Interleukin-36-receptor antagonist deficiency and generalized pustular psoriasis

Skin manifestations in spondyloarthritis

Spondyloarthritides (SpA) like psoriatic arthritis, axial spondyloarthritis/ankylosing spondylitis, reactive arthritis and inflammatory bowel disease (IBD)-associated SpA can present with characteristic skin manifestations. These SpA-associated skin disorders may precede joint involvement, reflect a loss of efficacy of a current systemic treatment or can even be treatment associated. Cutaneous manifestations in SpA not only add additional morbidity with physical impact but also impose a psychosocial burden on affected patients. Psoriasis (PsO) - the main skin disease in SpA - has a variety of clinical presentations, including plaque-type PsO, inverse PsO, guttate PsO, erythrodermic PsO, nail PsO and pustular types. SpA associated with IBD presents with neutrophilic and granulomatous skin disorders, including pyoderma gangrenosum, hidradenitis suppurativa and cutaneous Crohn's disease. Reactive arthritides has a favourable prognosis and may feature keratoderma blenorrhagicum or balanitis circinatum as typical skin manifestations. Immunologically, SpA-associated skin diseases share interleukin (IL)-17 and IL-23 dysregulation but show distinctive genetic and immunological profiles. Therefore, they vary in their treatment responses to targeted therapies with biologicals or small molecules. In this review, we highlight the clinical presentation of skin manifestations in SpA and discuss therapeutic approaches in this interdisciplinary field.

Involvement of the cytokine TWEAK in the pathogenesis of psoriasis vulgaris, pustular psoriasis, and erythrodermic psoriasis

Psoriasis is a common chronic inflammatory dermatitis in which various cytokines play a detrimental role. The cytokine tumor necrosis factor-related weak inducer of apoptosis (TWEAK) is involved in the pathogenesis of multiple inflammatory disorders. However, the potential role of TWEAK in various subtypes of psoriasis has not been studied in depth. To investigate whether the levels of TWEAK are associated with clinical traits and the levels of some known psoriasis-related cytokines, such as interleukin (IL)-17A, IL-22, interferon (IFN)-γ, and IL-36γ, 20 patients with psoriasis vulgaris (PV), 8 patients with pustular psoriasis (PP), 8 patients with erythrodermic psoriasis (EP), and 20 healthy controls (HCs) were recruited into this study. The levels of serum cytokines were detected by commercial enzyme-linked immunosorbent assay kits. The average levels of TWEAK, IL-17A, IL-22, IFN-γ, and IL-36γ were significantly higher in the psoriasis groups than in the HC group. Furthermore, there was a statistically significant correlation between TWEAK and IL-17A/IFN-γ in PV and IL-36γ in EP, but there was no correlation between TWEAK and IL-22 in any subtype of psoriasis. This study suggests that TWEAK may have a role in the pathogenesis of PV, PP, and EP via synergy with IL-17A, IFN-γ, or IL-36γ, but not with IL-22.

Neutrophil extracellular traps are induced in a psoriasis model of interleukin-36 receptor antagonist-deficient mice

Loss-of-function mutations in the interleukin (IL)-36 gene IL36RN are associated with psoriasis. The importance of neutrophil extracellular traps (NETs), web-like structures composed of neutrophil DNA, in the pathogenesis of psoriasis has been unclear. Here, we aimed to clarify the role of NET signaling in the deficiency of IL36 receptor antagonist (DITRA). We evaluated the severity of psoriasis-like lesions induced by imiquimod cream treatment in Il36rn^-/- mice. The mRNA levels of psoriasis-related cytokines were measured via real-time reverse transcription polymerase chain reaction, and the effects of Cl-amidine, a peptidyl arginine deiminase 4 (PAD4) inhibitor, on psoriasis-like lesions were evaluated. PAD4 is a histone-modifying enzyme that is involved in NET formation. Psoriasis area and severity index scores, epidermal thickness, and infiltrated neutrophil counts were significantly increased in Il36rn^-/- mice; NET formation was confirmed pathologically. Several cytokines and chemokines were upregulated in the skin lesions of Il36rn^-/- mice and Cl-amidine treatment improved these psoriasis-like lesions. These results suggest that NET formation plays an important role in the pathology of psoriasis-like lesions in these mice and might represent a promising therapeutic target for DITRA.

Association between mutation of interleukin 36 receptor antagonist and generalized pustular psoriasis: A PRISMA-compliant systematic review and meta-analysis

BACKGROUND

Generalized pustular psoriasis (GPP) is a systemic inflammatory disease with poor outcomes, and several studies have suggested that the mutation of the interleukin 36 receptor antagonist gene (IL36RN) is related to GPP, where the polymorphism c.115+6T>C is reported to be the most common mutation of IL36RN. This study was performed to clarify and comprehensively evaluate the relationship between IL36RN gene polymorphism and the susceptibility of GPP subtypes.

METHODS

To conduct a thorough literature review, studies were obtained using databases such as Pubmed, EMBASE, Cochrane, China National Knowledge Infrastructure, and the Wanfang database. Only studies published up to December 2019 were included. The quality of the research studies was estimated using the Newcastle-Ottawa scale. The total odds ratios (ORs) and corresponding 95% confidence intervals (95% CIs) were pooled and analysed using STATA 14. The publication bias was evaluated through the Egger test, performed using the aforementioned software. Five common gene models were built and analysed to assess the association between the polymorphism c.115+6T>C and subtypes of GPP.

RESULTS

A total of 10 studies were selected, including 683 cases of GPP patients. Meta-analyses showed that there was a significant statistical correlation of IL36RN mutation between GPP with or without psoriasis vulgaris (OR = 3.82, 95%CI 2.63-5.56) and between adult GPP and paediatric GPP (OR = 0.42, 95%CI 0.23-0.77). No obvious discrepancy between European patients (OR = 4.03, 95%CI 2.23-7.26) and Asian patients was found. The gene models showed clear associations between the polymorphism c.115+6T>C and GPP through the dominant model (CC+ TC vs TT, OR 2.74, 95%CI 2.06-3.64), recessive model (CC vs CT + TT, OR 4.33, 95%CI 2.84-6.60), homozygote model (CC vs TT, OR 4.37, 95%CI 2.88-6.62), heterozygote model (CT vs TT, OR 2.26, 95%CI 1.32-3.85) and allelic model (C vs T, OR 3.35, 95%CI 2.63-4.27).

CONCLUSION

The IL36RN mutation is strongly related to GPP without psoriasis vulgaris and the early onset of GPP. Furthermore, the single-nucleotide polymorphism c.115+6T>C of the IL36RN gene plays a significant role in GPP vulnerability, especially in homozygous mutation. GPP could be a different inflammatory disease, independent of psoriasis.

