Resistance to alopecia areata in C3H/HeJ mice is associated with increased expression of regulatory cytokines and a failure to recruit CD4+ and CD8+ cells

The Role of the Neurotrophin Network in Skin Squamous Cell Cancer and the Novel Use of the Zebrafish System

Cutaneous squamous cell carcinoma (cSCC) is the second most prevalent form of skin cancer. An increasing number of cSCCs are associated with dysregulation of key molecules that control skin homeostasis. These observations have increased interest in the role of neurotrophins and their receptors in the pathogenesis of cSCC. They have been demonstrated to have a considerable impact on the aggressiveness potential of skin cancer by both in vitro and in vivo models. In this context, mouse models are classically used to dissect proliferation versus differentiation balance, but they have some limitations in terms of time, space, and costs. Recently, zebrafish models have been implemented as a new tool to obtain information regarding the invasive capacity and metastasis of neoplastic cells. By xenotransplantation technique, cSCC cells from a patient's biopsy or cell line can be successfully characterized, with or without the presence of genetic manipulation or treatments. In addition, the evaluation of the immune microenvironment contributes to potentially identifying connections and homologies with humans. In this review, we retrace the role of the neurotrophin network in healthy and pathological skin, particularly in cSCC. We review how zebrafish models can be important tools for studying cSCC development, growth, and potential treatments.

Effectiveness and Predictive Factors of Response to Tofacitinib Therapy in 125 Patients with Alopecia Areata: A Single-centre Real-world Retrospective Study

Alopecia areata is an autoimmune disorder that greatly impacts patients' quality of life, and its management remains challenging. Tofacitinib is the first Janus kinase inhibitor to be approved for clinical use and is the most extensively studied. Several studies have demonstrated the clinical effectiveness of oral tofacitinib in treating patients with alopecia areata. However, despite being widely used in clinical practice, no prospective randomized controlled trials have been implemented and its indication criteria have not been thoroughly established. Moreover, little is known about the factors associated with response to therapy under real-world conditions. The aims of this retrospective cohort study of patients with alopecia areata treated with tofacitinib for 3 months were to assess the effectiveness of tofacitinib and to identify predictive factors of response to it. Primary outcome was the change in disease severity, as evaluated by Severity of Alopecia Tool (SALT) grade. A total of 125 patients with alopecia areata were included, the incidence of effectiveness was 83.2%, and 16.0% of patients achieved a result of complete remission. Total duration of alopecia areata and previous hair regrowth were independent predictors of response. Combined therapy was associated with relapse after discontinuation. No severe adverse event was observed. This study suggests that tofacitinib provides an effective treatment option for patients with alopecia areata, and that earlier intervention in the treatment of severe alopecia areata with tofacitinib may lead to better outcomes.

Inhibition of T-cell activity in alopecia areata: recent developments and new directions

Alopecia areata (AA) is an autoimmune disease that has a complex underlying immunopathogenesis characterized by nonscarring hair loss ranging from small bald patches to complete loss of scalp, face, and/or body hair. Although the etiopathogenesis of AA has not yet been fully characterized, immune privilege collapse at the hair follicle (HF) followed by T-cell receptor recognition of exposed HF autoantigens by autoreactive cytotoxic CD8+ T cells is now understood to play a central role. Few treatment options are available, with the Janus kinase (JAK) 1/2 inhibitor baricitinib (2022) and the selective JAK3/tyrosine kinase expressed in hepatocellular carcinoma (TEC) inhibitor ritlecitinib (2023) being the only US Food and Drug Administration-approved systemic medications thus far for severe AA. Several other treatments are used off-label with limited efficacy and/or suboptimal safety and tolerability. With an increased understanding of the T-cell-mediated autoimmune and inflammatory pathogenesis of AA, additional therapeutic pathways beyond JAK inhibition are currently under investigation for the development of AA therapies. This narrative review presents a detailed overview about the role of T cells and T-cell-signaling pathways in the pathogenesis of AA, with a focus on those pathways targeted by drugs in clinical development for the treatment of AA. A detailed summary of new drugs targeting these pathways with expert commentary on future directions for AA drug development and the importance of targeting multiple T-cell-signaling pathways is also provided in this review.

Effectiveness of Tofacitinib in Pre-adolescent Alopecia Areata: A Retrospective Case Series and Literature Review

Alopecia areata (AA) is a common cause of hair loss in children. Despite numerous therapeutic options for paediatric AA, none have been found to be both effective and safe. Recent studies have demonstrated the efficacy and safety of the Janus kinase (JAK) inhibitor tofacitinib in adult patients with AA, whereas data on paediatric patients with AA in real-world practice are limited. This was a single-centre, retrospective study that included 11 pre-adolescent patients with AA treated with tofacitinib between December 2021 and September 2022. Clinical characteristics of patients, clinical response and adverse events were evaluated. Overall, 82% (9/11) of patients experienced hair regrowth and 64% (7/11) of patients experienced over 50% improvement in their Severity of Alopecia Tool (SALT) scores. Adverse events were mild. In the literature, tofacitinib has been used to treat AA in 31 children ≤12 years of age who failed to respond to prior treatments. Eighty-seven percent (27/31) of these patients showed significant responses based on changes in their SALT scores. This case series demonstrates that oral tofacitinib is an effective and safe treatment option for paediatric AA, particularly for children who have failed to respond to traditional treatments or are not suitable for such treatments.

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.

