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

Vasoactive intestinal peptide, whose receptor-mediated signalling may be defective in alopecia areata, provides protection from hair follicle immune privilege collapse

BACKGROUND

Alopecia areata (AA) is an autoimmune disorder whose pathogenesis involves the collapse of the relative immune privilege (IP) of the hair follicle (HF). Given that vasoactive intestinal peptide (VIP) is an immunoinhibitory neuropeptide released by perifollicular sensory nerve fibres, which play a role in IP maintenance, it may modulate human HF-IP and thus be therapeutically relevant for AA.

OBJECTIVES

To answer the following questions: Do human HFs express VIP receptors, and does their stimulation protect from or restore experimentally induced HF-IP collapse? Is VIP signalling defective in AA HFs?

METHODS

Firstly, VIP and VIP receptor (VPAC1, VPAC2) expression in human scalp HFs and AA skin was assessed. In HF organ culture, we then explored whether VIP treatment can restore and/or protect from interferon-γ-induced HF-IP collapse, assessing the expression of the key IP markers by quantitative (immuno-)histomorphometry.

RESULTS

Here we provide the first evidence that VIP receptors are expressed in the epithelium of healthy human HFs at the gene and protein level. Furthermore, VIP receptor protein expression, but not VIP(+) nerve fibres, is significantly downregulated in lesional hair bulbs of patients with AA, suggesting defects in VIP receptor-mediated signalling. Moreover, we show that VIP protects the HF from experimentally induced IP collapse in vitro, but does not fully restore it once collapsed.

CONCLUSIONS

These pilot data suggest that insufficient VIP receptor-mediated signalling may contribute to impairing HF-IP in patients with AA, and that VIP is a promising candidate 'HF-IP guardian' that may be therapeutically exploited to inhibit the progression of AA lesions.

Efficacy of tofacitinib in treatment of alopecia universalis in two patients

BACKGROUND

Autoimmune-triggered non-scarring hair loss is a feature of alopecia areata (AA). Initially patchy and often self-limited, severe hair loss forms include the complete loss of scalp hair or alopecia totalis (AT) and complete loss of all hair or alopecia universalis (AU). For AT and AU a reliable treatment has remained elusive. The targeted kinase inhibitor tofacitinib, in current use for treatment of other immune diseases, has been hypothesized as a viable option for AA, AT and AU therapy and a few case reports support this.

OBJECTIVE

Our study aims to provide evidence for the effectiveness of tofacitinib in the treatment of AU.

METHODS

Two patients diagnosed with long-term AU were prescribed tofacitinib citrate at a dosage of 5 mg twice daily and observed for eight months.

RESULTS

In the first patient, beard growth was significant by 3 months of treatment. By 6 months of treatment, hair growth was apparent throughout the entire body. By 8 months of treatment, scalp hair continued to grow longer and thicker. In addition, eyelashes and eyebrows were established. In the second patient, a noticeable increase in scalp hair was present just 1 month into treatment. By 4 months into treatment, significant scalp regrowth was observed as well as eyelash, eyebrow and beard regrowth. Axillary hair regrowth and isolated leg hair was noted by 8 months.

CONCLUSION

In our patients, tofacitinib successfully alleviated AU in the absence of significant adverse side-effects. We recommend that further study be required to establish safety and confirm efficacy.

Alopecia areata and narcolepsy: a tale of obscure autoimmunity

Alopecia areata is an autoimmune dermatological disorder characterised by loss of hair in one or more discrete patches over the scalp. It has been linked to multiple disorders having an autoimmune origin. Like many autoimmune disorders it tends to be more common in females. To date, only five cases have been reported where alopecia has been associated with narcolepsy. Male gender is less commonly affected by alopecia areata. No case of alopecia areata in males has been associated with narcolepsy to the best of our knowledge. The current case represents the first ever-reported case of alopecia areata in a male patient with narcolepsy type 1. This coexistence is most likely the manifestation of a common underlying pathoimmunological mechanism that has not been completely understood, rather than a random association.