IL-36γ drives skin toxicity induced by EGFR/MEK inhibition and commensal Cutibacterium acnes

Epidermal growth factor receptor (EGFR) and MEK inhibitors (EGFRi/MEKi) are beneficial for the treatment of solid cancers but are frequently associated with severe therapy-limiting acneiform skin toxicities. The underlying molecular mechanisms are poorly understood. Using gene expression profiling we identified IL-36γ and IL-8 as candidate drivers of EGFRi/MEKi skin toxicity. We provide molecular and translational evidence that EGFRi/MEKi in concert with the skin commensal bacterium Cutibacterium acnes act synergistically to induce IL-36γ in keratinocytes and subsequently IL-8, leading to cutaneous neutrophilia. IL-36γ expression was the combined result of C. acnes–induced NF-κB activation and EGFRi/MEKi–mediated expression of the transcription factor Krüppel-like factor 4 (KLF4), due to the presence of both NF-κB and KLF4 binding sites in the human IL-36γ gene promoter. EGFRi/MEKi increased KLF4 expression by blockade of the EGFR/MEK/ERK pathway. These results provide an insight into understanding the pathological mechanism of the acneiform skin toxicities induced by EGFRi/MEKi and identify IL-36γ and the transcription factor KLF4 as potential therapeutic targets.

A brief guide to pustular psoriasis for primary care providers

Pustular psoriasis refers to a heterogeneous group of chronic inflammatory skin disorders that are clinically, histologically, and genetically distinct from plaque psoriasis. Pustular psoriasis may present as a recurrent systemic illness (generalized pustular psoriasis [GPP]), or as localized disease affecting the palms and/or soles (palmoplantar pustulosis [PPP], also known as palmoplantar pustular psoriasis), or the digits/nail beds (acrodermatitis continua of Hallopeau [ACH]). These conditions are rare, but their possible severity and consequences should not be underestimated. GPP, especially an acute episode (flare), may be a medical emergency, with potentially life-threatening complications. PPP and ACH are often debilitating conditions. PPP is associated with impaired health-related quality of life and psychiatric morbidity, while ACH threatens irreversible nail and/or bone damage. These conditions can be difficult to diagnose; thus, primary care providers should not hesitate to contact a dermatologist for advice and/or patient referral. The role of corticosteroids in triggering and leading to flares of GPP should also be noted, and physicians should avoid the use of systemic corticosteroids in the management of any form of psoriasis.

IL-36 receptor antagonist deficiency resulted in delayed wound healing due to excessive recruitment of immune cells

Loss-of-function homozygous or compound heterozygous mutations in IL36RN, which encodes interleukin-36 receptor antagonist (IL-36Ra), have been implicated in the pathogenesis of various skin disorders. Previous findings showed that IL-36γ promoted wound healing in mice; however, the pathogenic role of IL-36Ra in wound healing remains unclear. We elucidated the role of IL-36Ra, a regulator of IL-36 in tissue repair by investigating the recruitment of inflammatory cells and cytokine production in the absence of IL-36Ra. Full-thickness excisional wounds were made on the back of Il36rn^-/- mice and healing was assessed by monitoring macroscopic wound sizes, numbers of infiltrated cells, and gene expression of inflammatory cytokines. Macroscopic wound healing, re-epithelialization, and granulation tissue formation were delayed by 3 days post-injury in Il36rn^-/- mice. This delay was associated with increased infiltrations of neutrophils and macrophages, and increased expression of cytokines, such as IL-36γ, C-X-C motif chemokine ligand 1 (CXCL1), and transforming growth factor (TGF)-β. Importantly, administration of TAK-242, a toll-like receptor 4 (TLR4) inhibitor, caused normalization of wound healing in Il36rn^-/- mice, abrogating the initial delay in tissue repair. These results showed that targeting TLR4- mediated infiltrations of immune cells and cytokine production could be beneficial in regulating wound healing in IL-36Ra-deficient skin disorders.

IL-36 family cytokines in protective versus destructive inflammation

The IL-1 family of cytokines and receptors are critical regulators of inflammation. Within the IL-1 family and in contrast to its IL-1 and IL-18 subfamilies, the IL-36 subfamily is still poorly characterized. Three pro-inflammatory agonists IL-36α, IL-36β, IL-36γ, one IL-36 receptor (IL-1R6) antagonist, IL-36RA, and one putative IL-1R6 antagonist, IL-38, have been grouped into the IL-36 cytokine subfamily. IL-36 agonists signal through a common receptor complex to serve as early triggers of inflammatory responses by activating and cross-regulating a number of inflammatory pathways including NF-κB, MAPK and IFN signaling. IL-36RA binds to IL-1R6 to limit inflammatory signaling, while IL-38 may be an antagonist of more than one IL-1 family receptor. Expression patterns of IL-36 family cytokines, being most prominently expressed in epithelial barrier tissues such as the skin and intestines as well as in immune cells, suggest a role in protecting these barriers from infection. Dysregulation of IL-36 family cytokine signaling at physiological barriers, most prominently the skin, induces autoimmune inflammation. However, transferring the potential of IL-36 to induce tissue damage to tumors might benefit cancer patients. Here we summarize signaling pathways regulated by IL-36 family cytokines, including IL-38, and the consequences for physiological protective and pathophysiological destructive inflammation. Moreover, we discuss the limits of current knowledge on IL-36 family function to open potential avenues for research in the future.

Interleukin-36 Cytokine/Receptor Signaling: A New Target for Tissue Fibrosis

Tissue fibrosis is a major unresolved medical problem, which impairs the function of various systems. The molecular mechanisms involved are poorly understood, which hinders the development of effective therapeutic strategies. Emerging evidence from recent studies indicates that interleukin 36 (IL-36) and the corresponding receptor (IL-36R), a newly-characterized cytokine/receptor signaling complex involved in immune-inflammation, play an important role in the pathogenesis of fibrosis in multiple tissues. This review focuses on recent experimental findings, which implicate IL-36R and its associated cytokines in different forms of organ fibrosis. Specifically, it outlines the molecular basis and biological function of IL-36R in normal cells and sums up the pathological role in the development of fibrosis in the lung, kidney, heart, intestine, and pancreas. We also summarize the new progress in the IL-36/IL-36R-related mechanisms involved in tissue fibrosis and enclose the potential of IL-36R inhibition as a therapeutic strategy to combat pro-fibrotic pathologies. Given its high association with disease, gaining new insight into the immuno-mechanisms that contribute to tissue fibrosis could have a significant impact on human health.

The systemic autoinflammatory disorders for dermatologists. Part 2: disease examples

The systemic autoinflammatory disorders (SAIDS) or periodic fever syndromes are disorders of innate immunity, which can be inherited or acquired. They are almost all very rare and easily overlooked; typically, patients will have seen multiple specialities prior to diagnosis, so a high level of clinical suspicion is key. It is important to note that these are 'high-value' diagnoses as the majority of these syndromes can be very effectively controlled, dramatically improving quality of life and providing protection against the development of irreversible complications such as AA amyloidosis. In Part 1 of this review, we took an overview of SAIDS and described the common features; in this article, we take a more in-depth look at the better recognized or more dermatologically relevant conditions.