Selective inhibition of JAK3 signaling is sufficient to reverse alopecia areata

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) are key intracellular mediators in the signal transduction of many cytokines and growth factors. Common γ chain cytokines and interferon-γ that use the JAK/STAT pathway to induce biological responses have been implicated in the pathogenesis of alopecia areata (AA), a T cell-mediated autoimmune disease of the hair follicle. We previously showed that therapeutic targeting of JAK/STAT pathways using the first-generation JAK1/2 inhibitor, ruxolitinib, and the pan-JAK inhibitor, tofacitinib, was highly effective in the treatment of human AA, as well as prevention and reversal of AA in the C3H/HeJ mouse model. To better define the role of individual JAKs in the pathogenesis of AA, in this study, we tested and compared the efficacy of several next-generation JAK-selective inhibitors in the C3H/HeJ mouse model of AA, using both systemic and topical delivery. We found that JAK1-selective inhibitors as well as JAK3-selective inhibitors robustly induced hair regrowth and decreased AA-associated inflammation, whereas several JAK2-selective inhibitors failed to restore hair growth in treated C3H/HeJ mice with AA. Unlike JAK1, which is broadly expressed in many tissues, JAK3 expression is largely restricted to hematopoietic cells. Our study demonstrates inhibiting JAK3 signaling is sufficient to prevent and reverse disease in the preclinical model of AA.

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.

Fibroblast cell-based therapy prevents induction of alopecia areata in an experimental model

Alopecia areata (AA) is an autoimmune hair loss disease with infiltration of proinflammatory cells into hair follicles. Current therapeutic regimens are unsatisfactory mainly because of the potential for side effects and/or limited efficacy. Here we report that cultured, transduced fibroblasts, which express the immunomodulatory molecule indoleamine 2,3-dioxygenase (IDO), can be applied to prevent hair loss in an experimental AA model. A single intraperitoneal (IP) injection of IDO-expressing primary dermal fibroblasts was given to C3H/HeJ mice at the time of AA induction. While 60–70% of mice that received either control fibroblasts or vehicle injections developed extensive AA, none of the IDO-expressing fibroblast-treated mice showed new hair loss up to 20 weeks post injection. IDO cell therapy significantly reduced infiltration of CD4⁺ and CD8⁺ T cells into hair follicles and resulted in decreased expression of TNF-α, IFN-γ and IL-17 in the skin. Skin draining lymph nodes of IDO fibroblast-treated mice were significantly smaller, with more CD4⁺ CD25⁺ FoxP3⁺ regulatory T cells and fewer Th17 cells than those of control fibroblast and vehicle-injected mice. These findings indicate that IP injected IDO-expressing dermal fibroblasts can control inflammation and thereby prevent AA hair loss.

Critical evaluation of 2-ethylhexyl acrylate dermal carcinogenicity studies using contemporary criteria

Skin tumors have been observed in C3H/HeJ mice following treatment with high and strongly irritating concentrations of 2-ethylhexyl acrylate (2-EHA). Dermal carcinogenicity studies performed with 2-EHA are reviewed, contrasting the results in two mouse strains (C3H/HeJ and NMRI) under different dosing regimens. Application of contemporary evaluation criteria to the existing dermal carcinogenicity dataset demonstrates that 2-EHA induces skin tumors only at concentrations exceeding an maximum tolerated dose (MTD) and in the immune-dysregulated C3H/HeJ mouse model. Overall, the available chronic toxicity and genotoxicity data on 2-EHA support a non-genotoxic chemical irritant mechanism, whereby chronic irritation leads to inflammation, tissue injury, and wound repair, the latter of which is disrupted in C3H/HeJ mice and leads to tumor formation. Tumor response information in excess of an MTD should not be considered in a human hazard or risk assessment paradigm. For the purposes of an appropriate hazard assessment, 2-EHA did not cause or initiate dermal carcinogenesis in an immune competent (NMRI) mouse model, and, even in the immune compromised C3H/HeJ model, did not induce skin tumors at doses which did not exceed the MTD.

Alopecia areata is characterized by expansion of circulating Th2/Tc2/Th22, within the skin-homing and systemic T-cell populations

BACKGROUND

Characterizing blood profile of alopecia areata (AA) is important not only for treatment advancements, but also for possibly identifying peripheral biomarkers that will eliminate the need for scalp biopsies. We aimed to compare frequencies of skin homing (CLA⁺ ) vs systemic (CLA^- ) "polar" CD4⁺ and CD8⁺ and activated T-cell subsets in AA vs atopic dermatitis (AD) and control blood.

METHODS

Flow cytometry was used to measure IFN-γ, IL-13, IL-9, IL-17, and IL-22 cytokines in CD4⁺ and CD8⁺ T cells. Inducible co-stimulator molecule (ICOS) and HLA-DR were used to define mid- and long-term T-cell activation. We compared peripheral blood from 32 moderate-to-severe AA adults with 43 moderate-to-severe AD patients and 30 age-matched controls.

RESULTS

AA patients had increased CLA⁺ /CLA^- Th2 (P < .007), CLA⁺ Tc2 (P = .04), and CLA⁺ Th22 (P < .05) frequencies than controls. Except of CLA^- Tc1 cells (P = .03), IFN-γ levels were mostly similar between AA, AD, and controls (P > .1). ICOS and HLA-DR activation were significantly higher in AA than controls (P < .05). T regulatory cells were significantly decreased in AA patients than controls (P < .01) and were correlated with activated CD8⁺ T cells and with multiple cytokine subsets (P < .05). While Th2 and Tc2 clustered with disease severity, IFN-γ producing cells were linked with AA duration.

CONCLUSIONS

Alopecia areata is accompanied by Th2/Tc2 activation in skin-homing and systemic subsets, correlating with disease severity, while IFN-γ is linked to disease chronicity. These data hint for a possible role of diverse T-cells subsets in disease pathogenesis and emphasize the systemic nature of AA supporting the need for systemic therapeutic strategies in severe patients.