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.

B cell activating factor and T-helper 17 cells: possible synergistic culprits in the pathogenesis of Alopecia Areata

The role of T-helper 17 cells (Th17) and regulatory T-cells (Tregs) in the pathogenesis of alopecia areata (AA) has not been clearly elucidated. B cell activating factor (BAFF) being a regulator of T cell activation could be involved in this pathologic process as well. The current study evaluated the expression of IL-17, IL-22, Foxp3 and BAFF in tissue and sera of AA patients. Forty AA patients and 40 age and sex matched healthy controls were included. Tissue and serum levels of IL-17, IL-22, BAFF as well as serum level of Foxp3 were measured by enzyme-linked immunosorbent assay (ELISA). Immunohistochemical staining was used for assessment of tissue level of Foxp3. Tissue and serum levels of IL-17, tissue levels of IL-22 and BAFF were significantly higher in patients. Serum levels of IL-22, Foxp3 and BAFF were non-significantly higher in patients. Foxp3 immunostaining showed negativity in tissue of patients and controls. A significant positive correlation was found between both tissue levels of IL-17 and BAFF (r = 0.474, P = 0.035) and tissue level of IL-22 and disease duration (r = 0.766, P < 0.001) in AA patients. Th17 cells and BAFF are synergistically involved in the pathogenesis of AA. BAFF represents a promising therapeutic target for such a challenging disease. Defective Tregs number and/or function in AA warrants further studies.

Cicatricial alopecia: What’s new in etiology?

Cicatricial alopecia is a rare, clinically diversified set of disorders causing permanent and irreversible hair loss, which often results in serious discomfort and patient’s mental problems.

Clinically, this form of irreversible hair loss is characterized by visible loss of hair follicle openings in the bald spots. Histologically, it consists in destroying a hair follicle and replacing it with fibrocartilage. Such disorders are perceived as primary if a hair follicle itself is the target of the disease process and secondary if hair follicles are damaged incidentally in the context of more general tissue damage (e.g. deep skin infections, thermal burns, trauma or ionizing radiation).

In this article we tried to summarize the knowledge on possible pathogenic mechanisms of cicatricial alopecia. The presented factors usually overlap and affect prognosis of particular patients. Their profound understanding may enable further research on the treatment methods of this challenging disease unit.

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.

Hair regrowth in alopecia areata patients following Stem Cell Educator therapy

BACKGROUND

Alopecia areata (AA) is one of the most common autoimmune diseases and targets the hair follicles, with high impact on the quality of life and self-esteem of patients due to hair loss. Clinical management and outcomes are challenged by current limited immunosuppressive and immunomodulating regimens.

METHODS

We have developed a Stem Cell Educator therapy in which a patient's blood is circulated through a closed-loop system that separates mononuclear cells from the whole blood, allows the cells to briefly interact with adherent human cord blood-derived multipotent stem cells (CB-SC), and returns the "educated" autologous cells to the patient's circulation. In an open-label, phase 1/phase 2 study, patients (N = 9) with severe AA received one treatment with the Stem Cell Educator therapy. The median age was 20 years (median alopecic duration, 5 years).

RESULTS

Clinical data demonstrated that patients with severe AA achieved improved hair regrowth and quality of life after receiving Stem Cell Educator therapy. Flow cytometry revealed the up-regulation of Th2 cytokines and restoration of balancing Th1/Th2/Th3 cytokine production in the peripheral blood of AA subjects. Immunohistochemistry indicated the formation of a "ring of transforming growth factor beta 1 (TGF-β1)" around the hair follicles, leading to the restoration of immune privilege of hair follicles and the protection of newly generated hair follicles against autoimmune destruction. Mechanistic studies revealed that co-culture with CB-SC may up-regulate the expression of coinhibitory molecules B and T lymphocyte attenuator (BTLA) and programmed death-1 receptor (PD-1) on CD8β(+)NKG2D(+) effector T cells and suppress their proliferation via herpesvirus entry mediator (HVEM) ligands and programmed death-1 ligand (PD-L1) on CB-SCs.

