Unopposed IL-36 Activity Promotes Clonal CD4+ T-Cell Responses with IL-17A Production in Generalized Pustular Psoriasis

Interventions in cytokine signaling: novel horizons for psoriasis treatment

Intricate interactions between immune cells and cytokines define psoriasis, a chronic inflammatory skin condition that is immunological-mediated. Cytokines, including interleukins (ILs), interferons (IFNs), tumor necrosis factors (TNFs), chemokines, and transforming growth factor-β (TGF-β), are essential for controlling cellular activity and immunological responses, maintaining homeostasis and contributing to the pathogenesis of psoriasis. These molecules modulate the immune microenvironment by either promoting or suppressing inflammation, which significantly impacts therapeutic outcomes. Recent research indicates that treatment strategies targeting cytokines and chemokines have significant potential, offering new approaches for regulating the immune system, inhibiting the progression of psoriasis, and reducing adverse effects of traditional therapies. This review consolidates current knowledge on cytokine and chemokine signaling pathways in psoriasis and examines their significance in treatment. Specific attention is given to cytokines like IL-17, IL-23, and TNF-α, underscoring the necessity for innovative therapies to modulate these pathways and address inflammatory processes. This review emphasizes the principal part of cytokines in the -pathological process of psoriasis and explores the challenges and opportunities they present for therapeutic intervention. Furthermore, we examine recent advancements in targeted therapies, with a particular focus on monoclonal antibodies, in ongoing research and clinical trials.

Updated genetic background of generalized pustular psoriasis as an autoinflammatory keratinization disease

Generalized pustular psoriasis (GPP) is a severe autoinflammatory keratinization disease (AiKD) characterized by acute flares of widespread sterile pustules and high fever. GPP is potentially life-threatening. Recently clarified genetic predisposing factors for GPP suggest that the excessive activation of innate immune pathways in the skin, including of interleukin (IL)-1 and IL-36 signaling, plays a significant role in the GPP pathogenesis. IL36RN, CARD14, AP1S3, MPO, SERPINA3, BTN3A3, and MEFV have been identified as GPP-related genes. The pathogenesis of GPP provoked by variants in these seven genes is tightly associated with the excessive activation of innate immune pathways and the resulting autoinflammation in the skin. Various biologics, including inhibitors for the tumor necrosis factor, IL-17, and IL-23 pathways, are used as treatments for GPP. The new understanding of the genetic background of GPP, mentioned above, indicates that the genetic predisposing factors are predominantly related to the excessive activation of innate immunity and autoinflammation. In this context, inhibitors of inflammatory signaling, including of the IL-1 and IL-36 pathways, have been used in clinical practice and investigated as potential future therapies.

Spesolimab Reduces Inflammation in Generalized Pustular Psoriasis: Molecular Characterization of Flare Treatment in EFFISAYIL 1

EFFISAYIL 1 was a randomized, placebo-controlled study of spesolimab, an anti-IL-36 receptor antibody, in patients presenting with a generalized pustular psoriasis flare. Treatment with spesolimab led to more rapid pustular and skin clearance versus treatment with placebo in approximately half of the patients. In this study, we present histologic, transcriptomic, and proteomic analyses of lesional and nonlesional skin and whole-blood samples collected from EFFISAYIL 1. Treatment with spesolimab led to a transition toward a nonlesional profile, with a downregulation of gene expressions in the skin of IL-36 transcripts (IL36α, IL36β, IL36γ) and those associated with neutrophil recruitment (CXCL1, CXCL6, CXCL8), proinflammatory cytokines (IL6, IL19, IL20), and skin inflammation (DEFB4A, S100A7, S100A8). Changes were manifest at week 1 and sustained to week 8. At the systemic level, reductions in serum biomarkers of inflammation (IL-17, IL-8, IL-6) were sustained until 12 weeks after spesolimab treatment. Considerable overlap was observed in the spesolimab-induced changes in gene and protein expressions from skin and blood samples, demonstrating the molecular basis of the effects of spesolimab on controlling local and systemic inflammation. Data are consistent with the mode of action of spesolimab, whereby inhibition of the IL-36 pathway leads to subsequent reductions in the key local and systemic pathologic events associated with generalized pustular psoriasis flares.

IL-36-driven pustulosis: Transcriptomic signatures match between generalized pustular psoriasis (GPP) and acute generalized exanthematous pustulosis (AGEP)

BACKGROUND

Due to similarities, the distinction between generalized pustular psoriasis (GPP) and acute generalized exanthematous pustulosis (AGEP) has been a matter of debate for a long time.

OBJECTIVES

Our aim was to define the molecular features of GPP and AGEP.

METHODS

We analyzed skin biopsy samples and clinical data from 125 patients with AGEP, GPP, palmoplantar pustulosis (PPP), plaque psoriasis (PSO), and nonpustular cutaneous adverse drug reactions (ADRs), as well as from healthy skin controls using RNA-sequencing and blinded histopathologic analyses.

RESULTS

The transcriptome and histopathologic features of AGEP and GPP samples exhibited significant overlap (177 differentially expressed genes [DEGs] in GPP and AGEP compared to healthy skin, only 2 DEGs comparing AGEP and GPP). Yet, they displayed marked differences from those of PPP, PSO, and ADR samples, with a notable number of DEGs (131 DEGs comparing AGEP and PSO, 75 DEGs comparing AGEP and PPP, and 52 DEGs comparing AGEP and ADR). A transcriptome profile subgroup evaluation of >13,000 analyzed genes did not reveal any DEGs in drug-induced GPP and AGEP. Moreover, the immune response pattern and immune cell composition did not differ between drug-induced GPP and AGEP, whereas non-drug-induced GPP had higher expression of TH17-cell-related genes and a higher neutrophil count than AGEP.

CONCLUSIONS

We propose that AGEP is a drug-induced variant of GPP and therefore part of IL-36-related pustulosis. A key signature overarching this spectrum was identified, thereby opening the therapeutic approach of IL-36 inhibition to all subtypes of the disease.

Ixekizumab as a successful treatment in pediatric generalized pustular psoriasis

BACKGROUND

Generalized Pustular Psoriasis (GPP) is an autoinflammatory, multisystemic disease, characterized by widespread eruption of neutrophilic pustules on erythematous base, accompanied by systemic symptoms such as fever, leukocytosis, arthralgia, and general malaise. Globally, the disease is rare, particularly in children. If not adequately diagnosed and treated, systemic inflammation and multiorgan involvement can be life-threatening. The pathogenesis of GPP mainly involves the innate immune system, with inflammatory processes and neutrophil activation driven primarily by IL-36, but also by IL-1, TNF-alpha, IL-17 A. In particular, IL-17 A acts as a potent inducer of neutrophil recruitment. We report the case of a 7-years-old girl with GPP successfully treated with Ixekizumab, an IL-17 A antagonist.

CASE PRESENTATION

A 7-years-old girl with an history of plaque psoriasis came to our attention for the sudden appearance of erythematous patches surmounted by pustules on the trunk and lower limbs, following repeated episodes of purulent tonsillitis. We started therapy with cyclosporine at a dosage of 3,5 mg/kg/day, with no clinical benefit and progression of manifestations to a sub-erythrodermic state after 2 weeks. Blood tests showed neutrophilic leukocytosis, and the patient experienced hyperpyrexia and malaise. Since ixekizumab was recently approved for pediatric use in patients with moderate to severe plaque psoriasis, we started therapy with 80 mg Ixekizumab, combined with prednisone at a dosage of 12.5 mg/day, gradually tapered until discontinuation after 15 days. A second dose of Ixekizumab 40 mg was administered at week-4, according to the indication of ixekizumab in pediatric plaque psoriasis. At week-8 the patient achieved complete remission of skin manifestations and normalization of blood count. After achieving a stable remission, at week 36 we decided to increase the administration interval to 6 weeks. The patient is still on therapy with ixekizumab 40 mg every 6 weeks, maintaining complete remission during a 52-week follow-up, without safety concerns.