Myeloperoxidase Modulates Inflammation in Generalized Pustular Psoriasis and Additional Rare Pustular Skin Diseases

Generalized pustular psoriasis (GPP) is a severe multi-systemic inflammatory disease characterized by neutrophilic pustulosis and triggered by pro-inflammatory IL-36 cytokines in skin. While 19%–41% of affected individuals harbor bi-allelic mutations in IL36RN, the genetic cause is not known in most cases. To identify and characterize new pathways involved in the pathogenesis of GPP, we performed whole-exome sequencing in 31 individuals with GPP and demonstrated effects of mutations in MPO encoding the neutrophilic enzyme myeloperoxidase (MPO). We discovered eight MPO mutations resulting in MPO -deficiency in neutrophils and monocytes. MPO mutations, primarily those resulting in complete MPO deficiency, cumulatively associated with GPP (p = 1.85E−08; OR = 6.47). The number of mutant MPO alleles significantly differed between 82 affected individuals and >4,900 control subjects (p = 1.04E−09); this effect was stronger when including IL36RN mutations (1.48E−13) and correlated with a younger age of onset (p = 0.0018). The activity of four proteases, previously implicated as activating enzymes of IL-36 precursors, correlated with MPO deficiency. Phorbol-myristate-acetate-induced formation of neutrophil extracellular traps (NETs) was reduced in affected cells (p = 0.015), and phagocytosis assays in MPO-deficient mice and human cells revealed altered neutrophil function and impaired clearance of neutrophils by monocytes (efferocytosis) allowing prolonged neutrophil persistence in inflammatory skin. MPO mutations contribute significantly to GPP’s pathogenesis. We implicate MPO as an inflammatory modulator in humans that regulates protease activity and NET formation and modifies efferocytosis. Our findings indicate possible implications for the application of MPO inhibitors in cardiovascular diseases. MPO and affected pathways represent attractive targets for inducing resolution of inflammation in neutrophil-mediated skin diseases.

Treatment of acrodermatitis continua of Hallopeau: A case series of 39 patients

Acrodermatitis continua of Hallopeau (ACH) is a rare chronic inflammatory skin disease. Treatment is extremely challenging and mostly based on empirics as there is only scarce evidence from case reports and few small case series. In this retrospective study, patients with ACH treated at five university medical centers were analyzed according to patient and disease characteristics and treatment experience. We identified 39 patients with ACH with a mean age of 54.4 years at onset, of whom 22 (56.4%) were female. A total of 115 systemic treatment courses were analyzed with methotrexate as the most common therapy (27.0%). Overall, effectiveness of systemic treatments was low (excellent response rate: 14.8%). Among non-biologics, excellent response was noted in 21.1% (4/19) of treatment courses with methotrexate, followed by acitretin (13.3%; 2/15). Among biologics, guselkumab (excellent response: 100%; 2/2), secukinumab (excellent response: 42.9%; 3/7) and adalimumab (excellent response: 20.0%; 2/10) were most efficacious. The median drug survival was 7.0 months and did not differ significantly between the subgroup of non-biologic and biologic therapies. To our knowledge, this is the largest case series in ACH investigating patient characteristics and treatment outcomes. Based on our treatment experience, we suggest a treatment algorithm starting with acitretin or methotrexate as first-line therapy, followed by biologics. Cyclosporin may be used for short-term control. However, none of the applied systemic therapies yielded satisfying efficacy in our cohort. In patients with primary non-response, switch of treatment should be evaluated timely on an individual basis, considering possible irreversible disease complications such as nail loss. More research with prospective design is needed to further evaluate traditional and also particularly newer antipsoriatic drugs in ACH.

Laboratory options for risk assessment of pregnancy pathologies

The most effective method of screening for chromosomal abnormalities and evaluating the risk of pregnancy pathologies in the first trimester is combined screening. The algorithm of screening is based on the combination of maternal age, measuring of the nuchal translucency and the fetal heart rate and analysis of the placental products of free ß-hCG and PAPP-A. For the screening of preeclampsia, placental growth factor (PlGF) is added. To distinguish between preeclampsia and other pathologies caused by placental dysfunction it is recommended to also extend the screening with selected immunological markers. We concluded that elevated biochemical and immunological markers can help to predict the threat of preeclampsia in the third trimester. Some markers can probably predict the development of particularly severe pathological conditions.

"Autoinflammatory psoriasis"-genetics and biology of pustular psoriasis

Psoriasis is a chronic inflammatory skin condition that has a fairly wide range of clinical presentations. Plaque psoriasis, which is the most common manifestation of psoriasis, is located on one end of the spectrum, dominated by adaptive immune responses, whereas the rarer pustular psoriasis lies on the opposite end, dominated by innate and autoinflammatory immune responses. In recent years, genetic studies have identified six genetic variants that predispose to pustular psoriasis, and these have highlighted the role of IL-36 cytokines as central to pustular psoriasis pathogenesis. In this review, we discuss the presentation and clinical subtypes of pustular psoriasis, contribution of genetic predisposing variants, critical role of the IL-36 family of cytokines in disease pathophysiology, and treatment perspectives for pustular psoriasis. We further outline the application of appropriate mouse models for the study of pustular psoriasis and address the outstanding questions and issues related to our understanding of the mechanisms involved in pustular psoriasis.

The intrinsic and extrinsic elements regulating inflammation

Inflammation is a sophisticated biological tissue response to both extrinsic and intrinsic stimuli. Although the pathological aspects of inflammation are well appreciated, there are still rooms for understanding the physiological functions of the inflammation. Recent studies have focused on mechanisms, context and the role of physiological inflammation. Besides, there have been progress in the comprehension of commensal microbiota, immunometabolism, cancer and intracellular signaling events' roles that impact on the regulation of inflammation. Despite the fact that inflammatory responses are vital through tissue damage, understanding the mechanisms to turn off the finished or unnecessary inflammation is crucial for restoring homeostasis. Inflammation seems to be a smart process that acts like two edges of a sword, meaning that it has both protective and deleterious consequences. Knowing both edges and the regulation processes will help the future understanding and therapy for various diseases.

Diagnosis, Screening and Treatment of Patients with Palmoplantar Pustulosis (PPP): A Review of Current Practices and Recommendations

Palmoplantar pustulosis (PPP) is a rare, chronic, recurrent inflammatory disease that affects the palms and/or the soles with sterile, erupting pustules, which are debilitating and usually resistant to treatment. It has genetic, histopathologic and clinical features that are not present in psoriasis; thus, it can be classified as a variant of psoriasis or as a separate entity. Smoking and upper respiratory infections have been suggested as main triggers of PPP. PPP is a challenging disease to manage, and the treatment approach involves both topical and systemic therapies, as well as phototherapy and targeted molecules. No gold standard therapy has yet been identified, and none of the treatments are curative. In patients with mild disease, control may be achieved with on-demand occlusion of topical agents. In patients with moderate-to-severe PPP, phototherapy or a classical systemic agent (acitretin being the best treatment option, especially in combination with PUVA) may be effective. Refractory patients or those with contraindications to use these therapies may be good candidates for apremilast or biologic therapy, particularly anti-IL-17A and anti-IL-23 agents. Recent PPP trials are focusing on blockage of IL-36 or IL-1 pathways, which play an important role in innate immunity. Indeed, IL-36 isoforms have been strongly implicated in the pathogenesis of psoriasis. Therefore, blockage of the IL-36 pathway has become a new treatment target in PPP, and three studies are currently evaluating the use of monoclonal antibodies that block the IL-36 receptor in PPP: ANB019 and spesolimab (BI 655130). In this review, we explore the diagnosis, screening and treatment of patients with PPP.