CONCLUSIONS

Current clinical data demonstrated the safety and efficacy of the Stem Cell Educator therapy for the treatment of AA. This innovative approach produced lasting improvement in hair regrowth in subjects with moderate or severe AA.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01673789, 21 August 2012.

Colocalization of vitiligo and alopecia areata presenting as poliosis

Vitiligo and alopecia areata are two cutaneous diseases believed to be primarily autoimmune in pathogenesis. While the coexistence of the two conditions in the same patient has been well-described, reports of the two disease processes occurring in the same location are rare. We report the case of a 10-year-old male with an unremarkable past medical history who presented with a single localized area of poliosis with depigmented underlying skin on the frontal scalp. The hair in the affected area was relatively decreased in density. A punch biopsy of the depigmented patch demonstrated features consistent with both vitiligo and alopecia areata. The decreased number of large hair follicles and a focal peribulbar lymphocytic infiltrate around an anagen follicle were suggestive of alopecia areata. A panel of melanocyte-specific stains revealed absent melanocytes in the epidermis, consistent with vitiligo. Loss of microphthalmia-associated transcription factor-positive root sheath cells was seen, suggestive of loss of melanocyte stem cells. The combination of clinical and histopathologic findings supports the theory of a common pathogenesis of alopecia areata and vitiligo.

X-box binding protein 1 is a novel key regulator of peroxisome proliferator-activated receptor γ2

X-box binding protein 1 (XBP1), a transcription factor of the unfolded protein response, plays various roles in many biological processes. We examined its pro-adipogenic activity and target genes during adipogenic differentiation in wild-type and genetically modified 3T3-L1 cells. Signalling pathways that contribute to Xbp1 mRNA splicing, and the correlation of the transcriptionally active XBP1 isoform (XBP1s) level with body mass index and the level of peroxisome proliferator-activated receptor γ2 (PPARγ2) in human adipose tissues were also examined. The mRNA and nuclear protein expression levels of XBP1s increased immediately following hormonal induction of adipogenesis, reaching a peak at 6 h. Results from cDNA microarray and gene expression analyses using genetically modified cells indicated that PPARγ2 was a principal target of XBP1s. The XBP1s-specific binding motif, which is distinct from the CCAAT/enhancer-binding protein α binding site, was identified in the PPARγ2 promoter by site-directed mutagenesis. Fetal bovine serum, insulin, 3-isobutyl-1-methylxanthine and dexamethasone contributed independently to Xbp1 mRNA splicing. In human subcutaneous adipose tissues, the levels of both Xbp1s and Pparγ2 mRNA increased proportionally with body mass index, and there was a significant positive correlation between the two genes. These data suggest for the first time that positive regulation of PPARγ2 is a principal mechanism of XBP1s-mediated adipogenesis in 3T3-L1 cells.