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

One of the most common human autoimmune diseases, alopecia areata (AA), is characterized by sudden, often persisting and psychologically devastating hair loss. Animal models have helped greatly to elucidate critical cellular and molecular immune pathways in AA. The two most prominent ones are inbred C3H/HeJ mice which develop an AA-like hair phenotype spontaneously or after experimental induction, and healthy human scalp skin xenotransplanted onto SCID mice, in which a phenocopy of human AA is induced by injecting IL-2-stimulated PBMCs enriched for CD56+/NKG2D+ cells intradermally. The current review critically examines the pros and cons of the available AA animal models and how they have shaped our understanding of AA pathobiology, and the development of new therapeutic strategies. AA is thought to arise when the hair follicle's (HF) natural immune privilege (IP) collapses, inducing ectopic MHC class I expression in the HF epithelium and autoantigen presentation to autoreactive CD8+ T cells. In common with other autoimmune diseases, upregulation of IFN-γ and IL-15 is critically implicated in AA pathogenesis, as are NKG2D and its ligands, MICA, and ULBP3. The C3H/HeJ mouse model was used to identify key immune cell and molecular principles in murine AA, and proof-of-principle that Janus kinase (JAK) inhibitors are suitable agents for AA management in vivo, since both IFN-γ and IL-15 signal via the JAK pathway. Instead, the humanized mouse model of AA has been used to demonstrate the previously hypothesized key role of CD8+ T cells and NKG2D+ cells in AA pathogenesis and to discover human-specific pharmacologic targets like the potassium channel Kv1.3, and to show that the PDE4 inhibitor, apremilast, inhibits AA development in human skin. As such, AA provides a model disease, in which to contemplate general challenges, opportunities, and limitations one faces when selecting appropriate animal models in preclinical research for human autoimmune diseases.

The role of lymphocytes in the development and treatment of alopecia areata

Alopecia areata (AA) development is associated with both innate and adaptive immune cell activation, migration to peri- and intra-follicular regions, and hair follicle disruption. Both CD4(+) and CD8(+) lymphocytes are abundant in AA lesions; however, CD8(+) cytotoxic T lymphocytes are more likely to enter inside hair follicles, circumstantially suggesting that they have a significant role to play in AA development. Several rodent models recapitulate important features of the human autoimmune disease and demonstrate that CD8(+) cytotoxic T lymphocytes are fundamentally required for AA induction and perpetuation. However, the initiating events, the self-antigens involved, and the molecular signaling pathways, all need further exploration. Studying CD8(+) cytotoxic T lymphocytes and their fate decisions in AA development may reveal new and improved treatment approaches.

Androgenic alopecia is associated with less dietary soy, lower [corrected] blood vanadium and rs1160312 1 polymorphism in Taiwanese communities

Background

Although the genetic basis of androgenic alopecia has been clearly established, little is known about its non-genetic causes, such as environmental and lifestyle factors.

Objective

This study investigated blood and urine heavy metals concentrations, environmental exposure factors, personal behaviors, dietary intakes and the genotypes of related susceptibility genes in patients with androgenic alopecia (AGA).

Design

Age, AGA level, residence area, work hours, sleep patterns, cigarette usage, alcohol consumption, betel nut usage, hair treatments, eating habits, body heavy metals concentrations and rs1998076, rs913063, rs1160312 and rs201571 SNP genotype data were collected from 354 men. Logistic regression analysis was performed to examine whether any of the factors displayed odds ratios (ORs) indicating association with moderate to severe AGA (≧IV). Subsequently, Hosmer-Lemeshow, Nagelkerke R² and accuracy tests were conducted to help establish an optimal model.

Results

Moderate to severe AGA was associated with the AA genotype of rs1160312 (22.50, 95% CI 3.99–126.83), blood vanadium concentration (0.02, 95% CI 0.01–0.04), and regular consumption of soy bean drinks (0.23, 95% CI 0.06–0.85), after adjustment for age. The results were corroborated by the Hosmer-Lemeshow test (P = 0.73), Nagelkerke R² (0.59), accuracy test (0.816) and area under the curve (AUC; 0.90, 0.847–0.951) analysis.

Conclusions

Blood vanadium and frequent soy bean drink consumption may provide protect effects against AGA. Accordingly, blood vanadium concentrations, the AA genotype of rs1160312 and frequent consumption of soy bean drinks are associated with AGA.

What causes alopecia areata?

The pathobiology of alopecia areata (AA), one of the most frequent autoimmune diseases and a major unsolved clinical problem, has intrigued dermatologists, hair biologists and immunologists for decades. Simultaneously, both affected patients and the physicians who take care of them are increasingly frustrated that there is still no fully satisfactory treatment. Much of this frustration results from the fact that the pathobiology of AA remains unclear, and no single AA pathogenesis concept can claim to be universally accepted. In fact, some investigators still harbour doubts whether this even is an autoimmune disease, and the relative importance of CD8(+) T cells, CD4(+) T cells and NKGD2(+) NK or NKT cells and the exact role of genetic factors in AA pathogenesis remain bones of contention. Also, is AA one disease, a spectrum of distinct disease entities or only a response pattern of normal hair follicles to immunologically mediated damage? During the past decade, substantial progress has been made in basic AA-related research, in the development of new models for translationally relevant AA research and in the identification of new therapeutic agents and targets for future AA management. This calls for a re-evaluation and public debate of currently prevalent AA pathobiology concepts. The present Controversies feature takes on this challenge, hoping to attract more skin biologists, immunologists and professional autoimmunity experts to this biologically fascinating and clinically important model disease.

Tolerance induction by hair-specific keratins in murine alopecia areata

AA is a presumptive autoimmune disease, severely damaging the hair follicle. Hair- and nail-specific keratins are discussed as potential candidates, which we controlled in C3H/HeJ mice that develop AA spontaneously or after skin transplantation. From nine keratins, K71 and K31 peptides supported T cell activation when presented by DCs to syngeneic naive T cells, and young C3H/HeJ mice receiving s.c. injections of peptide-loaded DC developed AA. The frequency of K71- and K31-specific CD4(+) and CD8(+) T cells increased four- to fivefold by vaccination, which corresponds with the frequency seen in skin transplantation-induced AA mice. Also, accessory molecule expression, the cytokine profile with a dominance of IFN-γ-expressing T cells, the proliferative response against AA lysate or peptide-loaded DCs, as well as peptide-specific cytotoxic T cells were similar in keratin peptide- and skin transplantation-induced AA. Instead, vaccination with soluble K71 or K31 peptides significantly retarded AA induction and prevented progression. Soluble peptide vaccination did not provoke immunosuppression but induced long-lasting T cell anergy with unresponsiveness to DC-presented K71 and K31 peptides. Thus, keratins K71 and K31 contribute to AA induction, and peptide application in a nonimmunogenic form serves as an efficient therapeutic.

