Human skin CD141+ dendritic cells regulate cutaneous immunity via the neuropeptide urocortin 2

Skin immune homeostasis is a multi-faceted process where dermal dendritic cells (DDCs) are key in orchestrating responses to environmental stressors. We have previously identified CD141+CD14+ DDCs as a skin-resident immunoregulatory population that is vitamin-D3 (VitD3) inducible from monocyte-derived DCs (moDCs), termed CD141hi VitD3 moDCs. We demonstrate that CD141+ DDCs and CD141hi VitD3 moDCs share key immunological features including cell surface markers, reduced T cell stimulation, IL-10 production, and a common transcriptomic signature. Bioinformatic analysis identified the neuroactive ligand receptor pathway and the neuropeptide, urocortin 2 (UCN2), as a potential immunoregulatory candidate molecule. Incubation with VitD3 upregulated UCN2 in CD141+ DCs and UVB irradiation induced UCN2 in CD141+ DCs in healthy skin in vivo. Notably, CD141+ DDC generation of suppressive Tregs was dependent upon the UCN2 pathway as in vivo administration of UCN2 reversed skin inflammation in humanized mice. We propose the neuropeptide UCN2 as a novel skin DC-derived immunoregulatory mediator with a potential role in UVB and VitD3-dependent skin immune homeostasis.

GWAS meta-analysis of psoriasis identifies new susceptibility alleles impacting disease mechanisms and therapeutic targets

Psoriasis is a common, debilitating immune-mediated skin disease. Genetic studies have identified biological mechanisms of psoriasis risk, including those targeted by effective therapies. However, the genetic liability to psoriasis is not fully explained by variation at robustly identified risk loci. To move towards a saturation map of psoriasis susceptibility we meta-analysed 18 GWAS comprising 36,466 cases and 458,078 controls and identified 109 distinct psoriasis susceptibility loci, including 45 that have not been previously reported. These include susceptibility variants at loci in which the therapeutic targets IL17RA and AHR are encoded, and deleterious coding variants supporting potential new drug targets (including in STAP2, CPVL and POU2F3). We conducted a transcriptome-wide association study to identify regulatory effects of psoriasis susceptibility variants and cross-referenced these against single cell expression profiles in psoriasis-affected skin, highlighting roles for the transcriptional regulation of haematopoietic cell development and epigenetic modulation of interferon signalling in psoriasis pathobiology.

Manuka honey activates the aryl hydrocarbon receptor: Implications for skin inflammation

Manuka honey (MH) is a complex nutritional material with antimicrobial, antioxidant and anti-inflammatory activity. We have previously shown that MH down regulates IL-4-induced CCL26 expression in immortalized keratinocytes. As MH contains potential ligands of the Aryl Hydrocarbon Receptor (AHR), a key regulator of skin homeostasis, we hypothesize that this effect is mediated via AHR activation. Here, we treated HaCaT cell lines, either stable transfected with an empty vector (EV-HaCaT) or in which AHR had been stable silenced (AHR-silenced HaCaT); or primary normal human epithelial keratinocytes (NHEK) with 2% MH for 24 h. This induced a 15.4-fold upregulation of CYP1A1 in EV-HaCaTs, which was significantly reduced in AHR-silenced cells. Pre-treatment with the AHR antagonist CH223191 completely abrogated this effect. Similar findings were observed in NHEK. In vivo treatment of the Cyp1a1Cre x R26ReYFP reporter mice strain's skin with pure MH significantly induced CYP1A1 expression compared with Vaseline. Treatment of HaCaT with 2% MH significantly decreased baseline CYP1 enzymatic activity at 3 and 6 h but increased it after 12 h, suggesting that MH may activate the AHR both through direct and indirect means. Importantly, MH downregulation of IL-4-induced CCL26 mRNA and protein was abrogated in AHR-silenced HaCaTs and by pre-treatment with CH223191. Finally, MH significantly upregulated FLG expression in NHEK in an AHR-dependent manner. In conclusion, MH activates AHR, both in vitro and in vivo, thereby providing a mechanism of its IL4-induced CCL26 downregulation and upregulation of FLG expression. These results have potential clinical implications for atopic diseases and beyond.

Non-adherence to systemic immune-modifying therapy in people with psoriasis during the COVID-19 pandemic: findings from a global cross-sectional survey

BACKGROUND

Non-adherence to immune-modifying therapy is a complex behaviour which, before the COVID-19 pandemic, was shown to be associated with mental health disorders in people with immune-mediated diseases. The COVID-19 pandemic has led to a rise in the global prevalence of anxiety and depression, and limited data exist on the association between mental health and non-adherence to immune modifying therapy during the pandemic.

OBJECTIVES

To assess the extent of and reasons underlying non-adherence to systemic immune-modifying therapy during the COVID-19 pandemic in individuals with psoriasis, and the association between mental health and non-adherence.

METHODS

Online self-report surveys (PsoProtectMe), including validated screens for anxiety and depression, were completed globally during the first year of the pandemic. We assessed the association between anxiety or depression and non-adherence to systemic immune-modifying therapy using binomial logistic regression, adjusting for potential cofounders (age, sex, ethnicity, comorbidity), and country of residence.

RESULTS

Of 3980 participants from 77 countries, 1611 (40.5%) were prescribed a systemic immune-modifying therapy. Of these, 408 (25.3%) reported non-adherence during the pandemic, most commonly due to concerns about their immunity. In the unadjusted model, a positive anxiety screen was associated with non-adherence to systemic immune-modifying therapy (OR 1.36, 95%CI 1.07-1.76). Specifically, anxiety was associated with non-adherence to targeted therapy (OR 1.41, 95%CI 1.01-1.96) but not standard systemic therapy (OR 1.16, 95%CI 0.81-1.67). In the adjusted model, although the directions of the effects remained, anxiety was not significantly associated with non-adherence to overall systemic (OR 1.20, 95%CI 0.92-1.56) or targeted (OR 1.33, 95%CI 0.94-1.89) immune-modifying therapy. A positive depression screen was not strongly associated with non-adherence to systemic immune-modifying therapy in the unadjusted (OR 1.22, 95% CI 0.94-1.57) or adjusted models (OR 1.14, 95% CI 0.87-1.49).

