The IL-23/T17 pathogenic axis in psoriasis is amplified by keratinocyte responses

Crosstalk between skin inflammation and adipose tissue-derived products: pathogenic evidence linking psoriasis to increased adiposity

INTRODUCTION

Psoriasis is a chronic skin disorder associated with several comorbid conditions. In psoriasis pathogenesis, the role of some cytokines, including TNF-α and IL-17, has been elucidated. Beside their pro-inflammatory activity, they may also affect glucose and lipid metabolism, possibly promoting insulin resistance and obesity. On the other hand, adipose tissue, secreting adipokines such as chemerin, visfatin, leptin, and adiponectin, not only regulates glucose and lipid metabolism, and endothelial cell function regulation, but it may contribute to inflammation. Areas covered: This review provides an updated 'state-of-the-art' about the reciprocal contribution of a small subset of conventional cytokines and adipokines involved in chronic inflammatory pathways, upregulated in both psoriasis and increased adiposity. A systematic search was conducted using the PubMed Medline database for primary articles. Expert commentary: Because psoriasis is associated with increased adiposity, it would be important to define the contribution of chronic skin inflammation to the onset of obesity and vice versa. Clarifying the pathogenic mechanism underlying this association, a therapeutic strategy having favorable effects on both psoriasis and increased adiposity could be identified.

Influence of different types of contact hypersensitivity on imiquimod-induced psoriasis-like inflammation in mice

It is currently believed that psoriasis and allergic contact dermatitis (ACD) are different diseases; however, they share clinical similarities. The involvement of T helper 17 (Th17) cells in these disorders provides a novel opportunity to investigate the relationship between them. The present study aimed to determine whether the same or overlapping inflammatory pathways are involved in the two diseases, and the influence of different types of ACD on psoriasis. Compound mouse models of Th1 or Th2‑type contact hypersensitivity (CHS) combined with imiquimod (IMQ)‑induced psoriasis‑like inflammation were established, in order to mimic the characteristics of ACD and psoriasis. Histopathology, immunohistochemistry and cytokine detection in blood serum and tissues were used to compare the differences between the mice treated with IMQ alone or IMQ combined with Th1 and Th2‑type CHS. As compared with the IMQ‑treated mice or IMQ-treated Th1‑type CHS mice, the mice with Th2‑type CHS treated with IMQ exhibited more serious psoriasis‑like inflammation with increased epidermal thickness and infiltrating cells in the derma. High mRNA expression levels of interleukin (IL)‑17, IL‑22, IL‑23, TNF‑α and RORγt were detected in back skin lesions. Additionally, high levels of IL‑17 and IL‑22 in blood serum were detected in IMQ‑treated mice combined with Th2‑type CHS. The mice treated with IMQ alone, and IMQ treatment combined with Th1‑type CHS had a comparable psoriasis‑like inflammatory response in the back skin. In conclusion, these data demonstrate that Th2‑type CHS exacerbated the IMQ‑treated psoriatic inflammation of mice via the IL‑23/IL‑17 axis. Th17 cells and associated pathways may link ACD and psoriasis. Therefore, patients with psoriasis should avoid contact with specific sensitizers, such as fragrance and rubber products, which may induce Th2 polarization.

New therapies for psoriasis and psoriatic arthritis

PURPOSE OF REVIEW

Over the last several years, novel immunologic pathways pivotal in the development of the pathobiology of psoriasis and psoriatic arthritis (PsA) have been revealed. These discoveries catalyzed a search for new treatment targets resulting in many new therapies that are now available for patients with psoriatic disease.

RECENT FINDINGS

Helper T cells that secrete interleukin-17 (TH17) along with CD8+ cells, innate lymphocyte cells, and gamma delta T cells are important in the pathogenesis of psoriasis and PsA. Recently, agents that target interleukin-17, the interleukin-17 receptor, and interleukin-23 (antip19) have been approved or are in clinical trials. Apremilast, a new oral agent, was approved for the treatment of psoriasis and PsA.

SUMMARY

Secukinumab, an interleukin-17A antibody, has been approved for treatment of psoriasis and PsA in the United States. It is effective with a good safety profile. Ixekizumab, another anti-interleukin-17A antibody, is currently in clinical trials and brodalumab, an interleukin-17 receptor antagonist, was removed from clinical trials because of safety concerns despite demonstrated efficacy in psoriasis and PsA. Targeting interleukin-23 with antibodies to p19 is another approach with encouraging results in psoriasis. Apremilast, an oral agent, approved to treat psoriasis and PsA demonstrates moderate efficacy with an excellent safety record. The role of tofacitinib in psoriatic disease remains to be determined pending a safety review in psoriasis and completion of PsA trials.

The Regulation of Immunological Processes by Peripheral Neurons in Homeostasis and Disease

The nervous system and the immune system are the principal sensory interfaces between the internal and external environment. They are responsible for recognizing, integrating, and responding to varied stimuli, and have the capacity to form memories of these encounters leading to learned or 'adaptive' future responses. We review current understanding of the cross-regulation between these systems. The autonomic and somatosensory nervous systems regulate both the development and deployment of immune cells, with broad functions that impact on hematopoiesis as well as on priming, migration, and cytokine production. In turn, specific immune cell subsets contribute to homeostatic neural circuits such as those controlling metabolism, hypertension, and the inflammatory reflex. We examine the contribution of the somatosensory system to autoimmune, autoinflammatory, allergic, and infectious processes in barrier tissues and, in this context, discuss opportunities for therapeutic manipulation of neuro-immune interactions.

Streptococcus pyogenes-induced cutaneous lymphocyte antigen-positive T cell-dependent epidermal cell activation triggers TH17 responses in patients with guttate psoriasis

BACKGROUND

Guttate psoriasis (GP) is characterized by acute onset of small, rounded psoriatic lesions. Although this particular phenotype of psoriasis is usually associated with streptococcal throat infections and mainly occurs in HLA-Cw6(+) patients, the specific immunologic response to this innate stimulus that causes these skin lesions is poorly understood.