Biologics in dermatology

Skin and subcutaneous diseases affect millions of people worldwide, causing significant morbidity. Biologics are becoming increasingly useful for the treatment of many skin diseases, particularly as alternatives for patients who have failed to tolerate or respond to conventional systemic therapies. Biological therapies provide a targeted approach to treatment through interaction with specific components of the underlying immune and inflammatory disease processes. This review article examines the increasing evidence base for biologics in dermatology, including well-established treatments and novel agents.

Endogenous retinoids in the pathogenesis of alopecia areata

Alopecia areata (AA) is an autoimmune disease that attacks anagen hair follicles. Gene array in graft-induced C3H/HeJ mice revealed that genes involved in retinoic acid (RA) synthesis were increased, whereas RA degradation genes were decreased in AA compared with sham controls. This was confirmed by immunohistochemistry in biopsies from patients with AA and both mouse and rat AA models. RA levels were also increased in C3H/HeJ mice with AA. C3H/HeJ mice were fed a purified diet containing one of the four levels of dietary vitamin A or an unpurified diet 2 weeks before grafting and disease progression followed. High vitamin A accelerated AA, whereas mice that were not fed vitamin A had more severe disease by the end of the study. More hair follicles were in anagen in mice fed high vitamin A. Both the number and localization of granzyme B-positive cells were altered by vitamin A. IFNγ was also the lowest and IL13 highest in mice fed high vitamin A. Other cytokines were reduced and chemokines increased as the disease progressed, but no additional effects of vitamin A were seen. Combined, these results suggest that vitamin A regulates both the hair cycle and immune response to alter the progression of AA.

T-cell reconstitution after thymus xenotransplantation induces hair depigmentation and loss

Here we present a mouse model for T-cell targeting of hair follicles, linking the pathogenesis of alopecia to that of depigmentation disorders. Clinically, thymus transplantation has been successfully used to treat T-cell immunodeficiency in congenital athymia, but is associated with autoimmunity. We established a mouse model of thymus transplantation by subcutaneously implanting human thymus tissue into athymic C57BL/6 nude mice. These xenografts supported mouse T-cell development. Surprisingly, we did not detect multiorgan autoimmune disease. However, in all transplanted mice, we noted a striking depigmentation and loss of hair follicles. Transfer of T cells from transplanted nudes to syngeneic black-coated RAG^−/− recipients caused progressive, persistent coat-hair whitening, which preceded patchy hair loss in depigmented areas. Further transfer experiments revealed that these phenomena could be induced by CD4+ T cells alone. Immunofluorescent analysis suggested that Trp2+ melanocyte-lineage cells were decreased in depigmented hair follicles, and pathogenic T cells upregulated activation markers when exposed to C57BL/6 melanocytes in vitro, suggesting that these T cells are not tolerant to self-melanocyte antigens. Our data raise interesting questions about the mechanisms underlying tissue-specific tolerance to skin antigens.

The basic science of hair biology: what are the causal mechanisms for the disordered hair follicle?

A hair disorder can be difficult to define, but patients are typically motivated to seek treatment when their hair growth patterns are significantly different from their cultural group or when growth patterns change significantly. The causes of hair disorders are many and varied, but fundamentally the disorder is a consequence of aberrant alterations of normal hair biology. The potential trigger factors for hair disorders can be attributed to inflammation, genetics, the environment, or hormones, of which the relative contributions vary for different diagnoses, between individuals, and over time. This article discusses the causal mechanisms for the disordered hair follicle.

Prevention and treatment of alopecia areata with quercetin in the C3H/HeJ mouse model

Alopecia areata (AA) is an autoimmune non-scarring hair loss disorder. AA can be acute, recurrent, or chronic. Current therapeutic options for AA are limited, and there is no effective prevention for recurrent AA. We have previously shown a correlation between the expression of HSP70 (HSPA1A/B), a heat shock protein involved in the inflammatory response, and the onset of AA in the C3H/HeJ mouse model. In this study, we tested the effects of quercetin, a bioflavonoid with anti-inflammatory properties, on AA development and HSP70 expression in the C3H/HeJ model. Mice with spontaneous AA were treated with subcutaneous quercetin or sham injections. Hair regrowth was observed in lesional areas in all the quercetin-treated mice, but in none of the sham-treated mice. In addition, non-alopecic C3H/HeJ mice were heat-treated to induce alopecia, along with quercetin or sham injections. Whereas 24% of the heat-treated mice with sham injections developed alopecia, none of the mice receiving quercetin injections did. As expected, the level of HSP70 expression in quercetin-treated areas was comparable to control. Furthermore, we showed that systemic delivery of quercetin by intraperitoneal injections prevented/reduced spontaneous onset of AA. Our results demonstrated that quercetin provided effective treatment for AA as well as prevention of onset of AA in the C3H/HeJ model, and warrant further clinical studies to determine whether quercetin may provide both treatment for preexisting AA and prevention of recurrent AA. The ready availability of quercetin as a dietary supplement may lead to increased patient compliance and positive outcomes for AA.

Endogenous retinoids in the hair follicle and sebaceous gland

Vitamin A and its derivatives (retinoids) are critically important in the development and maintenance of multiple epithelial tissues, including skin, hair, and sebaceous glands, as shown by the detrimental effects of either vitamin A deficiency or toxicity. Thus, precise levels of retinoic acid (RA, active metabolite) are needed. These precise levels of RA are achieved by regulating several steps in the conversion of dietary vitamin A (retinol) to RA and RA catabolism. This review discusses the localization of RA synthesis to specific sites within the hair follicle and sebaceous gland, including their stem cells, during both homeostasis and disease states. It also discusses what is known about the specific roles of RA within the hair follicle and sebaceous gland. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.