CONCLUSION

These data indicate substantial non-adherence to immune-modifying therapy in people with psoriasis during the pandemic, with attenuation of the association with mental health after adjusting for confounders. Future research in larger populations should further explore pandemic-specific drivers of treatment non-adherence. Clear communication of the reassuring findings from population-based research regarding immune-modifying therapy-associated adverse COVID-19 risks to people with psoriasis is essential, to optimise adherence and disease outcomes.

Biomarkers of systemic treatment response in people with psoriasis: a scoping review

BACKGROUND

Responses to the systemic treatments commonly used to treat psoriasis vary. Biomarkers that accurately predict effectiveness and safety would enable targeted treatment selection, improved patient outcomes and more cost-effective healthcare.

OBJECTIVES

To perform a scoping review to identify and catalogue candidate biomarkers of systemic treatment response in psoriasis for the translational research community.

METHODS

A systematic search of CENTRAL, Embase, LILACS and MEDLINE was performed for relevant articles published between 1990 and December 2021. Eligibility criteria were studies involving patients with psoriasis (any age, n ≥ 50) reporting biomarkers associated with systemic treatment response. The main outcomes were any measure of systemic treatment efficacy or safety. Data were extracted by one reviewer and checked by a second; studies meeting minimal quality criteria (use of methods to control for confounding) were formally assessed for bias. Candidate biomarkers were identified by an expert multistakeholder group using a majority voting consensus exercise and mapped to relevant cellular and molecular pathways.

RESULTS

Of 71 included studies (67 studying effectiveness outcomes and eight safety outcomes; four studied both), most reported genomic or proteomic biomarkers associated with response to biologics (48 studies). Methodological or reporting limitations frequently compromised the interpretation of findings, including inadequate control for key covariates, lack of adjustment for multiple testing, and selective outcome reporting. We identified candidate biomarkers of efficacy to tumour necrosis factor inhibitors [variation in CARD14, CDKAL1, IL1B, IL12B and IL17RA loci, and lipopolysaccharide-induced phosphorylation of nuclear factor (NF)-κB in type 2 dendritic cells] and ustekinumab (HLA-C*06:02 and variation in an IL1B locus). None were supported by sufficient evidence for clinical use without further validation studies. Candidate biomarkers were found to be involved in the immune cellular crosstalk implicated in psoriasis pathogenesis, most notably antigen presentation, T helper (Th)17 cell differentiation, positive regulation of NF-κB, and Th17 cell activation.

CONCLUSIONS

This comprehensive catalogue provides a key resource for researchers and reveals a diverse range of biomarker types and outcomes in the included studies. The candidate biomarkers identified require further evaluation in methodologically robust studies to establish potential clinical utility. Future studies should aim to address the common methodological limitations highlighted in this review to expedite discovery and validation of biomarkers for clinical use. What is already known about this topic? Responses to the systemic treatments commonly used to treat psoriasis vary. Biomarkers that accurately predict effectiveness and safety would enable targeted treatment selection, improved patient outcomes and more cost-effective healthcare. What does this study add? This review provides a comprehensive catalogue of investigated biomarkers of systemic treatment response in psoriasis. A diverse range of biomarker types and outcomes was found in the included studies, serving as a key resource for the translational research community.

Biomarkers of disease progression in people with psoriasis: a scoping review

BACKGROUND

Identification of those at risk of more severe psoriasis and/or associated morbidities offers opportunity for early intervention, reduced disease burden and more cost-effective healthcare. Prognostic biomarkers of disease progression have thus been the focus of intense research, but none are part of routine practice.

OBJECTIVES

To identify and catalogue candidate biomarkers of disease progression in psoriasis for the translational research community.

METHODS

A systematic search of CENTRAL, Embase, LILACS and MEDLINE was performed for relevant articles published between 1990 and December 2021. Eligibility criteria were studies involving patients with psoriasis (any age, n ≥ 50) reporting biomarkers associated with disease progression. The main outcomes were any measure of skin severity or any prespecified psoriasis comorbidity. Data were extracted by one reviewer and checked by a second; studies meeting minimal quality criteria (longitudinal design and/or use of methods to control for confounding) were formally assessed for bias. Candidate biomarkers were identified by an expert multistakeholder group using a majority voting consensus exercise, and mapped to relevant cellular and molecular pathways.

RESULTS

Of 181 included studies, most investigated genomic or proteomic biomarkers associated with disease severity (n = 145) or psoriatic arthritis (n = 30). Methodological and reporting limitations compromised interpretation of findings, most notably a lack of longitudinal studies, and inadequate control for key prognostic factors. The following candidate biomarkers with future potential utility were identified for predicting disease severity: LCE3D, interleukin (IL)23R, IL23A, NFKBIL1 loci, HLA-C*06:02 (genomic), IL-17A, IgG aHDL, GlycA, I-FABP and kallikrein 8 (proteomic), tyramine (metabolomic); psoriatic arthritis: HLA-C*06:02, HLA-B*27, HLA-B*38, HLA-B*08, and variation at the IL23R and IL13 loci (genomic); IL-17A, CXCL10, Mac-2 binding protein, integrin b5, matrix metalloproteinase-3 and macrophage-colony stimulating factor (proteomic) and tyramine and mucic acid (metabolomic); and type 2 diabetes mellitus: variation in IL12B and IL23R loci (genomic). No biomarkers were supported by sufficient evidence for clinical use without further validation.

CONCLUSIONS

This review provides a comprehensive catalogue of investigated biomarkers of disease progression in psoriasis. Future studies must address the common methodological limitations identified herein to expedite discovery and validation of biomarkers for clinical use. What is already known about this topic? The current treatment paradigm in psoriasis is reactive. There is a need to develop effective risk-stratified management approaches that can proactively attenuate the substantial burden of disease. Prognostic biomarkers of disease progression have therefore been the focus of intense research. What does this study add? This review is the first to scope, collate and catalogue research investigating biomarkers of disease progression in psoriasis. The review identifies potentially promising candidate biomarkers for further investigation and highlights common important limitations that should be considered when designing and conducting future studies in this area.

