermatologists, and industry. Greying is of profound psychological and commercial relevance in increasingly ageing populations. In addition, the onset and perpetuation of defective melanin production in the human anagen hair follicle pigmentary unit (HFPU) provides a superb model for interrogating the molecular mechanisms of ageing in a complex human mini-organ, and greying-associated defects in bulge melanocyte stem cells (MSCs) represent an intriguing system of neural crest-derived stem cell senescence. Here, we emphasize that human greying invariably begins with the gradual decline in melanogenesis, including reduced tyrosinase activity, defective melanosome transfer and apoptosis of HFPU melanocytes, and is thus a primary event of the anagen hair bulb, not the bulge. Eventually, the bulge MSC pool becomes depleted as well, at which stage greying becomes largely irreversible. There is still no universally accepted model of human hair greying, and the extent of genetic contributions to greying remains unclear. However, oxidative damage likely is a crucial driver of greying via its disruption of HFPU melanocyte survival, MSC maintenance, and of the enzymatic apparatus of melanogenesis itself. While neuroendocrine factors [e.g. alpha melanocyte-stimulating hormone (α-MSH), adrenocorticotropic hormone (ACTH), ß-endorphin, corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH)], and micropthalmia-associated transcription factor (MITF) are well-known regulators of human hair follicle melanocytes and melanogenesis, how exactly these and other factors [e.g. thyroid hormones, hepatocyte growth factor (HGF), P-cadherin, peripheral clock activity] modulate greying requires more detailed study. Other important open questions include how HFPU melanocytes age intrinsically, how psychoemotional stress impacts this process, and how current insights into the gerontobiology of the human HFPU can best be translated into retardation or reversal of greying.

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.

Migration and Function of Memory CD8+ T Cells in Skin

CD8+ memory T cells provide anamnestic host defense against intracellular pathogens and cancer immunosurveillance but are also pathogenic in some autoimmune diseases. In mouse skin, there are two unique subsets of CD8+ memory T cells, resident memory cells that reside long-term in steady state skin and recirculating memory cells that are transient. They have distinct mechanisms of recruitment, development, and maintenance in response to skin-derived signals. In this review, we will focus on these mechanisms and the functional relationship of these two types of CD8+ memory cells with host defense and disease.

Toward Predicting the Spatio-Temporal Dynamics of Alopecia Areata Lesions Using Partial Differential Equation Analysis

Hair loss in the autoimmune disease, alopecia areata (AA), is characterized by the appearance of circularly spreading alopecic lesions in seemingly healthy skin. The distinct spatial patterns of AA lesions form because the immune system attacks hair follicle cells that are in the process of producing hair shaft, catapults the mini-organs that produce hair from a state of growth (anagen) into an apoptosis-driven regression state (catagen), and causes major hair follicle dystrophy along with rapid hair shaft shedding. In this paper, we develop a model of partial differential equations (PDEs) to describe the spatio-temporal dynamics of immune system components that clinical and experimental studies show are primarily involved in the disease development. Global linear stability analysis reveals there is a most unstable mode giving rise to a pattern. The most unstable mode indicates a spatial scale consistent with results of the humanized AA mouse model of Gilhar et al. (Autoimmun Rev 15(7):726-735, 2016) for experimentally induced AA lesions. Numerical simulations of the PDE system confirm our analytic findings and illustrate the formation of a pattern that is characteristic of the spatio-temporal AA dynamics. We apply marginal linear stability analysis to examine and predict the pattern propagation.

Efficacy and Influence Factors of 308-nm Excimer Lamp with Minoxidil in the Treatment of Alopecia Areata

BACKGROUND AND OBJECTIVES

Alopecia areata (AA) is an autoimmune disease characterized by T cell-mediated attack on the hair follicle. Although there are a wide range of therapies, the majority of them are not satisfactory due to side effects or limited efficacy. In this study, we sought to evaluate the efficacy, influence factors, and safety of 308-nm excimer lamp with minoxidil in the treatment of AA.

STUDY DESIGN/MATERIALS AND METHODS

This was a prospective, single-blinded, self-control study, using 308-nm excimer lamp with minoxidil for the treatment of AA. One selected alopecia lesion was divided into the control and treated side. Topical minoxidil (2% solution) was used on both sides, but 308-nm excimer lamp was only added to the treated side. The primary endpoint was the discrepancy of hair growth on each side.

RESULTS

A total of 38 patients (24 males and 14 females) with AA were enrolled in this study, and 34 of them (21 males and 13 females) completed the whole treatment. Thirty-two (94.2%) patients achieved clinical response, and 21 (44.1%) patients achieved with >50% hair regrowth on the treated side after a 12-week treatment. The hair number and diameter on the treated side had significantly increased compared with the control side with statistical differences. Hyperpigmentation and erythema occurred on the treated side of all the patients but they were considered tolerable. Patients of younger age or with smaller area of lesion had better effect.

