Transgenic mice expressing IFN-gamma in the epidermis have eczema, hair hypopigmentation, and hair loss

Gut-tropic T cells and extra-intestinal autoimmune diseases

Gut-tropic T cells primarily originate from gut-associated lymphoid tissue (GALT), and gut-tropic integrins mediate the trafficking of the T cells to the gastrointestinal tract, where their interplay with local hormones dictates the residence of the immune cells in both normal and compromised gastrointestinal tissues. Targeting gut-tropic integrins is an effective therapy for inflammatory bowel disease (IBD). Gut-tropic T cells are further capable of entering the peripheral circulatory system and relocating to multiple organs. There is mounting evidence indicating a correlation between gut-tropic T cells and extra-intestinal autoimmune disorders. This review aims to systematically discuss the origin, migration, and residence of gut-tropic T cells and their association with extra-intestinal autoimmune-related diseases. These discoveries are expected to offer new understandings into the development of a range of autoimmune disorders, as well as innovative approaches for preventing and treating the diseases.

A ZFYVE21-Rubicon-RNF34 signaling complex promotes endosome-associated inflammasome activity in endothelial cells

Internalization of complement membrane attack complexes (MACs) assembles NLRP3 inflammasomes in endothelial cells (EC) and promotes IL-β-mediated tissue inflammation. Informed by proteomics analyses of FACS-sorted inflammasomes, we identify a protein complex modulating inflammasome activity on endosomes. ZFVYE21, a Rab5 effector, partners with Rubicon and RNF34, forming a "ZRR" complex that is stabilized in a Rab5- and ZFYVE21-dependent manner on early endosomes. There, Rubicon competitively disrupts inhibitory associations between caspase-1 and its pseudosubstrate, Flightless I (FliI), while RNF34 ubiquitinylates and degradatively removes FliI from the signaling endosome. The concerted actions of the ZRR complex increase pools of endosome-associated caspase-1 available for activation. The ZRR complex is assembled in human tissues, its associated signaling responses occur in three mouse models in vivo, and the ZRR complex promotes inflammation in a skin model of chronic rejection. The ZRR signaling complex reflects a potential therapeutic target for attenuating inflammasome-mediated tissue injury.

The Experimental Animal Models in Psoriasis Research: A Comprehensive Review

Psoriasis is an autoimmune, chronic, inflammatory skin condition mediated by T cells. It differs from other inflammatory conditions by causing significant alterations in epidermal cell proliferation and differentiation that are both complicated and prominent. The lack of an appropriate animal model has significantly hindered studies into the pathogenic mechanisms of psoriasis since animals other than humans typically do not exhibit the complex phenotypic features of human psoriasis. A variety of methods, including spontaneous mutations, drug-induced mutations, genetically engineered animals, xenotransplantation models, and immunological reconstitution approaches, have all been employed to study specific characteristics in the pathogenesis of psoriasis. Although some of these approaches have been used for more than 50 years and far more models have been introduced recently, they have surprisingly not yet undergone detailed validation. Despite their limitations, these models have shown a connection between keratinocyte hyperplasia, vascular hyperplasia, and a cell-mediated immune response in the skin. The xenotransplantation of diseased or unaffected human skin onto immune-compromised recipients has also significantly aided psoriasis research. This technique has been used in a variety of ways to investigate the function of T lymphocytes and other cells, including preclinical therapeutic studies. The design of pertinent in vivo and in vitro psoriasis models is currently of utmost concern and a crucial step toward its cure. This article outlines the general approach in the development of psoriasis-related animal models, aspects of some specific models, along with their strengths and limitations.

IFN-γ and TGF-β, Crucial Players in Immune Responses: A Tribute to Howard Young

Interferon gamma (IFN-γ) and transforming growth factor beta (TGF-β), both pleiotropic cytokines, have been long studied and described as critical mediators of the immune response, notably in T cells. One of the investigators who made seminal and critical discoveries in the field of IFN-γ biology is Dr. Howard Young. In this review, we provide an overview of the biology of IFN-γ as well as its role in cancer and autoimmunity with an emphasis on Dr. Young's critical work in the field. We also describe how Dr. Young's work influenced our own research studying the role of TGF-β in the modulation of immune responses.

Inhibitory effect of α-cubebenoate on atopic dermatitis-like symptoms by regulating Th2/Th1/Th17 balance in vivo

ETHNOPHARMACOLOGICAL RELEVANCE

Bakumijiogan (Kampo herbal formulation) and Kangqian decoction (Chinese herbal medicine formulation) have been used for the treatment of atopic dermatitis (AD) like symptoms. Schisandra chinensis Baill (Family: Magnoliaceae) is a component of both formulations. Its extracts showed inhibition of AD.

AIM OF THE STUDY

We aimed to elucidate an active phytochemical from Schisandra chinensis and evaluated its effects on AD-like symptoms.

MATERIALS AND METHODS

We fractionated a component from Schisandra chinensis by chasing inhibitory activity on mast cell degranulation. We identified α-cubebenoate as an active phytochemical and investigated its effects by using an in vivo 1-chloro-2,4-dinitrobenzene (CDNB)-induced AD model in BALB/c mice.

RESULTS

α-Cubebenoate significantly decreased CDNB-induced skin hypertrophy and accumulation of mast cells in the epidermis and dermis. Increases in pro-inflammatory chemokine and cytokine levels in the skin, lymph node size, and immunoglobulin E levels in the serum were significantly ameliorated by α-cubebenoate.

CONCLUSION

α-Cubebenoate regulates dermal immune responses by suppressing the Th2/Th17/Th1 immune balances, resulting in amelioration of AD-like symptoms and suppression of immune response in lymph nodes. Thereby, this study provides evidence for its therapeutic efficacy in the treatment of AD symptoms.

Pinus thunbergii bark extract rich in flavonoids promotes hair growth in dorsal skin by regulating inflammatory cytokines and increasing growth factors in mice

Korean maritime pine bark (Pinus thunbergii) has been used as an alternative medicine due to its beneficial properties, including anti-inflammatory effects. To date, the anti-inflammatory and hair growth-promoting effects of Pinus densiflora bark extract have remained elusive. Therefore, in the present study, Pinus thunbergii bark was extracted with pure water (100°C) and the extract was examined to determine its polyphenol and flavonoid content. C57BL/6 mice were used to assess the effects of the extract to promote hair growth. The extract (1, 2 and 4%) was topically applied onto shaved dorsal skin and hair growth was observed for 17 days. A significant increase in hair growth was observed with 2 and 4% extract. Based on this finding, the optimal dose of the extract for effective hair growth promotion was determined to be 2%. The mechanisms of hair growth promotion were investigated via immunohistochemical analysis of changes in inflammatory cytokines and growth factors in the hair follicles following treatment with 2% extract. The treatment reduced the levels of TNF-α and IL-1β, which are pro-inflammatory cytokines, while it enhanced the levels of IL-4 and IL-13, which are anti-inflammatory cytokines, in the hair follicles. In addition, elevated insulin-like growth factor I and vascular epidermal growth factor were detected in hair follicles following treatment. Based on these findings, it was suggested that the extract of Pinus thunbergii bark may be utilized for hair loss prevention and/or hair growth promotion.