OBJECTIVE

This study aims to elucidate how key cellular elements of patients with GP respond to Streptococcus pyogenes and whether this initial immune response is favored by the genetic and environmental background of these patients.

METHODS

Circulating memory T cells and autologous epidermal cells from samples from either patients with GP (n = 14) or healthy control subjects (n = 6) were cocultured ex vivo in the presence of an S pyogenes extract. Levels of the psoriasis-associated cytokines IL-17A, IL-17F, IFN-γ, TNF-α, IL-6, and IL-8 were determined. The expression of several genes with increased (DEFB4, S100A7, LCN2, IL36G, IL8, CXCL9, CXCL10, and CXCL11) or decreased (FLG and LOR) transcripts in psoriatic lesions was examined in keratinocytes treated with coculture supernatants.

RESULTS

When skin-homing effector memory cutaneous lymphocyte antigen-positive T cells were used in cocultures, a TH17-dominant response was observed, as reflected by the higher amounts of IL-17A and IL-17F than IFN-γ. Moreover, a higher TH17 response was observed in cells isolated from patients with flares associated with a streptococcal tonsillitis and with the HLA-Cw6 allele (cohort 1). In addition, in normal keratinocytes the supernatants from these cocultures induced an increase in IL-17-associated genes, such as DEFB4, S100A7, LCN2, IL36G, and IL8 but a decrease in FLG and LOR, thereby confirming the role of activated TH17 cells.

CONCLUSION

This study reveals a dominant TH17 response of cutaneous lymphocyte antigen-positive T cells activated by epidermal cells and S pyogenes in patients with GP.

CX3CR1 deficiency attenuates imiquimod-induced psoriasis-like skin inflammation with decreased M1 macrophages

BACKGROUND

CX3C chemokine receptor 1 (CX3CR1), a receptor for CX3CL1, mediates migration of inflammatory cells. Psoriasis is a common skin disorder that causes skin inflammation. The role of CX3CL1 and CX3CR1 in psoriasis remains unclear.

OBJECTIVE

To elucidate the role of CX3CL1 and CX3CR1 in psoriasis, we assessed imiquimod-induced psoriasis-like dermatitis in CX3CR1-deficient mice.

METHODS

We evaluated skin inflammation by assessing erythema, scaling, and ear thickness in CX3CR1(-/-) mice and wild-type (WT) mice. Furthermore, we measured cytokine production by quantitative reverse transcription-PCR. We investigated infiltrating cells in skin by immunohistochemistry and flow cytometry. After confirming phenotypical differences in macrophages between WT and CX3CR1(-/-) mice, we analyzed expression levels of IL-1β, IL-6, and TNF-α in peritoneal macrophages with or without stimulation of CX3CL1. We finally transferred peritoneal macrophages into the ear before IMQ application.

RESULTS

Skin inflammation assessed by erythema, scaling, and epidermal thickness was significantly reduced in CX3CR1(-/-) mice compared with wild-type (WT) mice, accompanied by decreases in cytokine production for IL-12, IL-23, IL-17A, IL-22, IL-1β, IL-6, TNF-α, and IL-36. On day 6, increase in ear thickness from the baseline of CX3CR1(-/-) mice was one third of that of WT mice. Skin macrophages of CX3CR1(-/-) mice contained increased levels of CCR2 and decreased levels of MCP-1 compared with those from WT mice. Spontaneous expression levels of IL-1β, IL-6, and TNF-α in peritoneal macrophages of naïve CX3CR1(-/-) mice were significantly lower than those of WT mice. Furthermore, stimulation of WT macrophages with CX3CL1 decreased expression of these cytokines, suggesting that altered macrophage populations, but not loss of interaction between CX3CL1 and CX3CR1 signaling, caused differences in cytokine expression and skin inflammation. Moreover, transfer of macrophages from WT mice normalized IMQ-induced psoriasis-like inflammation in CX3CR1(-/-) mice, suggesting that macrophages contributed to the decreased inflammation resulted from CX3CR1 deficiency.

CONCLUSION

These data show that interactions between CX3CL1 and CX3CR1 play important roles for infiltration of M1 macrophages in a non-inflammatory setting. Decreased M1 macrophages in naïve CX3CR1(-/-) mice may be related to decreased cytokine expression and attenuated psoriasis-like inflammation.

[Significance of Th17/Treg imbalance in children with primary immune thrombocytopenia]

OBJECTIVE

To investigate the significance of Th17/Treg imbalance in the development and treatment of primary immune thrombocytopenia (ITP) in children.

METHODS

Thirty-two children diagnosed with ITP between May and August, 2015 and 22 healthy children were enrolled. Flow cytometry was used to determine the Th17/Treg ratio in peripheral blood of healthy children and children with ITP before and after treatment with immunoglobulin.

RESULTS

Compared with the patients with ITP before treatment, the healthy children and the patients treated with immunoglobulin had a significantly lower percentage of Th17 cells in CD4+ T cells, a significantly lower Th17/Treg ratio, and a significantly higher percentage of Treg cells in CD4+ T cells in peripheral blood (P<0.05). In the 32 ITP children treated with immunoglobulin, 20 had complete response, 4 had response, and 8 had no response. The patients with complete response had a significantly lower percentage of Th17 cells in CD4+ T cells and a significantly lower Th17/Treg ratio in peripheral blood than the patients without response (P<0.05).

CONCLUSIONS

The Th17/Treg imbalance can be found in children with ITP. Immunoglobulin can improve the cellular immune function by regulation of the Th17/Treg ratio. The Th17/Treg ratio may serve as an indicator for assessing the therapeutic effects of ITP.

[Significance of Th17/Treg imbalance in children with primary immune thrombocytopenia]

OBJECTIVE

To investigate the significance of Th17/Treg imbalance in the development and treatment of primary immune thrombocytopenia (ITP) in children.