Differences in Clinical Features and Comorbid Burden between HLA-C∗06:02 Carrier Groups in >9,000 People with Psoriasis

The identification of robust endotypes-disease subgroups of clinical relevance-is fundamental to stratified medicine. We hypothesized that HLA-C∗06:02 status, the major genetic determinant of psoriasis, defines a psoriasis endotype of clinical relevance. Using two United Kingdom-based cross-sectional datasets-an observational severe-psoriasis study (Biomarkers of Systemic Treatment Outcomes in Psoriasis; n = 3,767) and a large population-based bioresource (UK Biobank, including n = 5,519 individuals with psoriasis)-we compared demographic, environmental, and clinical variables of interest in HLA-C∗06:02-positive (one or two copies of the HLA-C∗06:02 allele) with those in HLA-C∗06:02‒negative (no copies) individuals of European ancestry. We used multivariable regression analyses to account for mediation effects established a priori. We confirm previous observations that HLA-C∗06:02-positive status is associated with earlier age of psoriasis onset and extend findings to reveal an association with disease expressivity in females (Biomarkers of Systemic Treatment Outcomes in Psoriasis: P = 2.7 × 10-14, UK Biobank: P = 1.0 × 10-8). We also show HLA-C∗06:02-negative status to be associated with characteristic clinical features (large plaque disease, OR for HLA-C∗06:02 = 0.73, P = 7.4 × 10-4; nail involvement, OR = 0.70, P = 2.4 × 10-6); higher central adiposity (Biomarkers of Systemic Treatment Outcomes in Psoriasis: waist circumference difference of 2.0 cm, P = 8.4 × 10-4; UK Biobank: waist circumference difference of 1.4 cm, P = 1.5 × 10-4), especially in women; and a higher prevalence of other cardiometabolic comorbidities. These findings extend the clinical phenotype delineated by HLA-C∗06:02 and highlight its potential as an important biomarker to consider in future multimarker stratified medicine approaches.

Exploring the role of immune pathways in the risk and development of depression in adolescence: Research protocol of the IDEA-FLAME study

Extensive research suggests a role for the innate immune system in the pathogenesis of depression, but most of the studies are conducted in adult populations, in high-income countries and mainly focus on the study of inflammatory proteins alone, which provides only a limited understanding of the immune pathways involved in the development of depression. The IDEA-FLAME study aims to identify immune phenotypes underlying increased risk of developing depression in adolescence in a middle-income country. To this end, we will perform deep-immunophenotyping of peripheral blood mononuclear cells and RNA genome-wide gene expression analyses in a longitudinal cohort of Brazilian adolescents stratified for depression risk. The project will involve the 3-year follow-up of an already recruited cohort of 150 Brazilian adolescents selected for risk/presence of depression on the basis of a composite risk score we developed using sociodemographic characteristics (50 adolescents with low-risk and 50 with high-risk of developing depression, and 50 adolescents with a current major depressive disorder). We will 1) test whether the risk group classification at baseline is associated with differences in immune cell frequency, phenotype and functional status, 2) test whether baseline immune markers (cytokines and immune cell markers) are associated with severity of depression at 3-year follow-up, and 3) identify changes in gene expression of immune pathways over the 3-year follow-up in adolescents with increased risk and presence of depression. Because of the exploratory nature of the study, the findings would need to be replicated in a separate and larger sample. Ultimately, this research will contribute to elucidating key immune therapeutic targets and inform the development of interventions to prevent onset of depression among adolescents.

Guardians of the barrier: Microbiota engage AHR in keratinocytes to mantain skin homeostasis

The skin barrier is critical in ensuring homeostasis, yet factors influencing its development, repair, and maintenance are ill-defined. In this issue of Cell Host & Microbe, Uberoi et al. demonstrate the skin microbiota's role in maintaining barrier integrity via AHR signaling in keratinocytes, which has implications for skin disease management.

Meeting Report: Psoriasis Stratification to Optimize Relevant Therapy Showcase

A stratified medicine approach for the treatment of psoriasis promises greater certainty of clinical decision making through prediction of response on the basis of clinical, pharmacological, and -omics data from an individual patient. As yet, there is no predictive model for treatment response in routine clinical use for psoriasis. The Psoriasis Stratification to Optimise Relevant Therapy (PSORT) Consortium is a United Kingdom Medical Research Council‒funded, academic‒industrial stratified medicine consortium established with the objective of discovering the predictors and stratifiers of response of psoriasis to biologic therapies. A showcase meeting was convened and attended by 80 stakeholders at the Royal College of Physicians, London, United Kingdom on 18 November 2019. The purpose was to disseminate the research findings from the PSORT consortium discovered thus far. This report summarizes the presentations made on the day and the significant advances made by PSORT toward a stratified medicine approach to the management of psoriasis.

Factors associated with adverse COVID-19 outcomes in patients with psoriasis-insights from a global registry-based study

BACKGROUND

The multimorbid burden and use of systemic immunosuppressants in people with psoriasis may confer greater risk of adverse outcomes of coronavirus disease 2019 (COVID-19), but the data are limited.

OBJECTIVE

Our aim was to characterize the course of COVID-19 in patients with psoriasis and identify factors associated with hospitalization.

METHODS

Clinicians reported patients with psoriasis with confirmed/suspected COVID-19 via an international registry, Psoriasis Patient Registry for Outcomes, Therapy and Epidemiology of COVID-19 Infection. Multiple logistic regression was used to assess the association between clinical and/or demographic characteristics and hospitalization. A separate patient-facing registry characterized risk-mitigating behaviors.

RESULTS

Of 374 clinician-reported patients from 25 countries, 71% were receiving a biologic, 18% were receiving a nonbiologic, and 10% were not receiving any systemic treatment for psoriasis. In all, 348 patients (93%) were fully recovered from COVID-19, 77 (21%) were hospitalized, and 9 (2%) died. Increased hospitalization risk was associated with older age (multivariable-adjusted odds ratio [OR] = 1.59 per 10 years; 95% CI = 1.19-2.13), male sex (OR = 2.51; 95% CI = 1.23-5.12), nonwhite ethnicity (OR = 3.15; 95% CI = 1.24-8.03), and comorbid chronic lung disease (OR = 3.87; 95% CI = 1.52-9.83). Hospitalization was more frequent in patients using nonbiologic systemic therapy than in those using biologics (OR = 2.84; 95% CI = 1.31-6.18). No significant differences were found between classes of biologics. Independent patient-reported data (n = 1626 across 48 countries) suggested lower levels of social isolation in individuals receiving nonbiologic systemic therapy than in those receiving biologics (OR = 0.68; 95% CI = 0.50-0.94).