Pathogenesis of psoriasis in the "omic" era. Part II. Genetic, genomic and epigenetic changes in psoriasis

Psoriasis is a multifactorial disease in which genetic, environmental and epigenetic factors regulating gene expression play a key role. In the “genomic era”, genome-wide association studies together with target genotyping platforms performed in different ethnic populations have found more than 50 genetic susceptible markers associated with the risk of psoriasis which have been identified so far. Up till now, the strongest association with the risk of the disease has been proved for HLA-C*06 gene. The majority of other psoriasis risk SNPs are situated near the genes encoding molecules involved in adaptive and innate immunity, and skin barrier function. Many contemporary studies indicate that the epigenetic changes: histone modification, promoter methylations, long non-coding and micro-RNA hyperexpression are considered as factors contributing to psoriasis pathogenesis as they regulate abnormal keratinocyte differentiation and proliferation, aberrant keratinocytes – inflammatory cells communication, neoangiogenesis and chronic inflammation. The circulating miRNAs detected in the blood may become specific markers in the diagnosis, prognosis and response to the treatment of the disease. The inhibition of expression in selected miRNAs may be a new promising therapy option for patients with psoriasis.

Novel Analgesics with Peripheral Targets

A limited number of peripheral targets generate pain. Inflammatory mediators can sensitize these. The review addresses targets acting exclusively or predominantly on sensory neurons, mediators involved in inflammation targeting sensory neurons, and mediators involved in a more general inflammatory process, of which an analgesic effect secondary to an anti-inflammatory effect can be expected. Different approaches to address these systems are discussed, including scavenging proinflammatory mediators, applying anti-inflammatory mediators, and inhibiting proinflammatory or facilitating anti-inflammatory receptors. New approaches are contrasted to established ones; the current stage of progress is mentioned, in particular considering whether there is data from a molecular and cellular level, from animals, or from human trials, including an early stage after a market release. An overview of publication activity is presented, considering a IuPhar/BPS-curated list of targets with restriction to pain-related publications, which was also used to identify topics.

Novel use of Autoinflammatory Diseases Activity Index (AIDAI) captures skin and extracutaneous features to help manage pediatric DITRA: A case report and a proposal for a modified disease activity index in autoinflammatory keratinization disorders

Generalized pustular psoriasis (GPP) is a severe form of psoriasis, which is rare in pediatric and adult patients. It is characterized by sterile pustular lesions that appear on erythematous skin, associated with systemic features. A recent identification of mutations in the IL36RN gene in some GPP patients has led to a diagnosis of new autoinflammatory disease, interleukin-36-receptor antagonist deficiency (DITRA). DITRA represents an emerging group of autoinflammatory diseases with hyperkeratotic skin involvement, called autoinflammatory keratinization diseases (AIKD). DITRA diagnosis and management are challenging as neither DITRA-specific clinical assessment tools nor treatment trials exist. Autoinflammatory Diseases Activity Index (AIDAI) is a validated tool originally developed to evaluate disease activity and treatment response in other inherited autoinflammatory diseases with systemic and skin involvement. We report the first use of AIDAI in a pediatric DITRA patient with the following goals: (a) to describe the contribution of AIDAI to our patient's management; (b) to identify potential limitations of AIDAI in DITRA; (c) to review literature for current psoriasis assessment tools; and (d) to propose a preliminary DITRA/AIKD disease activity index (DITRA/AIDAI) to be validated in future studies.

Animal models of psoriasis-highlights and drawbacks

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

Dithranol targets keratinocytes, their crosstalk with neutrophils and inhibits the IL-36 inflammatory loop in psoriasis

Despite the introduction of biologics, topical dithranol (anthralin) has remained one of the most effective anti-psoriatic agents. Serial biopsies from human psoriatic lesions and both the c-Jun/JunB and imiquimod psoriasis mouse model allowed us to study the therapeutic mechanism of this drug. Top differentially expressed genes in the early response to dithranol belonged to keratinocyte and epidermal differentiation pathways and IL-1 family members (i.e. IL36RN) but not elements of the IL-17/IL-23 axis. In human psoriatic response to dithranol, rapid decrease in expression of keratinocyte differentiation regulators (e.g. involucrin, SERPINB7 and SERPINB13), antimicrobial peptides (e.g. ß-defensins like DEFB4A, DEFB4B, DEFB103A, S100 proteins like S100A7, S100A12), chemotactic factors for neutrophils (e.g. CXCL5, CXCL8) and neutrophilic infiltration was followed with much delay by reduction in T cell infiltration. Targeting keratinocytes rather than immune cells may be an alternative approach in particular for topical anti-psoriatic treatment, an area with high need for new drugs.

IL-36 signaling in keratinocytes controls early IL-23 production in psoriasis-like dermatitis

IL-36R signaling plays an important role in the pathogenesis of psoriasis. We ought to assess the specific function of IL-36R in keratinocytes for the pathology of Aldara-induced psoriasis-like dermatitis. Il36r ΔK mice presenting deletion of IL-36R in keratinocytes were similarly resistant to Aldara-induced ear inflammation as Il36r -/- mice, but acanthosis was only prevented in Il36r -/- mice. FACS analysis revealed that IL-36R signaling in keratinocytes is mandatory for early neutrophil infiltration in Aldara-treated ears. RNASeq and qRT-PCR experiments demonstrated the crucial role of IL-36R signaling in keratinocytes for induction of IL-23, IL-17, and IL-22 at early time points. Taken together, our results demonstrate that IL-36R signaling in keratinocytes plays a major role in the induction of Aldara-induced psoriasis-like dermatitis by triggering early production of IL-23/IL-17/IL-22 cytokines and neutrophil infiltration.

Palmoplantar Pustulosis: Recent Advances in Etiopathogenesis and Emerging Treatments

Palmoplantar pustulosis (PPP) is a chronic, recurrent skin disease belonging to the spectrum of psoriasis. It is characterized by an eruption of sterile pustules on the palms and soles. Recent studies in PPP have focused on genetic differences between pustular phenotypes and the role of the innate immunological system and the microbiome in the etiopathogenesis of the disease. Mutations in IL36RN (a major predisposing factor for generalized pustular psoriasis) were found in selected patients with PPP and were associated with earlier disease onset. Studies have shown that the interleukin (IL)-17 and IL-36 pathways might be involved in the pathogenesis of PPP. A microbiome has been demonstrated in the vesicopustules of PPP, and an abundance of Staphylococcus appears to be increased by smoking. Improved understanding of the underlying etiopathogenesis of PPP has led to advances in treatment options, and targeted therapies for PPP have been evaluated or are under evaluation against more than 12 molecules in ongoing clinical trials. These targets include CXCR2 (IL-8 receptor type B), granulocyte colony-stimulating factor receptor, IL-1 receptor, IL-8, IL-12, IL-23, IL-17A, IL-17 receptor, IL-36 receptor, phosphodiesterase-4, and tumor necrosis factor-α.