CONCLUSIONS

This report supports the use of ixekizumab as a safe and effective option, both in the short and long-term, in the treatment of GPP, even at pediatric age. Larger studies are needed to confirm this positive, real-life experience.

Case report: Successful treatment with spesolimab of acrodermatitis continua of Hallopeau in an older patient without IL36RN mutations

Background

Acrodermatitis continua of Hallopeau (ACH) is a rare, sterile pustular psoriasis variant refractory to many conventional treatments. The eruption typically occurs after local trauma or infection; other etiologies include neural, inflammatory, and genetic causes. Herein we reported a single case of a 64-year-old patient with ACH that was successfully treated with spesolimab for 19 weeks.

Case summary

A 64-year-old Chinese male with no personal or known family history of psoriasis had recurrent episodes of redness, swelling, and pustules in the nail bed on seven fingers with progressive degeneration of the nails. The patient was monitored as to the evolution of the disease over half of a year before he referred his case to our attention. A diagnosis of ACH was made, allowing for the administration of local steroids and oral acitretin. However, after 3 months of acitretin treatment, no improvement was observed. In December 2023, this patient came to our inpatient department; his modified nail psoriasis severity index score was 32. Before starting treatment, a comprehensive set of laboratory and instrumental tests were all found to be negative. Moreover, whole-exome sequencing was performed in our patient, and it revealed no rare coding variant in IL36RN, CARD14, or AP1S3. Therefore, the patient was administrated with a dose of 900 mg spesolimab. After 10 days, the patient showed a significant decrease in discomfort and pain. In order to strengthen the therapeutic effect, he was given the second dose of 900 mg spesolimab after 4 weeks. After 19 weeks of spesolimab treatment, the patient's nail lesions showed complete resolution, and no adverse effects were reported.

Conclusion

The case report suggests that spesolimab may offer significant therapeutic benefits for ACH.

Rapid and sustained resolution in generalized pustular psoriasis with IL-17A inhibitors required high adherence: a 96-week analysis in a real-life setting

BACKGROUND

Generalized pustular psoriasis (GPP) is a rare, potentially life-threatening skin disease often requiring long-term therapy. We aimed to evaluate the use of Interleukin (IL)-17A inhibitors (secukinumab and ixekizumab) in GPP patients over 96 weeks.

METHODS

We retrospectively analyzed a case series of 18 patients with GPP who received secukinumab (n = 13) and ixekizumab (n = 5) therapy with a 96-week follow-up period. The primary effectiveness analysis included determining the percentage of patients who achieved ≥90% or 100% improvement in the Generalized Pustular Psoriasis Area and Severity Index (GPPASI) score. Adherence was captured using the medication possession ratio (MPR).

RESULTS

Using the as-observed (AO) method, 87% and 67% of patients treated with secukinumab or ixekizumab achieved GPPASI 90 and 100 responses, respectively. At Week 96, the mean GPPASI improvements from baseline GPPASI were 96.3% (95% CI: 0.91-1.01) using the AO method. After Week 48, 14 patients tapered (n = 8) or terminated (n = 6) the treatment. High-adherence therapy (MPR ≥ 80%) was significantly superior to the low-adherence group in the rate of patients achieving a GPPASI 100 response (AO, 100% vs. 38%, P < 0.05). By Week 96, 5 (27.8%) patients had new GPP flares, and 4 (80%) were in the low-adherence group. No new safety signals occurred.

CONCLUSION

IL-17A inhibitors led to effective and sustained improvement in GPP patients, and high-adherence therapy had long-term positive effects on skin clearance. Given its relapsing nature, improving compliance is beneficial for long-term clinical management.

The Contribution of the Skin Microbiome to Psoriasis Pathogenesis and Its Implications for Therapeutic Strategies

Psoriasis is a common chronic inflammatory skin disease, associated with significant morbidity and a considerable negative impact on the patients' quality of life. The complex pathogenesis of psoriasis is still incompletely understood. Genetic predisposition, environmental factors like smoking, alcohol consumption, psychological stress, consumption of certain drugs, and mechanical trauma, as well as specific immune dysfunctions, contribute to the onset of the disease. Mounting evidence indicate that skin dysbiosis plays a significant role in the development and exacerbation of psoriasis through loss of immune tolerance to commensal skin flora, an altered balance between Tregs and effector cells, and an excessive Th1 and Th17 polarization. While the implications of skin dysbiosis in psoriasis pathogenesis are only starting to be revealed, the progress in the characterization of the skin microbiome changes in psoriasis patients has opened a whole new avenue of research focusing on the modulation of the skin microbiome as an adjuvant treatment for psoriasis and as part of a long-term plan to prevent disease flares. The skin microbiome may also represent a valuable predictive marker of treatment response and may aid in the selection of the optimal personalized treatment. We present the current knowledge on the skin microbiome changes in psoriasis and the results of the studies that investigated the efficacy of the different skin microbiome modulation strategies in the management of psoriasis, and discuss the complex interaction between the host and skin commensal flora.

The role of interleukin-36 in health and disease states

The interleukin (IL)-1 superfamily upregulates immune responses and maintains homeostasis between the innate and adaptive immune systems. Within the IL-1 superfamily, IL-36 plays a pivotal role in both innate and adaptive immune responses. Of the four IL-36 isoforms, three have agonist activity (IL-36α, IL-36β, IL-36γ) and the fourth has antagonist activity (IL-36 receptor antagonist [IL-36Ra]). All IL-36 isoforms bind to the IL-36 receptor (IL-36R). Binding of IL-36α/β/γ to the IL-36R recruits the IL-1 receptor accessory protein (IL-1RAcP) and activates downstream signalling pathways mediated by nuclear transcription factor kappa B and mitogen-activated protein kinase signalling pathways. Antagonist binding of IL-36Ra to IL-36R inhibits recruitment of IL-1RAcP, blocking downstream signalling pathways. Changes in the balance within the IL-36 cytokine family can lead to uncontrolled inflammatory responses throughout the body. As such, IL-36 has been implicated in numerous inflammatory diseases, notably a type of pustular psoriasis called generalized pustular psoriasis (GPP), a chronic, rare, potentially life-threatening, multisystemic skin disease characterised by recurrent fever and extensive sterile pustules. In GPP, IL-36 is central to disease pathogenesis, and the prevention of IL-36-mediated signalling can improve clinical outcomes. In this review, we summarize the literature describing the biological functions of the IL-36 pathway. We also consider the evidence for uncontrolled activation of the IL-36 pathway in a wide range of skin (e.g., plaque psoriasis, pustular psoriasis, hidradenitis suppurativa, acne, Netherton syndrome, atopic dermatitis and pyoderma gangrenosum), lung (e.g., idiopathic pulmonary fibrosis), gut (e.g., intestinal fibrosis, inflammatory bowel disease and Hirschsprung's disease), kidney (e.g., renal tubulointerstitial lesions) and infectious diseases caused by a variety of pathogens (e.g., COVID-19; Mycobacterium tuberculosis, Pseudomonas aeruginosa, Streptococcus pneumoniae infections), as well as in cancer. We also consider how targeting the IL-36 signalling pathway could be used in treating inflammatory disease states.

Molecular aspects of Interleukin-36 cytokine activation and regulation

Interleukin-36 (IL-36) cytokines are structurally similar to other Interleukin-1 superfamily members and are essential to convey inflammatory responses at epithelial barriers including the skin, lung, and gut. Due to their potent effects on immune cells, IL-36 cytokine activation is regulated on multiple levels, from expression and activation to receptor binding. Different IL-36 isoforms convey specific responses as a consequence of particular danger- or pathogen-associated molecular patterns. IL-36 expression and activation are regulated by exogenous pathogens, including fungi, viruses and bacteria but also by endogenous factors such as antimicrobial peptides or cytokines. Processing of IL-36 into potent bioactive forms is necessary for host protection but can elevate tissue damage. Indeed, exacerbated IL-36 signalling and hyperactivation are linked to the pathogenesis of diseases such as plaque and pustular psoriasis, emphasising the importance of understanding the molecular aspects regulating IL-36 activation. Here, we summarise facets of the electrochemical properties, regulation of extracellular cleavage by various proteases and receptor signalling of the pro-inflammatory and anti-inflammatory IL-36 family members. Additionally, this intriguing cytokine subfamily displays many characteristics that are unique from prototypical members of the IL-1 family and these key distinctions are outlined here.