CONCLUSION

In this international case series of patients with moderate-to-severe psoriasis, biologic use was associated with lower risk of COVID-19-related hospitalization than with use of nonbiologic systemic therapies; however, further investigation is warranted on account of potential selection bias and unmeasured confounding. Established risk factors (being older, being male, being of nonwhite ethnicity, and having comorbidities) were associated with higher hospitalization rates.

CYP1A1 Enzymatic Activity Influences Skin Inflammation Via Regulation of the AHR Pathway

The AHR is an environmental sensor and transcription factor activated by a variety of man-made and natural ligands, which has recently emerged as a critical regulator of homeostasis at barrier organs such as the skin. Activation of the AHR pathway downmodulates skin inflammatory responses in animal models and psoriasis clinical samples. In this study, we identify CYP1A1 enzymatic activity as a critical regulator of beneficial AHR signaling in the context of skin inflammation. Mice constitutively expressing Cyp1a1 displayed increased CYP1A1 enzymatic activity in the skin, which resulted in exacerbated immune cell activation and skin pathology, mirroring that observed in Ahr-deficient mice. Inhibition of CYP1A1 enzymatic activity ameliorated the skin immunopathology by restoring beneficial AHR signaling. Importantly, patients with psoriasis displayed reduced activation of the AHR pathway and increased CYP1A1 enzymatic activity compared with healthy donors, suggesting that dysregulation of the AHR/CYP1A1 axis may play a role in inflammatory skin disease. Thus, modulation of CYP1A1 activity may represent a promising alternative strategy to harness the anti-inflammatory effect exerted by activation of the AHR pathway in the skin.

An analysis of IL-36 signature genes and individuals with IL1RL2 knockout mutations validates IL-36 as a psoriasis therapeutic target

Interleukin (IL)-36α, IL-36β, and IL-36γ are innate mediators of acute epithelial inflammation. We sought to demonstrate that these cytokines are also required for the pathogenesis of plaque psoriasis, a common and chronic skin disorder, caused by abnormal T helper 17 (T_H17) cell activation. To investigate this possibility, we first defined the genes that are induced by IL-36 cytokines in primary human keratinocytes. This enabled us to demonstrate a significant IL-36 signature among the transcripts that are up-regulated in plaque psoriasis and the susceptibility loci associated with the disease in genome-wide studies. Next, we investigated the impact of in vivo and ex vivo IL-36 receptor blockade using a neutralizing antibody or a recombinant antagonist. Both inhibitors had marked anti-inflammatory effects on psoriatic skin, demonstrated by statistically significant reductions in IL-17 expression, keratinocyte activation, and leukocyte infiltration. Finally, we explored the potential safety profile associated with IL-36 blockade by phenotyping 12 individuals carrying knockout mutations of the IL-36 receptor gene. We found that normal immune function was broadly preserved in these individuals, suggesting that IL-36 signaling inhibition would not substantially compromise host defenses. These observations, which integrate the results of transcriptomics and model system analysis, pave the way for early-stage clinical trials of IL-36 antagonists.

AP1S3 Mutations Cause Skin Autoinflammation by Disrupting Keratinocyte Autophagy and Up-Regulating IL-36 Production

Prominent skin involvement is a defining characteristic of autoinflammatory disorders caused by abnormal IL-1 signaling. However, the pathways and cell types that drive cutaneous autoinflammatory features remain poorly understood. We sought to address this issue by investigating the pathogenesis of pustular psoriasis, a model of autoinflammatory disorders with predominant cutaneous manifestations. We specifically characterized the impact of mutations affecting AP1S3, a disease gene previously identified by our group and validated here in a newly ascertained patient resource. We first showed that AP1S3 expression is distinctively elevated in keratinocytes. Because AP1S3 encodes a protein implicated in autophagosome formation, we next investigated the effects of gene silencing on this pathway. We found that AP1S3 knockout disrupts keratinocyte autophagy, causing abnormal accumulation of p62, an adaptor protein mediating NF-κB activation. We showed that as a consequence, AP1S3-deficient cells up-regulate IL-1 signaling and overexpress IL-36α, a cytokine that is emerging as an important mediator of skin inflammation. These abnormal immune profiles were recapitulated by pharmacological inhibition of autophagy and verified in patient keratinocytes, where they were reversed by IL-36 blockade. These findings show that keratinocytes play a key role in skin autoinflammation and identify autophagy modulation of IL-36 signaling as a therapeutic target.

The genetic architecture of the human immune system: a bioresource for autoimmunity and disease pathogenesis

Despite recent discoveries of genetic variants associated with autoimmunity and infection, genetic control of the human immune system during homeostasis is poorly understood. We undertook a comprehensive immunophenotyping approach, analyzing 78,000 immune traits in 669 female twins. From the top 151 heritable traits (up to 96% heritable), we used replicated GWAS to obtain 297 SNP associations at 11 genetic loci, explaining up to 36% of the variation of 19 traits. We found multiple associations with canonical traits of all major immune cell subsets and uncovered insights into genetic control for regulatory T cells. This data set also revealed traits associated with loci known to confer autoimmune susceptibility, providing mechanistic hypotheses linking immune traits with the etiology of disease. Our data establish a bioresource that links genetic control elements associated with normal immune traits to common autoimmune and infectious diseases, providing a shortcut to identifying potential mechanisms of immune-related diseases.

The aryl hydrocarbon receptor: multitasking in the immune system

The aryl hydrocarbon receptor (AhR), for many years almost exclusively studied by the pharmacology/toxicology field for its role in mediating the toxicity of xenobiotics such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), has more recently attracted the attention of immunologists. The evolutionary conservation of this transcription factor and its widespread expression in the immune system point to important physiological functions that are slowly being unraveled. In particular, the emphasis is now shifting from the role of AhR in the xenobiotic pathway toward its mode of action in response to physiological ligands. In this article, we review the current understanding of the molecular interactions and functions of AhR in the immune system in steady state and in the presence of infection and inflammation, with a focus on barrier organs such as the skin, the gut, and the lung.