[Pathophysiology of autoinflammatory dermatoses]

Autoinflammation leads to inflammation that mostly occurs without any clinically obvious reason. It can be so severe that organ damage with relevant tissue damage occurs. Inflammasomes are the drivers of autoinflammation. Although IL‑1 beta and the inflammasomes as its critical regulators are very important in autoinflammation, not all patients respond to inhibition of this signalling pathway. Several autoinflammatory diseases were associated with mutations in proteasome-immunoproteasome components. Autoinflammatory diseases caused by highly relevant genetic variants are mostly hereditary. Usually in childhood but not always. The coming years will show whether inflammatory dermatoses will be increasingly treated with suppression of the innate immune system in addition to inhibition of adaptive immunity.

Psoriasis Caught in the NET

A report in the June 2019 issue of the Journal of Investigative Dermatology reveals a role of neutrophil extracellular traps (NETs) in the induction of T helper type 17 cell responses and shows the relevance of this pathway in patients with psoriasis carrying a common risk variant in the TRAF3IP2 gene (Lambert et al., 2019). This work provides a new piece to the puzzle that links neutrophils to the T helper type 17-mediated pathogenesis of psoriasis.

Guselkumab for the treatment of palmoplantar pustulosis

INTRODUCTION

Palmoplantar pustulosis, or pustulosis palmaris et plantaris (PPP), is a chronic, recurrent inflammatory skin disease that is sometimes unresponsive to conventional therapy. The anti-interleukin 23 antibody guselkumab is effective for treating PPP.

AREAS COVERED

This review details the current understanding of PPP and discusses why guselkumab may be effective. Guselkumab is only approved for the treatment of PPP in Japan. In the United States, Canada, the European Union, and several other countries, it is approved for the treatment of moderate-to-severe plaque psoriasis, but not for PPP. Furthermore, guselkumab was approved only 1 year ago; its efficacy will be proven only by phase 2 and 3 clinical trials.

EXPERT OPINION

The first double-blinded randomized placebo-controlled trial (RCT) of guselkumab for PPP has been completed. The drug was effective, and guselkumab could be used as a new agent for PPP treatment, in addition to several conventional therapeutics. However, several issues remain. For example, there is no mouse model of PPP, so careful observation of human PPP patients and establishment of a good experimental PPP model are essential.

X-ray crystal structure localizes the mechanism of inhibition of an IL-36R antagonist monoclonal antibody to interaction with Ig1 and Ig2 extra cellular domains

Cellular signaling via binding of the cytokines IL‐36α, β, and γ along with binding of the accessory protein IL‐36RAcP, to their cognate receptor IL‐36R is believed to play a major role in epithelial and immune cell‐mediated inflammation responses. Antagonizing the signaling cascade that results from these binding events via a directed monoclonal antibody provides an opportunity to suppress such immune responses. We report here the molecular structure of a complex between an extracellular portion of human IL‐36R and a Fab derived from a high affinity anti‐IL‐36R neutralizing monoclonal antibody at 2.3 Å resolution. This structure, the first of IL‐36R, reveals similarities with other structurally characterized IL‐1R family members and elucidates the molecular determinants leading to the high affinity binding of the monoclonal antibody. The structure of the complex reveals that the epitope recognized by the Fab is remote from both the putative ligand and accessory protein binding interfaces on IL‐36R, suggesting that the functional activity of the antibody is noncompetitive for these binding events.

Innate Lymphocyte Mechanisms in Skin Diseases

Innate lymphocyte populations are emerging as key effectors in tissue homeostasis, microbial defense, and inflammatory skin disease. The cells are evolutionarily ancient and carry conserved principles of function, which can be achieved through shared or unique specific mechanisms. Recent technological and treatment advances have provided insight into heterogeneity within and between individuals and species. Similar pathways can extend through to adaptive lymphocytes, which softens the margins with innate lymphocyte populations and allows investigation of nonredundant pathways of immunity and inflammation that might be amenable to therapeutic intervention. Here, we review advances in understanding of innate lymphocyte biology with a focus on skin disease and the roles of commensal and pathogen responses and tissue homeostasis.

Generalized Pustular Psoriasis: Clinical Management and Update on Autoinflammatory Aspects

Generalized pustular psoriasis (GPP) is a chronic, systemic inflammatory disease accompanied by high fever and general malaise. Diffuse erythema and swelling of the extremities occur, with multiple sterile pustules all over the body in GPP patients. GPP often relapses over the lifetime and can be life-threatening. Recent discoveries of the underlying molecular genetic basis of many cases of this disorder have provided major advances to clinicians and researchers towards an understanding of the pathomechanism of GPP. However, the therapeutic management of GPP still faces many challenges and much uncertainty, and an evidence-based review summarizing the available clinical data on the management of this heterogeneous disease is needed. The present review addresses challenges regarding the precise clinical diagnosis and evaluation of clinical symptoms in GPP. In addition, we update and briefly summarize the current understanding of molecular pathomechanisms behind GPP as an autoinflammatory keratinization disease. Recent publications have clarified the genetic backgrounds of patients with GPP and ethnic differences in predisposing factors. Although there are ethnic differences in the prevalences of these pathogenic alleles, from recent reports, at most 60.5% (IL36RN), 5.9% (CARD14), and 10.8% (AP1S3) of GPP patients have the mutations/variations of these genes. All the reported biologics studied seemed effective and relatively well tolerated. Although it is difficult to evaluate therapeutic efficacy from studies on just a few cases, recent findings suggest that biologics can be a useful, powerful tool for controlling skin and systemic inflammation in GPP and for improving the quality of life of GPP patients.

Loricrin: Past, Present, and Future

The terminal differentiation of the epidermis is a complex physiological process. During the past few decades, medical genetics has shown that defects in the stratum corneum (SC) permeability barrier cause a myriad of pathological conditions, ranging from common dry skin to lethal ichthyoses. Contrarily, molecular phylogenetics has revealed that amniotes have acquired a specialized form of cytoprotection cornification that provides mechanical resilience to the SC. This superior biochemical property, along with desiccation tolerance, is attributable to the proper formation of the macromolecular protein-lipid complex termed cornified cell envelopes (CE). Cornification largely depends on the peculiar biochemical and biophysical properties of loricrin, which is a major CE component. Despite its quantitative significance, loricrin knockout (LKO) mice have revealed it to be dispensable for the SC permeability barrier. Nevertheless, LKO mice have brought us valuable lessons. It is also becoming evident that absent loricrin affects skin homeostasis more profoundly in many more aspects than previously expected. Through an extensive review of aggregate evidence, we discuss herein the functional significance of the thiol-rich protein loricrin from a biochemical, genetic, pathological, metabolic, or immunological aspect with some theoretical and speculative perspectives.