Clinical efficacy and safety of secukinumab in the treatment of generalized pustular psoriasis in the pediatric population: a systematic review of the literature

Background

Generalized pustular psoriasis (GPP) is a severe type of psoriasis. The current treatment primarily relies on corticosteroids and immunosuppressants. In recent years, biologics have been increasingly utilized in the treatment of this disease, and have demonstrated good clinical efficacy. However, children and adolescents are primarily treated with immunosuppressants, which have limited clinical application due to the serious side effects they may cause. At the same time, the effectiveness of current treatments is unsatisfactory. Secukinumab has been widely reported to be effective and safe in treating this disease. However, there are still insufficient data on its use in treating GPP in children.

Objective

To conduct a systematic review of the existing literature on the use of secukinumab for treating generalized pustular psoriasis in children and adolescents, and to evaluate its clinical effectiveness and safety.

Methods

We conducted a systematic review of all the literature reporting on the treatment of GPP in children and adolescents with secukinumab.

Results

A total of 7 papers (46 patients) were included in this study. After 12 weeks of treatment, all 46 participants were able to achieve a GPPASI score of 90 or higher, with approximately 96% of patients achieving complete clearing of the lesions (GPPASI 100 or JDA0). Adverse events were reported in 8 patients, the rate of adverse reactions was approximately 17%.

Conclusion

The treatment of GPP in children and adolescents with secukinumab has a rapid onset of action and a high safety profile. However, the results of the literature may be influenced by publication bias.

NETs contribute to psoriasiform skin inflammation: A novel therapeutic approach targeting IL-36 cytokines by a small molecule tetrahydroxystilbene glucoside

BACKGROUND

Psoriasis, a chronic immune-mediated skin disease with pathological features such as aberrant differentiation of keratinocytes, dermal-epidermal inflammation, and angiogenesis. 2,3,5,4'-Tetrahydroxy stilbene 2-Ο-β-d-glucoside (2354Glu) is a natural small molecule polyhydrostilbenes isolated from Polygonum multiglorum Thunb. The regulation of IL-36 subfamily has led to new pharmacologic strategies to reverse psoriasiform dermatitis.

PURPOSE

Here we investigated the therapeutic potential of 2354Glu and elucidated the underlying mechanism in psoriasis.

METHODS

The effects of 2354Glu on IL-36 signaling were assessed by psoriasiform in vivo, in vitro and ex vivo model. The in vivo mice model of psoriasis-like skin inflammation was established by applying imiquimod (IMQ), and the in vitro and ex vitro models were established by stimulating mouse primary keratinocyte, human keratinocytes cells (HaCaT) and ex vivo skin tissue isolated from the mice back with Polyinosine-polycytidylic acid (Poly(I:C)), IMQ, IL-36γ and Lipopolysaccharide (LPS) respectively. Moreover, NETs formation was inhibited by Cl-amidine to evaluate the effect of NETs in psoriatic mouse model. The effects of 2354Glu on skin inflammation were assessed by western blot, H&E, immunohistochemistry, immunofluorescence, enzyme-linked immunosorbent assay and real-time quantitative PCR.

RESULTS

In Poly(I:C)-stimulated keratinocytes, the secretion of IL-36 was inhibited after treatment with 2354Glu, similar to the effects of TLR3, P2X7R and caspase-1 inhibitors. In aldara (imiquimod)-induced mice, 2354Glu (100 and 25 mg/kg) improved immune cell infiltration and hyperkeratosis in psoriasis by directly targeting IL-36 in keratinocytes through P2X7R-caspase-1. When treatment with 2354Glu (25 mg/kg) was insufficient to inhibit IL-36γ, NETs reduced pathological features and IL-36 signaling by interacting with keratinocytes to combat psoriasis like inflammation.

CONCLUSION

These results indicated that NETs had a beneficial effect on psoriasiform dermatitis. 2354Glu alleviates psoriasis by directly targeting IL-36/P2X7R axis and NET formation, providing a potential candidate for the treatment of psoriasis.

Effect of smoking cessation on psoriasis vulgaris, palmoplantar pustulosis and generalized pustular psoriasis

BACKGROUND

Smoking is a known risk factor for psoriasis; however, the impact of smoking cessation on psoriasis has seldom been evaluated.

OBJECTIVES

We aimed to examine the effects of smoking cessation on the development of psoriasis vulgaris (PsV), palmoplantar pustulosis (PPP) and generalized pustular psoriasis (GPP).

METHODS

Using the Korean National Health Insurance Service database, we retrospectively compiled a cohort of 5 784 973 participants without psoriasis, analysed their changes in smoking status from 2004 to 2007 and followed up new cases of psoriasis until 2021. The psoriasis risks were compared with those of sustained smokers, smoking quitters, sustained ex-smokers and never smokers using multivariate Cox proportional hazard models.

RESULTS

The mean age of the participants was 47.1 years (SD 13.5) and 3 092 426 (53.5%) were male. During 77 990 688 person-years, 67 364 psoriasis cases were identified. Compared with sustained smokers, smoking quitters showed a reduced risk of developing psoriasis [adjusted hazard ratio (aHR) 0.91; 95% confidence interval (CI) 0.87-0.95], specifically PsV (aHR 0.92; 95% CI 0.88-0.97) and PPP (aHR 0.71; 95% CI 0.63-0.79). The reduction in risk due to smoking cessation was more prominent in sustained ex-smokers (psoriasis: aHR 0.77, 95% CI 0.74-0.79; PsV: aHR 0.76, 95% CI 0.73-0.79; PPP: aHR 0.56, 95% CI 0.51-0.61; GPP: aHR 0.64; 95% CI 0.52-0.78). When conducting sensitivity analyses to address the potential for changes in smoking habits after 2007, the results and trends were consistent with the main findings, and a more pronounced significance was observed.

CONCLUSIONS

Compared with continuous smoking, smoking cessation was associated with a decreased risk of developing psoriasis. The risk-reducing effect of smoking cessation was more pronounced in those maintaining a smoke-free status. Smoking cessation and the maintenance of a smoke-free status should be encouraged to prevent the development of psoriasis and all other smoking-related diseases.

Cytokines in psoriasis: From pathogenesis to targeted therapy

Psoriasis is a multifactorial disease that affects 0.84% of the global population and it can be associated with disabling comorbidities. As patients present with thick scaly lesions, psoriasis was long believed to be a disorder of keratinocytes. Psoriasis is now understood to be the outcome of the interaction between immunological and environmental factors in individuals with genetic predisposition. While it was initially thought to be solely mediated by cytokines of type-1 immunity, namely interferon-γ, interleukin-2, and interleukin-12 because it responds very well to cyclosporine, a reversible IL-2 inhibitor; the discovery of Th-17 cells advanced the understanding of the disease and helped the development of biological therapy. This article aims to provide a comprehensive review of the role of cytokines in psoriasis, highlighting areas of controversy and identifying the connection between cytokine imbalance and disease manifestations. It also presents the approved targeted treatments for psoriasis and those currently under investigation.

Targeted review of IL36RN mutations in patients with generalised pustular psoriasis

Background

Generalised pustular psoriasis (GPP) is a rare and chronic skin disease historically treated with therapies that were originally intended to treat plaque psoriasis (PsO). However, GPP and plaque PsO have distinct pathogeneses and clinical courses.