IL-22 fate reporter reveals origin and control of IL-22 production in homeostasis and infection

IL-22 is a cytokine that regulates tissue homeostasis at barrier surfaces. A variety of IL-22-producing cell types is known, but identification on the single-cell level remains difficult. Therefore, we generated a fate reporter mouse that would allow the identification of IL-22-producing cells and their fate mapping in vivo. To trace IL-22-expressing cells, a sequence encoding Cre recombinase was cloned into the Il22 locus, and IL22(Cre) mice were crossed with reporter mice expressing enhanced yellow fluorescence protein (eYFP) under control of the endogenous Rosa26 promoter. In IL22(Cre)R26R(eYFP) mice, the fluorescent reporter permanently labels cells that have switched on Il22 expression, irrespective of cytokine production. Despite a degree of underreporting, eYFP expression was detectable in nonimmune mice and restricted to group 3 innate lymphoid cells (ILC3) in the gut and γδ T cells in skin or lung. Upon skin challenge with imiquimod, eYFP(+) γδ and CD4 T cells expanded in the skin. Infection with Citrobacter rodentium initially was controlled by ILC3, followed by expansion of eYFP(+) CD4 T cells, which were induced in innate lymphoid follicles in the colon. No eYFP expression was detected in small intestinal Th17 cells, and they did not expand in the immune response. Colonic eYFP(+) CD4 T cells exhibited plasticity during infection with expression of additional cytokines, in contrast to ILC3, which remained largely stable. Single-cell quantitative PCR analysis of eYFP(+) CD4 T cells confirmed their heterogeneity, suggesting that IL-22 expression is not confined to particular subsets or a dedicated Th22 subset.

Psoriasis

Psoriasis is a common chronic inflammatory skin disease with a spectrum of clinical phenotypes and results from the interplay of genetic, environmental, and immunological factors. Four decades of clinical and basic research on psoriasis have elucidated many of the pathogenic mechanisms underlying disease and paved the way to effective targeted therapies. Here, we review this progress and identify future directions of study that are supported by a more integrative research approach and aim at further improving the patients' life.

Activation of the aryl hydrocarbon receptor dampens the severity of inflammatory skin conditions

Environmental stimuli are known to contribute to psoriasis pathogenesis and that of other autoimmune diseases, but the mechanisms are largely unknown. Here we show that the aryl hydrocarbon receptor (AhR), a transcription factor that senses environmental stimuli, modulates pathology in psoriasis. AhR-activating ligands reduced inflammation in the lesional skin of psoriasis patients, whereas AhR antagonists increased inflammation. Similarly, AhR signaling via the endogenous ligand FICZ reduced the inflammatory response in the imiquimod-induced model of skin inflammation and AhR-deficient mice exhibited a substantial exacerbation of the disease, compared to AhR-sufficient controls. Nonhematopoietic cells, in particular keratinocytes, were responsible for this hyperinflammatory response, which involved upregulation of AP-1 family members of transcription factors. Thus, our data suggest a critical role for AhR in the regulation of inflammatory responses and open the possibility for novel therapeutic strategies in chronic inflammatory disorders.

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Physiological AhR signals reduce psoriasis gene expression in patient biopsies

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Blocking AhR signals exacerbates psoriasis gene expression in patient biopsies

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AhR-deficient mice show exacerbated skin inflammation in imiquimod model

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Absence of AhR on mouse or human keratinocytes causes excessive inflammation

Characterization of innate lymphoid cells in human skin and blood demonstrates increase of NKp44+ ILC3 in psoriasis

Innate lymphoid cells (ILCs) are increasingly appreciated as key regulators of tissue immunity. However, their role in human tissue homeostasis and disease remains to be fully elucidated. Here we characterize the ILCs in human skin from healthy individuals and from the inflammatory skin disease psoriasis. We show that a substantial proportion of IL-17A and IL-22 producing cells in the skin and blood of normal individuals and psoriasis patients are CD3-negative innate lymphocytes. Deep immunophenotyping of human ILC subsets showed a statistically significant increase in the frequency of circulating NKp44+ ILC3 in the blood of psoriasis patients compared with healthy individuals or atopic dermatitis patients. More than 50% of circulating NKp44+ ILC3 expressed cutaneous lymphocyte-associated antigen, indicating their potential for skin homing. Analysis of skin tissue revealed a significantly increased frequency of total ILCs in the skin compared with blood. Moreover, the frequency of NKp44+ ILC3 was significantly increased in non-lesional psoriatic skin compared with normal skin. A detailed time course of a psoriasis patient treated with anti-tumor necrosis factor showed a close association between therapeutic response, decrease in inflammatory skin lesions, and decrease of circulating NKp44+ ILC3. Overall, data from this initial observational study suggest a potential role for NKp44+ ILC3 in psoriasis pathogenesis.

Differential influences of the aryl hydrocarbon receptor on Th17 mediated responses in vitro and in vivo

The aryl hydrocarbon receptor (AhR) has been attributed with anti-inflammatory effects in the development of pathological immune responses leading to experimental autoimmune encephalomyelitis (EAE) via the induction of regulatory T cells. In agreement with previously published findings, we find that TCDD administration confers protection from EAE, however, this immuno-modulatory effect was not the consequence of de novo Treg generation, but the inhibition of Th17 cell differentiation. Systemic application of FICZ at the time of immunization also reduced EAE pathology albeit to a lesser degree than TCDD. In vitro Th17 differentiation in the presence of AhR agonists, including TCDD, promoted IL-17 and IL-22 expression, but did not induce Treg differentiation. AhR affinity influenced the amounts of IL-17 and IL-22 protein that was secreted by Th17 cells, but did not seem to affect susceptibility to EAE in vivo. Making use of conditional AhR-deficient mice, we show that the anti-inflammatory effect of TCDD depends on AhR activation in both T cells and dendritic cells, further emphasising the ability of TCDD to interfere with T effector cell differentiation in vivo. The dichotomy between the in vivo and in vitro effects of AhR reveals the complexity of the AhR pathway, which has the capacity of affecting different AhR-expressing cell types involved in mounting immune responses, thus participating in defining their outcome.