METHODS

Thirty-two children diagnosed with ITP between May and August, 2015 and 22 healthy children were enrolled. Flow cytometry was used to determine the Th17/Treg ratio in peripheral blood of healthy children and children with ITP before and after treatment with immunoglobulin.

RESULTS

Compared with the patients with ITP before treatment, the healthy children and the patients treated with immunoglobulin had a significantly lower percentage of Th17 cells in CD4+ T cells, a significantly lower Th17/Treg ratio, and a significantly higher percentage of Treg cells in CD4+ T cells in peripheral blood (P<0.05). In the 32 ITP children treated with immunoglobulin, 20 had complete response, 4 had response, and 8 had no response. The patients with complete response had a significantly lower percentage of Th17 cells in CD4+ T cells and a significantly lower Th17/Treg ratio in peripheral blood than the patients without response (P<0.05).

CONCLUSIONS

The Th17/Treg imbalance can be found in children with ITP. Immunoglobulin can improve the cellular immune function by regulation of the Th17/Treg ratio. The Th17/Treg ratio may serve as an indicator for assessing the therapeutic effects of ITP.

Current knowledge on psoriasis and autoimmune diseases

Psoriasis is a prevalent, chronic inflammatory disease of the skin, mediated by crosstalk between epidermal keratinocytes, dermal vascular cells, and immunocytes such as antigen presenting cells (APCs) and T cells. Exclusive cellular “responsibility” for the induction and maintenance of psoriatic plaques has not been clearly defined. Increased proliferation of keratinocytes and endothelial cells in conjunction with APC/T cell/monocyte/macrophage inflammation leads to the distinct epidermal and vascular hyperplasia that is characteristic of lesional psoriatic skin. Despite the identification of numerous susceptibility loci, no single genetic determinant has been identified as responsible for the induction of psoriasis. Thus, numerous other triggers of disease, such as environmental, microbial and complex cellular interactions must also be considered as participants in the development of this multifactorial disease. Recent advances in therapeutics, especially systemic so-called “biologics” have provided new hope for identifying the critical cellular targets that drive psoriasis pathogenesis. Recent recognition of the numerous co-morbidities and other autoimmune disorders associated with psoriasis, including inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, and systemic lupus erythematosus suggest common signaling elements and cellular mediators may direct disease pathogenesis. In this review, we discuss common cellular pathways and participants that mediate psoriasis and other autoimmune disorders that share these cellular signaling pathways.

A Review of Biologic Therapies Targeting IL-23 and IL-17 for Use in Moderate-to-Severe Plaque Psoriasis

The development of several highly effective biologic drugs in the past decade has revolutionized the treatment of moderate-to-severe plaque psoriasis. With increased understanding of the immunopathogenesis of psoriasis, the emphasis has turned toward more specific targets for psoriasis drugs. Although the complex immunological pathway of psoriasis is not yet completely understood, current models emphasize the significant importance of interleukin (IL)-23 and IL-17. Several biologic drugs targeting these cytokines are now in various stages of drug development. Drugs targeting IL-23 include BI-655066, briakinumab, guselkumab, tildrakizumab, and ustekinumab. Drugs targeting IL-17 include brodalumab, ixekizumab, and secukinumab. While many of these have shown safety and good efficacy in clinical trials of moderate-to-severe plaque psoriasis, long-term safety is still to be established.

Opposing Effects of Zac1 and Curcumin on AP-1-Regulated Expressions of S100A7

ZAC, an encoding gene mapped at chromosome 6q24-q25 within PSORS1, was previously found over-expressed in the lower compartment of the hyperplastic epidermis in psoriatic lesions. Cytokines produced in the inflammatory dermatoses may drive AP-1 transcription factor to induce responsive gene expressions. We demonstrated that mZac1 can enhance AP-1-responsive S100A7 expression of which the encoding gene was located in PSORS4 with HaCaT keratinocytes. However, the mZac1-enhanced AP-1 transcriptional activity was suppressed by curcumin, indicating the anti-inflammatory property of this botanical agent and is exhibited by blocking the AP-1-mediated cross-talk between PSORS1 and PSORS4. Two putative AP-1-binding sites were found and demonstrated to be functionally important in the regulation of S100A7 promoter activity. Moreover, we found curcumin reduced the DNA-binding activity of AP-1 to the recognition element located in the S100A7 promoter. The S100A7 expression was found to be upregulated in the lesioned epidermis of atopic dermatitis and psoriasis, which is where this keratinocyte-derived chemoattractant engaged in the pro-inflammatory feedback loop. Understanding the regulatory mechanism of S100A7 expression will be helpful to develop therapeutic strategies for chronic inflammatory dermatoses via blocking the reciprocal stimuli between the inflammatory cells and keratinocytes.

Increased expression of interleukin-17 pathway genes in nonlesional skin of moderate-to-severe psoriasis vulgaris

BACKGROUND

Psoriasis vulgaris is an inflammatory immune-mediated disease, with lesional skin characterized by sharply demarcated, erythematous scaly plaques. Uninvolved psoriatic skin appears clinically similar to normal skin. However, it has been hypothesized that inflammatory cytokines, e.g. interleukin (IL)-17, may affect any organ or tissue having a vascular supply; thus, distant uninvolved skin could be exposed to increased circulating IL-17.

OBJECTIVES

To establish comparative genomic profiles between noninvolved skin and normal skin, in particular, determining immune abnormalities in distant uninvolved skin.

METHODS

We performed a meta-analysis on three gene array studies, comparing the nonlesional (NL) psoriatic skin transcriptome with normal gene expression. We investigated immunological features of noninvolved skin, particularly linked to IL-17 signalling.

RESULTS

We detected 252 differentially expressed gene transcripts in uninvolved skin compared with normal skin; multiple immune-related genes, including IL-17-downstream genes, were upregulated. Increased expression of IL-17-signature genes (e.g. DEFB4 and S100A7) was associated with an increased number of CD3+, CD8+ and DC-LAMP+ cells in NL skin vs. normal controls. Inducible T-cell costimulator (ICOS) expression was detected only in a few T-cells within NL skin.