CONCLUSIONS

The 308-nm excimer lamp with minoxidil therapy can be considered as an effective and safe treatment for single or multiple AA. Lasers Surg. Med. © 2020 Wiley Periodicals, Inc.

JAK-inhibitors. New players in the field of immune-mediated diseases, beyond rheumatoid arthritis

Janus kinase (JAK)/signal transducers and activators of transcription (STATs) are a group of molecules associated with one of the major pathways through which many cytokines exert and integrate their function, and as such they are increasingly recognized as playing critical role in the pathogenesis subserving various immune-mediated diseases, including RA, PsA, SpAs, IBD, skin disorders (e.g. alopecia areata, atopic dermatitis), single-gene disorders like interferonopathies, and others. JAKs are the key initiating players of the JAK/STAT pathway. Upon binding of their respective effector molecules (cytokines, IFNs, growth factors and others) to type I and type II receptors, JAKs are activated, and through phosphorylation of themselves and of other molecules (including STATs), they mediate signal transduction to the nucleus. A class of drugs—called JAK inhibitors or JAKinibs—that block one or more JAKs has been developed in the last decade, and now numbers >20 members. Although, so far, JAK inhibitors have been marketed only for RA and PsA, these drugs have been tested in phase 2 and phase 3 clinical trials for other inflammatory conditions and beyond. In this review, we summarize the clinical data, including efficacy and safety, available for JAK inhibitors used in some immune-mediated conditions other than RA.

Frontiers in alopecia areata pathobiology research

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

JAK inhibitors for the treatment of autoimmune and inflammatory diseases

Cytokines play a central role in the pathophysiology of autoimmune and inflammatory diseases. Several cytokines signal through the JAK-STAT pathway, which is now recognized as a major target to inhibit the effect of a wide array of cytokines. JAK inhibitors are increasingly used in the setting of inflammatory and autoimmune diseases. While the currently approved drugs are panJAK inhibitors, more selective small molecules are being developed and tested in various rheumatic disorders. In this extensive review, we present evidence- or hypothesis-based perspectives for these drugs in various rheumatologic conditions, such as rheumatoid arthritis, systemic lupus erythematosus, giant cell arteritis, and autoinflammatory diseases.

Serum concentrations of selected proinflammatory cytokines in children with alopecia areata

Introduction

Alopecia areata (AA) is considered an autoimmune disorder characterized by patchy loss of hair from the scalp and other body parts. Many patients develop the disease in childhood.

Aim

To answer the question whether abnormal production of some proinflammatory cytokines (IL-2, IL-6, IL-15, IL-17A and IFNγ) in children with AA may facilitate the development or progression of the disease.

Material and methods

The study group consisted of 42 children with AA, the control group – 37 healthy children. Peripheral venous blood samples were collected from patients with AA and healthy controls and the concentrations of serum cytokines, namely IL-2, IL-6, IL-15, IL-17A, IFN-γ were determined quantitatively by ELISA method.

Results

The serum IL-6, IL-15, IL-17A and IFNγ levels were significantly increased in patients with AA compared with control subjects (p < 0.05). The serum IL-15 level was found to be increased when the total duration of AA was increased (q = 0.30; p = 0.05). The serum cytokine level of IL-17A was found to be decreased when duration of the current episode was longer than 2 years (p < 0.05), but the correlation between IL-17A serum level and duration of the current episode was not confirmed in the Spearman test (q = –0.06; p = 0.68). The serum IL-17A level was found to be significantly decreased when the thyroiditis was present (q = –2.378; p < 0.05).

Conclusions

The increased levels of serum IL-6, IL-15, IL-17A and IFNγ in children suggest imbalance in the serum proinflammatory cytokines production in AA.

The Use of Janus Kinase Inhibitors in Alopecia Areata: A Review of the Literature

Alopecia areata (AA) is a chronic, immune-mediated disorder that targets hair follicle epithelium, thereby restricting hair growth in localized patches. Although several therapies for AA have been tested, responses with traditional therapies have been limited. In recent years, numerous reports have been published of patients with AA responding to Janus kinase (JAK) inhibitors. This literature review aims to describe AA pathophysiology, explore how and why JAK inhibitors can be used for AA treatment, and review published case reports, case series, and open-label studies published to date. Pathogenesis of AA includes interactions between genetic, environmental, and immune factors and is mediated by the cytokines interferon-γ and interleukin (IL)-15. JAK inhibition resulting in hair regrowth in some cases supports that AA is associated with the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway. The emergence of JAK inhibitors for AA therapy is changing the way health care providers think about and treat AA. A mixture of animal model studies and human case studies have reported the use of baricitinib (JAK 1/2), ruxolitinib (JAK 1/2), and tofacitinib (JAK 1/3) for the management of AA. JAK inhibition has shown potential as an effective AA therapy when used in case studies, case series, and open-label trials. Formal clinical trials are ongoing and will yield more definitive conclusions about the safety and efficacy of JAK inhibitors.