Objectives

This study aimed to further characterise the unique genetic background of GPP by summarising evidence on the frequency and type of IL36RN gene mutation, a gene that normally suppresses proinflammatory responses, in patients with GPP compared to patients with GPP and plaque PsO, and patients with plaque PsO only.

Methods and Results

A targeted literature review was conducted to identify studies reporting IL36RN mutations and/or HLA-Cw6 allele frequency in patients with GPP. Meta-analyses showed a significantly higher rate of IL36RN mutations in the GPP-only population compared to the GPP + plaque PsO population (OR 3.51; 95% CI 2.29, 5.38). Monoallelic mutations of IL36RN were found in up to 33.3%, and biallelic mutations in up to 73.2% of patients with GPP (GPP-only and GPP + plaque PsO), in contrast with mono- and biallelic frequencies of only 0%-11.9% and 0%, respectively, in patients with plaque PsO only. Mean age-of-onset ranged from 5.9 to 48.9 years old, with most studies reporting a GPP age-of-onset between 20 and 40 years old. Twenty-one mutations were identified in the biallelic state and three in monoallelic. The most reported mutations were c.115 + 6T > C (p. Arg10ArgfsX1) (18 studies); c.227 C > T (p.Pro76Leu) (10 studies); and c.338 C > T (p.Ser113Leu) (8 studies). Mutations varied depending on geography and ethnicity, with the most frequently reported mutation predominantly reported in East Asian studies and international studies that included Asian patients. Rates of HLA-Cw6, the risk allele most strongly associated with plaque PsO, were 0%-28.6% for patients with GPP, similar to rates in the general population (10.5%-20%).

Conclusion

Considering the differences between GPP and plaque PsO in aetiology and disease symptoms, effective, GPP-specific treatment options are needed, and recent research suggests that blockade of IL-36 signalling may be an effective target for treatment of GPP.

Case report: Successful treatment of acute generalized pustular psoriasis with multiple comorbidities with oral tacrolimus

Acute generalized pustular psoriasis (GPP) is a serious illness. Despite various treatment methods, there is still lack of effective treatment plans for refractory cases with multiple comorbidities. This case report presents a 67-year-old woman with acute GPP, stage 4 chronic kidney disease (CKD), type 2 diabetes, and cardiovascular disease, in whom skin symptom disappearance and kidney function improvement were observed after the use of oral tacrolimus as the sole therapy. This is the first report on the application of tacrolimus in the treatment of acute GPP, especially refractory acute GPP. The successful treatment indicates that there are shared immune pathways between acute GPP and CKD, and the pathways can be interdicted by tacrolimus. Further studies are needed to optimize the therapy to maximize efficacy and minimize toxicity.

Interleukin-36 receptor antagonist stimulation in vitro inhibits peripheral and lung-resident T cell response isolated from patients with ventilator-associated pneumonia

Interleukin-36 (IL-36) cytokine family members play an immunomodulatory function to immune cells through IL-36 receptor signaling pathway. However, the regulatory role of IL-36 exerted on T cells is not completely elucidated in patients with ventilator-associated pneumonia (VAP). For this purpose, this study enrolled 51 VAP patients and 27 controls. IL-36 levels were measured by ELISA. The mRNA levels of IL-36 receptor subunits were determined by real-time PCR. CD4+ and CD8+ T cells were enriched, and stimulated with recombinant IL-36 receptor antagonist (IL-36RA). The influence of IL-36RA on transcription factors and cytokine secretions by CD4+ T cells was investigated. The modulatory function of IL-36RA on CD8+ T cells was assessed by measuring target cell death and cytokine secretions. There were no significant differences in serum IL-36 levels between VAP patients and controls. Only IL-36RA, but not IL-36α, IL-36β, or IL-36γ, in bronchoalveolar lavage fluid was elevated in infection site of VAP patients. IL-36 receptor subunits in CD4+ and CD8+ T cells were comparable between VAP patients and controls. 10 ng/mL of IL-36RA stimulation dampened peripheral effector CD4+ T cell response isolated from both VAP patients and controls. Target cell death mediated by CD8+ T cells isolated from BAFL of VAP patients was suppressed by 100 ng/mL of IL-36RA stimulation in vitro. The down-regulations of perforin, granzyme B, interferon-γ, tumor necrosis factor-α, and Fas ligand following IL-36RA stimulation in vitro were responsible for reduced CD8+ T cell-mediated cytotoxicity. IL-36RA revealed an immunosuppressive property for T cell response in vitro, and may be involved in the protective mechanism in VAP patients.

Successful treatment of acrodermatitis continua of Hallopeau coexisting with generalized pustular psoriasis with spesolimab: a case report

Generalized pustular psoriasis (GPP) is a rare chronic inflammatory pustular dermatosis that presents as painful erythema with sterile pustules on nonacral skin. No unified standard and guideline for the treatment of GPP has been established. Several biologics have been tried for GPP, with varying success. Acrodermatitis continua of Hallopeau (ACH) is a very rare disabling variant of pustular psoriasis characterized by sterile pustules on the fingers and toes, including the nail bed. Comparatively, treating ACH is highly challenging due to its commonly therapy-resistant disease course. The pathogenic role of IL-36 signaling axis has been currently identified in GPP development. Spesolimab, the first anti-interleukin-36 receptor biologic, has been approved for treating GPP flares and shown promising results. In view of a shared pathogenesis between GPP and ACH, specolimab may be an effective treatment for ACH. Currently, there is no case and clinical trial data exist on this condition. Therefore, this case was aim to describe real-world experience of spesolimab use in ACH coexisting with GPP. We report an Asian patient with a 16-year-history of GPP and ACH with marked pustulosis on the nail bed and onychodystrophy. He received conventional systemic regimen acitretin, cyclosporine and biologics adalimumab and secukinumab, but experienced relapse for skin lesions and refractory for nail lesions. He was then treated with a single dose of spesolimab in combination with secukinumab, which resulted in skin clearance and nearly complete resolution of nail lesions over a 32-week period. Our observation suggests that spesolimab should be considered for the treatment of ACH, especially in the patients with intractable nail lesions and concomitant GPP.

Increased neutrophil-derived IL-17A identified in generalized pustular psoriasis

Generalized pustular psoriasis (GPP) is considered to be a distinct clinical entity from psoriasis vulgaris (PV), with different clinical and histological manifestations. The pathogenesis of GPP has not been thoroughly elucidated, especially in those patients lacking interleukin (IL)36RN. In present study, we performed RNA sequence analysis on skin lesions from 10 GPP patients (4 with and 6 without IL36RN mutation) and 10 PV patients without IL36RN mutation. Compared with PV, significantly overexpressed genes in GPP patients were enriched in IL-17 signalling pathway (MMP1, MMP3, DEFB4A and DEFB4B, etc.) and associated with neutrophil infiltration (MMP1, MMP3, ANXA and SERPINB, etc.). GPP with IL36RN mutations evidenced WNT11 upregulation and IL36RN downregulation in comparison to those GPP without IL36RN mutations. The expression of IL-17A/IL-36 in skin or serum and the origin of IL-17A in skin were also investigated. IL-17A expression in skin was significantly higher in GPP than PV patients, whereas, there were no differences in skin IL-36α/IL-36γ/IL-36RA or serum IL-17A/IL-36α/IL-36γ between GPP than PV. Besides, double immunofluorescence staining of MPO/IL-17A or CD3/IL-17A further confirmed that the majority of IL-17A in GPP skin was derived from neutrophils, but not T cells. These data emphasized the role of neutrophil-derived IL-17A in the pathogenesis of GPP with or without IL36RN mutations. Targeting neutrophil-derived IL-17A might be a promising treatment for GPP.