Effects of Decursin and Angelica gigas Nakai Root Extract on Hair Growth in Mouse Dorsal Skin via Regulating Inflammatory Cytokines

This current study investigates the facilitative effects and mechanisms of decursin, a major component of Angelica gigas Nakai (AGN), and AGN root extract on hair growth in mice. We perform high-performance liquid chromatography on AGN extract to show it contains 7.3% decursin. Hairs in mouse dorsal skin are shaved distilled in water, 0.15% decursin, and 2% AGN root extract (0.15% decursin in the diluted extract) and topically applied twice a day for 17 days. Hematoxylin and eosin staining are done to examine the morphological changes in the hair follicles. To compare the effects of decursin and AGN extract on inflammatory cytokines in the dorsal skin, Western blot analysis and immunohistochemistry for tumor necrosis factor α (TNF-α) and interleukin (IL)-1β as pro-inflammatory cytokines, and IL-4 and IL-13 as anti-inflammatory cytokines are conducted. The results show that the application of decursin and AGN extract confer effects on hair growth. Hair growth is significantly facilitated from seven days after the treatments compared to that in the control group, and completely grown hair was found 17 days after the treatments. The protein levels and immunoreactivity of TNF-α and IL-1β in this case are significantly decreased, whereas the IL-4 and IL-13 levels and immunoreactivity are significantly increased compared to those in the control group. Additionally, high-mobility group box 1, an inflammatory mediator, is elevated by the topical application of decursin and AGN extract. Taken together, the treatment of mouse dorsal skin with AGE root extract containing decursin promotes hair growth by regulating pro- and/or anti-inflammatory cytokines. We, therefore, suggest that AGN root extract as well as decursin can be utilized as materials for developing hair growth-facilitating treatments.

Animal models of psoriasis-highlights and drawbacks

Research into the pathophysiology of psoriasis remains challenging, because this disease does not occur naturally in laboratory animals. However, specific aspects of its complex immune-pathology can be illuminated through transgenic, knockout, xenotransplantation, immunological reconstitution, drug-induced, or spontaneous mutation models in rodents. Although some of these approaches have already been pursued for more than 5 decades and even more models have been described in recent times, they have surprisingly not yet been systematically validated. As a consequence, researchers regularly examine specific aspects that only partially reflect the complex overall picture of the human disease. Nonetheless, animal models are of great utility to investigate inflammatory mediators, the communication between cells of the innate and the adaptive immune systems, the role of resident cells as well as new therapies. Of note, various manipulations in experimental animals resulted in rather similar phenotypes. These were called "psoriasiform", "psoriasis-like" or even "psoriasis" usually on the basis of some similarities with the human disorder. Xenotransplantation of human skin onto immunocompromised animals can overcome this limitation only in part. In this review, we elucidate approaches for the generation of animal models of psoriasis and assess their strengths and limitations with a certain focus on more recently developed models.

The female-biased factor VGLL3 drives cutaneous and systemic autoimmunity

Autoimmune disease is 4 times more common in women than men. This bias is largely unexplained. Female skin is "autoimmunity prone," showing upregulation of many proinflammatory genes, even in healthy women. We previously identified VGLL3 as a putative transcription cofactor enriched in female skin. Here, we demonstrate that skin-directed overexpression of murine VGLL3 causes a severe lupus-like rash and systemic autoimmune disease that involves B cell expansion, autoantibody production, immune complex deposition, and end-organ damage. Excess epidermal VGLL3 drives a proinflammatory gene expression program that overlaps with both female skin and cutaneous lupus. This includes increased B cell-activating factor (BAFF), the only current biologic target in systemic lupus erythematosus (SLE); IFN-κ, a key inflammatory mediator in cutaneous lupus; and CXCL13, a biomarker of early-onset SLE and renal involvement. Our results demonstrate that skin-targeted overexpression of the female-biased factor VGLL3 is sufficient to drive cutaneous and systemic autoimmune disease that is strikingly similar to SLE. This work strongly implicates VGLL3 as a pivotal orchestrator of sex-biased autoimmunity.

From the Cover: Interplay Between IFN-γ and IL-6 Impacts the Inflammatory Response and Expression of Interferon-Regulated Genes in Environmental-Induced Autoimmunity

IFN-γ has been found to be robustly important to disease pathogenesis in both idiopathic and induced models of murine lupus. In transgenic mice, over production of IFN-γ in the skin results in an inflammatory response and autoimmunity. This suggests that localized exposure to environmental factors that induce autoimmunity may be associated with expression of an IFN-γ-dependent inflammatory response. Using murine mercury-induced autoimmunity (mHgIA), the severity of inflammation and proinflammatory cytokine expression, including the cellular source of IFN-γ, were assessed at the site of subcutaneous exposure and in secondary lymphoid organs. Exposure induced a localized chronic inflammation comprising both innate and adaptive immune cells but only CD8+ T and NK cells were reduced in the absence of IFN-γ. IFN-γ+ cells began to appear as early as day 1 and comprised both resident (γδ T) and infiltrating cells (CD8+ T, NKT, CD11c+). The requirements for inflammation were examined in mice deficient in genes required (Ifng, Il6) or not required (Casp1) for mHgIA. None of these genes were essential for induction of inflammation, however IFN-γ and IL-6 were required for exacerbation of other proinflammatory cytokines. Additionally, lack of IFN-γ or IL-6 impacted expression of genes regulated by either IFN-γ or type I IFN. Significantly, both IFN-γ and IL-6 were required for increased expression of IRF-1 which regulates IFN stimulated genes and is required for mHgIA. Thus IRF-1 may be at the nexus of the interplay between IFN-γ and IL-6 in exacerbating a xenobiotic-induced inflammatory response, regulation of interferon responsive genes and autoimmunity.