CONCLUSIONS

Our data described the genomic profile in NL skin, characterizing the immune activation that was mainly attributed to IL-17 signalling.

Psoriasis

Psoriasis is an immune-mediated, genetic disease manifesting in the skin or joints or both. A diverse team of clinicians with a range of expertise is often needed to treat the disease. Psoriasis provides many challenges including high prevalence, chronicity, disfiguration, disability, and associated comorbidity. Understanding the role of immune function in psoriasis and the interplay between the innate and adaptive immune system has helped to manage this complex disease, which affects patients far beyond the skin. In this Seminar, we highlight the clinical diversity of psoriasis and associated comorbid diseases. We describe recent developments in psoriasis epidemiology, pathogenesis, and genetics to better understand present trends in psoriasis management. Our key objective is to raise awareness of the complexity of this multifaceted disease, the potential of state-of-the-art therapeutic approaches, and the need for early diagnosis and comprehensive management of patients with psoriasis.

Differential effects of anti-TNF-α and anti-IL-12/23 agents on human leukocyte-endothelial cell interactions

Enhanced leukocyte recruitment is an inflammatory process that occurs during early phases of the vascular dysfunction that characterises atherosclerosis. We evaluated the impact of anti-TNF-α (adalimumab, infliximab and etanercept) and anti-IL-12/23 (ustekinumab) on interactions between human leukocytes and endothelial cells in a flow chamber that reproduced in vivo conditions. Clinical concentrations of anti-TNF-α were evaluated on the leukocyte recruitment induced by a variety of endothelial (TNF-α, interleukin-1β, lymphotoxin-α and angiotensin-II) and leukocyte (PAF, IL-12 and IL-23) stimuli related to inflammation and atherosclerosis. Treatment with anti-TNF-α, even before or after establishing the inflammatory situation induced by TNF-α, diminished leukocyte-endothelial cell interactions induced by this stimuli. Our results also implicated adhesion molecules (ICAM-1, VCAM-1 and E-selectin) in the actions of anti-TNF-α in terms of leukocyte adhesion to endothelium. However, anti-TNF-α drugs did not influence the actions of interleukin-1β, but prevented those of lymphotoxin-α and angiotensin-II. However, once established, inflammatory response elicited by the latter three stimuli could not be reversed. Pre-treatment with anti-TNF-α, also prevented leukocyte actions induced by IL-23 on PBMC rolling flux and rolling velocity and by IL-12 on PMN adhesion. Ustekinumab exhibited a more discreet profile, having no effect on leukocyte recruitment induced by any of the endothelial stimuli, while blocking the effects of IL-23 on leukocyte activation and those of IL-12 on PMN adhesion and PAF on PBMC rolling velocity. These findings endorse the idea that biological anti-inflammatory drugs, in particular anti-TNF-α, have the capacity to influence cardiovascular risk accompanying psoriasis and rheumatoid arthritis by ameliorating vascular inflammation.

Systemic Autoimmune, Rheumatic Diseases and Coinciding Psoriasis: Data from a Large Single-Centre Registry and Review of the Literature

Psoriasis is a systemic immune-inflammatory disease characterized by chronic or recurrent skin symptoms, psoriatic arthritis, enthesopathy, and uveitis. Psoriasis has recently been published to appear with various autoimmune disorders, but the coexistence has been systematically reviewed by only few studies until now. In the present study, charts and electronic database of 4344 patients with various systemic autoimmune disorders, under regular medical control at our department, were reviewed retrospectively searching for association with psoriasis. Hereby, we demonstrate 25 psoriatic patients coinciding with various systemic autoimmune diseases. The coexistence of psoriasis and autoimmune diseases resulted in the worsening of the clinical outcome of the autoimmune diseases as indicated by higher frequency and dosages of glucocorticoid use, need for biologicals, and other comorbidities. These results suggest common environmental and genetic background as well as therapeutic possibilities in the future.

CCL20 and IL22 Messenger RNA Expression After Adalimumab vs Methotrexate Treatment of Psoriasis: A Randomized Clinical Trial

IMPORTANCE

Methotrexate is a first-line systemic agent for treating of psoriasis, although its onset of effects is slower and overall it is less effective than tumor necrosis factor blockers.

OBJECTIVE

To differentiate the response of psoriatic disease to adalimumab and methotrexate sodium.

DESIGN, SETTING, AND PARTICIPANTS

Single-center, randomized, assessor-blind, 2-arm clinical trial of 30 patients from the outpatient dermatology center of Tufts Medical Center, enrolled from August 18, 2009, to October 11, 2011. Patients aged 18 to 85 years with chronic plaque-type psoriasis, a minimum Physician Global Assessment score of 3 (higher scores indicate more severe disease), and a psoriatic plaque of at least 2 cm were randomized in a 1:1 fashion to receive subcutaneous adalimumab or oral methotrexate. Skin biopsy specimens obtained at baseline and weeks 1, 2, 4, and 16 were given a histologic grade by blinded assessors to evaluate treatment response. Analyses were conducted from April 16, 2013, to January 5, 2015.

INTERVENTIONS

A 16-week course of subcutaneous adalimumab (40 mg every 2 weeks after a loading dose) or low-dosage oral methotrexate sodium (7.5-25 mg/wk).

MAIN OUTCOMES AND MEASURES

Changes in genomic, immunohistochemical, and messenger RNA (mRNA) profiles.