Gene expression changes with age in skin, adipose tissue, blood and brain

BACKGROUND

Previous studies have demonstrated that gene expression levels change with age. These changes are hypothesized to influence the aging rate of an individual. We analyzed gene expression changes with age in abdominal skin, subcutaneous adipose tissue and lymphoblastoid cell lines in 856 female twins in the age range of 39-85 years. Additionally, we investigated genotypic variants involved in genotype-by-age interactions to understand how the genomic regulation of gene expression alters with age.

RESULTS

Using a linear mixed model, differential expression with age was identified in 1,672 genes in skin and 188 genes in adipose tissue. Only two genes expressed in lymphoblastoid cell lines showed significant changes with age. Genes significantly regulated by age were compared with expression profiles in 10 brain regions from 100 postmortem brains aged 16 to 83 years. We identified only one age-related gene common to the three tissues. There were 12 genes that showed differential expression with age in both skin and brain tissue and three common to adipose and brain tissues.

CONCLUSIONS

Skin showed the most age-related gene expression changes of all the tissues investigated, with many of the genes being previously implicated in fatty acid metabolism, mitochondrial activity, cancer and splicing. A significant proportion of age-related changes in gene expression appear to be tissue-specific with only a few genes sharing an age effect in expression across tissues. More research is needed to improve our understanding of the genetic influences on aging and the relationship with age-related diseases.

Integration of lyoplate based flow cytometry and computational analysis for standardized immunological biomarker discovery

Discovery of novel immune biomarkers for monitoring of disease prognosis and response to therapy in immune-mediated inflammatory diseases is an important unmet clinical need. Here, we establish a novel framework for immunological biomarker discovery, comparing a conventional (liquid) flow cytometry platform (CFP) and a unique lyoplate-based flow cytometry platform (LFP) in combination with advanced computational data analysis. We demonstrate that LFP had higher sensitivity compared to CFP, with increased detection of cytokines (IFN-γ and IL-10) and activation markers (Foxp3 and CD25). Fluorescent intensity of cells stained with lyophilized antibodies was increased compared to cells stained with liquid antibodies. LFP, using a plate loader, allowed medium-throughput processing of samples with comparable intra- and inter-assay variability between platforms. Automated computational analysis identified novel immunophenotypes that were not detected with manual analysis. Our results establish a new flow cytometry platform for standardized and rapid immunological biomarker discovery with wide application to immune-mediated diseases.

Biomarkers in psoriasis and psoriatic arthritis

Psoriasis is a common immune-mediated disease of the skin, which associates in 20-30% of patients with psoriatic arthritis (PsA). The immunopathogenesis of both conditions is not fully understood as it is the result of a complex interaction between genetic, environmental and immunological factors. At present there is no cure for psoriasis and there are no specific markers that can accurately predict disease progression and therapeutic response. Therefore, biomarkers for disease prognosis and response to treatment are urgently needed to help clinicians with objective indications to improve patient management and outcomes. Although many efforts have been made to identify psoriasis/PsA biomarkers none of them has yet been translated into routine clinical practice. In this review we summarise the different classes of possible biomarkers explored in psoriasis and PsA so far and discuss novel strategies for biomarker discovery.

CD8 T Cells and IFN-γ emerge as critical players for psoriasis in a novel model of mouse psoriasiform skin inflammation

A pathogenic crosstalk between epithelial and immune cells underpins the aberrant immune and epidermal responses seen in psoriasis. Data from a novel mouse model of psoriasiform skin inflammation not only highlight the importance of the interplay between keratinocytes, targets of genetic manipulation, and T cells as the major effector cells, but also reveal a critical role for CD8 T cells and IFN-γ in disease initiation.

Mapping cis- and trans-regulatory effects across multiple tissues in twins

Sequence-based variation in gene expression is a key driver of disease risk. Common variants regulating expression in cis have been mapped in many expression quantitative trait locus (eQTL) studies, typically in single tissues from unrelated individuals. Here, we present a comprehensive analysis of gene expression across multiple tissues conducted in a large set of mono- and dizygotic twins that allows systematic dissection of genetic (cis and trans) and non-genetic effects on gene expression. Using identity-by-descent estimates, we show that at least 40% of the total heritable cis effect on expression cannot be accounted for by common cis variants, a finding that reveals the contribution of low-frequency and rare regulatory variants with respect to both transcriptional regulation and complex trait susceptibility. We show that a substantial proportion of gene expression heritability is trans to the structural gene, and we identify several replicating trans variants that act predominantly in a tissue-restricted manner and may regulate the transcription of many genes.

Resident CD141 (BDCA3)+ dendritic cells in human skin produce IL-10 and induce regulatory T cells that suppress skin inflammation

Human skin-resident IL-10⁺ regulatory dendritic cells induce T reg cells that suppress allogeneic skin graft inflammation.

Human skin immune homeostasis, and its regulation by specialized subsets of tissue-residing immune sentinels, is poorly understood. In this study, we identify an immunoregulatory tissue-resident dendritic cell (DC) in the dermis of human skin that is characterized by surface expression of CD141, CD14, and constitutive IL-10 secretion (CD141⁺ DDCs). CD141⁺ DDCs possess lymph node migratory capacity, induce T cell hyporesponsiveness, cross-present self-antigens to autoreactive T cells, and induce potent regulatory T cells that inhibit skin inflammation. Vitamin D₃ (VitD3) promotes certain phenotypic and functional properties of tissue-resident CD141⁺ DDCs from human blood DCs. These CD141⁺ DDC-like cells can be generated in vitro and, once transferred in vivo, have the capacity to inhibit xeno-graft versus host disease and tumor alloimmunity. These findings suggest that CD141⁺ DDCs play an essential role in the maintenance of skin homeostasis and in the regulation of both systemic and tumor alloimmunity. Finally, VitD3-induced CD141⁺ DDC-like cells have potential clinical use for their capacity to induce immune tolerance.

The multitasking organ: recent insights into skin immune function

The skin provides the first line defense of the human body against injury and infection. By integrating recent findings in cutaneous immunology with fundamental concepts of skin biology, we portray the skin as a multitasking organ ensuring body homeostasis. Crosstalk between the skin and its microbial environment is also highlighted as influencing the response to injury, infection, and autoimmunity. The importance of the skin immune network is emphasized by the identification of several skin-resident cell subsets, each with its unique functions. Lessons learned from targeted therapy in inflammatory skin conditions, such as psoriasis, provide further insights into skin immune function. Finally, we look at the skin as an interacting network of immune signaling pathways exemplified by the development of a disease interactome for psoriasis.