Clinical Signs, Pathophysiology and Management of Cutaneous Side Effects of Anti-Tumor Necrosis Factor Agents

Approximately one in four patients treated with anti-TNF agents (infliximab, etanercept, adalimumab, certolizumab, and golimumab) develops cutaneous adverse events, typically months to years after the initiation of treatment, with xerosis cutis, eczema (often psoriasiform), psoriasis, palmoplantar pustulosis, cutaneous infections, alopecia, and skin cancer being the most frequently encountered. The typical skin lesion of anti-tumor necrosis factor (TNF)-treated patients is orange-red psoriasiform eczema affecting the flexures, genitalia, scalp, or face, with high susceptibility to bacterial superinfection with Staphylococcus aureus. When adequate dermatological treatment is administered to patients with skin lesions receiving anti-TNF treatment, the discontinuation of anti-TNF agents is only rarely required. Smoking, female sex, and Crohn's disease are most frequently observed as risk factors for anti-TNF-induced cutaneous adverse events. The underlying pathophysiology is still poorly understood, but epidermal permeability barrier dysfunction, increased susceptibility to bacterial superinfection, and cytokines derived from T helper (Th) 1 (interferon-γ), Th17 cells (interleukin [IL]-17A and IL-22), plasmocytic dendritic cells (interferon-α), and keratinocytes (IL-36γ and IL-17C) appear to play a role. In this review, we describe the clinical characteristics, risk factors, pathophysiology, and management of cutaneous adverse events of patients treated with anti-TNF agents. In addition, we try to give some practical guidance on how to prevent and manage the skin changes in anti-TNF-treated patients, based on our own experience with dermatological care in a large cohort of inflammatory bowel disease patients receiving anti-TNF therapy.

Models in the Research Process of Psoriasis

Psoriasis is an ancient, universal chronic skin disease with a significant geographical variability, with the lowest incidence rate at the equator, increasing towards the poles. Insights into the mechanisms responsible for psoriasis have generated an increasing number of druggable targets and molecular drugs. The development of relevant in vitro and in vivo models of psoriasis is now a priority and an important step towards its cure. In this review, we summarize the current cellular and animal systems suited to the study of psoriasis. We discuss the strengths and limitations of the various models and the lessons learned. We conclude that, so far, there is no one model that can meet all of the research needs. Therefore, the choice model system will depend on the questions being addressed.

Vitiligo Skin Is Imprinted with Resident Memory CD8 T Cells Expressing CXCR3

Vitiligo is a chronic autoimmune depigmenting skin disorder that results from a loss of melanocytes. Multiple combinatorial factors have been involved in disease development, with a prominent role of the immune system, in particular T cells. After repigmentation, vitiligo frequently recurs in the same area, suggesting that vitiligo could involve the presence of resident memory T cells (T_RM). We sought to perform a thorough characterization of the phenotype and function of skin memory T cells in vitiligo. We show that stable and active vitiligo perilesional skin is enriched with a population of CD8 T_RM expressing both CD69 and CD103 compared with psoriasis and control unaffected skin. CD8 T_RM expressing CD103 are mainly localized in the epidermis. Expression of CXCR3 is observed on most CD8 T_RM in vitiligo, including the population of melanocyte-specific CD8 T cells. CD8 T_RM displayed increased production of IFN-γ and tumor necrosis factor-α with moderate cytotoxic activity. Our study highlights the presence of functional CD8 T_RM in both stable and active vitiligo, reinforcing the concept of vitiligo as an immune memory skin disease. The CD8 T_RM that remain in stable disease could play a role during disease flares, emphasizing the interest in targeting this cell subset in vitiligo.

Cross-talk between interferon-gamma and interleukin-18 in melanogenesis

Skin is the largest organ in our body and strategically placed to provide a metabolically active biological barrier against a range of noxious stressors. A lot of inflammatory cytokines, which are increased after ultraviolet (UV) irradiation produced by keratinocytes or other immunocytes, are closely related to pigmentary changes, including interleukin-18 (IL-18) and interferon-γ (IFN-γ). In this study, the effect of cross-talk between IL-18 and IFN-γ on melanogenesis was investigated. Treatment with IL-18 resulted in a dose-dependent increase of melanogenesis, while IFN-γ made an opposite effect. This influence of IL-18 and IFN-γ was mediated by regulations of microphthalmia-associated transcription factor (MITF) and its downstream enzymatic cascade expressions. Furthermore, IFN-γ inhibited basal and IL-18-induced melanogenesis. IFN-γ increased signal transducer and activator of transcription-1 (STAT-1) phosphorylation to play its position in regulating melanin pigmentation, and its inhibitory effect could be prevented by Janus Kinase 1 (JAK 1) inhibitor. IFN-γ could inhibit melanogenesis by decreasing melanocyte dendrite formation. In addition, IFN-γ inhibited the expressions of Rab Pases to suppress the mature and transport of melanosomes. IL-18 could rapidly induce Akt and PTEN phosphorylation and p65 expression in B16F10 cells. When treatment with IL-18 and IFN-γ together, the phosphorylation level of Protein Kinase B (Akt) and phosphatase and tensin homolog deleted on chromosome ten (PTEN) and expression of p65 NF-κB were inhibited, compared with treated with IL-18 only. Our studies indicated that IFN-γ could directly induce B16F10 cells apoptosis in vitro. Furthermore, we demonstrated that IFN-γ markedly up-regulated IL-18 binding protein (BP) production in normal human foreskin-derived epidermal keratinocytes in dose-dependent manner. UVB irradiation induced protease-activated receptor-2 (PAR-2) expression in NHEK, IFN-γ could inhibit this enhancement in a dose-dependent manner. These data suggest that IFN-γ plays a role in regulating inflammation- or UV-induced pigmentary changes, in direct/indirect manner.

The Silk-protein Sericin Induces Rapid Melanization of Cultured Primary Human Retinal Pigment Epithelial Cells by Activating the NF-κB Pathway

Restoration of the retinal pigment epithelial (RPE) cells to prevent further loss of vision in patients with age-related macular degeneration represents a promising novel treatment modality. Development of RPE transplants, however, requires up to 3 months of cell differentiation. We explored whether the silk protein sericin can induce maturation of primary human retinal pigment epithelial (hRPE) cells. Microarray analysis demonstrated that sericin up-regulated RPE-associated transcripts (RPE65 and CRALBP). Upstream analysis identified the NF-κB pathway as one of the top sericin-induced regulators. ELISA confirmed that sericin stimulates the main NF-κB pathway. Increased levels of RPE-associated proteins (RPE65 and the pigment melanin) in the sericin-supplemented cultures were confirmed by western blot, spectrophotometry and transmission electron microscopy. Sericin also increased cell density and reduced cell death following serum starvation in culture. Inclusion of NF-κB agonists and antagonists in the culture medium showed that activation of the NF-κB pathway appears to be necessary, but not sufficient, for sericin-induced RPE pigmentation. We conclude that sericin promotes pigmentation of cultured primary hRPE cells by activating the main NF-κB pathway. Sericin’s potential role in culture protocols for rapid differentiation of hRPE cells derived from embryonic or induced pluripotent stem cells should be investigated.