Immune cells in the epithelial immune microenvironment of psoriasis: emerging therapeutic targets

Psoriasis is a chronic autoimmune inflammatory disease characterized by erroneous metabolism of keratinocytes. The development of psoriasis is closely related to abnormal activation and disorders of the immune system. Dysregulated skin protective mechanisms can activate inflammatory pathways within the epithelial immune microenvironment (EIME), leading to the development of autoimmune-related and inflammatory skin diseases. In this review, we initially emphasized the pathogenesis of psoriasis, paying particular attention to the interactions between the abnormal activation of immune cells and the production of cytokines in psoriasis. Subsequently, we delved into the significance of the interactions between EIME and immune cells in the emergence of psoriasis. A thorough understanding of these immune processes is crucial to the development of targeted therapies for psoriasis. Finally, we discussed the potential novel targeted therapies aimed at modulating the EIME in psoriasis. This comprehensive examination sheds light on the intricate underlying immune mechanisms and provides insights into potential therapeutic avenues of immune-mediated inflammatory diseases.

Clinical characteristics and heterogeneity of generalized pustular psoriasis: A comparative study in a large retrospective cohort

Generalized pustular psoriasis (GPP) is a rare and potentially life-threatening skin disease and the clinical heterogeneity of which is largely unknown. Retrospective cohort analysis was conducted on hospitalized GPP patients between January 2010 and November 2022. A total of 416 patients with GPP and psoriasis vulgaris (PV) respectively were included, matched 1:1 by sex and age. The heterogeneity of GPP was stratified by PV history and age. Compared with PV, GPP was significantly associated with prolonged hospitalization (11.7 vs. 10.3 day, p < 0.001), elevated neutrophil lymphocyte ratio (NLR) (5.93 vs. 2.44, p < 0.001) and anemia (13.9% vs. 1.2%, p < 0.001). Moreover, GPP alone (without PV history) was a relatively severer subtype with higher temperature (37.6°C vs. 38.0°C, p = 0.002) and skin infections (5.2% vs. 11.4%, p = 0.019) than GPP with PV. For patients across different age, compared with juvenile patients, clinical features support a severer phenotype in middle-aged, including higher incidence of anaemia (7.5% vs. 16.0%, p = 0.023) and NLR score (3.83 vs. 6.88, p < 0.001). Interleukin-6 (r = 0.59), high density lipoprotein cholesterol (r = -0.56), albumin (r = -0.53) and C-reactive protein-to-albumin ratio (r = 0.49) were the most relevant markers of severity in GPP alone, GPP with PV, juvenile and middle-aged GPP, respectively. This retrospective cohort suggests that GPP is highly heterogeneous and GPP alone and middle-aged GPP exhibit severe disease phenotypes. More attention on the heterogeneity of this severe disease is warranted to meet the unmet needs and promote the individualized management of GPP.

The Interaction of Borrelia burgdorferi with Human Dendritic Cells: Functional Implications

Dendritic cells bridge the innate and adaptive immune responses by serving as sensors of infection and as the primary APCs responsible for the initiation of the T cell response against invading pathogens. The naive T cell activation requires the following three key signals to be delivered from dendritic cells: engagement of the TCR by peptide Ags bound to MHC molecules (signal 1), engagement of costimulatory molecules on both cell types (signal 2), and expression of polarizing cytokines (signal 3). Initial interactions between Borrelia burgdorferi, the causative agent of Lyme disease, and dendritic cells remain largely unexplored. To address this gap in knowledge, we cultured live B. burgdorferi with monocyte-derived dendritic cells (mo-DCs) from healthy donors to examine the bacterial immunopeptidome associated with HLA-DR. In parallel, we examined changes in the expression of key costimulatory and regulatory molecules as well as profiled the cytokines released by dendritic cells when exposed to live spirochetes. RNA-sequencing studies on B. burgdorferi-pulsed dendritic cells show a unique gene expression signature associated with B. burgdorferi stimulation that differs from stimulation with lipoteichoic acid, a TLR2 agonist. These studies revealed that exposure of mo-DCs to live B. burgdorferi drives the expression of both pro- and anti-inflammatory cytokines as well as immunoregulatory molecules (e.g., PD-L1, IDO1, Tim3). Collectively, these studies indicate that the interaction of live B. burgdorferi with mo-DCs promotes a unique mature DC phenotype that likely impacts the nature of the adaptive T cell response generated in human Lyme disease.

A viewpoint on the genetic determinants of generalised pustular psoriasis

Generalised pustular psoriasis (GPP) is a rare and severe neutrophilic skin disorder, manifesting with acute episodes of pustulation and systemic upset. The discovery of recessive IL36RN mutations associated with GPP has transformed our understanding of disease drivers, paving the way for the development of targeted anti-IL36 therapeutics. In the light of these remarkable successes, this viewpoint reviews the significance of IL36RN mutations in GPP, their functional impact and their correlation with clinical phenotypes. It then covers the discovery of further genetic determinants (recessive MPO mutations) and risk factors (AP1S3 and CARD14 low-frequency variants) for the disease. It discusses the growing evidence for genetic complexity in GPP and concludes by outlining collaborative strategies that may be adopted to overcome the challenges ahead.

Prevalence, comorbidities and mortality of generalized pustular psoriasis: A literature review

Generalized pustular psoriasis (GPP) is a rare auto-inflammatory skin disease characterised by acute episodes of sterile pustule formation. Diagnosis and treatment of the disease have historically been complicated by a lack of awareness, and no consistent global definition or clinical coding standards. Now acknowledged as a distinct clinical entity with a recognised genetic component, GPP can take a serious and life-threatening course due to systemic inflammatory complications and its association with various comorbidities. As with other rare diseases, there are significant challenges to understanding the epidemiology of GPP, notably a small patient population, non-standardised study methodologies and ethnic differences in its presentation. A clearer understanding of GPP is therefore required for clinicians to better manage patients with this rare condition. In this review article, we present an overview of the available data on GPP prevalence estimates in key demographics and report the frequency of genetic mutations associated with the disease. We detail the incidence of known comorbidities and summarise the data on mortality and assigned causes of death. Lastly, we discuss the various factors that impact the collection, interpretation and comparison of these data.

Immunogenic self-peptides - the great unknowns in autoimmunity: Identifying T-cell epitopes driving the autoimmune response in autoimmune diseases

HLA-associated autoimmune diseases likely arise from T-cell-mediated autoimmune responses against certain self-peptides from the broad HLA-presented immunopeptidomes. The limited knowledge of the autoimmune target peptides has so far compromised the basic understanding of autoimmune pathogenesis. This is due to the complexity of antigen processing and presentation as well as the polyspecificity of T-cell receptors (TCRs), which pose high methodological challenges on the discovery of immunogenic self-peptides. HLA-class I molecules present peptides to CD8⁺ T cells primarily derived from cytoplasmic proteins. Therefore, HLA-class I-restricted autoimmune responses should be directed against target cells expressing the corresponding parental protein. In HLA-class II-associated diseases, the origin of immunogenic peptides is not pre-specified, because peptides presented by HLA-class II molecules to CD4⁺ T cells may originate from both extracellular and cellular self-proteins. The different origins of HLA-class I and class II presented peptides determine the respective strategy for the discovery of immunogenic self-peptides in approaches based on the TCRs isolated from clonally expanded pathogenic T cells. Both involve identifying the respective restricting HLA allele as well as determining the recognition motif of the TCR under investigation by peptide library screening, which is required to search for homologous immunogenic self-peptides. In HLA-class I-associated autoimmune diseases, identification of the target cells allows for defining the restricting HLA allotype from the 6 different HLA-class I alleles of the individual HLA haplotype. It furthermore limits the search for immunogenic self-peptides to the transcriptome or immunopeptidome of the target cells, although neoepitopes generated by peptide splicing or translational errors may complicate identification. In HLA class II-associated autoimmune diseases, the lack of a defined target cell and differential antigen processing in different antigen-presenting cells complicate identification of the HLA restriction of autoreactive TCRs from CD4⁺ T cells. To avoid that all corresponding HLA-class II allotypes have to be included in the peptide discovery, autoantigens defined by autoantibodies can guide the search for immunogenic self-peptides presented by the respective HLA-class II risk allele. The objective of this article is to highlight important aspects to be considered in the discovery of immunogenic self-peptides in autoimmune diseases.