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

Alopecia areata (AA) is a CD8+ T-cell dependent autoimmune disease of the hair follicle (HF) in which the collapse of HF immune privilege (IP) plays a key role. Mast cells (MCs) are crucial immunomodulatory cells implicated in the regulation of T cell-dependent immunity, IP, and hair growth. Therefore, we explored the role of MCs in AA pathogenesis, focusing on MC interactions with CD8+ T-cells in vivo, in both human and mouse skin with AA lesions. Quantitative (immuno-)histomorphometry revealed that the number, degranulation and proliferation of perifollicular MCs are significantly increased in human AA lesions compared to healthy or non-lesional control skin, most prominently in subacute AA. In AA patients, perifollicular MCs showed decreased TGFβ1 and IL-10 but increased tryptase immunoreactivity, suggesting that MCs switch from an immuno-inhibitory to a pro-inflammatory phenotype. This concept was supported by a decreased number of IL-10+ and PD-L1+ MCs, while OX40L+, CD30L+, 4–1BBL+ or ICAM-1+ MCs were increased in AA. Lesional AA-HFs also displayed significantly more peri- and intrafollicular- CD8+ T-cells as well as more physical MC/CD8+ T-cell contacts than healthy or non-lesional human control skin. During the interaction with CD8+ T-cells, AA MCs prominently expressed MHC class I and OX40L, and sometimes 4–1BBL or ICAM-1, suggesting that MC may present autoantigens to CD8+ T-cells and/or co-stimulatory signals. Abnormal MC numbers, activities, and interactions with CD8+ T-cells were also seen in the grafted C3H/HeJ mouse model of AA and in a new humanized mouse model for AA. These phenomenological in vivo data suggest the novel AA pathobiology concept that perifollicular MCs are skewed towards pro-inflammatory activities that facilitate cross-talk with CD8+ T-cells in this disease, thus contributing to triggering HF-IP collapse in AA. If confirmed, MCs and their CD8+ T-cell interactions could become a promising new therapeutic target in the future management of AA.

The immune system of mouse vibrissae follicles: cellular composition and indications of immune privilege

Although vibrissae hair follicles (VHFs) have long been a key research model in the life sciences, their immune system (IS) is essentially unknown. Therefore, we have characterized basic parameters of the VHF-IS of C57BL/6J mice by quantitative (immuno-)histomorphometry. Murine anagen VHF harbour few CD4+ and CD8+ T cells in the distal mesenchyme and sinuses but hardly any gamma-delta T cells in their distal epithelium. MHC class II+ Langerhans cells are seeded in the VHF infundibulum, which is also surrounded by MHC class II+ and CD11b+ cells (macrophages). The number of Langerhans cells then declines sharply in the VHF bulge, and the VHF bulb lacks MHC class II+ cells. Mast cells densely populate the VHF connective tissue sheath, where they strikingly cluster around the bulge. Both the bulge and the bulb of VHF display signs of immune privilege, that is, low MHC class I and MHC class II expression and local immunoinhibitor expression (CD200, TGFβ1). This immunophenotyping study fills an important gap in the immunobiology of murine skin and identifies differences between the IS of VHF, mouse pelage and human terminal HFs. This facilitates utilizing murine VHF as a versatile organ culture model for general immunology and immune privilege research in situ.

The role of hair follicle immune privilege collapse in alopecia areata: status and perspectives

Alopecia areata (AA) may represent a CD8+T cell-mediated, organ-specific autoimmune disease in which as yet elusive autoantigens are recognized, once they become exposed by ectopic major histocompatibility complex class I expression by anagen hair follicles (HFs) that have lost their relative immune privilege (IP). On this basis, AA research is chiefly challenged with identifying the autoreactive CD8+T cells and their cognate autoantigens as well as key inducers of HF-IP collapse and "HF-IP guardians" that prevent and/or can restore IP collapse. However, natural killer group 2D-positive (NKG2D+) cells (incl. NK, NKT, and CD8+T cells) and NKG2D-activating ligands from the MICA (MHC I-related chain A) family may also have a key role in AA pathogenesis, as a massive infiltrate of IFN-γ-secreting NKG2D+ cells alone suffices to induce the AA phenotype. Therefore, we speculate that AA may represent a stereotypic, but distinct HF response pattern to inflammatory insults associated with HF-IP collapse.