Cutting edge: NF-κB p65 and c-Rel control epidermal development and immune homeostasis in the skin

Psoriasis is an inflammatory skin disease in which activated immune cells and the proinflammatory cytokine TNF are well-known mediators of pathogenesis. The transcription factor NF-κB is a key regulator of TNF production and TNF-induced proinflammatory gene expression, and both the psoriatic transcriptome and genetic susceptibility further implicate NF-κB in psoriasis etiopathology. However, the role of NF-κB in psoriasis remains controversial. We analyzed the function of canonical NF-κB in the epidermis using CRE-mediated deletion of p65 and c-Rel in keratinocytes. In contrast to animals lacking p65 or c-Rel alone, mice lacking both subunits developed severe dermatitis after birth. Consistent with its partial histological similarity to human psoriasis, this condition could be prevented by anti-TNF treatment. Moreover, regulatory T cells in lesional skin played an important role in disease remission. Our results demonstrate that canonical NF-κB in keratinocytes is essential for the maintenance of skin immune homeostasis and is protective against spontaneous dermatitis.

Interferon gamma in autoimmunity: A complicated player on a complex stage

Early views of autoimmune disease cast IFNγ as a prototypic pro-inflammatory factor. It is now clear that IFNγ is capable of both pro- and anti-inflammatory activities with the functional outcome dependent on the physiological and pathological setting examined. Here, the major immune modulatory activities of IFNγ are reviewed and current evidence for the impact of IFNγ on pathology and regulation of several autoimmune diseases and disease models is summarized.

Mycophenolate antagonizes IFN-γ-induced catagen-like changes via β-catenin activation in human dermal papilla cells and hair follicles

Recently, various immunosuppressant drugs have been shown to induce hair growth in normal hair as well as in alopecia areata and androgenic alopecia; however, the responsible mechanism has not yet been fully elucidated. In this study, we investigate the influence of mycophenolate (MPA), an immunosuppressant, on the proliferation of human dermal papilla cells (hDPCs) and on the growth of human hair follicles following catagen induction with interferon (IFN)-γ. IFN-γ was found to reduce β-catenin, an activator of hair follicle growth, and activate glycogen synthase kinase (GSK)-3β, and enhance expression of the Wnt inhibitor DKK-1 and catagen inducer transforming growth factor (TGF)-β2. IFN-γ inhibited expression of ALP and other dermal papillar cells (DPCs) markers such as Axin2, IGF-1, and FGF 7 and 10. MPA increased β-catenin in IFN-γ-treated hDPCs leading to its nuclear accumulation via inhibition of GSK3β and reduction of DKK-1. Furthermore, MPA significantly increased expression of ALP and other DPC marker genes but inhibited expression of TGF-β2. Therefore, we demonstrate for the first time that IFN-γ induces catagen-like changes in hDPCs and in hair follicles via inhibition of Wnt/β-catenin signaling, and that MPA stabilizes β-catenin by inhibiting GSK3β leading to increased β-catenin target gene and DP signature gene expression, which may, in part, counteract IFN-γ-induced catagen in hDPCs.

Genetically Modified Mice as a Tool to Study Inflammatory Skin Diseases

Although mice have a long tradition as models for human skin diseases, they have recently received increasingly more attention. This is because of the rapid advancement of genetic engineering methods which made it possible to create mice with precisely defined genetic changes. Many of these mice develop impressive and sometimes unexpected, puzzling phenotypes. Their interpretation is a major challenge to the basic researcher and can often be ameliorated by the input of an experienced dermatologist. Together with recent examples of genetically modified mouse models of inflammatory skin diseases we give a short overview of the methods used to generate such mice, describe possible ways to analyse them, and discuss problems that arise in the interpretation of the findings.

Antibody against chromatin assembly factor-1 is a novel autoantibody specifically recognized in systemic lupus erythematosus

Autoantibodies to proliferating cell nuclear antigen (PCNA) are specifically, if rarely, present in systemic lupus erythematosus (SLE) patient sera. Even SLE patients lacking PCNA reactivity often show reaction to PCNA-binding protein. Here, immunoreactivity to chromatin assembly factor-1 (CAF-1), an essential molecule for DNA replication and a PCNA-binding protein, was compared for the sera of SLE patients, normal healthy controls (NHCs) and other disease controls, and in autoimmune sera reactive to standard autoantigens, by enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence, and immunoblotting. CAF1 and IRF1 expression in SLE and NHC peripheral mononuclear cells were compared by quantitative real-time polymerase chain reaction. Serum interferon-γ-inducing protein-10 and anti-double-stranded (ds)DNA antibody levels were measured by ELISA. Increased CAF-1 autoimmune reactivity was recognized in SLE or serum anti-dsDNA antibody-positive patients. Significantly greater central nervous system (CNS) involvement (aseptic meningitis) and serum anti-dsDNA antibody titers were present more often in anti-CAF-1 antibody-positive than antibody-negative SLE patients. IFN-γ positively regulated CAF-1 expression in vitro and was associated with anti-CAF-1 antibody production in SLE. Thus, a novel anti-CAF-1 autoantibody is frequently found in patients with SLE and is a useful biomarker for diagnosis, especially in cases with CNS involvement. Aberrant IFN-γ regulation appears to play an important role in anti-CAF-1 antibody production in SLE.

IFN-γ signaling maintains skin pigmentation homeostasis through regulation of melanosome maturation

Cellular homeostasis is an outcome of complex interacting processes with nonlinear feedbacks that can span distinct spatial and temporal dimensions. Skin tanning is one such dynamic response that maintains genome integrity of epidermal cells. Although pathways underlying hyperpigmentation cascade are recognized, negative feedback regulatory loops that can dampen the activated melanogenesis process are not completely understood. In this study, we delineate a regulatory role of IFN-γ in skin pigmentation biology. We show that IFN-γ signaling impedes maturation of the key organelle melanosome by concerted regulation of several pigmentation genes. Withdrawal of IFN-γ signal spontaneously restores normal cellular programming. This effect in melanocytes is mediated by IFN regulatory factor-1 and is not dependent on the central regulator microphthalmia-associated transcription factor. Chronic IFN-γ signaling shows a clear hypopigmentation phenotype in both mouse and human skin. Interestingly, IFN-γ KO mice display a delayed recovery response to restore basal state of epidermal pigmentation after UV-induced tanning. Together, our studies delineate a new spatiotemporal role of the IFN-γ signaling network in skin pigmentation homeostasis, which could have implications in various cutaneous depigmentary and malignant disorders.