Pustular psoriasis with a focus on generalized pustular psoriasis: classification and diagnostic criteria. An Italian expert consensus

Generalized pustular psoriasis (GPP) is a severe and life-threatening systemic disease associated with significant morbidity and mortality. Recent progress has been made in understanding the pathogenetic pathways involved in GPP and an intricate interaction between innate and adaptive immune mechanisms has been suggested. Despite formal consensus guidelines on pustular psoriasis currently available in the literature, the definitions and classifications of GPP used across studies were inconsistent. Consequently, there are no unified criteria that can be universally adopted for precise diagnosis, classification and effective treatment of GPP patients with new targeted drugs. The aim of this review was to collect all the main evidence on available diagnostic criteria for GPP and to establish recommendations in order to promote a better stratification and therapeutic management of this severe and heterogeneous disease.

Plasma Levels of Interleukins 36α, 36β, and 37 in Patients with Psoriasis and Their Correlation with Disease Activity Parameters

Psoriasis is a chronic, proliferative, inflammatory skin disease characterised by skin lesions and systemic symptoms. Numerous cytokines are produced in psoriasis as a result of inflammation. The aim of this study was to examine the plasma concentrations of IL-36α, IL-36β, and IL-37 in psoriasis and their correlations with disease activity parameters. This study recruited 84 individuals, 53 with plaque-type psoriasis and 31 healthy controls. The plaque type of psoriasis is the most common type and is typically characterized by circular-to-oval red plaques distributed over body surfaces of the extremities and scalp. In patients with psoriasis, we observed statistically significantly decreased plasma concentrations of IL-36β and IL-37. The concentrations of IL-36α were increased in comparison with control group. The plasma concentrations of IL-36α and IL-36β were statistically significantly correlated with all tested parameters of disease activity: the Psoriasis Activity Severity Index, Dermatology Life Quality Index, and Body Surface Area Index. There were no statistically significant correlations between plasma levels of IL-37 and the tested parameters of disease activity. These results indicate a role of IL36α, IL-36β, and IL-37 in the pathogenesis of psoriasis.

Generalized pustular psoriasis: the new era of treatment with IL-36 receptor inhibitors

Generalized pustular psoriasis (GPP) is a rare yet severe variant of psoriasis, characterized by the eruption of superficial sterile pustules that appear suddenly and widely distributed, potentially life-threatening. It more commonly presents through recurrent acute flares triggered by stress, corticosteroid withdrawals, pregnancy, or infections. The pathogenesis of this disease is yet to be fully understood. Nevertheless, studies have suggested an important role of an IL-1 subfamily of cytokines, due to an imbalance of the IL-36 axis favoring of pro-inflammatory activity. The therapeutic intervention for this condition is still a challenge as its rarity and scarce available information contribute to the absence of specific treatment. Current options stand on small, open-label trials or follows standard treatment for plaque psoriasis. Spesolimab and imsidolimab are two IL-36 receptor inhibitors which completed phase 1 and 2 trials with a good efficacy and safety profile in the treatment of this disease, including in the fast control of its acute flares. The most common adverse events reported with spesolimab were mild to moderate infections, and imsidolimab was well tolerated. GPP clinical trials remain to have their small sample size as a major limitation, but IL-36 receptor inhibitors are promising therapeutic options currently under investigation.

Generalized pustular psoriasis: overview of the status quo and results of a panel discussion

Generalized pustular psoriasis (GPP) is a rare, severe, potentially life-threatening, autoinflammatory, neutrophilic skin disease that may be accompanied by fever and leukocytosis. This paper describes the current state of knowledge on GPP in terms of classification, (differential) diagnosis and prevalence. We present a comparison of the genetics and pathoimmunology of GPP and psoriasis vulgaris with the central mechanisms of autoimmunology and autoinflammation. The currently available therapeutic options, expert recommendations for therapy, and data from early clinical trials investigating targeted therapies will be summarized. We present the results of our discussion with 13 experts for psoriasis vulgaris and GPP and give an integrated overview of indication and therapy based on our personal experience and present an outlook on further research questions. Collectively, this article highlights the high unmet need in GPP, as there exists no satisfactory method of diagnosis or treatment to date and new treatment options will be of great therapeutic benefit to those affected.

Enhanced Migratory Ability of Neutrophils Toward Epidermis Contributes to the Development of Psoriasis via Crosstalk With Keratinocytes by Releasing IL-17A

Microabscess of neutrophils in epidermis is one of the histological hallmarks of psoriasis. The axis of neutrophil–keratinocyte has been thought to play a critical role in the pathogenesis of psoriasis. However, the features and mechanism of interaction between the two cell types remain largely unknown. Herein, we found that blood neutrophils were increased in psoriasis patients, positively correlated with disease severity and highly expressed CD66b, but not CD11b and CD62L compared to healthy controls. Keratinocytes expressed high levels of psoriasis-related inflammatory mediators by direct and indirect interaction with neutrophils isolated from psoriasis patients and healthy controls. The capacity of neutrophils in provoking keratinocytes inflammatory response was comparable between the two groups and is dependent on IL-17A produced by itself. Neutrophils isolated from psoriasis patients displayed more transcriptome changes related to integrin and increased migration capacity toward keratinocytes with high CD11b expression on cell surface. Of interest, neutrophils were more susceptible to keratinocyte stimulation than to fibroblasts and human umbilical vein endothelial cells (HUVECs) in terms of CD11b expression and the production of ROS and NETs. In conclusion, neutrophils from psoriasis patients gain a strong capacity of IL-17A production and integrins expression that possibly facilitates their abilities to promote production of psoriasis-related inflammatory mediators and migration, a phenomenon likely induced by their interaction with keratinocytes but not with fibroblasts. These findings provide a proof-of-concept that development of new drugs targeting migration of neutrophils could be a more specific and safe solution to treat psoriasis.

The Protective Role of IL-36/IL-36R Signal in Con A-Induced Acute Hepatitis

The IL-36 family, including IL-36α, IL-36β, IL-36γ, and IL-36R antagonist, belong to the IL-1 superfamily. It was reported that IL-36 plays a role in immune diseases. However, it remains unclear how IL-36 regulates inflammation. To determine the role of IL-36/IL-36R signaling pathways, we established an acute hepatitis mouse model (C57BL/6) by i.v. injection of the plant lectin Con A. We found that the levels of IL-36 were increased in the liver after Con A injection. Our results demonstrated the infiltrated neutrophils, but not the hepatocytes, were the main source of IL-36 in the liver. Using the IL-36R-/- mouse model (H-2b), we surprisingly found that the absence of IL-36 signals led to aggravated liver injury, as evidenced by increased mortality, elevated serum alanine aminotransferase and aspartate aminotransferase levels, and severe liver pathological changes. Further investigations demonstrated that a lack of IL-36 signaling induced intrahepatic activation of CD4+ and CD8+ T lymphocytes and increased the production of inflammatory cytokines. In addition, IL-36R-/- mice had reduced T regulatory cell numbers and chemokines in the liver. Together, our results from the mouse model suggested a vital role of IL-36 in regulating T cell function and homeostasis during liver inflammation.

The Immunological Impact of IL-1 Family Cytokines on the Epidermal Barrier

The skin barrier would not function without IL-1 family members, but their physiological role in the immunological aspects of skin barrier function are often overlooked. This review summarises the role of IL-1 family cytokines (IL-1α, IL-1β, IL-1Ra, IL-18, IL-33, IL-36α, IL-36β, IL-36γ, IL-36Ra, IL-37 and IL-38) in the skin. We focus on novel aspects of their interaction with commensals and pathogens, the important impact of proteases on cytokine activity, on healing responses and inflammation limiting mechanisms. We discuss IL-1 family cytokines in the context of IL-4/IL-13 and IL-23/IL-17 axis-driven diseases and highlight consequences of human loss/gain of function mutations in activating or inhibitory pathway molecules. This review highlights recent findings that emphasize the importance of IL-1 family cytokines in both physiological and pathological cutaneous inflammation and emergent translational therapeutics that are helping further elucidate these cytokines.