RESULTS

Methotrexate responders experienced significant downregulation of helper T-cell-related (T(H)1, T(H)17, and T(H)22) mRNA expression compared with methotrexate nonresponders. Comparisons among adalimumab-treated patients were limited by the number of nonresponders (n = 1). Between adalimumab and methotrexate responders, we found no significant differences in gene expression at any study point or in the expression of T-cell-related mRNA at week 16. Adalimumab responders demonstrated early downregulation of chemokine (C-C motif) ligand 20 (CCL20) mRNA (mean [SE] at week 2, -1.83 [0.52], P < .001; week 16, -3.55 [0.54], P < .001) compared with late downregulation for methotrexate responders (week 2, 0.02 [0.51], P = .96; week 16, -2.96 [0.51], P < .001). Similar differences were observed with interleukin 22 (IL22) mRNA showing early downregulation for adalimumab responders (week 2, -3.17 [1.00], P < .001; week 16, -3.58 [1.00], P < .001) compared with late downregulation for methotrexate responders (week 2, -0.44 [0.68], P = .64; week 16, -5.14 [0.68], P < .001). Analysis of variance findings for key mRNA and immunohistochemical marker expression over the study course were significant only for CCL20 (P = .03) and IL22 (P = .006) mRNA comparing adalimumab and methotrexate responders.

CONCLUSIONS AND RELEVANCE

Methotrexate is an immunomodulator with effects on helper T-cell signaling in psoriasis. Similar genomic and immunohistochemical response signatures and levels of mRNA downregulation at study completion among adalimumab and methotrexate responders suggest a disease-driven instead of therapeutic-driven pathway regulation. Adalimumab and methotrexate responses are differentiated by patterns of normalization of CCL20 and IL22 mRNA expression and may explain the varied onset and degree of clinical responses by each treatment.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00932113.

The immunopathogenesis of psoriasis

Psoriasis vulgaris is a chronic inflammatory skin disease that results from the complex interplay between keratinocytes, dendritic cells, and T cells. Keratinocytes trigger innate and adaptive immune responses. Dermal myeloid dendritic cells regulate T cell activation and production of cytokines and chemokines that amplify inflammation. Most of the psoriatic T cells discretely produce interferon-γ, interleukin (IL)-17, and IL-22. The initiation phase of psoriasis involves Toll-like receptors, antimicrobial peptide LL37, and plasmacytoid dendritic cells. Keratinocytes are the main cutaneous cell type expressing IL-17 receptors and hence the immune circuit is amplified by keratinocytes upregulating mRNAs for a range of inflammatory products.

IL-12 and IL-23 cytokines: from discovery to targeted therapies for immune-mediated inflammatory diseases

The cytokine interleukin-12 (IL-12) was thought to have a central role in T cell-mediated responses in inflammation for more than a decade after it was first identified. Discovery of the cytokine IL-23, which shares a common p40 subunit with IL-12, prompted efforts to clarify the relative contribution of these two cytokines in immune regulation. Ustekinumab, a therapeutic agent targeting both cytokines, was recently approved to treat psoriasis and psoriatic arthritis, and related agents are in clinical testing for a variety of inflammatory disorders. Here we discuss the therapeutic rationale for targeting these cytokines, the unintended consequences for host defense and tumor surveillance and potential ways in which these therapies can be applied to treat additional immune disorders.

Obesity exacerbates imiquimod-induced psoriasis-like epidermal hyperplasia and interleukin-17 and interleukin-22 production in mice

Psoriasis is a chronic inflammatory skin disorder that is accompanied by an imbalance between the proliferation and differentiation of keratinocytes. A number of studies have suggested an association between obesity and severe psoriasis; however, it remains to be clarified whether obesity exacerbates psoriasis. To address this unsolved question, we induced psoriasiform dermatitis in mouse models for obesity. We found that obesity exaggerated the severity of psoriasiform dermatitis induced by topical application of the Toll-like receptor (TLR) 7 agonist, imiquimod. Ear swelling and epidermal hyperplasia were more prominent in the obese mice than in the control mice. When compared to imiquimod-treated control mice, imiquimod-treated obese mice expressed higher levels of psoriasis mediators, interleukin-17A (IL-17A) and IL-22 in the skin. Food intake restriction partially abrogated enhanced ear swelling and cytokine overproduction in obese mice. Furthermore, the obesity environment and imiquimod treatment synergistically induced an IL-17A downstream molecule, regenerating islet-derived 3γ (Reg3γ), which is a critical molecule for psoriatic epidermal hyperplasia. Palmitic acid, one of the fatty acids released by subcutaneous adipocytes, increased the expression of REG3A (a human homologue of mouse Reg3γ) in both the HaCaT keratinocyte cell line and normal human keratinocytes. Taken together, these results strongly suggest that obesity exacerbates psoriasiform dermatitis in mice by upregulating IL-17A, IL-22 and Reg3γ.

Pyoderma gangrenosum: challenges and solutions

Pyoderma gangrenosum (PG) is a rare disease, but commonly related to important morbidity. PG was first assumed to be infectious, but is now considered an inflammatory neutrophilic disease, often associated with autoimmunity, and with chronic inflammatory and neoplastic diseases. Currently, many aspects of the underlying pathophysiology are not well understood, and etiology still remains unknown. PG presents as painful, single or multiple lesions, with several clinical variants, in different locations, with a non specific histology, which makes the diagnosis challenging and often delayed. In the classic ulcerative variant, characterized by ulcers with inflammatory undermined borders, a broad differential diagnosis of malignancy, infection, and vasculitis needs to be considered, making PG a diagnosis of exclusion. Moreover, there are no definitively accepted diagnostic criteria. Treatment is also challenging since, due to its rarity, clinical trials are difficult to perform, and consequently, there is no “gold standard” therapy. Patients frequently require aggressive immunosuppression, often in multidrug regimens that are not standardized. We reviewed the clinical challenges of PG in order to find helpful clues to improve diagnostic accuracy and the treatment options, namely topical care, systemic drugs, and the new emerging therapies that may reduce morbidity.