A mouse model of clonal CD8+ T lymphocyte-mediated alopecia areata progressing to alopecia universalis

Alopecia areata is among the most prevalent autoimmune diseases, yet compared with other autoimmune conditions, it is not well studied. This in part results from limitations in the C3H/HeJ mouse and DEBR rat model systems most commonly used to study the disease, which display a low frequency and late onset. We describe a novel high-incidence model for spontaneous alopecia areata. The 1MOG244 T cell expresses dual TCRA chains, one of which, when combined with the single TCRB present, promotes the development of CD8(+) T cells with specificity for hair follicles. Retroviral transgenic mice expressing this TCR develop spontaneous alopecia areata at nearly 100% incidence. Disease initially follows a reticular pattern, with regionally cyclic episodes of hair loss and regrowth, and ultimately progresses to alopecia universalis. Alopecia development is associated with CD8(+) T cell activation, migration into the intrafollicular region, and hair follicle destruction. The disease may be adoptively transferred with T lymphocytes and is class I and not class II MHC-dependent. Pathologic T cells primarily express IFNG and IL-17 early in disease, with dramatic increases in cytokine production and recruitment of IL-4 and IL-10 production with disease progression. Inhibition of individual cytokines did not significantly alter disease incidence, potentially indicating redundancy in cytokine responses. These results therefore characterize a new high-incidence model for alopecia areata in C57BL/6J mice, the first to our knowledge to apply a monoclonal TCR, and indicate that class I MHC-restricted CD8(+) T lymphocytes can independently mediate the pathologic response.

Etiopathogenesis of alopecia areata: Why do our patients get it?

Alopecia areata (AA) is a nonscarring, inflammatory skin disease that results in patchy hair loss. AA is unpredictable in its onset, severity, and duration making it potentially very stressful for affected individuals. Currently, the treatment options for AA are limited and the efficacy of these treatments varies from patient to patient. The exact etiology of AA is unknown. This article provides some insights into the etiopathogenesis of AA and why some people develop it. The current knowledge on the pathogenesis of AA is summarized and some of the recent hypotheses and studies on AA are presented to allow for a fuller understanding of the possible biological mechanisms of AA.

Development of alopecia areata is associated with higher central and peripheral hypothalamic-pituitary-adrenal tone in the skin graft induced C3H/HeJ mouse model

The relationship of the stress response to the pathogenesis of alopecia areata (AA) was investigated by subjecting normal and skin graft-induced, AA-affected C3H/HeJ mice to light ether anesthesia or restraint stress. Plasma corticosterone (CORT), adrenocorticotropic hormone (ACTH), and estradiol (E2) levels were determined by RIA, whereas gene expression in brains, lymphoid organs, and skin was measured by quantitative RT-PCR for corticotropin-releasing hormone (Crh), arginine vasopressin (Avp), proopiomelanocortin (Pomc), glucocorticoid receptor (Nr3c1), mineralocorticoid receptor (Nr3c2), corticotropin-releasing hormone receptor types 1 and 2 (Crhr1, Crhr2), interleukin-12 (Il12), tumor necrosis factor-alpha (Tnf alpha), and estrogen receptors type-1 (Esr1) and type-2 (Esr2). AA mice had a marked increase in hypothalamic-pituitary-adrenal (HPA) tone and activity centrally, and peripherally in the skin and lymph nodes. There was also altered interaction between the adrenal and gonadal axes compared with that in normal mice. Stress further exacerbated changes in AA mouse HPA activity both centrally and peripherally. AA mice had significantly blunted CORT and ACTH responses to acute ether stress (physiological stressor) and a deficit in habituation to repeated restraint stress (psychological stressor). The positive correlation of HPA hormone levels with skin Th1 cytokines suggests that altered HPA activity may occur as a consequence of the immune response associated with AA.

Controlled delivery of T-box21 small interfering RNA ameliorates autoimmune alopecia (Alopecia Areata) in a C3H/HeJ mouse model

Autoimmune alopecia (alopecia areata) is considered to be triggered by a collapse of immune privilege in hair follicles. Here we confirmed that infiltrating CD4 T lymphocytes around hair follicles of patients with alopecia areata were primarily CCR5-positive with few CCR4-positive cells, suggesting a dominant role of Th1 cells in the alopecic lesion. Given this finding, we sought to elucidate the effect of cytokine therapy in C3H/HeJ mice, a mouse model of alopecia areata, by applying recombinant interleukin-4 and neutralizing anti-interferon-gamma antibody. We found that local injections of both interleukin-4 and neutralizing anti-interferon-gamma antibody effectively treated alopecia in C3H/HeJ mice. Results from immunohistochemistry and semiquantitative reverse transcription-polymerase chain reaction demonstrated that intralesional injection of interleukin-4 suppressed CD8 T cell infiltrates around the hair follicles and repressed enhanced interferon-gamma mRNA expression in the affected alopecic skin. Furthermore, Th1 transcription factor T-box21 small interfering RNAs conjugated to cationized gelatin showed mitigating effects on alopecia in C3H/HeJ mice, resulting in the restoration of hair shaft elongation. Taken together, the use of gelatin-small interfering RNA conjugates promises to be a novel, efficient, and safe tool as an alternative gene therapy for the treatment of various human diseases. To our knowledge, this is the first report of effective controlled delivery of small interfering RNA using biodegradable cationized gelatin microspheres in an animal model of disease.

Lymphocytes, neuropeptides, and genes involved in alopecia areata

Many lessons in autoimmunity - particularly relating to the role of immune privilege and the interplay between genetics and neuroimmunology - can be learned from the study of alopecia areata, the most common cause of inflammation-induced hair loss. Alopecia areata is now understood to represent an organ-restricted, T cell-mediated autoimmune disease of hair follicles. Disease induction is associated with collapse of hair follicle immune privilege in both humans and in animal models. Here, the role of HLA associations, other immunogenetic factors, and neuroendocrine parameters in alopecia areata pathogenesis are reviewed. This instructive and clinically significant model disease deserves more widespread interest in the immunology community.

