CD8+ T cells in psoriatic lesions preferentially use T-cell receptor V beta 3 and/or V beta 13.1 genes

Etiopathogenesis of Psoriasis: Integration of Proposed Theories

Psoriasis is a chronic inflammatory disease characterized by squamous and erythematous plaques on the skin and the involvement of the immune system. Global prevalence for psoriasis has been reported around 1-3% with a higher incidence in adults and similar proportions between men and women. The risk factors associated with psoriasis are both extrinsic and intrinsic, out of which a polygenic predisposition is a highlight out of the latter. Psoriasis etiology is not yet fully described, but several hypothesis have been proposed: 1) the autoimmunity hypothesis is based on the over-expression of antimicrobial peptides such as LL-37, the proteins ADAMTSL5, K17, and hsp27, or lipids synthesized by the PLA2G4D enzyme, all of which may serve as autoantigens to promote the differentiation of autoreactive lymphocytes T and unleash a chronic inflammatory response; 2) dysbiosis of skin microbiota hypothesis in psoriasis has gained relevance due to the observations of a loss of diversity and the participation of pathogenic bacteria such as Streptococcus spp. or Staphylococcus spp. the fungi Malassezia spp. or Candida spp. and the virus HPV, HCV, or HIV in psoriatic plaques; 3) the oxidative stress hypothesis, the most recent one, describes that the cell injury and the release of proinflammatory mediators and antimicrobial peptides that leads to activate of the Th1/Th17 axis observed in psoriasis is caused by a higher release of reactive oxygen species and the imbalance between oxidant and antioxidant mechanisms. This review aims to describe the mechanisms involved in the three hypotheses on the etiopathogeneses of psoriasis.

Multiple environmental antigens may trigger autoimmunity in psoriasis through T-cell receptor polyspecificity

Introduction

Psoriasis is a T-cell mediated autoimmune skin disease. HLA-C*06:02 is the main psoriasis-specific risk gene. Using a Vα3S1/Vβ13S1 T-cell receptor (TCR) from a lesional psoriatic CD8+ T-cell clone we had discovered that, as an underlying pathomechanism, HLA-C*06:02 mediates an autoimmune response against melanocytes in psoriasis, and we had identified an epitope from ADAMTS-like protein 5 (ADAMTSL5) as a melanocyte autoantigen. The conditions activating the psoriatic autoimmune response in genetically predisposed individuals throughout life remain incompletely understood. Here, we aimed to identify environmental antigens that might trigger autoimmunity in psoriasis because of TCR polyspecificity.

Methods

We screened databases with the peptide recognition motif of the Vα3S1/Vβ13S1 TCR for environmental proteins containing peptides activating this TCR. We investigated the immunogenicity of these peptides for psoriasis patients and healthy controls by lymphocyte stimulation experiments and peptide-loaded HLA-C*06:02 tetramers.

Results

We identified peptides from wheat, Saccharomyces cerevisiae, microbiota, tobacco, and pathogens that activated both the Vα3S1/Vβ13S1 TCR and CD8+ T cells from psoriasis patients. Using fluorescent HLA-C*06:02 tetramers loaded with ADAMTSL5 or wheat peptides, we find that the same CD8+ T cells may recognize both autoantigen and environmental antigens. A wheat-free diet could alleviate psoriasis in several patients.

Discussion

Our results show that due to TCR polyspecificity, several environmental antigens corresponding to previously suspected psoriasis risk conditions converge in the reactivity of a pathogenic psoriatic TCR and might thus be able to stimulate the psoriatic autoimmune response against melanocytes. Avoiding the corresponding environmental risk factors could contribute to the management of psoriasis.

Discovery of natural bispecific antibodies: Is psoriasis induced by a toxigenic Corynebacterium simulans and maintained by CIDAMPs as autoantigens?