Serum IL-33 levels are increased in patients with psoriasis

BACKGROUND

Interleukin (IL)-33 is a recently identified cytokine, which is a member of the IL-1 family and binds to a heterodimeric receptor comprising ST2 (suppression of tumorigenicity 2) and IL-1 receptor accessory protein. Serum levels of IL-33 have been reported to be upregulated in various T helper (Th)1/Th17-mediated diseases, such as rheumatoid arthritis and inflammatory bowel disease. IL-33 expression is increased in lesional skin in patients with psoriasis, but serum levels in patients with psoriasis have not yet been studied.

AIM

To study serum IL-33 levels in patients with psoriasis, a Th1/Th17-mediated skin disease, before and after anti-tumour necrosis factor (TNF)-α therapy.

METHODS

Serum IL-33 levels were measured in patients with psoriasis vulgaris (PV), psoriatic arthritis (PsA) or pustular psoriasis (PP), and compared with those of healthy controls. Associations between serum IL-33 levels and serum TNF-α, IL-6, vascular endothelial growth factor and C-reactive protein levels were also studied. In addition, the effect of IL-33 stimulation on IL-6, IL-8, TNF-α and VEGF secretion by human keratinocyte was analysed.

RESULTS

Serum IL-33 levels in patients with PV, PsA and PP were significantly higher than those in healthy controls. Serum IL-33 levels correlated with serum TNF-α levels in patients with psoriasis, and decreased after anti-TNF-α therapy. IL-33 stimulated IL-6 and IL-8 secretion by human keratinocytes.

CONCLUSIONS

These results suggest that serum IL-33 levels generally reflect increased inflammation in patients with psoriasis.

Evidence that a neutrophil-keratinocyte crosstalk is an early target of IL-17A inhibition in psoriasis

The response of psoriasis to antibodies targeting the interleukin (IL)-23/IL-17A pathway suggests a prominent role of T-helper type-17 (Th17) cells in this disease. We examined the clinical and immunological response patterns of 100 subjects with moderate-to-severe psoriasis receiving 3 different intravenous dosing regimens of the anti-IL-17A antibody secukinumab (1 × 3 mg/kg or 1 × 10 mg/kg on Day 1, or 3 × 10 mg/kg on Days 1, 15 and 29) or placebo in a phase 2 trial. Baseline biopsies revealed typical features of active psoriasis, including epidermal accumulation of neutrophils and formation of microabscesses in >60% of cases. Neutrophils were the numerically largest fraction of infiltrating cells containing IL-17 and may store the cytokine preformed, as IL-17A mRNA was not detectable in neutrophils isolated from active plaques. Significant clinical responses to secukinumab were observed 2 weeks after a single infusion, associated with extensive clearance of cutaneous neutrophils parallel to the normalization of keratinocyte abnormalities and reduction of IL-17-inducible neutrophil chemoattractants (e.g. CXCL1, CXCL8); effects on numbers of T cells and CD11c-positive dendritic cells were more delayed. Histological and immunological improvements were generally dose dependent and not observed in the placebo group. In the lowest-dose group, a recurrence of neutrophils was seen in some subjects at Week 12; these subjects relapsed faster than those without microabscesses. Our findings are indicative of a neutrophil-keratinocyte axis in psoriasis that may involve neutrophil-derived IL-17 and is an early target of IL-17A-directed therapies such as secukinumab.

Role of IL-17 in the pathogenesis of psoriatic arthritis and axial spondyloarthritis

Th17 cells are a discrete subset of T cell subpopulation, which produce IL-17 and certain other pro-inflammatory cytokines. A regulatory role of Th17 cells have been proposed in several autoimmune diseases including psoriasis, psoriatic arthritis (PsA), ankylosing spondylitis (AS), rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, and multiple sclerosis. Psoriatic disease is an autoimmune disease which mainly involves skin and joints. Until recently, psoriasis and PsA were thought to be Th1 mediated disease, but after the discovery of IL-17 and IL-17 knockout animal studies as well as human experimental data indicate a crucial role of the Th17 cells in the pathogenesis of psoriasis and PsA. Our research group have not only found abundance of CD4(+)IL-17(+) T cells, mainly the memory phenotype (CD4RO(+)CD45RA(-)CD11a(+)) in the synovial fluid, but also have shown the existence of a functional IL-17 receptor in synovial fibroblast of psoriatic arthritis patients. Similarly, both animal and human studies indicate a regulatory role of the Th17 cells in AS; most critical observations are that Th17 cytokines (IL-17 and IL-22) can contribute to bone erosion, osteitis and new bone formation the hall mark skeletal features associated with the pathophysiology of AS. In this review article, we have discussed the contributing role of the IL-23/IL-17 axis in the pathogenesis of PsA and AS.

Laser capture microdissection followed by next-generation sequencing identifies disease-related microRNAs in psoriatic skin that reflect systemic microRNA changes in psoriasis

Psoriasis is a systemic disease with cutaneous manifestations. MicroRNAs (miRNAs) are small non-coding RNA molecules that are differentially expressed in psoriatic skin; however, only few cell- and region-specific miRNAs have been identified in psoriatic lesions. We used laser capture microdissection (LCM) and next-generation sequencing (NGS) to study the specific miRNA expression profiles in the epidermis (Epi) and dermal inflammatory infiltrates (RD) of psoriatic skin (N = 6). We identified 24 deregulated miRNAs in the Epi and 37 deregulated miRNAs in the RD of psoriatic plaque compared with normal psoriatic skin (FCH > 2, FDR < 0.05). Interestingly, 9 of the 37 miRNAs in RD, including miR-193b and miR-223, were recently described as deregulated in circulating peripheral blood mononuclear cells (PBMCs) from patients with psoriasis. Using flow cytometry and qRT-PCR, we found that miR-193b and miR-223 were expressed in Th17 cells. In conclusion, we demonstrate that LCM combined with NGS provides a robust approach to explore the global miRNA expression in the epidermal and dermal compartments of psoriatic skin. Furthermore, our results indicate that the altered local miRNA changes seen in the RD are reflected in the circulating immune cells, suggesting that miRNAs may contribute to the pathogenesis of psoriasis.