Allele-specific cytokine responses at the HLA-C locus: implications for psoriasis

Psoriasis is an inflammatory skin disorder that is inherited as a complex trait. Genetic studies have repeatedly highlighted HLA-C as the major determinant for psoriasis susceptibility, with the Cw*0602 allele conferring significant disease risk in a wide-range of populations. Despite the potential importance of HLA-C variation in psoriasis, either via an effect on peptide presentation or immuno-inhibitory activity, allele-specific expression patterns have not been investigated. Here, we used reporter assays to characterize two regulatory variants, which virtually abolished the response to TNF-α (rs2524094) and IFN-γ (rs10657191) in HLA-Cw*0602 and a cluster of related alleles. We validated these findings through the analysis of HLA-Cw*0602 expression in primary keratinocytes treated with TNF-α and IFN-γ. Finally, we showed that HLA-Cw*0602 transcripts are not increased in psoriatic skin lesions, despite highly elevated TNF-α levels. Thus, our findings demonstrate the presence of allele-specific differences in HLA-C expression and indicate that HLA-Cw*0602 is unresponsive to up-regulation by key pro-inflammatory cytokines in psoriasis. These data pave the way for functional studies into the pathogenic role of the major psoriasis susceptibility allele.

Psoriasis

Psoriasis is a common relapsing and remitting immune-mediated inflammatory disease that affects the skin and joints. This review focuses on current immunogenetic concepts, key cellular players, and axes of cytokines that are thought to contribute to disease pathogenesis. We highlight potential therapeutic targets and give an overview of the currently used immune-targeted therapies.

Identification of a novel proinflammatory human skin-homing Vγ9Vδ2 T cell subset with a potential role in psoriasis

γδ T cells mediate rapid tissue responses in murine skin and participate in cutaneous immune regulation including protection against cancer. The role of human γδ cells in cutaneous homeostasis and pathology is characterized poorly. In this study, we show in vivo evidence that human blood contains a distinct subset of proinflammatory cutaneous lymphocyte Ag and CCR6-positive Vγ9Vδ2 T cells, which is rapidly recruited into perturbed human skin. Vγ9Vδ2 T cells produced an array of proinflammatory mediators including IL-17A and activated keratinocytes in a TNF-α- and IFN-γ-dependent manner. Examination of the common inflammatory skin disease psoriasis revealed a striking reduction of circulating Vγ9Vδ2 T cells in psoriasis patients compared with healthy controls and atopic dermatitis patients. Decreased numbers of circulating Vγ9Vδ2 T cells normalized after successful treatment with psoriasis-targeted therapy. Taken together with the increased presence of Vγ9Vδ2 T cells in psoriatic skin, these data indicate redistribution of Vγ9Vδ2 T cells from the blood to the skin compartment in psoriasis. In summary, we report a novel human proinflammatory γδ T cell involved in skin immune surveillance with immediate response characteristics and with potential clinical relevance in inflammatory skin disease.

The IL23R R381Q gene variant protects against immune-mediated diseases by impairing IL-23-induced Th17 effector response in humans

IL-23 and Th17 cells are key players in tissue immunosurveillance and are implicated in human immune-mediated diseases. Genome-wide association studies have shown that the IL23R R381Q gene variant protects against psoriasis, Crohn's disease and ankylosing spondylitis. We investigated the immunological consequences of the protective IL23R R381Q gene variant in healthy donors. The IL23R R381Q gene variant had no major effect on Th17 cell differentiation as the frequency of circulating Th17 cells was similar in carriers of the IL23R protective (A) and common (G) allele. Accordingly, Th17 cells generated from A and G donors produced similar amounts of Th17 cytokines. However, IL-23-mediated Th17 cell effector function was impaired, as Th17 cells from A allele carriers had significantly reduced IL-23-induced IL-17A production and STAT3 phosphorylation compared to G allele carriers. Our functional analysis of a human disease-associated gene variant demonstrates that IL23R R381Q exerts its protective effects through selective attenuation of IL-23-induced Th17 cell effector function without interfering with Th17 differentiation, and highlights its importance in the protection against IL-23-induced tissue pathologies.

Harnessing dendritic cells in inflammatory skin diseases

The skin immune system harbors a complex network of dendritic cells (DCs). Recent studies highlight a diverse functional specialization of skin DC subsets. In addition to generating cellular and humoral immunity against pathogens, skin DCs are involved in tolerogenic mechanisms to ensure the maintenance of immune homeostasis, as well as in pathogenesis of chronic inflammation in the skin when excessive immune responses are initiated and unrestrained. Harnessing DCs by directly targeting DC-derived molecules or selectively modulate DC subsets is a convincing strategy to tackle inflammatory skin diseases. In this review we discuss recent advances underlining the functional specialization of skin DCs and discuss the potential implication for future DC-based therapeutic strategies.

A model for harmonizing flow cytometry in clinical trials

Complexities in sample handling, instrument setup and data analysis are barriers to the effective use of flow cytometry to monitor immunological parameters in clinical trials. The novel use of a central laboratory may help mitigate these issues.

Cutting edge: A critical functional role for IL-23 in psoriasis

Interleukin-23 is a key cytokine involved in the generation of Th17 effector cells. Clinical efficacy of an anti-p40 mAb blocking both IL-12 and IL-23 and disease association with single nucleotide polymorphisms in the IL23R gene raise the question of a functional role of IL-23 in psoriasis. In this study, we provide a comprehensive analysis of IL-23 and its receptor in psoriasis and demonstrate its functional importance in a disease-relevant model system. The expression of IL-23 and its receptor was increased in the tissues of patients with psoriasis. Injection of a mAb specifically neutralizing human IL-23 showed IL-23-dependent inhibition of psoriasis development comparable to the use of anti-TNF blockers in a clinically relevant xenotransplant mouse model of psoriasis. Together, our results identify a critical functional role for IL-23 in psoriasis and provide the rationale for new treatment strategies in chronic epithelial inflammatory disorders.