Interferon-gamma-deficient mice are resistant to the development of alopecia areata

BACKGROUND

Alopecia areata (AA) is a T-cell mediated putative autoimmune disease of hair follicles, which can be transferred by CD4(+) T cells. However, whether T-helper (Th) 1 or Th2 cytokines are predominant has not yet been defined.

OBJECTIVES

To elucidate the importance of Th1 cells in the pathogenesis of AA we investigated the functional role of interferon (IFN)-gamma in the experimental induction of AA.

METHODS

AA was experimentally induced by grafting full-thickness skin from AA-affected C3H/HeJ mice on to C3H/HeJ mice with a targeted deletion of the Th1 cytokine IFN-gamma gene (IFNgamma(-/-)) and on to wild-type mice (IFNgamma(+/+)).

RESULTS

While 90% of wild-type mice developed AA, none of the IFNgamma(-/-) mice exhibited hair loss. Immunohistochemistry of skin sections revealed a dense perifollicular and intrafollicular infiltrate of CD4(+) and CD8(+) T cells in controls, while in IFNgamma(-/-) mice skin-infiltrating CD8(+) T cells were absent and the number of CD4(+) cells was significantly reduced. Aberrant expression of major histocompatibility complex class I and II molecules in the putative immune-privileged infrainfundibular site of the hair follicle was found to be weaker in AA-resistant IFNgamma(-/-) mice than in control mice with AA. Flow cytometry revealed that leucocytes of IFNgamma(-/-) mice did not respond to the transfer of AA-affected skin. As distinct from IFNgamma(+/+) mice, neither T-cell activation markers nor Th1 cytokines were upregulated in draining lymph node cells or skin-infiltrating leucocytes of AA-resistant IFNgamma(-/-) mice. However, there was no evidence for a shift towards a Th2 cytokine profile, nor for upregulation of regulatory T cells in IFNgamma(-/-) mice.

CONCLUSIONS

IFNgamma(-/-) mice fail to activate Th1 cells in response to the transplanted (auto)antigens, which suggests an essential requirement for IFN-gamma-mediated Th1 activation in the induction of AA.

Phenotypic analysis of T-cells in extensive alopecia areata scalp suggests partial tolerance

This study demonstrates the feasibility and efficacy of using flow cytometric analysis with intracellular cytokine staining for characterization of T-cell phenotype and functional status in extensive alopecia areata (EAA) scalp skin. Cell suspensions were made from scalp punch biopsies taken from 12 patients with long-standing EAA (average disease duration 14 years, 95% hair loss) and six control subjects. EAA samples had a lower percentage of CD-3-expressing cells, but CD-4/CD-8 ratios remained similar to controls. Expression of CD-69 was found only in EAA scalp biopsies, suggesting that T-cells from EAA scalp have undergone activation. No difference was found in tumor necrosis factor alpha expression. Surprisingly, EAA scalp T-cells produced less IL-2 and CD-8 T-cells produced less IFN-gamma. Immunohistochemical staining of formalin-fixed paraffin-embedded specimens demonstrated that IFN-gamma-producing cells in EAA scalp were not greater in number than in normal specimens. The few identified IFN-gamma-producing cells demonstrated no tendency to localize to the perifollicular region, and were similarly distributed as in control specimens. The abnormalities in cytokine production may explain the relative paucity of inflammatory change observed in the clinical setting and suggest that T-cell responses in EAA scalp are tightly, albeit aberrantly, regulated via mechanisms of peripheral T-cell tolerance.

Reduced expression of interleukin-2 decreases the frequency of alopecia areata onset in C3H/HeJ mice

Alopecia areata (AA) is an autoimmune hair loss disease, that can be transferred between C3H/HeJ mice by skin grafting. We explored whether AA susceptibility is influenced by the availability of interleukin (IL)-2, a cytokine with leukocyte activating and regulatory properties. Mice heterozygous for a targeted deletion of IL-2 from the histocompatible C3.129P2(B6)-Il2(tm1Hor) substrain, that produce reduced levels of IL-2, were examined for AA development after grafting skin from AA-affected C3H/HeJ mice. After grafting, nine of 19 (47%) heterozygous IL-2+/-versus 16 of 18 (88%) IL-2+/+ wild-type littermates developed AA. Although dense follicular leukocyte infiltrates were apparent in AA affected wild-type mice, AA-developing IL-2+/- littermates had a reduced leukocyte infiltration, and AA-resistant IL-2+/- mice had no inflammation. Lymph node cell analysis revealed a reduction in leukocyte activation markers in AA-developing IL-2+/- mice. IL-2+/- mice presented with low level expression of cytokines (IL-4, IL-10, interferon-gamma, transforming growth factor-beta), upregulation of tumor necrosis factor receptors, and increased leukocyte apoptosis susceptibility independent of AA expression. In the skin, CD4+ cells and monocytes were reduced; activation markers were not upregulated and very few CD44v3+ or CD44v10+ leukocytes were recovered. Taken together, our data suggest that AA resistance of IL-2+/- mice is because of the failure of activated leukocyte recruitment, thus pointing toward an involvement of IL-2 in AA pathogenesis.

Alopecia Areata: A tissue specific autoimmune disease of the hair follicle

The goal of this review is to introduce the immunologic community to alopecia areata as a model system for the study of tissue directed autoimmune disease. Alopecia areata is marked by autoimmune assault on the hair follicle resulting in hair loss. It is linked to HLA-DQ3 and evidence suggests it is mediated by T-lymphocytes with a TH1 cytokine profile. Hair follicles are an immune protected site with deficient MHC expression. Evidence is presented suggesting that alopecia areata results from loss of immune privilege with presentation of autoantigens. Alopecia areata is one of the most common human autoimmune conditions, with a lifetime risk of approximately 1.7%. Study of alopecia areata in humans is facilitated by the accessibility of scalp for biopsy. It is possible to transfer the condition with lesional human lymphocytes in a human scalp graft/SCID mouse model. There are also spontaneous animal models which share the features of the human condition. For these reasons, alopecia areata is a powerful model for study of the induction and pathogenesis of tissue directed autoimmune disease.