Sleep loss and cytokines levels in an experimental model of psoriasis

Up to 80% of people develop a cutaneous condition closely connected to their exposure to stressful life events. Psoriasis is a chronic recurrent inflammatory skin disorder with multifactorial etiology, including genetic background, environmental factors, and immune system disturbances with a strong cytokine component. Moreover, psoriasis is variably associated with sleep disturbance and sleep deprivation. This study evaluated the influence of sleep loss in the context of an animal model of psoriasis by measuring cytokine and stress-related hormone levels. Male adult Balb/C mice with or without psoriasis were subjected to 48 h of selective paradoxical sleep deprivation (PSD). Sleep deprivation potentiated the activities of kallikrein-5 and kallikrein-7 in the skin of psoriatic groups. Also, mice with psoriasis had significant increases in specific pro-inflammatory cytokines (IL-1β, IL-6 and IL-12) and decreases in the anti-inflammatory cytokine (IL-10) after PSD, which were normalized after 48 h of sleep rebound. Linear regression showed that IL-2, IL-6 and IL-12 levels predicted 66% of corticosterone levels, which were selectively increased in psoriasis mice subject to PSD. Kallikrein-5 was also correlated with pro-inflammatory cytokines, explaining 58% of IL-6 and IL-12 variability. These data suggest that sleep deprivation plays an important role in the exacerbation of psoriasis through modulation of the immune system in the epidermal barrier. Thus, sleep loss should be considered a risk factor for the development of psoriasis.

Oral administration of artemisinin analog SM934 ameliorates lupus syndromes in MRL/lpr mice by inhibiting Th1 and Th17 cell responses

OBJECTIVE

SM934, an artemisinin derivative, possesses potent antiproliferative and antiinflammatory properties. The aim of this study was to examine the effects and explore the mechanisms of SM934 to treat autoimmune disease in lupus-prone female MRL/lpr mice.

METHODS

In vitro, the effects of SM934 on the activation of polyclonal CD4+ T cells and the differentiation of naive CD4+ T cells were examined. In vivo, the preventative or therapeutic effects of SM934 in MRL/lpr mice were investigated. Ex vivo, the mechanisms of treatment were explored according to the immunologic correlates of disease.

RESULTS

In vitro, SM934 inhibited interferon-γ (IFNγ) and interleukin-17 (IL-17) production from polyclonal CD4+ T cells activated by T cell receptor engagement and the differentiation of naive CD4+ T cells into Th1 and Th17 cells, but not Treg cells. In vivo, 12-week-old MRL/lpr mice treated with SM934 for 4 weeks showed significantly ameliorated proteinuria and renal lesion severity; decreased levels of blood urea nitrogen, serum IFNγ, and serum anti-double-stranded DNA antibodies; decreased spleen size; and a lower percentage of CD3+B220+CD4-CD8- T cells; 16-week-old MRL/lpr mice treated with SM934 for 8 weeks avoided severe proteinuria and survived longer. Ex vivo, SM934 treatment elevated the percentage of Treg cells, inhibited the development of Th1 and Th17 cells, and impeded the comprehensive activation of STAT-1, STAT-3, and STAT-5 proteins in splenocytes.

CONCLUSION

Taken together, the results of this study demonstrated that the artemisinin analog SM934 had therapeutic effects in lupus-prone female MRL/lpr mice by inhibiting both Th1 cell and Th17 cell responses. Moreover, this study indicated that both IFNγ and IL-17 are required for the elicitation and development of murine lupus.

HIF-1α in epidermis: oxygen sensing, cutaneous angiogenesis, cancer, and non-cancer disorders

Besides lung, postnatal human epidermis is the only epithelium in direct contact with atmospheric oxygen. Skin epidermal oxygenation occurs mostly through atmospheric oxygen rather than tissue vasculature, resulting in a mildly hypoxic microenvironment that favors increased expression of hypoxia-inducible factor-1α (HIF-1α). Considering the wide spectrum of biological processes, such as angiogenesis, inflammation, bioenergetics, proliferation, motility, and apoptosis, that are regulated by this transcription factor, its high expression level in the epidermis might be important to HIF-1α in skin physiology and pathophysiology. Here, we review the role of HIF-1α in cutaneous angiogenesis, skin tumorigenesis, and several skin disorders.

Depletion of antigen-presenting cells by clodronate liposomes reverses the psoriatic skin phenotype in KC-Tie2 mice

BACKGROUND

There is ongoing debate regarding the initiation of psoriatic plaque as primarily arising from an anomaly in epidermal keratinocytes (KCs) or from abnormalities in immunocytes that secondarily activate otherwise normal KCs. In mice engineered to overexpress the angiopoietin receptor Tie2 in KCs, skin spontaneously develops the characteristic clinical, histological and immune cell phenotypes of psoriasis which can be reversed with either transgene repression or ciclosporin administration, suggesting key roles for both KCs and T cells in mediating the skin disease in this murine model.

OBJECTIVES

To determine if antigen-presenting cells (APCs) and macrophages alone are sufficient to sustain psoriasiform inflammation in the KC-Tie2 murine model of psoriasis.

METHODS

Clodronate liposomes were intradermally injected into involved dorsal skin of KC-Tie2 or control animals once a week for 6weeks and acanthosis, angiogenesis, immune cell infiltration and cytokine production were quantitated using immunohistochemistry and interactive image analyses, enzyme-linked immunosorbent assay (ELISAs) and quantitative real-time polymerase chain reaction (qRT-PCR).

RESULTS

Clodronate liposome injection eliminated CD11c+, F4/80+ and CD11b+ cells in the skin and returned CD8+ T-cell numbers to control mouse levels. APC depletion in KC-Tie2 mouse skin resulted in resolution of the acanthotic skin phenotype, decreased dermal angiogenesis, and a return to control mouse levels for interleukin (IL)-1α, IL-6, IL-23 and tumour necrosis factor (TNF)-α expression and modest reductions in interferon-γ and IL-17.

CONCLUSIONS

These findings suggest a critical role for APCs and myeloid cell-derived IL-23 and TNF-α and underscore the importance of Th1 and Th17 T cells in maintaining the psoriasiform skin phenotype in the KC-Tie2 mouse model.

Natural killer cells target HCV core proteins during the innate immune response in HCV transgenic mice

The mechanism of the innate immune response to hepatitis C virus (HCV) has not been fully elucidated, largely due to the lack of an appropriate model. We used HCV transgenic (Tg) mice, which express core, E1, E2, and NS2 proteins regulated by the Cre/loxP switching expression system, to examine the innate immune response to HCV structural proteins. Twelve hours after HCV transgene expression, HCV core protein levels in Tg mouse livers were 15-47 pg/mg. In contrast, in Tg mice with a depletion of natural killer (NK) cells, we observed much higher levels of HCV core proteins (1,597 pg/ml). Cre-mediated genomic DNA recombination efficiency in the HCV-Tg mice was strongly observed in NK cell-depleted mice between 0.5 and 1 day as compared to non-treated mice. These data indicated that NK cells participate in the elimination of core-expressing hepatocytes in the innate immune responses during the acute phase of HCV infection.