The role of IL-23 in the immunopathogenesis of psoriasis

In just 10 years from its discovery in 2000, interleukin-23 has quickly moved from being recognized as a pro-inflammatory cytokine to a key player and potential therapeutic target in psoriasis.

Skin immune sentinels in health and disease

Human skin and its immune cells provide essential protection of the human body from injury and infection. Recent studies reinforce the importance of keratinocytes as sensors of danger through alert systems such as the inflammasome. In addition, newly identified CD103(+) dendritic cells are strategically positioned for cross-presentation of skin-tropic pathogens and accumulating data highlight a key role of tissue-resident rather than circulating T cells in skin homeostasis and pathology. This Review focuses on recent progress in dissecting the functional role of skin immune cells in skin disease.

Sequence variants in the genes for the interleukin-23 receptor (IL23R) and its ligand (IL12B) confer protection against psoriasis

Psoriasis is an inflammatory skin disorder that is inherited as a multifactorial trait. Genetic analyses have repeatedly identified a primary disease susceptibility locus lying within the major histocompatibility complex (MHC), on chromosome 6p21. A small number of non-MHC susceptibility loci have also been identified. These regions tend to overlap with susceptibility intervals for Crohn's disease and atopic dermatitis, suggesting the possibility that genetic variants affecting inflammatory pathways may contribute to the pathogenesis of multiple disorders. Here, we report a genetic analysis of the interleukin 23 receptor gene (IL23R), which was recently identified as a susceptibility determinant for Crohn's disease. We initially examined the results of a whole-genome association scan, carried out on 318 cases and 288 controls. We observed a significant increase of a non-synonymous substitution (p.Arg381Gln) among controls (P = 0.00036). We validated this finding by extending our cohort to include a further 519 cases and 528 controls. In the overall sample, the frequency of the 381Gln allele was 3.6% in cases and 7% in controls, yielding a P value of 0.00014. Next, we examined genetic variation at the IL12RB1, IL23A and IL12B genes, respectively, encoding the second subunit of the IL23R receptor and the two subunits of its ligand. This analysis identified independent associations for IL12B SNPs rs10045431 (P value for the extended dataset = 0.0001) and rs3212227 (P = 0.036). Altogether, these findings indicate that genes participating in IL23 signalling play a significant role in the pathogenesis of chronic epithelial inflammation.

Neutralization of Interleukin-18 Inhibits Neointimal Formation in a Rat Model of Vascular Injury

Background— Studies in humans and animal models suggest that interleukin-18 (IL-18) plays a crucial role in vascular pathologies. IL-18 is a predictor of cardiovascular death in angina and is involved in atherotic plaque destabilization. Higher IL-18 plasma levels also are associated with restenosis after coronary artery angioplasty performed in patients with acute myocardial infarction. We investigated the effective role of IL-18 in neointimal formation in a balloon-induced rat model of vascular injury.

Methods and Results— Endothelial denudation of the left carotid artery was performed by use of a balloon embolectomy catheter. Increased expression of IL-18 and IL-18Rα/β mRNA was detectable in carotid arteries from days 2 to 14 after angioplasty. The active form of IL-18 was highly expressed in injured arteries. Strong immunoreactivity for IL-18 was detected in the medial smooth muscle cells at days 2 and 7 after balloon injury and in proliferating/migrating smooth muscle cells in neointima at day 14. Moreover, serum concentrations of IL-18 were significantly higher among rats subjected to vascular injury. Treatment with neutralizing rabbit anti-rat IL-18 immunoglobulin G significantly reduced neointimal formation (by 27%; P <0.01), reduced the number of proliferating cells, and inhibited interferon-γ, IL-6, and IL-8 mRNA expression and nuclear factor-κB activation in injured arteries. In addition, in vitro data show that IL-18 affects smooth muscle cell proliferation.

Conclusions— These results identify a critical role for IL-18 in neointimal formation in a rat model of vascular injury and suggest a potential role for IL-18 neutralization in the reduction of neointimal development.

A novel lipid A fromHalomonas magadiensis inhibits enteric LPS-induced human monocyte activation

Lipopolysaccharide (LPS) endotoxin is the bacterial product responsible for the clinical syndrome of Gram-negative septicemia and endotoxic shock. During sepsis, microbial antigens, such as LPS, activate monocytes and macrophages to produce several pro-inflammatory cytokines, among which tumor necrosis factor-alpha (TNF-alpha) appears to be very important for the development of endotoxic shock. The endotoxic properties of LPS principally reside in the lipid A (LIP A) component, which is the primary immunostimulatory center of Gram-negative bacteria. In recent years there has been a continuous effort to identify molecules able to antagonize the deleterious effects of endotoxic shock. In this study we show that a novel LIP A fraction from the LPS of Halomonas magadiensis (Hm), a Gram-negative extremophilic and alkaliphilic bacterium, significantly inhibits the synthesis of TNF-alpha by human monocytes activated by Escherichia coli LPS. LIP A from Hm exerts these effects by interfering with E. coli LPS for activation of Toll-like receptor 4 expressed in human cells. This result defines Hm LIP A as a novel class of LPS antagonist whose structural features could be utilized for the design of compounds for the treatment of Gram-negative sepsis.

Discovery and Biological Evaluation of the Novel Naturally Occurring Diterpene Pepluanone as Antiinflammatory Agent

From the whole plant of Euphorbia peplus L., a new diterpene based on a rare pepluane skeleton, named pepluanone (1), was isolated together with a known pepluane diterpene (2). The stereostructure of pepluanone was determined on the basis of an extensive NMR study, MS data, and chemical reaction. The ability of these compounds to act as antiinflammatory agents has been evaluated for the first time by in vivo tests on carrageenin-induced rat paw edema, an experimental model of acute inflammation. Comparison of the bioactivity of pepluanone and compound 2 in terms of chemical structure, evidenced the high efficiency of pepluanone and the absence of appreciable activity for compound 2, thus giving a first insight into the structure-activity relationship. Further in vitro experiments performed on pepluanone let us hypothesize that its activity could be explained in reducing the production of nitric oxide, prostaglandin E(2), and TNF-alpha by inhibiting the expression of inducible nitric oxide synthase, cyclooxygenase-2, and TNF-alpha mRNA through the down-regulation of NF-kappaB binding activity.