Treatment Options and Goals for Patients with Generalized Pustular Psoriasis

Generalized pustular psoriasis (GPP) is a rare, severe neutrophilic skin disorder characterized by sudden widespread eruption of superficial sterile pustules with or without systemic inflammation. GPP flares can be life-threatening if untreated due to potential severe complications such as cardiovascular failure and serious infections. Currently, there are no GPP-specific therapies approved in the USA or Europe. Retinoids, cyclosporine, and methotrexate are the most commonly used non-biologic therapies for GPP. The evidence that supports the currently available treatment options is mainly based on case reports and small, open-label, single-arm studies. However, recent advances in our understanding of the pathogenic mechanisms of GPP and the identification of gene mutations linked to the disease have paved the way for the development of specific targeted therapies that selectively suppress the autoinflammatory and autoimmune mechanisms induced during GPP flares. Several biologic agents that target key cytokines involved in the activation of inflammatory pathways, such as tumor necrosis factor-α blockers and interleukin (IL)-17, IL-23, and IL-12 inhibitors, have emerged as potential treatments for GPP, with several being approved in Japan. The evidence supporting the efficacy of these agents is mainly derived from small, uncontrolled trials. A notable recent advance is the discovery of IL36RN mutations and the central role of IL-36 receptor ligands in the pathogenesis of GPP, which has defined key therapeutic targets for the disease. Biologic agents that target the IL-36 pathway have demonstrated promising efficacy in patients with GPP, marking the beginning of a new era of targeted therapy for GPP.

Transcriptomes of MPO-deficient patients with generalized pustular psoriasis reveals expansion of CD4+ cytotoxic T cells and an involvement of the complement system

Generalized pustular psoriasis (GPP) is a severe psoriatic subtype characterized by epidermal neutrophil infiltration. Although variants in IL36RN and MPO have been shown to affect immune cells, a systematic analysis of neutrophils and peripheral blood mononuclear cells (PBMCs) subsets and their differential gene expression dependent on MPO genotypes was not performed yet. We assessed transcriptomes of MPO-deficient patients using single cell RNA-sequencing (scRNAseq) of PBMCs and RNA-sequencing of neutrophils in stable disease state. Cell type annotation by multimodal reference mapping of scRNAseq data was verified by flow cytometry of surface and intracellular markers; proportions of CD4⁺ cytotoxic T-lymphocytes (CTLs) and other CD4⁺ effector cells were increased in GPP, while frequencies of naïve CD4⁺ T cells were significantly lower. The expression of FGFBP2 marking CD4⁺ CTLs and CD8⁺ effector memory T-cells (TEMs) was elevated in GPP patients with disease-contributing variants compared to non-carriers (p=0.0015). In neutrophils, differentially expressed genes (DEGs) were significantly enriched in genes of the classical complement activation pathway. Future studies assessing affected cell-types and pathways will show their contribution to GPP's pathogenesis, and indicate whether findings can be transferred to the acute epidermal situation and whether depletion or inactivation of CD4⁺ CTLs may be a reasonable therapeutic approach.

Pustular psoriasis as an autoinflammatory keratinization disease (AiKD): Genetic predisposing factors and promising therapeutic targets

Pustular psoriasis is a chronic inflammatory skin disease characterized by erythematous plaques with sterile pustules. It includes the distinct clinical entities generalized pustular psoriasis (GPP), acrodermatitis continua of Hallopeau (ACH) and palmoplantar pustular psoriasis (PPPP). Recently clarified pathomechanisms of pustular psoriasis indicate that hyperactivation of the skin innate immunity, including of the IL-1/IL-36 axis, plays an important role in the pathogenesis of pustular psoriasis. Autoinflammatory keratinization disease (AiKD) is the umbrella clinical entity for inflammatory keratinization disorders with genetic autoinflammatory pathomechanisms, and pustular psoriasis is a representative AiKD. To date, mutations/variants in five genes-IL36RN, CARD14, AP1S3, MPO and SERPINA3-have been reported to be genetic causative or predisposing factors for pustular psoriasis. The pathogenic mechanisms induced by the mutations/variants in these genes are all closely related to the excessive activation of skin innate immunity and autoinflammation. A number of biologics (e.g., tumor necrosis factor inhibitors, IL-17/IL-17 receptor inhibitors and IL-23 inhibitors) and granulocyte and monocyte adsorption apheresis are used to treat pustular psoriasis. Recently, based on novel information on the pathomechanisms of pustular psoriasis, which are mainly associated with autoinflammation, inhibitors of several pathogenic pathways, including of the IL-1, IL-36, IL-8 and granulocyte colony-stimulating factor signaling pathways, have been studied as emerging treatments.

Pustular Psoriasis: From Pathophysiology to Treatment

Pustular psoriasis (PP) is a clinicopathological entity encompassing different variants, i.e., acute generalized PP (GPP), PP of pregnancy (impetigo herpetiformis), annular (and circinate) PP, infantile/juvenile PP, palmoplantar PP/palmoplantar pustulosis, and acrodermatitis continua of Hallopeau (ACH), which have in common an eruption of superficial sterile pustules on an erythematous base. Unlike psoriasis vulgaris, in which a key role is played by the adaptive immune system and interleukin (IL)-17/IL-23 axis, PP seems to be characterized by an intense inflammatory response resulting from innate immunity hyperactivation, with prominent involvement of the IL-36 axis. Some nosological aspects of PP are still controversial and debated. Moreover, owing to the rarity and heterogeneity of PP forms, data on prognosis and therapeutic management are limited. Recent progresses in the identification of genetic mutations and immunological mechanisms have promoted a better understanding of PP pathogenesis and might have important consequences on diagnostic refinement and treatment. In this narrative review, current findings in the pathogenesis, classification, clinical features, and therapeutic management of PP are briefly discussed.

ERAP1 Controls the Autoimmune Response against Melanocytes in Psoriasis by Generating the Melanocyte Autoantigen and Regulating Its Amount for HLA-C*06:02 Presentation

Autoimmune diseases develop when autoantigens activate previously quiescent self-reactive lymphocytes. Gene-gene interaction between certain HLA class I risk alleles and variants of the endoplasmic reticulum aminopeptidase ERAP1 controls the risk for common immune-mediated diseases, including psoriasis, ankylosing spondylitis, and Behçet disease. The functional mechanisms underlying this statistical association are unknown. In psoriasis, HLA-C*06:02 mediates an autoimmune response against melanocytes by autoantigen presentation. Using various genetically modified cell lines together with an autoreactive psoriatic TCR in a TCR activation assay, we demonstrate in this study that in psoriasis, ERAP1 generates the causative melanocyte autoantigen through trimming N-terminal elongated peptide precursors to the appropriate length for presentation by HLA-C*06:02. An ERAP1 risk haplotype for psoriasis produced the autoantigen much more efficiently and increased HLA-C expression and stimulation of the psoriatic TCR by melanocytes significantly more than a protective haplotype. Compared with the overall HLA class I molecules, cell surface expression of HLA-C decreased significantly more upon ERAP1 knockout. The combined upregulation of ERAP1 and HLA-C on melanocytes in psoriasis lesions emphasizes the pathogenic relevance of their interaction in patients. We conclude that in psoriasis pathogenesis, the increased generation of an ERAP1-dependent autoantigen by an ERAP1 risk haplotype enhances the likelihood that autoantigen presentation by HLA-C*06:02 will exceed the threshold for activation of potentially autoreactive T cells, thereby triggering CD8+ T cell-mediated autoimmune disease. These data identify ERAP1 function as a central checkpoint and promising therapeutic target in psoriasis and possibly other HLA class I-associated diseases with a similar genetic predisposition.