Psoriasis: what we have learned from mouse models

Psoriasis is a common inflammatory skin disease of unknown etiology, for which there is no cure. This heterogeneous, cutaneous, inflammatory disorder is clinically characterized by prominent epidermal hyperplasia and a distinct inflammatory infiltrate. Crosstalk between immunocytes and keratinocytes, which results in the production of cytokines, chemokines and growth factors, is thought to mediate the disease. Given that psoriasis is only observed in humans, numerous genetic approaches to model the disease in mice have been undertaken. In this Review, we describe and critically assess the mouse models and transplantation experiments that have contributed to the discovery of novel disease-relevant pathways in psoriasis. Research performed using improved mouse models, combined with studies employing human cells, xenografts and patient material, will be key to our understanding of why such distinctive patterns of inflammation develop in patients with psoriasis. Indeed, a combination of genetic and immunological investigations will be necessary to develop both improved drugs for the treatment of psoriasis and novel curative strategies.

Meyerson-Phenomenon hides a nevus flammeus

Facial eczema is a common disease in daily dermatological practice. The cause of facial eczema is often atopic dermatitis or allergic contact dermatitis. Usually, the eczema resolves with correct topical treatment and by avoiding allergic trigger factors. A 49-year-old woman presented with persistent eczema on her forehead which recurred over decades despite correct topical therapy. A skin biopsy revealed the astonishing diagnosis of a nevus flammeus with an overlying eczema known as the Meyerson phenomenon. The Meyerson phenomenon is often described in children with nevi flammei suffering from atopic dermatitis - in adults the phenomenon is rarely recognized as a reason for eczema. We show the interesting case of an adult woman with the Meyerson phenomenon on a nevus flammeus and discuss the possible pathomechanisms.

Mechanisms of spatial and temporal development of autoimmune vitiligo in tyrosinase-specific TCR transgenic mice

Generalized vitiligo is thought to have an autoimmune etiology and has been correlated with the presence of CD8 T cells specific for melanocyte differentiation Ag. However, limited animal models for the disease have hampered its understanding. Thus, we generated TCR transgenic mice that recognize an epitope of the melanocyte protein, tyrosinase. These animals develop vitiligo with strikingly similar characteristics to the human disease. Vitiligo develops temporally and spatially, with juvenile lesions forming bilaterally in head and facial areas, and only arising later in the body of adult animals. Vitiligo is entirely dependent on CD8 T cells, whereas CD4 T cells exert a negative regulatory effect. Importantly, CD8 T cells can be pervasively present in the skin in the steady state without inducing vitiligo in most areas. This points to developmental differences in melanocyte susceptibility and/or immunological effector mechanisms over time, or in different body locations. Disease is strongly dependent on both IFN-gamma and CXCR3, whereas dependence on CCR5 is more limited, and both CCR4 and perforin are dispensable. Genetic ablation of CXCR3 or IFN-gamma also resulted in scarce CD8 T cell infiltration into the skin. Our results identify unexpected complexity in vitiligo development and point toward possible therapeutic interventions.

Toll-like receptor 2 is important for the T(H)1 response to cutaneous sensitization

BACKGROUND

Atopic dermatitis and allergic contact dermatitis are skin disorders triggered by epicutaneous sensitization with protein antigens and contact sensitization with haptens, respectively. Skin is colonized with bacteria, which are a source of Toll-like receptor (TLR) 2 ligands.

OBJECTIVE

We sought to examine the role of TLR2 in murine models of atopic dermatitis and allergic contact dermatitis.

METHODS

TLR2(-/-) mice and wild-type littermates were epicutaneously sensitized with ovalbumin (OVA) or contact sensitized with oxazolone (OX). Skin histology was assessed by means of hematoxylin and eosin staining and immunohistochemistry. Ear swelling was measured with a micrometer. Cytokine mRNA expression was examined by means of quantitative RT-PCR. Antibody levels and splenocyte secretion of cytokines in response to OVA stimulation were measured by means of ELISA. Dendritic cells were examined for their ability to polarize T-cell receptor/OVA transgenic naive T cells to T(H)1 and T(H)2.

RESULTS

In response to OVA sensitization, TLR2(-/-) mice experienced skin infiltration with eosinophils and CD4(+) cells, as well as upregulation of T(H)2 cytokine mRNAs that was comparable with that seen in wild-type littermates. In contrast, epidermal thickening, IFN-gamma expression in the skin, IFN-gamma production by splenocytes, and IgG2a anti-OVA antibody levels were impaired in TLR2(-/-) mice. After OX ear challenge, contact sensitized TLR2(-/-) mice exhibited defective ear swelling with impaired cellular infiltration, decreased epidermal thickening and local IFN-gamma expression, and impaired OX-specific IgG2a responses. Dendritic cells from TLR2(-/-) mice induced significantly lower production of IFN-gamma but normal IL-4 and IL-13 production in naive T cells.

CONCLUSIONS

These results indicate that TLR2 promotes the IFN-gamma response to cutaneously introduced antigens.

[Photosensitivity in lupus erythematosus]

Photosensitivity is one of the ARA diagnostic criteria of systemic lupus erythematosus. Sun exposure can also induce extracutaneous manifestations of the disease. Photosensitivity may be difficult to prove by history taking in lupus patients, as the delay between sun exposure and the onset of specific skin lesions is rather long. Photo-induction of lupus can occur by ultraviolet A (UVA) radiation in the shadow or behind window glass, so that the relationship between radiation exposure and exacerbation of the disease may not seem obvious to the patient. Phototesting procedures for lupus erythematosus have been described, but they are not used in routine practice. Both UVB and UVA play a role in the pathogenesis of lupus erythematosus: in the epidermis they induce DNA damage, they expose nuclear antigens and photo-induced neo-antigens at the cell surface, they lead to an accumulation of apoptotic material, and they induce several pro-inflammatory cytokines. In the dermis, UV radiation triggers skin infiltration by inflammatory cells by modulation of microvascular flow rates and by upregulation of white blood cell migration from dermal capillaries to the skin. Photodistribution of skin lesions and a delay of their onset of more than 48 hours after sun exposure are clinical hallmarks of cutaneous lupus erythematosus that are usually completed by histological confirmation. Photoprotection is essential in the treatment of lupus patients: it comprises sun avoidance suitable for both UVB and UVA radiation, protective clothing, and topical broad-spectrum filters.