Lichen planopilaris is characterized by immune privilege collapse of the hair follicle's epithelial stem cell niche

Lichen planopilaris (LPP) is a chronic inflammatory disease of unknown pathogenesis that leads to permanent hair loss. Whilst destruction of epithelial hair follicle stem cells (eHFSCs) that reside in an immunologically protected niche of the HF epithelium, the bulge, is a likely key event in LPP pathogenesis, this remains to be demonstrated. We have tested the hypotheses that bulge immune privilege (IP) collapse and inflammation-induced eHFSC death are key components in the pathogenesis of LPP. Biopsies of lesional and non-lesional scalp skin from adult LPP patients (n = 42) were analysed by quantitative (immuno)histomorphometry, real-time quantitative polymerase chain reaction (qRT-PCR), laser capture microdissection and microarray analysis, or skin organ culture. At both the protein and transcriptional level, lesional LPP HFs showed evidence for bulge IP collapse (ie increased expression of MHC class I and II, β2microglobulin; reduced TGFβ2 and CD200 expression). This was accompanied by a Th1-biased cytotoxic T cell response (ie increased CD8(+) GranzymeB(+) T cells and CD123(+) plasmacytoid dendritic cells, with increased CXCR3 expression) and increased expression of interferon-inducible chemokines (CXCL9/10/11). Interestingly, lesional LPP eHFSCs showed both increased proliferation and apoptosis in situ. Microarray analysis revealed a loss of eHFSC signatures and increased expression of T cell activation/binding markers in active LPP, while bulge PPARγ transcription was unaltered compared to non-lesional LPP HFs. In organ culture of non-lesional LPP skin, interferon-γ (IFNγ) induced bulge IP collapse. LPP is an excellent model disease for studying and preventing immune destruction of human epithelial stem cells in situ. These novel findings raise the possibility that LPP represents an autoimmune disease in whose pathogenesis IFNγ-induced bulge IP collapse plays an important role. Therapeutically, bulge IP protection/restoration may help to better manage this highly treatment-resistant cicatricial alopecia.

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.

Tumour necrosis factor alpha, interferon gamma and substance P are novel modulators of extrapituitary prolactin expression in human skin

Human scalp skin and hair follicles (HFs) are extra-pituitary sources of prolactin (PRL). However, the intracutaneous regulation of PRL remains poorly understood. Therefore we investigated whether well-recognized regulators of pituitary PRL expression, which also impact on human skin physiology and pathology, regulate expression of PRL and its receptor (PRLR) in situ. This was studied in serum-free organ cultures of microdissected human scalp HFs and skin, i.e. excluding pituitary, neural and vascular inputs. Prolactin expression was confirmed at the gene and protein level in human truncal skin, where its expression significantly increased (p = 0.049) during organ culture. There was, however, no evidence of PRL secretion into the culture medium as measured by ELISA. PRL immunoreactivity (IR) in female human epidermis was decreased by substance P (p = 0.009), while neither the classical pituitary PRL inhibitor, dopamine, nor corticotropin-releasing hormone significantly modulated PRL IR in HFs or skin respectively. Interferon (IFN) γ increased PRL IR in the epithelium of human HFs (p = 0.044) while tumour necrosis factor (TNF) α decreased both PRL and PRLR IR. This study identifies substance P, TNFα and IFNγ as novel modulators of PRL and PRLR expression in human skin, and suggests that intracutaneous PRL expression is not under dopaminergic control. Given the importance of PRL in human hair growth regulation and its possible role in the pathogenesis of several common skin diseases, targeting intracutaneous PRL production via these newly identified regulatory pathways may point towards novel therapeutic options for inflammatory dermatoses.

PTPN22 gene polymorphism in Egyptian alopecia areata patients and its impact on response to diphencyprone immunotherapy