[Alopecia areata in animal models--new insights into pathogenesis and treatment of a T cell-mediated autoimmune disorder]

Alopecia areata is a common disease, but for ethical reasons it seems difficult to perform large-scale studies to elucidate the pathogenesis and to develop new therapeutic approaches in man. It is therefore helpful to develop appropriate animal models. The Dundee experimental bald rat (DEBR) and the C3H/HeJ mouse are well-established animal models for alopecia areata and can be used for the study of genetic aspects, pathogenesis and therapy of the disease. In C3H/HeJ mice alopecia areata can be experimentally induced by grafting lesional skin from an affected mouse to a histocompatible recipient which offers the possibility to study the influence of various factors on the development of the disease. Studies on the C3H/HeJ mouse and the DEBR have corroborated the concept that alopecia areata is a T-cell mediated autoimmune disease and various steps and aspects of the pathogenesis have been elucidated. Based on this knowledge new therapeutic options may be developed such as inhibition of lymphocyte-homing by an anti-CD44v10 antibody, or inhibition of costimulation by monoclonal antibodies. Therapeutic studies in the C3H/HeJ mouse and the DEBR suggest that alopecia areata can be treated by topical tacrolimus but treatment in humans may only be successful after development of an improved vehicle that facilitates penetration of tacrolimus down to the hair bulb. Current investigations in mice are designed to elucidate the mechanisms how contact sensitizers act in the treatment of alopecia areata, and this will hopefully lead to the development of more specific approaches based on the beneficial effect of contact sensitizers.

What Can We Learn from Animal Models of Alopecia areata?

Alopecia areata (AA) is a hair loss disease marked by a focal inflammatory infiltrate of dystrophic anagen stage hair follicles by CD4+ and CD8+ lymphocytes. Although AA is thought to be an autoimmune disorder, definitive proof is lacking. Moreover, characterization of the primary pathogenic mechanisms by which hair loss is induced in AA is limited. In this context, animal models may provide a vital contribution to understanding AA. Recent research using animal models of AA has focused on providing evidence in support of a lymphocyte-mediated pathogenic mechanism consistent with AA as an autoimmune disease. In the future, research with both humans and animal models shall likely concentrate on identifying the primary antigenic epitopes involved in AA and the genetics of AA susceptibility. With a comprehensive understanding of the key elements in AA pathogenesis, new avenues for therapeutic research and intervention will be defined.

Transfer of CD8(+) cells induces localized hair loss whereas CD4(+)/CD25(-) cells promote systemic alopecia areata and CD4(+)/CD25(+) cells blockade disease onset in the C3H/HeJ mouse model

Alopecia areata (AA) is a suspected hair follicle specific autoimmune disease. The potential for cell transfer of AA using the C3H/HeJ mouse model was examined. Cells isolated from lymph nodes and spleens of AA-affected mice using magnetic bead conjugated monoclonal antibodies were subcutaneously injected into normal C3H/HeJ recipients. Within 5 wk, all CD8(+) cell-injected mice exhibited localized hair loss exclusively at the site of injection that persisted until necropsy. In contrast, some CD4(+) and CD4(+)/CD25(-) cell-injected mice developed extensive, systemic AA, and a combination of CD8(+) and CD4(+)/CD25(-) cells injected yielded the highest frequency of systemic AA induction. CD4(+)/CD25(+) cells were less able to transfer the disease phenotype, partially blockaded systemic AA induction by CD4(+)/CD25(-) cells, and prevented CD8(+) cell-induced, injection site-localized hair loss. CD11c(+) and CD19(+) cells failed to promote significant phenotype changes. Increases in co-stimulatory ligands CD40 and CD80, plus increased leukocyte apoptosis resistance with reduced CD95, CD95L, and CD120b expression, were associated with successful alopecia induction. The results suggest that CD8(+) cells may be the primary instigators of the hair loss phenotype. However, systemic disease expression fate is, apparently determined by CD4(+)/CD25(-) cells, while CD4(+)/CD25(+) lymphocytes may play a predominantly regulatory role.

Apoptosis resistance in peripheral blood lymphocytes of alopecia areata patients

Alopecia areata (AA) is a putative, cell-mediated autoimmune disease of anagen stage hair follicles. Inter- and intra-follicular lymphocytic infiltrates are associated with alopecia that may progress from an initially patchy presentation to extensive, even universal, hair loss. We previously noted in a mouse model of AA that regulatory T cells (Treg) are absent from draining lymph nodes and that expression of CD44v7 is transiently upregulated. Both features might explain autoreactive T cell persistence. Here we explored whether similar changes are seen in AA patients' peripheral blood mononuclear cells (PBMC). There was no clear evidence for a reduction in Treg as a possible means to support sustained T cell activation. However, progressive AA patients' PBMC displayed increased resistance towards apoptosis, which was accompanied by a decrease in CD95L+ and an increase in CD44v7+ cells. Notably, an expanded population of CD4+CD25+CD154+ T cells in progressive AA patients' PBMC was apoptosis resistant and expressed CD44v7. Thus, survival of activated T cells in progressive AA patients' PBMC is apparently sustained by downregulation of CD95L and upregulation of CD44v7 which is known to be associated with anti-apoptotic gene expression.