The C3H/HeJ mouse and DEBR rat models for alopecia areata: review of preclinical drug screening approaches and results

The C3H/HeJ inbred mouse strain and the Dundee Experimental Bald Rat (DEBR) strain spontaneously develop adult onset alopecia areata (AA), a cell-mediated disease directed against actively growing hair follicles. The low frequency of AA and the inability to predict the stage of AA as it evolves in the naturally occuring C3H/HeJ model of AA can be converted into a highly predictable system by grafting full thickness skin from AA-affected mice to normal haired mice of the same strain. The rat DEBR model develops spontaneous AA at a higher frequency than in the mouse model but they are more expensive to use in drug studies owing to their larger size. Regardless of the shortcomings of either model, these rodent models can be used succesfully to screen novel or approved drugs for efficacy to treat human AA. As the pathogenesis of AA follows the canonical lymphocytic co-stimulatory cascade in the mouse AA model, it can be used to screen compounds potentially useful to treat a variety of cell-mediated diseases. Efficacy of various agents can easily be screened by simply observing the presence, rate, and cosmetic acceptability of hair regrowth. More sophisticated assays can refine how the drugs induce hair regrowth and evaluate the underlying pathogenesis of AA. Some drugs commonly used to treat human AA patients work equally as well in both rodent models validating their usefulness as models for drug efficacy and safety for humanAA.

Inactivation of FIP200 leads to inflammatory skin disorder, but not tumorigenesis, in conditional knock-out mouse models

FIP200 (focal adhesion kinase family interacting protein of 200 kDa) has been shown to interact with other proteins to regulate several intracellular signaling pathways. To study a potential role of FIP200 in tumorigenesis and possibly other disease processes in vivo, we created and analyzed murine mammary tumor virus-Cre-mediated FIP200 conditional knock-out (CKO) mice. We found that deletion of FIP200 in mammary epithelial cells did not result in spontaneous development of breast cancer. Moreover, deletion of FIP200 did not further accelerate or inhibit lymphomagenesis induced by inactivation of p53 in mice. Interestingly, however, FIP200 and p53 double conditional knock-out (dCKO) mice exhibited significant hyperplasia of epidermis (acanthosis), thickening of the cornified layer (hyperkeratosis), and increased vascularity in the dermis. FIP200 CKO mice also showed similar, although less severe, skin defects as dCKO mice. Analyses of primary keratinocytes isolated from dCKO mice did not detect increased proliferation of these cells in vitro, suggesting that epidermis hyperproliferation is not epidermal cell-autonomous but may be a consequence of increased inflammation triggered by immune cells in vivo. Consistent with this possibility, we found infiltration of leukocytes including T cells, macrophages, and granulocytes into the dermis and epidermis, associated with activation of NF-kappaB and increased expression of several proinflammatory cytokines and chemokines in skin of the dCKO mice. We further found that cultured FIP200 KO keratinocytes showed reduced NF-kappaB phosphorylation in response to tumor necrosis factor alpha stimulation, suggesting a paracrine regulation of aberrant NF-kappaB activation in the skin microenviroment of dCKO and FIP200 CKO mice. Together, these results demonstrate that ablation of FIP200, although not promoting tumorigenesis, can lead to skin inflammatory disorders, suggesting a novel function of FIP200 in the maintenance of normal skin homeostasis in vivo.

Topically applied diterpenoids from Egletes viscosa (Asteraceae) attenuate the dermal inflammation in mouse ear induced by tetradecanoylphorbol 13-acetate- and oxazolone

The diterpene compounds, centipedic acid (CA) and 12-acetoxyhawtriwaic acid lactone (AHAL, tanabalin) isolated from the flower buds of Egletes viscosa LESS. (Asteraceae) were evaluated on acute and chronic models of mouse ear dermatitis. A single topical application of CA (0.125; 0.25 and 0.5 mg/ear) or AHAL (0.125, 0.25, 0.5 mg/ear) immediately before 12-O-tetradecanoylphorbol-13-acetate (TPA, 2.5 mug/ear) caused a dose-related significant inhibition of ear inflammatory edema and influx of polymorphonuclear cells, as evidenced by a decrease in ear thickness and reduced myeloperoxidase (MPO) activity and tumor necrosis factor-alpha (TNF-alpha) in ear tissue homogenates. The maximal obtained inhibition for both ear edema and neutrophil influx were almost similar to that of topically applied dexamethasone (0.05 mg/ear). The extent of inhibitions for the respective treatments of CA (0.5 mg/ear), AHAL (0.5 mg/ear), or dexamethasone (0.05 mg/ear) were in the order of 63%, 61% and 81% for the ear edema, and 90%, 95% and 95% for the neutrophil influx. Also, at similar doses, both diterpenes and dexamethasone effectively inhibited the delayed-type hypersensitivity reaction induced by repeated topical application of 1% oxazolone (OXA, 20 microl/ear), as evidenced by significant decreases in ear thickness and interferon-gamma (INF-gamma) levels in ear tissue. Histopathological analysis revealed a marked decrease in epidermal hyperplasia and neutrophil infiltration in animals pretreated with CA or AHAL, in a manner similar to dexamethasone. These data provide evidence for the anti-dermatitis effect of Egletes viscosa diterpenes, by mechanisms that involve a reduced neutrophil influx and decreased production of inflammatory cytokines, TNF-alpha and IFN-gamma.

Animal models of psoriasis

Research into the pathogenesis of psoriasis has been severely hampered by the lack of a naturally occurring disorder in laboratory animals that mimics the complex phenotype and pathogenesis of the human disease. A large variety of spontaneous mutations, genetically engineered rodents, immunological reconstitution approaches, and xenotransplantation models have been used to study specific aspects of the pathophysiology of psoriasis, however. Several manipulations of resident cutaneous cell types or immigrating immunocytes appear to result in remarkably similar hyperproliferative inflammatory phenotypes in mice, thus suggesting that interfering with cutaneous homeostasis in general may ultimately result in a rather uniform reaction pattern that mirrors some features of psoriasis. Fully animal models of psoriasis have nonetheless not only shed light on the biological functions of given inflammatory mediators or other molecules but also tremendously contributed to the discussion on central pathogenic questions, such as the roles of innate and adaptive immune mechanisms, keratinocytes, and endothelial cells in psoriasis. Psoriasis research has also been greatly nourished by xenotransplantation of diseased or unaffected human skin onto immunocompromised recipients, an approach that has in many variations been used to study the role of T lymphocytes and other cells and that has been used for preclinical therapeutic studies. General approaches to generate animal models of psoriasis, features of some specific models, their value for psoriasis research, and their use for drug development are discussed in this article.