Keratinocyte: A trigger or an executor of psoriasis?

Psoriasis is a common chronic inflammatory skin disease characterized by abnormal proliferation/differentiation of keratinocytes and excessive immune cell infiltration in the dermis and epidermis. Over the past 2 decades, immune cells have been considered as the main driver of psoriasis because the neutralizing antibodies targeting the IL-23/IL-17 axis that regulates cross-talk between dendritic cells and T cells achieve tremendous success in the treatment of psoriasis. However, whether keratinocyte would be a driver of psoriasis or just an executor in response to immune cells is still under debate. In this review, we focus on the recent advances in the identification of keratinocyte as a trigger of psoriasis, summarize on the role of keratinocytes in self-perpetuating loop to maintain inflammation in psoriasis, and then discuss the possible roles of keratinocytes in the relapse of psoriasis.

Palmoplantar pustulosis: Current understanding of disease definition and pathomechanism

Pustulosis palmaris et plantaris, or palmoplantar pustulosis (PPP), is a chronic pustular dermatitis involving the palms and soles and is characterized by vesicles, pustules, erythema, lichenification, and abnormal desquamation. It is one of the most common skin diseases in Japan but its pathomechanism is unclear and the disease remains poorly defined. Consequently, adequate treatment for PPP is lacking. As a localized type of pustular psoriasis, PPP has long been treated with the conventional therapies used for plaque-type psoriasis, especially in Western countries. However, PPP may be a distinct entity, with a much lower prevalence in Western countries than in Japan. Furthermore, while treatment has yielded insights into the underlying pathology in plaque-type psoriasis, the pathogenesis of PPP has yet to be elucidated. In 2018, Gulselkumab, a monoclonal antibody against interleukin (IL)-23, was certified for use in Japan and is the first biologic effective in PPP both in Japanese and other patients. In this review, we summarize the current understanding of PPP, including the revised definition and possible pathomechanism. The information presented herein provides a more complete picture of PPP and may facilitate the development of improved treatment options.

Neutrophil extracellular traps activate IL-8 and IL-1 expression in human bronchial epithelia

Neutrophil extracellular traps (NETs) provide host defense but can contribute to the pathobiology of diverse human diseases. We sought to determine the extent and mechanism by which NETs contribute to human airway cell inflammation. Primary normal human bronchial epithelial cells (HBEs) grown at air-liquid interface and wild-type (wt)CFBE41o- cells (expressing wtCFTR) were exposed to cell-free NETs from unrelated healthy volunteers for 18 h in vitro. Cytokines were measured in the apical supernatant by Luminex, and the effect on the HBE transcriptome was assessed by RNA sequencing. NETs consistently stimulated IL-8, TNF-α, and IL-1α secretion by HBEs from multiple donors, with variable effects on other cytokines (IL-6, G-CSF, and GM-CSF). Expression of HBE RNAs encoding IL-1 family cytokines, particularly IL-36 subfamily members, was increased in response to NETs. NET exposure in the presence of anakinra [recombinant human IL-1 receptor antagonist (rhIL-1RA)] dampened NET-induced changes in IL-8 and TNF-α proteins as well as IL-36α RNA. rhIL-36RA limited the increase in expression of proinflammatory cytokine RNAs in HBEs exposed to NETs. NETs selectively upregulate an IL-1 family cytokine response in HBEs, which enhances IL-8 production and is limited by rhIL-1RA. The present findings describe a unique mechanism by which NETs may contribute to inflammation in human lung disease in vivo. NET-driven IL-1 signaling may represent a novel target for modulating inflammation in diseases characterized by a substantial NET burden.

Ixekizumab for the treatment of psoriasis: up-to-date

Introduction: Ixekizumab (an IL-17A antagonist) is a biologic therapeutic licensed for use in moderate-to-severe plaque psoriasis and psoriatic arthritis. IL-17 antagonists (also including Secukinumab and Brodalumab) represent a new generation of biologic therapy with rapid and high response rates, quickly becoming a crucial part of the psoriasis treatment armamentarium.Areas covered: In this review, we describe how IL-17A antagonists disrupt inflammatory cascades in psoriasis and summarize results from clinical trials examining the safety and efficacy of ixekizumab against placebo and comparators.Expert opinion: Ixekizumab induces a 75% reduction in psoriasis area severity index (PASI 75) in 89% of patients after 12 weeks and after 1 year, PASI 75 is maintained in 80% of patients. Ixekizumab is superior to both etanercept and ustekinumab, however, further comparator trials are needed to determine superiority between newer agents. Network meta-analysis suggests that ixekizumab is one of the most rapid and efficacious agents for treating psoriasis, but ideally more long-term real-world data are needed to determine the persistence of response. Candida may be commonly encountered during treatment and IL-17 agents should be avoided in patients with inflammatory bowel disease. Overall, ixekizumab represents an efficacious and well-studied therapeutic that can offer biologic-naïve and bio-failure patients durable disease control.

Keratinocyte interleukin-36 receptor expression orchestrates psoriasiform inflammation in mice

IL-36 stimulation of keratinocytes orchestrates key pathogenic inflammatory responses in psoriatic skin.

The IL-36 family cytokines have emerged as important mediators of dermal inflammation in psoriasis and have been reported to provide a proinflammatory stimulus to a variety of immune and stromal cell subsets in the inflamed skin. However, it remains to be determined which cell type, if any, in the skin plays a predominant role in mediating IL-36 cytokines instructive role in disease. Here, we demonstrate that targeted deletion of Il36r in keratinocytes results in similar levels of protection from psoriasiform inflammation observed in “global” Il36r-deficient mice. Mice with deficiency in IL-36 receptor expression on keratinocytes had significantly decreased expression, comparable with Il36r-deficient mice, of established mediators of psoriatic inflammation, including, IL-17a, IL-23, IL-22, and a loss of chemokine-induced neutrophil and IL-17A–expressing γδ T-cell subset infiltration to the inflamed skin. These data demonstrate that keratinocytes are the primary orchestrating cell in mediating the effects of IL-36–driven dermal inflammation in the imiquimod model of psoriasiform inflammation and shed new light on the cell-specific roles of IL-36 cytokines during psoriatic disease.

A randomised placebo controlled trial of anakinra for treating pustular psoriasis: statistical analysis plan for stage two of the APRICOT trial

BACKGROUND

Current treatment options for Palmoplantar Pustulosis (PPP), a debilitating chronic skin disease which affects the hands and feet, are limited. The Anakinra for Pustular psoriasis: Response in a Controlled Trial (APRICOT) aims to determine the efficacy of anakinra in the treatment of PPP. This article describes the statistical analysis plan for the final analysis of this two-staged trial, which was determined prior to unblinding and database lock. This is an update to the published protocol and stage one analysis plan.