PTPN22 1858C>T gene polymorphism has been associated with several autoimmune disorders including alopecia areata. The aim of the current study was to investigate the effect of the inherited genetic polymorphism 1858C>T of PTPN22 gene on the predisposition to severe forms of alopecia areata and its effect on the response to DPC treatment. To achieve our aim, PTPN22 1858C>T genotyping was performed by PCR-based restricted fragment length polymorphism (PCR-RFLP) analysis. The study included 103 Egyptian patients with extensive alopecia areata treated by DPC. Hundred healthy age and sex matched blood donors were included in the current study as a control group. Results of genotyping showed that PTPN22 CT and TT mutant genotypes were significantly higher in AA patients compared to controls and conferred increase risk of AA (OR=2.601, 95% CI=1.081-6.255). Statistical comparison between AA patients with wild and mutant genotypes revealed that the duration of the illness was significantly longer in those harboring the mutant genotypes. Moreover, the association of other autoimmune diseases as atopy and diabetes mellitus was higher in patients with mutant genotypes. Furthermore, PTPN22 1858C>T genetic polymorphism did not affect the patients' response to DPC immunotherapy.

Effects of calcitonin gene-related peptide on the immune privilege of human hair follicles

The hair follicle is a widely available and instructive miniature organ in the human body that experiences major histocompatibility complex (MHC) class I dependent immune privilege (IP). There are various regulation factors that act on the generation, maintenance, and collapse of hair follicle IP. Neuropeptides such as calcitonin gene-related peptide (CGRP) are created in many organs, including skin, and display various immune regulation effects. The purpose of this study was to investigate the phenotypic effect of CGRP on the hair follicle's IP. First, we used interferon-γ (IFN-γ) to generate ectopic MHC antigen expression model in cultured human hair follicles as previously described. Then, we examined the effects of CGRP on the regulation of ectopic MHC antigen expression in cultured human hair follicles using reverse transcriptase-polymerase chain reaction (RT-PCR) and immunohistochemical staining techniques. IFN-γ (75 IU/ml) induced ectopic MHC expression. CGRP down-regulated INF-γ-induced ectopic MHC class I mRNA expression. These down-regulated effects were especially evident in 10(-8)M. In addition, CGRP also suppressed the staining intensity related to the expression of MHC class I and MHC class I-pathway related molecules (β2-microglobulin), but had no effect on MHC class II antigen expression. Taken together, these results indicate that CGRP might be an important regulatory factor for IP maintenance and restoration of IP via suppression of MHC class I antigen.

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.

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.

Epidermal growth factor receptor inhibition augments the expression of MHC class I and II genes

PURPOSE

Diverse immune-related effects occur with the use of epidermal growth factor receptor inhibitors (EGFRI). In addition to the cutaneous inflammation induced by EGFRIs, these agents have been associated with the exacerbation of autoimmune skin disease and contact hypersensitivity, antiviral effects, and fatal alveolar damage in the setting of lung transplantation. Because EGFR ligands can modulate MHC class I (MHCI) and II (MHCII) molecule expression, we hypothesized that some of the immune-related effects of EGFRIs are due to direct effects on the expression of MHCI and/or MHCII molecules.

EXPERIMENTAL DESIGN

Primary human keratinocytes and a malignant keratinocyte cell line (A431) were treated with EGFRIs alone or prior to IFN-γ, a potent inducer of MHCI and MHCII molecule expression. CIITA, MHCI, and MHCII RNA expression was measured using quantitative real-time reverse transcriptase PCR, and cell surface MHCI and MHCII protein expression was measured using flow cytometry. Skin biopsies from patients were analyzed for MHCI and MHCII protein expression before and during therapy with an EGFRI using immunohistochemistry.

RESULTS

Both EGFR tyrosine kinase inhibitors and ligand-blocking antibodies (cetuximab) augmented the induction of MHCI and MHCII molecules by IFN-γ in primary and malignant human keratinocytes. Unexpectedly, the increase in MHCI protein expression did not require the presence of IFN-γ. Consistent with these in vitro findings, skin biopsies from cancer patients exhibited increased epidermal MHCI protein expression during therapy with an EGFRI as well as increases in MHCI and MHCII molecule RNA.

CONCLUSIONS

These studies suggest that EGFRIs may influence immune/inflammatory responses by directly modulating MHC expression. Clin Cancer Res; 17(13); 4400-13. ©2011 AACR.