Innate immunity and antimicrobial defense systems in psoriasis

Psoriasis is a chronic inflammatory disorder that is mediated by elements of the innate and adaptive immune systems. Its characteristic features in the skin consist of inflammatory changes in both dermis and epidermis, with abnormal keratinocyte differentiation and proliferation. Despite the elucidation of many aspects of psoriasis pathogenesis, some puzzling questions remain to be answered. A major question currently debated is whether psoriasis is a primary abnormality of the epidermal keratinocyte or a reflection of dysregulated bone marrow-derived immunocytes. In this review we will focus on understanding the role of the innate immune system in psoriasis and how this provides a rational solution to address the origin of this multifactorial disease. Innate immunity is nonspecific and genetically based. It protects the body against the constant risk of pathogens through the use of rapidly mobilized defenses that are able to recognize and kill a variety of threats (bacteria, fungi, viruses, etc). The key mechanisms of innate immune responses are the existence of receptors to recognize pathogens and the production of factors that kill pathogens, such as antimicrobial peptides and proteins. Any combination of excessive sensitivity of the innate detection system, or dysregulation of the response system, can manifest both an epidermal phenotype and an abnormal T-cell function. Thus, the multidimensional action of the innate immune system, its triggers, and its recently understood role in T-cell function argue for an important role for innate mechanisms of recognition and response in the pathogenesis of psoriasis.

Crosstalk between keratinocytes and adaptive immune cells in an IkappaBalpha protein-mediated inflammatory disease of the skin

Inflammatory diseases at epithelial borders develop from aberrant interactions between resident cells of the tissue and invading immunocytes. Here, we unraveled basic functions of epithelial cells and immune cells and the sequence of their interactions in an inflammatory skin disease. Ubiquitous deficiency of the IkappaBalpha protein (Ikba(Delta)(/Delta)) as well as concomitant deletion of Ikba specifically in keratinocytes and T cells (Ikba(K5Delta/K5Delta lckDelta/lckDelta)) resulted in an inflammatory skin phenotype that involved the epithelial compartment and depended on the presence of lymphocytes as well as tumor necrosis factor and lymphotoxin signaling. In contrast, mice with selective ablation of Ikba in keratinocytes or lymphocytes showed inflammation limited to the dermal compartment or a normal skin phenotype, respectively. Targeted deletion of RelA from epidermal keratinocytes completely rescued the inflammatory skin phenotype of Ikba(Delta)(/Delta) mice. This finding emphasizes the important role of aberrant NF-kappaB activation in both keratinocytes and lymphocytes in the development of the observed inflammatory skin changes.

The evolution of the psoriatic lesion

Psoriasis comprises a host of abnormalities, and various aspects of the pathogenesis of psoriasis have been suggested to be of primary relevance. The aim of this review is to identity driving factors in the pathogenesis of psoriasis and to explore the dynamics of processes eventually resulting in a psoriatic lesion. In this review observations on the evolution from the symptomless skin to lesional skin in patients with psoriasis will be integrated with observations in various animal models of psoriasis.

Mouse models of psoriasis

Psoriasis is a T-cell-mediated chronic inflammatory skin disease believed to be of autoimmune nature that can be triggered or worsened by streptococcal throat infections. In addition to conventional chronic inflammatory changes, psoriasis is characterized by complex and striking alterations in epidermal growth and differentiation. Psoriasis is generally not observed in animals other than man, and this lack of a suitable animal model has greatly hindered research into the pathogenesis of psoriasis. Multiple transgenic, knockout, and reconstituted models of psoriasis have been developed over the past two decades. Despite their limitations, these models have demonstrated that keratinocyte hyperplasia, vascular hyperplasia, and cell-mediated immunity in the skin are closely interrelated. Xenograft models, in which involved and uninvolved psoriatic skin are transplanted onto immunodeficient mice, are the only models that come close to incorporating the complete genetic, immunologic, and phenotypic changes of the disease. They have shown conclusively that psoriasis is a T-cell-mediated disease, and have been used to elucidate novel pathogenic pathways. In this review, we describe various animal models, detail the immunologic and intracellular pathways that mediate these phenotypes and assess the utility of these models to better understand this disease.

Hypopigmenting agents: an updated review on biological, chemical and clinical aspects

An overview of agents causing hypopigmentation in human skin is presented. The review is organized to put forward groups of biological and chemical agents. Their mechanisms of action cover (i) tyrosinase inhibition, maturation and enhancement of its degradation; (ii) Mitf inhibition; (iii) downregulation of MC1R activity; (iv) interference with melanosome maturation and transfer; (v) melanocyte loss, desquamation and chemical peeling. Tyrosinase inhibition is the most common approach to achieve skin hypopigmentation as this enzyme catalyses the rate-limiting step of pigmentation. Despite the large number of tyrosinase inhibitors in vitro, only a few are able to induce effects in clinical trials. The gap between in-vitro and in-vivo studies suggests that innovative strategies are needed for validating their efficacy and safety. Successful treatments need the combination of two or more agents acting on different mechanisms to achieve a synergistic effect. In addition to tyrosinase inhibition, other parameters related to cytotoxicity, solubility, cutaneous absorption, penetration and stability of the agents should be considered. The screening test system is also very important as keratinocytes play an active role in modulating melanogenesis within melanocytes. Mammalian skin or at least keratinocytes/melanocytes co-cultures should be preferred rather than pure melanocyte cultures or soluble tyrosinase.

Th1 and type 1 cytotoxic T cells dominate responses in T-bet overexpression transgenic mice that develop contact dermatitis

Contact dermatitis in humans and contact hypersensitivity (CHS) in animal models are delayed-type hypersensitivity reactions mediated by hapten-specific T cells. Recently, it has become clear that both CD4(+) Th1 and CD8(+) type 1 cytotoxic T (Tc1) cells can act as effectors in CHS reactions. T-bet has been demonstrated to play an important role in Th1 and Tc1 cell differentiation, but little is known about its contribution to CHS. In the present study, we used C57BL/6 mice transgenic (Tg) for T-bet to address this issue. These Tg mice, which overexpressed T-bet in their T lymphocytes, developed dermatitis characterized by swollen, flaky, and scaly skin in regions without body hair. Skin histology showed epidermal hyperkeratosis, neutrophil, and lymphocyte infiltration similar to that seen in contact dermatitis. T-bet overexpression in Tg mice led to elevated Th1 Ig (IgG2a) and decreased Th2 Ig (IgG1) production. Intracellular cytokine analyses demonstrated that IFN-gamma was increased in both Th1 and Tc1 cells. Furthermore, Tg mice had hypersensitive responses to 2,4-dinitrofluorobenzene, which is used for CHS induction. These results suggest that the level of expression of T-bet might play an important role in the development of contact dermatitis and that these Tg mice should be a useful model for contact dermatitis.