METHODS

APRICOT is a randomised, double-blind, placebo-controlled trial of anakinra versus placebo, with two stages and an adaptive element. Stage one compared treatment arms to ensure proof-of-concept and determined the primary outcome for stage two of the trial. The primary outcome was selected to be the change in Palmoplantar Pustulosis Psoriasis Area and Severity Index (PPPASI) at 8 weeks. Secondary outcomes include other investigator-assessed efficacy measures of disease severity, participant-reported measures of efficacy and safety measures. This manuscript describes in detail the outcomes, sample size, general analysis principles, the pre-specified statistical analysis plan for each of the outcomes, the handling of missing outcome data and the planned sensitivity and supplementary analyses for the second stage of the APRICOT trial.

DISCUSSION

This statistical analysis plan was developed in compliance with international trial guidelines and is published to increase transparency of the trial analysis. The results of the trial analysis will indicate whether anakinra has a role in the treatment of PPP.

TRIAL REGISTRATION

ISCRTN, ISCRTN13127147. Registered on 1 August 2016. EudraCT Number 2015-003600-23. Registered on 1 April 2016.

Review-Current Concepts in Inflammatory Skin Diseases Evolved by Transcriptome Analysis: In-Depth Analysis of Atopic Dermatitis and Psoriasis

During the last decades, high-throughput assessment of gene expression in patient tissues using microarray technology or RNA-Seq took center stage in clinical research. Insights into the diversity and frequency of transcripts in healthy and diseased conditions provide valuable information on the cellular status in the respective tissues. Growing with the technique, the bioinformatic analysis toolkit reveals biologically relevant pathways which assist in understanding basic pathophysiological mechanisms. Conventional classification systems of inflammatory skin diseases rely on descriptive assessments by pathologists. In contrast to this, molecular profiling may uncover previously unknown disease classifying features. Thereby, treatments and prognostics of patients may be improved. Furthermore, disease models in basic research in comparison to the human disease can be directly validated. The aim of this article is not only to provide the reader with information on the opportunities of these techniques, but to outline potential pitfalls and technical limitations as well. Major published findings are briefly discussed to provide a broad overview on the current findings in transcriptomics in inflammatory skin diseases.

TAK-242 ameliorates contact dermatitis exacerbated by IL-36 receptor antagonist deficiency

Loss-of-function mutations in IL36RN cause generalized pustular psoriasis (GPP), which is characterized by neutrophil-infiltrated lesions. Neutrophils are important during contact hypersensitivity in mice. However, it has never been determined whether interleukin-36 receptor antagonist (IL-36Ra) deficiency is an exacerbating factor in contact dermatitis. We examined whether a loss-of-function IL36RN mutation exacerbates contact dermatitis and evaluated the changes in contact dermatitis-related cytokines. Wild-type and Il36rn^−/− mice were treated with 1-fluoro-2,4-dinitorobenzene (DNFB) and evaluated for ear thickness, histopathological features, numbers of infiltrated neutrophils, and numbers of CD4 + and CD8 + T cells. Furthermore, mRNA levels of contact dermatitis-related cytokines were measured by real-time polymerase chain reaction, and effects of TAK-242, a toll-like receptor 4 (TLR4) inhibitor, on the contact hypersensitivity (CHS) response were evaluated. We found that the ear thickness, cytokine expression, and neutrophil infiltration significantly increased in Il36rn^−/− mice compared with that in wild-type mice. TAK-242 alleviated CHS and prevented neutrophil infiltration, cytokine expression, and ear thickening in Il36rn^−/− mice. These data indicate that Il36rn^−/− mutations are an exacerbating factor for CHS and that TAK-242 can reduce the inflammatory responses that are associated with the CHS response.

Review of treatments for generalized pustular psoriasis

BACKGROUND

Generalized pustular psoriasis (GPP) is an uncommon variant of psoriasis that is characterized clinically by sterile pustule formation superimposed over inflamed, erythematous skin.

METHODS

In June 2019, we conducted a systematic search of the PubMed Medline database using the keywords 'pustular psoriasis' and 'treatment'.

RESULTS

First-line treatment for the condition consists of established therapies, such as acitretin, cyclosporine, methotrexate, and infliximab. Several medications targeting IL-17 or IL-23 have also emerged recently with drugs such as ixekizumab, secukinumab, brodalumab, guselkumab, and ustekinumab having shown some efficacy.

CONCLUSIONS

This review highlights the research in support of common treatments of GPP, including classically used medications and newer monoclonal antibodies, and addresses the continued need for high quality studies regarding treatments for this condition.

Interleukin-36: Structure, Signaling and Function

The IL-36 family belongs to a larger IL-1 superfamily and consists of three agonists (IL-36α/β/γ), one antagonist (IL-36Ra), one cognate receptor (IL-36R) and one accessory protein (IL-1RAcP). The receptor activation follows a two-step mechanism in that the agonist first binds to IL-36R and the resulting binary complex recruits IL-1RAcP. Assembled ternary complex brings together intracellular TIR domains of receptors which activate downstream NF-κB and MAPK signaling. Antagonist IL-36Ra inhibits the signaling by binding to IL-36R and preventing recruitment of IL-1RAcP. Members of IL-36 are normally expressed at low levels. Upon stimulation, they are inducted and act on a variety of cells including epithelial and immune cells. Protease mediated N-terminal processing is needed for cytokine activation. In the skin, the functional role of IL-36 is to contribute to host defense through inflammatory response. However, when dysregulated, IL-36 stimulates keratinocyte and immune cells to enhance the Th17/Th23 axis and induces psoriatic-like skin disorder. Genetic mutations of the antagonist IL-36Ra are associated with occurrence of generalized pustular psoriasis, a rare but life-threatening skin disease. Anti-IL-36 antibodies attenuate IMQ or IL-23 induced skin inflammation in mice, illustrating IL-36's involvement in mouse model of psoriasis. Other organs such as the lungs, the intestine, the joints and the brain also express IL-36 family members upon stimulation. The physiological and pathological roles of IL-36 are less well defined in these organs than in the skin. In this chapter, current progress on IL-36 protein and biology is reviewed with a discussion on investigative tools for this novel target.

Periodic fever syndromes and the autoinflammatory diseases (AIDs)

Innate immune system represents the ancestral defense against infectious agents preserved along the evolution and species; it is phylogenetically older than the adaptive immune system, which exists only in the vertebrates. Cells with phagocytic activity such as neutrophils, macrophages, and natural killer (NK) cells play a key role in innate immunity. In 1999 Kastner et al. first introduced the term “autoinflammation” describing two diseases characterized by recurrent episodes of systemic inflammation without any identifiable infectious trigger: Familial Mediterranean Fever (FMF) and TNF Receptor Associated Periodic Syndrome (TRAPS). Autoinflammatory diseases (AIDs) are caused by self-directed inflammation due to an alteration of innate immunity leading to systemic inflammatory attacks typically in an on/off mode. In addition to inflammasomopathies, nuclear factor (NF)-κB-mediated disorders (also known as Rhelopathies) and type 1 interferonopathies are subjects of more recent studies.

This review aims to provide an overview of the field with the most recent updates (see “Most recent developments in..” paragraphs) and a description of the newly identified AIDs.

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Autoinflammatory diseases are caused by self-directed inflammation.

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Alteration of innate immunity leads to systemic inflammation attacks.