IGF-1 and atherothrombosis: relevance to pathophysiology and therapy

IGF-1 (insulin-like growth factor-1) plays a unique role in the cell protection of multiple systems, where its fine-tuned signal transduction helps to preserve tissues from hypoxia, ischaemia and oxidative stress, thus mediating functional homoeostatic adjustments. In contrast, its deprivation results in apoptosis and dysfunction. Many prospective epidemiological surveys have associated low IGF-1 levels with late mortality, MI (myocardial infarction), HF (heart failure) and diabetes. Interventional studies suggest that IGF-1 has anti-atherogenic actions, owing to its multifaceted impact on cardiovascular risk factors and diseases. The metabolic ability of IGF-1 in coupling vasodilation with improved function plays a key role in these actions. The endothelial-protective, anti-platelet and anti-thrombotic activities of IGF-1 exert critical effects in preventing both vascular damage and mechanisms that lead to unstable coronary plaques and syndromes. The pro-survival and anti-inflammatory short-term properties of IGF-1 appear to reduce infarct size and improve LV (left ventricular) remodelling after MI. An immune-modulatory ability, which is able to suppress 'friendly fire' and autoreactivity, is a proposed important additional mechanism explaining the anti-thrombotic and anti-remodelling activities of IGF-1. The concern of cancer risk raised by long-term therapy with IGF-1, however, deserves further study. In the present review, we discuss the large body of published evidence and review data on rhIGF-1 (recombinant human IGF-1) administration in cardiovascular disease and diabetes, with a focus on dosage and safety issues. Perhaps the time has come for the regenerative properties of IGF-1 to be assessed as a new pharmacological tool in cardiovascular medicine.

A neuroendocrinological perspective on human hair follicle pigmentation

The role of neurohormones and neuropeptides in human hair follicle (HF) pigmentation extends far beyond the control of melanin synthesis by α-MSH and ACTH and includes melanoblast differentiation, reactive oxygen species scavenging, maintenance of HF immune privilege, and remodeling of the HF pigmentary unit (HFPU). It is now clear that human HFs are not only a target of multiple neuromediators, but also are a major non-classical production site for neurohormones such as CRH, proopiomelanocortin, ACTH, α-MSH, ß-endorphin, TRH, and melatonin. Moreover, human HFs have established a functional peripheral equivalent of the hypothalamic-pituitary-adrenal axis. By charting the author's own meanderings through the jungle of hair pigmentation research, the current perspectives essay utilizes four clinical observations - hair repigmentation, canities, poliosis, and 'overnight greying'- as points of entry into the enigmas and challenges of .pigmentary HF neuroendocrinology. After synthesizing key principles and defining major open questions in the field, selected research avenues are delineated that appear clinically most promising. In this context, novel neuroendocrinological strategies to retard or reverse greying and to reduce damage to the HFPU are discussed.

An unexpected twist in alopecia areata pathogenesis: are NK cells protective and CD49b+ T cells pathogenic?

Natural killer (NK) cells have become a recent focus of interest in alopecia areata (AA) research. To further investigate their role in an established mouse model of AA, lesional skin from older C3H/HeJ mice with AA was grafted to young C3H/HeJ female mice, and NK cells were depleted by continuous administration of rabbit anti-asialo GM1. As expected, this significantly reduced the number of pure NK cells in murine skin, as assessed by NKp46 quantitative immunohistochemistry. Quite unexpectedly, however, the onset of hair loss in C3H/HeJ mice was accelerated, rather than retarded. NK cell depletion was accompanied by a significant increase in the number of perifollicular CD49b+T cells in the alopecic skin of anti-asialo GM1-treated mice. These findings underscore the need to carefully distinguish in future AA research between pure NK cells and defined subsets of CD49b+ lymphocytes, as they may exert diametrically opposed functions in hair follicle immunology and immunopathology.