Pustular psoriasis: Molecular pathways and effects of spesolimab in generalized pustular psoriasis

BACKGROUND

The IL-36 pathway plays a key role in the pathogenesis of generalized pustular psoriasis (GPP). In a proof-of-concept clinical trial, treatment with spesolimab, an anti-IL-36 receptor antibody, resulted in rapid skin and pustular clearance in patients presenting with GPP flares.

OBJECTIVE

We sought to compare the molecular profiles of lesional and nonlesional skin from patients with GPP or palmoplantar pustulosis (PPP) with skin from healthy volunteers, and to investigate the molecular changes after spesolimab treatment in the skin and blood of patients with GPP flares.

METHODS

Pre- and post-treatment skin and blood samples were collected from patients with GPP who participated in a single-arm, phase I study (n = 7). Skin biopsies from patients with PPP (n = 8) and healthy volunteers (n = 16) were obtained for comparison at baseline. Biomarkers were assessed by RNA-sequencing, histopathology, and immunohistochemistry.

RESULTS

In GPP and PPP lesions, 1287 transcripts were commonly upregulated or downregulated. Selected transcripts from the IL-36 signaling pathway were upregulated in untreated GPP and PPP lesions. In patients with GPP, IL-36 pathway-related signatures, T_H1/T_H17 and innate inflammation signaling, neutrophilic mediators, and keratinocyte-driven inflammation pathways were downregulated by spesolimab as early as week 1. Spesolimab also decreased related serum biomarkers and cell populations in the skin lesions from patients with GPP, including CD3⁺ T, CD11c⁺, and IL-36γ⁺ cells and lipocalin-2-expressing cells.

CONCLUSIONS

In patients with GPP, spesolimab showed rapid modulation of commonly dysregulated molecular pathways in GPP and PPP, which may be associated with improved clinical outcomes.

Generalized Pustular Psoriasis: Divergence of Innate and Adaptive Immunity

Generalized pustular psoriasis (GPP) is a severe, relapsing, immune-mediated disease characterized by the presence of multiple sterile pustules all over the body. The exact pathomechanisms behind GPP remain elusive, although increased interest in the genetic basis and immunological disturbances have provided some revealing insights into the underlying signaling pathways and their mutual interaction. The genetic background of GPP has been thoroughly investigated over the past few years. The conducted studies have identified genetic variants that predispose to pustular forms of psoriasis. The loss-of-function mutation of the interleukin 36 receptor antagonist gene, along with rare gain-of-function mutations in the gene that encodes the keratinocyte signaling molecule (CARD14), are examples of the uncovered abnormalities. Interleukin 36 (IL-36), along with neutrophils, is now considered a central cytokine in GPP pathogenesis, with IL-36 signaling providing a link between innate and adaptive immune responses. More recently, a new concept of inflammation, caused by a predominantly genetically determined abnormal activation of innate immune response and leading to inflammatory keratinization, has arisen. GPP is currently considered a representative of this novel group of skin conditions, called autoinflammatory keratinization diseases. As no therapeutic agents have been approved for GPP to date in the United States and Europe, the novel anti-IL-36R antibodies are particularly promising and may revolutionize management of the disease.

Antigen Processing, Presentation, and Tolerance: Role in Autoimmune Skin Diseases

Autoreactive T cells pose a constant risk for the emergence of autoimmune skin diseases in genetically predisposed individuals carrying certain HLA risk alleles. Immune tolerance mechanisms are opposed by broad HLA-presented self-immunopeptidomes, a predefined repertoire of polyspecific TCRs, the continuous generation of new antibody specificities by somatic recombination of Ig genes in B cells, and heightened proinflammatory reactivity. Increased autoantigen presentation by HLA molecules, cross-activation of pathogen-induced T cells against autologous structures, altered metabolism of self-proteins, and excessive production of proinflammatory signals may all contribute to the breakdown of immune tolerance and the development of autoimmune skin diseases.

Lesional activation of Tc 17 cells in Behçet's disease and psoriasis supports HLA-class I-mediated autoimmune responses

BACKGROUND

Behçet's disease (BD) presents with lymphocytic and neutrophilic vasculitis of unknown aetiology. HLA-B*51 ERAP1 and IL12R/IL23R are genetic risk factors. IL-23 regulates IL-17A, which controls recruitment and activation of neutrophils.

OBJECTIVES

To determine pathological changes in BD skin lesions related to the complex genetic predisposition METHODS: We characterised the expression of IL-17A and IL-23A in various cell types by immunohistological double staining of sections from papulopustular skin lesions (PPL) of acute attacks of BD and lesions of psoriasis vulgaris (PV), another HLA-class I-associated T-cell mediated autoimmune disease in which excessive T-cell derived IL-17A production promotes neutrophil activation.

RESULTS

We found that in BD lesions, as in psoriasis, actively expanding CD8⁺ T cells were the predominant source of IL-17A. IL-17A⁺ CD8⁺ T (Tc17) cells outnumbered infiltrating IL-17A⁺ CD4⁺ T cells. Unlike the epidermal localisation of CD8⁺ T cells in psoriasis, Tc17 cells in BD lesions infiltrated mainly the perivascular tissue and also the blood vessel walls of dermis and subcutaneous tissue. They colocalised with a marked IL-23A expression by CD11c⁺ dendritic cells (DCs) and CD68⁺ macrophages. IL-17A expression was associated with extensive recruitment of neutrophils around blood vessels that formed neutrophil extracellular traps (NETs).

CONCLUSIONS

In BD, the genetic predisposition may mediate antigen-specific activation and differentiation of a T_c 17 response, possibly targeting endothelial antigens. Neutrophils recruited by IL-17A in this process may enhance tissue damage by extensive NET formation (NETosis). Thus, the IL-23/IL-17 axis presumably controls neutrophilic inflammation in BD vasculitis in the context of a predominant antigen-specific CD8⁺ T-cell response.

Cigarette Smoke Underlies the Pathogenesis of Palmoplantar Pustulosis via an IL-17A-Induced Production of IL-36γ in Tonsillar Epithelial Cells

Palmoplantar pustulosis (PPP) is characterized by sterile pustules on the palms and soles. A strong association between PPP and tobacco smoking has been reported, and it has been speculated that the IL-17A pathway may play an important role in PPP. Recent studies have suggested that IL-36 plays a pivotal role in the pathogenesis of psoriasis and its subtypes. The relationships among IL-36, smoking, and PPP have not been examined. Here, we investigated the relationships among the smoking index, severity of the clinical condition of PPP, and in vitro dynamics of IL-36 in human tonsillar epithelial cells under the condition of exposure to a cigarette smoke extract. The results demonstrated that the Palmoplantar Pustulosis Area and Severity Index was strongly and positively correlated with the smoking index in female patients. Immunohistochemical examinations showed that IL-36γ was highly expressed in tonsillar epithelial cells from patients with PPP but not in those from patients with recurrent tonsillitis without PPP. The in vitro study revealed that IL-17A synergistically induced a release of IL-36γ under cigarette smoke extract exposure. These results suggest that local production of IL-36γ by epithelial cells induced by cigarette smoke exposure plays an important role in the pathogenesis of PPP.

Exploring the Role of IL-36 Cytokines as a New Target in Psoriatic Disease

Unmet needs in the treatment of psoriasis call for novel therapeutic strategies. Pustular psoriasis and psoriatic arthritis often represent a therapeutic challenge. Focus on IL-36 cytokines offers an interesting approach, as the IL-36 axis has been appointed a critical driver of the autoinflammatory responses involved in pustular psoriasis. Two IL-36R blocking antibodies, imsidolimab and spesolimab, are currently undergoing phase II and III clinical trials, with promising results.