The progressive state, in contrast to the stable or regressive state of alopecia areata, is reflected in peripheral blood mononuclear cells

Alopecia areata (AA) is a putative autoimmune disease of the skin with an inflammatory component that can be treated by the local application of contact sensitizers. Here, we explored whether responsiveness toward diphenylcyclopropenone (DPCP) is reflected by the composition and the activation state of peripheral blood mononuclear cells (PBMCs). PBMCs of 43 AA patients, 26 treated and 17 untreated, and of 31 healthy volunteers were tested. AA patients' PBMCs differed from that of healthy donors by a slight increase in CD16- and tumor necrosis factor-alpha (TNF-alpha)-expressing cells. These features were independent of the disease state and treatment. Additional changes in the activation state of PBMCs, upregulation of the costimulatory molecules CD40 and CD80, of the accessory molecule CD154, and of interferon-gamma expression were identified only in AA patients where the disease was advancing, i.e. these changes were independent of the extent of hair loss and were not seen in patients with spontaneous or DPCP treatment-induced, regressing AA. Thus, the progressive state of AA is accompanied by a systemic activation of T cells, and the therapeutic efficacy of treatment can be estimated by restoration of the non-activated state. Furthermore, an increase in CD16(+)- and TNF-alpha-expressing cells may contribute to AA susceptibility.

Mouse alopecia areata models: an array of data on mechanisms and genetics

Laboratory mice have become the premier animal model for most human and domestic animal diseases, and they have long been the model of choice for studying mammalian genetics, especially since the advent of genetic engineering. Many remarkable discoveries have been made through intense study of these wonderful small mammals, and undoubtably many more will be made. It is no surprise that one mouse model for alopecia areata (AA) has been found possibly many more will be, some of which exhibit rare phenotypes found in subpopulations of humans with the disease, such as nail deformities, thyroid disease, inflammatory bowel disease, and autoimmune polyendocrine syndrome type 1. Intense investigation by many groups into the first model, the adult onset form of AA (using the C3H/HeJ inbred strain), found similarities as well as differences with commonly held ideas concerning human AA. Regardless of some of the controversies, much insight has been gained from studying these and other rodent and domestic animal models which has opened up new ideas and discussions of AA and its treatment.

Alopecia areata susceptibility in rodent models

With our current view of alopecia areata as an autoimmune disease, it is probable that disease development in an individual is dependent on multiple genetic and environmental factors interacting in a complex system. Rodent models afford the opportunity to investigate alopecia areata development and to define the significance of the different factors involved. Recently, rodent model characterization has been conducted using flow cytometry, microarray analysis, and functional studies. From these a pattern of events in alopecia areata development has emerged. Although the preliminary activation events for the onset of alopecia areata remain unknown, the response of the immune system is characterized by antigen presentation and costimulation of lymphocytes in the lymph nodes and skin, a deficiency of CD4+/CD25+ regulatory cells, and an action of activated lymphocytes on hair follicles via Fas/FasL signaling and cytokines. Thus, onset of disease may require appropriate (or inappropriate) expression of stimulatory antigens within the hair follicle, the breakdown of the putative hair follicle immune privilege, the presentation of antigens to the immune system, a failure of immune system regulation, and the ability of the activated immune system to disrupt anagen-stage hair follicles. Once the sequence of events is initiated, it may become a self-perpetuating cycle, with epitope spreading leading to a wider range of targets in chronic alopecia areata. Rodent model studies have provided significant insight into alopecia areata, but much more remains to be explained about the mechanisms of disease development.

Chronic delayed-type hypersensitivity reaction as a means to treat alopecia areata

The acute phase of alopecia areata (AA) is characterized by an increase in CD44v3+ and CD44v10+ skin-infiltrating leucocytes (SkIL). Induction of a contact eczema, one of the therapeutic options in AA, can be mitigated strongly by a blockade of CD44v10. The observation that induction of a delayed type hypersensitivity (DTH) reaction abrogates an autoimmune reaction, where both responses apparently use similar effector mechanisms, is surprising and prompted us to search for the underlying mechanisms. AA-affected C3H/HeJ mice were treated with the contact sensitizer SADBE (squaric acid dibutylester) and leucocyte subpopulations and their activation state was evaluated in SkIL and draining lymph nodes. AA-affected mice exhibited an increased number of SkIL with a predominance of T lymphocytes. After treatment with the contact sensitizer SADBE recovery of SkIL was reduced and monocytes predominated. However, a significantly increased number of leucocytes was recovered from draining lymph nodes. Draining lymph node cells from untreated and treated AA mice exhibited all signs of recent activation with high-level expression of co-stimulatory and accessory molecules and an increased percentage of CD44v3+ and CD44v10+ leucocytes. In contrast, SkIL of SADBE-treated AA mice contained relatively few activated T cells and reduced numbers of CD44v3+ and CD44v10+ cells. Thus, the activation state and the distribution of leucocyte subsets in SADBE-treated AA mice are consistent with a blockade of leucocyte extravasation. Accordingly, the therapeutic effect of long-term SADBE treatment may rely on impaired leucocyte traffic.

Neurotrophins and their role in pathogenesis of alopecia areata

Neurotrophins comprise a family of structurally and functionally related proteins that are critical for the development and maintenance of cutaneous innervation. They also fulfill multiple non-neurotrophic functions in skin, including regulation of epidermal proliferation and apoptosis, control of hair follicle development and cycling, and melanogenesis. Numerous indications suggest that neurotrophins play an important role in the pathogenesis of a variety of autoimmune diseases. In this review, we focus on the role of neurotrophins in the pathogenesis of alopecia areata, an autoimmune disorder that affects actively growing hair follicles. Recent data suggest that neurotrophins and their receptors are differentially expressed among the subsets of immune cells in alopecia areata-affected skin. Experimental data suggest that neurotrophins may regulate both the cyclic activity of the hair follicle and the functions of immune cells of inflammatory infiltrates. Additional research is required to bridge the gap between our current knowledge of neurotrophin functions in skin affected by alopecia areata and our knowledge of their potential clinical applications. Progress in this area of research will hopefully lead to the development of multiple applications for neurotrophins and their agonists/antagonists in alopecia areata and other hair growth disorders.