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The autoinflammatory field is exponentially expanding.

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The advances in AIDs have led to new insights into immune system understanding.

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Autoimmunity and autoinflammation features may be simultaneously present.

Clinicopathologic overlap of psoriasis, eczema, and psoriasiform dermatoses: A retrospective study of T helper type 2 and 17 subsets, interleukin 36, and β-defensin 2 in spongiotic psoriasiform dermatitis, sebopsoriasis, and tumor necrosis factor α inhibitor-associated dermatitis

BACKGROUND

T helper (Th) type 17 and Th2 cells mediate psoriasis and eczema, respectively. Some dermatoses exhibit overlapping clinicopathologic features, and their immunopathology is relatively unexplored.

OBJECTIVE

To determine whether Th17 and Th2 subsets and interleukin (IL) 36 and β-defensin 2 (BD-2) markers of IL-17 signaling expression can discriminate between biopsy samples of psoriasis and eczematous/spongiotic dermatitis and to use those markers to immunophenotype cases with clinicopathologic overlap.

METHODS

A retrospective study was performed on biopsy samples of psoriasis, eczema/spongiotic dermatitis, sebopsoriasis, tumor necrosis factor α inhibitor-associated psoriasiform dermatitis, and ambiguous cases diagnosed as spongiotic psoriasiform dermatitis. Dual CD4/GATA3 and CD4/RORC, IL-36, and BD-2 immunohistochemistry was performed.

RESULTS

IL-36 and BD-2 were strongly expressed in biopsy samples of psoriasis compared with eczema/spongiotic dermatitis. No significant differences were observed in the percentages of Th2 and Th17 cells between disease types. Strong expression of IL-36 and BD-2 was observed in a subset of spongiotic psoriasiform dermatitis, sebopsoriasis, and tumor necrosis factor α inhibitor-associated psoriasiform dermatitis biopsy samples.

LIMITATIONS

This was an exploratory study with a small sample size. No multiple testing adjustment was done. Clinical follow-up was limited.

CONCLUSIONS

In cases with clinicopathologic overlap between psoriasis and spongiotic dermatitis, IL-36, and to a lesser extent BD-2, may be used to assess for a psoriasis-like/IL-17 phenotype, which could inform therapeutic clinical decisions.

Immune Dysregulation in the Tonsillar Microenvironment of Periodic Fever, Aphthous Stomatitis, Pharyngitis, Adenitis (PFAPA) Syndrome

Periodic Fever, Aphthous stomatitis, Pharyngitis and Adenitis (PFAPA) syndrome is an inflammatory disorder of childhood classically characterized by recurrent fevers, pharyngitis, stomatitis, cervical adenitis, and leukocytosis. While the mechanism is unclear, previous studies have shown that tonsillectomy can be a therapeutic option with improvement in quality of life in many patients with PFAPA, but the mechanisms behind surgical success remain unknown. In addition, long-term clinical follow-up is lacking. In our tertiary care center cohort, 62 patients with PFAPA syndrome had complete resolution of symptoms after surgery (95.3%). Flow cytometric evaluation demonstrates an inflammatory cell population, distinct from patients with infectious pharyngitis, with increased numbers of CD8+ T cells (5.9% vs. 3.8%, p < 0.01), CD19+ B cells (51% vs. 35%, p < 0.05), and CD19+CD20+CD27+CD38-memory B cells (14% vs. 7.7%, p < 0.01). Cells are primed at baseline with increased percentage of IL-1β positive cells compared to control tonsil-derived cells, which require exogenous LPS stimulation. Gene expression analysis demonstrates a fivefold upregulation in IL1RN and TNF expression in whole tonsil compared to control tonsils, with persistent activation of the NF-κB signaling pathway, and differential microbial signatures, even in the afebrile period. Our data indicates that PFAPA patient tonsils have localized, persistent inflammation, in the absence of clinical symptoms, which may explain the success of tonsillectomy as an effective surgical treatment option. The differential expression of several genes and microbial signatures suggests the potential for a diagnostic biomarker for PFAPA syndrome.

Lack of association between mutation in IL36RN and palmoplantar pustular psoriasis in Chinese patients

Background

Palmoplantar pustulosis is considered to be a localized pustular psoriasis confined to the palms and soles. Mutation of the IL36RN gene, encoding interleukin-36 receptor antagonist (IL-36Ra), is associated with generalized pustular psoriasis, but IL36RN mutations in Chinese palmoplantar pustulosis patients have not previously been investigated.

Objective

The aim of this study was to evaluate the mutation of IL36RN in Chinese patients with palmoplantar pustulosis.

Methods

Fifty-one Han Chinese patients with palmoplantar pustulosis were recruited. All exons and exon-intron boundary sequences of IL36RN were amplified in polymerase chain reactions, and Sanger sequencing of the amplicons was performed.

Results

Among the 51 palmoplantar pustulosis patients, four different single-base substitutions were identified in nine patients. The mutations were c.140A>G/p.Asn47Ser in five patients, c.258G>A/p.Met86IIe in two patients, and c.115+6T>C and c.169G>A/p.Val57IIe in one patient each. All mutations were heterozygous. Comparison with the human genome database and reported literature suggested that these variants may not be pathogenic mutations causing palmoplantar pustulosis. Furthermore, there was no difference in disease severity, onset age, or disease duration between patients with these heterozygous IL36RN variants and those without (p > 0.1).

Study limitation

Lack of the further evaluation of IL36Ra protein in palmoplantar pustulosis lesions.

Conclusions

The four variants of IL36RN identified did not appear to be associated with the specific phenotypes of palmoplantar pustulosis.

Function and Regulation of IL-36 Signaling in Inflammatory Diseases and Cancer Development

The IL-36 subfamily of cytokines belongs to the IL-1 superfamily and consists of three pro-inflammatory agonists IL-36α, IL-36β, IL-36γ, and an IL-36 receptor (IL-36R) antagonist, IL-36Ra. These IL-36 cytokines function through a common receptor to modulate innate and adaptive immune responses. IL-36 cytokines are expressed as inactive precursors and require proteolytic processing to become fully active. Upon binding to IL-36R, IL-36 agonists augment the expression and production of inflammatory cytokines via activating signaling pathways. IL-36 is mainly expressed in epidermal, bronchial, and intestinal epithelial cells that form the barrier structures of the body and regulates the balance between pro-inflammatory and anti-inflammatory cytokine production at these tissue sites. Dysregulation of IL-36 signaling is a major etiological factor in the development of autoimmune and inflammatory diseases. Besides its critical role in inflammatory skin diseases such as psoriasis, emerging evidence suggests that aberrant IL-36 activities also promote inflammatory diseases in the lung, kidneys, and intestines, underscoring the potential of IL-36 as a therapeutic target for common inflammatory diseases. The role of IL-36 signaling in cancer development is also under investigation, with limited studies suggesting a potential anti-tumor effect. In this comprehensive review, we summarize current knowledge regarding the expression, activation, regulatory mechanisms, and biological functions of IL-36 signaling in immunity, inflammatory diseases, and cancer development.