Effects of baicalin cream in two mouse models: 2,4-dinitrofluorobenzene-induced contact hypersensitivity and mouse tail test for psoriasis

BACKGROUND

Scutellaria baicalensis is a Chinese herbal medicine that has been used for centuries to treat psoriasis. Baicalin is one of the major flavonoids and bioactive components of S. baicalensis and is responsible for the pharmacologic actions of the plant.

OBJECTIVE

This study aimed to investigate the anti-inflammatory effect and keratinocyte differentiation-inducing activity of baicalin in vivo.

METHODS

Baicalin was formulated into topical creams at concentrations of 1%, 3%, and 5%. The anti-inflammatory effect of baicalin cream was evaluated in 2,4-dinitrofluorobenzene (DNFB)-induced contact hypersensitivity (CHS) mice, and its keratinocyte-modulating action was assessed using the mouse tail model for psoriasis.

RESULTS

During the topical application of baicalin cream, no evidence of irritant effect was observed in both tests. In the inflammation model, mice exposed to baicalin cream displayed a reduction in DNFB-induced CHS responses compared with vehicle-treated animals, showing that the topical application of baicalin cream exerted an anti-inflammatory effect. In the second model, baicalin cream dose-dependently increased the orthokeratosis of granular layers and the relative epidermal thickness of mouse tail skin, indicative of the keratinocyte differentiation-inducing activity of this topical preparation.

CONCLUSIONS

Taking the in vivo findings together, the present study indicated that baicalin cream may be a promising antipsoriatic agent worthy of further investigation for psoriasis treatment.

Tofacitinib for the treatment of moderate-to-severe psoriasis

Because of the increased knowledge about the underlying cytokine network in psoriasis, selective systemic agents for the treatment of moderate-to-severe psoriasis have been developed during the past decade. The marked upregulation of JAK/STAT pathways in psoriasis and the identification of multiple key mediators in psoriasis pathogenesis that signal through JAK/STAT pathways led to investigation of JAK proteins as potential therapeutic targets for psoriasis treatment. A novel JAK-STAT inhibitor, tofacitinib, has been tested in preclinical studies for the treatment of psoriasis. Considering the satisfactory safety profile and the encouraging efficacy observed in the Phase II and Phase III trials, tofacitinib may represent an important therapeutic to be included into the psoriasis paradigm.

The expression and regulation of chemerin in the epidermis

Chemerin is a protein ligand for the G protein-coupled receptor CMKLR1 and also binds to two atypical heptahelical receptors, CCRL2 and GPR1. Chemerin is a leukocyte attractant, adipokine, and antimicrobial protein. Although chemerin was initially identified as a highly expressed gene in healthy skin keratinocytes that was downregulated during psoriasis, the regulation of chemerin and its receptors in the skin by specific cytokines and microbial factors remains unexplored. Here we show that chemerin, CMKLR1, CCRL2 and GPR1 are expressed in human and mouse epidermis, suggesting that this tissue may be both a source and target for chemerin mediated effects. In human skin cultures, chemerin is significantly downregulated by IL-17 and IL-22, key cytokines implicated in psoriasis, whereas it is upregulated by acute phase cytokines oncostatin M and IL-1β. Moreover, we show that human keratinocytes in vitro and mouse skin in vivo respond to specific microbial signals to regulate expression levels of chemerin and its receptors. Furthermore, in a cutaneous infection model, chemerin is required for maximal bactericidal effects in vivo. Together, our findings reveal previously uncharacterized regulators of chemerin expression in skin and identify a physiologic role for chemerin in skin barrier defense against microbial pathogens.

The role of IL-17 in psoriasis

BACKGROUND

Psoriasis is a chronic skin condition traditionally believed to involve the Th1 pathway. Recently, the IL-23/Th17/IL-17 pathway has been highlighted in the pathogenesis of psoriasis and other autoimmune inflammatory conditions. From a clinician's perspective, we sought to review the basic science data relevant to IL-17's role in psoriasis pathogenesis.

METHODS

We performed a Pubmed and Web of Knowledge search for English articles starting from 1990 that discussed the Th17 pathway. Search terms such as "IL-17" and "psoriasis" were utilized.

RESULTS

The IL-17 pathway is regulated by IL-23, a cytokine that is vital for the expansion and maintenance of the Th17 cell population. Th17 derived cytokines (IL-17A, IL-17F, IL-17A/F and IL-22) were elevated in both psoriasis-like murine models and human psoriatic lesional biopsies. Ixekizumab (anti-IL-17A) treatment of psoriasis was found to normalize levels of IL-17 downstream gene products.

CONCLUSION

Both preclinical and clinical studies support the central role of IL-17 in the pathogenesis of psoriasis.

Genetic and epigenetic basis of psoriasis pathogenesis

Psoriasis is a chronic inflammatory skin disease whose prevalence varies among different populations worldwide. It is a complex multi-factorial disease and the exact etiology is largely unknown. Family based studies have indicated a genetic predisposition; however they cannot fully explain the disease pathogenesis. In addition to genetic susceptibility, environmental as well as gender and age related factors were also been found to be associated. Recently, imbalances in epigenetic networks are indicated to be causative elements in psoriasis. The present knowledge of epigenetic involvement, mainly the DNA methylation, chromatin modifications and miRNA deregulation is surveyed here. An integrated approach considering genetic and epigenetic anomalies in the light of immunological network may explore the pathogenesis of psoriasis.

Periostin contributes to epidermal hyperplasia in psoriasis common to atopic dermatitis

BACKGROUND

Epidermal hyperplasia is a histological hallmark observed in both atopic dermatitis (AD) and psoriasis, although the clinical features and the underlying immunological disorders of these diseases are different. We previously showed that periostin, a matricellular protein, plays a critical role in epidermal hyperplasia in AD, using a mouse model and a 3-dimensional organotypic coculture system. In this study, we explore the hypothesis that periostin is involved in epidermal hyperplasia in psoriasis.

METHODS

To examine expression of periostin in psoriasis patients, we performed immunohistochemical analysis on skin biopsies from six such patients. To investigate periostin's role in the pathogenesis of psoriasis, we evaluated periostin-deficient mice in a psoriasis mouse model induced by topical treatment with imiquimod (IMQ).

RESULTS

Periostin was substantially expressed in the dermis of all investigated psoriasis patients. Epidermal hyperplasia induced by IMQ treatment was impaired in periostin-deficient mice, along with decreased skin swelling. However, upon treatment with IMQ, periostin deficiency did not alter infiltration of inflammatory cells such as neutrophils; production of IL-17, -22, or -23; or induction/expansion of IL-17- and IL-22-producing group 3 innate lymphoid cells.

CONCLUSIONS

Periostin plays an important role during epidermal hyperplasia in IMQ-induced skin inflammation, independently of the IL-23-IL-17/IL-22 axis. Periostin appears to be a mediator for epidermal hyperplasia that is common to AD and psoriasis.

T cell responses in psoriasis and psoriatic arthritis

According to the current view the histological features of psoriasis arise as a consequence of the interplay between T cells, dendritic cells and keratinocytes giving rise to a self-perpetuating loop that amplifies and sustains inflammation in lesional skin. In particular, myeloid dendritic cell secretion of IL-23 and IL-12 activates IL-17-producing T cells, Th22 and Th1 cells, leading to the production of inflammatory cytokines such as IL-17, IFN-γ, TNF and IL-22. These cytokines mediate effects on keratinocytes thus establishing the inflammatory loop. Unlike psoriasis the immunopathogenic features of psoriatic arthritis are poorly characterized and there is a gap in the knowledge of the pathogenic link between inflammatory T cell responses arising in the skin and the development of joint inflammation. Here we review the knowledge accumulated over the years from the early evidence of autoreactive CD8 T cells that was studied mainly in the years 1990s and 2000s to the recent findings of the role of Th17, Tc17 cells and γδ T cells in psoriatic disease pathogenesis. The review will also focus on common and distinguishing features of T cell responses in psoriatic plaques and in synovial fluid of patients with psoriatic arthritis. The integration of this information could help to distinguish the role played by T cells in the initiation phase of the disease from the role of T cells as downstream effectors sustaining inflammation in psoriatic plaques and potentially leading to disease manifestation in distant joints.

Involvement of TNF-α converting enzyme in the development of psoriasis-like lesions in a mouse model

TNF-α plays a crucial role in psoriasis; therefore, TNF inhibition has become a gold standard for the treatment of psoriasis. TNF-α is processed from a membrane-bound form by TNF-α converting enzyme (TACE) to soluble form, which exerts a number of biological activities. EGF receptor (EGFR) ligands, including heparin-binding EGF-like growth factor (HB-EGF), amphiregulin and transforming growth factor (TGF)-α are also TACE substrates and are psoriasis-associated growth factors. Vascular endothelial growth factor (VEGF), one of the downstream molecules of EGFR and TNF signaling, plays a key role in angiogenesis for developing psoriasis. In the present study, to assess the possible role of TACE in the pathogenesis of psoriasis, we investigated the involvement of TACE in TPA-induced psoriasis-like lesions in K5.Stat3C mice, which represent a mouse model of psoriasis. In this mouse model, TNF-α, amphiregulin, HB-EGF and TGF-α were significantly up-regulated in the skin lesions, similar to human psoriasis. Treatment of K5.Stat3C mice with TNF-α or EGFR inhibitors attenuated the skin lesions, suggesting the roles of TACE substrates in psoriasis. Furthermore, the skin lesions of K5.Stat3C mice showed down-regulation of tissue inhibitor of metalloproteinase-3, an endogenous inhibitor of TACE, and an increase in soluble TNF-α. A TACE inhibitor abrogated EGFR ligand-dependent keratinocyte proliferation and VEGF production in vitro, suggesting that TACE was involved in both epidermal hyperplasia and angiogenesis during psoriasis development. These results strongly suggest that TACE contributes to the development of psoriatic lesions through releasing two kinds of psoriasis mediators, TNF-α and EGFR ligands. Therefore, TACE could be a potential therapeutic target for the treatment of psoriasis.

A GRHL3-regulated repair pathway suppresses immune-mediated epidermal hyperplasia

Dermal infiltration of T cells is an important step in the onset and progression of immune-mediated skin diseases such as psoriasis; however, it is not known whether epidermal factors play a primary role in the development of these diseases. Here, we determined that the prodifferentiation transcription factor grainyhead-like 3 (GRHL3), which is essential during epidermal development, is dispensable for adult skin homeostasis, but required for barrier repair after adult epidermal injury. Consistent with activation of a GRHL3-regulated repair pathway in psoriasis, we found that GRHL3 is upregulated in lesional skin and binds known epidermal differentiation gene targets. Using an imiquimod-induced model of immune-mediated epidermal hyperplasia, we found that mice lacking GRHL3 have an exacerbated epidermal damage response, greater sensitivity to disease induction, delayed resolution of epidermal lesions, and resistance to anti-IL-22 therapy compared with WT animals. ChIP-Seq and gene expression profiling of murine skin revealed that while GRHL3 regulates differentiation pathways both during development and during repair from immune-mediated damage, it targets distinct sets of genes in the 2 processes. In particular, GRHL3 suppressed a number of alarmin and other proinflammatory genes after immune injury. This study identifies a GRHL3-regulated epidermal barrier repair pathway that suppresses disease initiation and helps resolve existing lesions in immune-mediated epidermal hyperplasia.

AHR: making the keratinocytes thick skinned

Dysregulated signals from the external environment and/or the internal milieu of the skin can lead to pathological conditions such as psoriasis. Di Meglio et al. (2014) show that the environment-responsive transcription factor AhR acts in keratinocytes to suppress psoriatic lesions.