The high abundance of Corynebacterium simulans in psoriasis skin suggests a contribution to the psoriasis aetiology. This hypothesis was tested in an exploratory study, where western blot (WB) analyses with extracts of heat-treated C. simulans and psoriasis serum-derived IgG exhibited a single 16 kDa-WB-band. Proteomic analyses revealed ribosomal proteins as candidate C. s.-antigens. A peptidomic analysis unexpectedly showed that psoriasis serum-derived IgG already contained 31 immunopeptides of Corynebacteria ssp., suggesting the presence of natural bispecific antibodies (BsAbs). Moreover, peptidomic analyses gave 372 DECOY-peptides with similarity to virus- and phage proteins, including Corynebacterium diphtheriae phage, and similarity to diphtheria toxin. Strikingly, a peptidomic analysis for human peptides revealed 64 epitopes of major psoriasis autoantigens such as the spacer region of filaggrin, hornerin repeats and others. Most identified immunopeptides represent potential cationic intrinsically disordered antimicrobial peptides (CIDAMPs), which are generated within the epidermis. These may form complexes with bacterial disordered protein regions, representing chimeric antigens containing discontinuous epitopes. In addition, among 128 low-abundance immunopeptides, 48 are putatively psoriasis-relevant such as epitope peptides of PGE2-, vitamin D3- and IL-10-receptors. Further, 47 immunopeptides originated from tumour antigens, and the endogenous retrovirus HERV-K. I propose that persistent infection with a toxigenic C. simulans initiates psoriasis, which is exacerbated as an autoimmune disease by CIDAMPs as autoantigens. The discovery of natural BsAbs allows the identification of antigen epitopes from microbes, viruses, autoantigens and tumour-antigens, and may help to develop epitope-specific peptide-vaccines and therapeutic approaches with antigen-specific regulatory T cells to improve immune tolerance in an autoimmune disease-specific-manner.

Assessment of Treatment-Relevant Immune Biomarkers in Psoriasis and Atopic Dermatitis: Toward Personalized Medicine in Dermatology

Immunologically targeted therapies have revolutionized the treatment of inflammatory dermatoses, including atopic dermatitis and psoriasis. Although immunologic biomarkers hold great promise for personalized classification of skin disease and tailored therapy selection, there are no approved or widely used approaches for this in dermatology. This review summarizes the translational immunologic approaches to measuring treatment-relevant biomarkers in inflammatory skin conditions. Tape strip profiling, microneedle-based biomarker patches, molecular profiling from epidermal curettage, RNA in situ hybridization tissue staining, and single-cell RNA sequencing have been described. We discuss the advantages and limitations of each and open questions for the future of personalized medicine in inflammatory skin disease.

Complimentary electrostatics dominate T Cell Receptor binding to a psoriasis-associated-peptide-antigen presented by Human Leukocyte Antigen (HLA) C*06:02

Psoriasis is a chronic skin disease characterised by hyperproliferative epidermal lesions infiltrated by autoreactive T cells. Individuals expressing the Human Leukocyte antigen (HLA) C*06:02 allele are at highest risk for developing psoriasis. An autoreactive T cell clone (termed Vα3S1/Vβ13S1) isolated from psoriatic plaques is selective for HLA-C*06:02-presenting a peptide derived from the melanocyte-specific auto-antigen ADAMTSL5 (VRSRRCLRL). Here we determine the crystal structure of this psoriatic TCR-HLA-C*06:02- ADAMTSL5 complex with a stabilised peptide. Docking of the TCR involves an extensive complementary charge network formed between negatively charged TCR residues interleaving with exposed arginine residues from the self-peptide and the HLA-C*06:02 α1 helix. We probed these interactions through mutagenesis and activation assays. The charged interface spans the polymorphic region of the C1/C2 HLA group. Notably the peptide binding groove of HLA C*06:02 appears exquisitely suited for presenting highly charged Arg-rich epitopes recognised by this acidic psoriatic TCR. Overall, we provide a structural basis for understanding engagement of melanocyte antigen-presenting cells by a TCR implicated in psoriasis, while simultaneously expanding our knowledge of how TCRs engage HLA-C.

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.

The biological basis of disease recurrence in psoriasis: a historical perspective and current models

A key challenge in psoriasis therapy is the tendency for lesions to recur in previously affected anatomical locations after treatment discontinuation following lesion resolution. Available evidence supports the concept of a localized immunological ‘memory’ that persists in resolved skin after complete disappearance of visible inflammation, as well as the role of a specific subpopulation of T cells characterized by the dermotropic CCR4⁺ phenotype and forming a local memory. Increasing knowledge of the interleukin (IL)‐23/T helper 17 (Th17) cell pathway in psoriasis immunopathology is pointing away from the historical classification of psoriasis as primarily a Th1‐type disease. Research undertaken from the 1990s to the mid‐2000s provided evidence for the existence of a large population of CD8⁺ and CD4⁺ tissue‐resident memory T cells in resolved skin, which can initiate and perpetuate immune responses of psoriasis in the absence of T‐cell recruitment from the blood. Dendritic cells (DCs) are antigen‐presenting cells that contribute to psoriasis pathology via the secretion of IL‐23, the upstream regulator of Th17 cells, while plasmacytoid DCs are involved via IL‐36 signalling and type I interferon activation. Overall, the evidence discussed in this review indicates that IL‐23‐driven/IL‐17‐producing T cells play a critical role in psoriasis pathology and recurrence, making these cytokines logical therapeutic targets. The review also explains the clinical efficacy of IL‐17 and IL‐23 receptor blockers in the treatment of psoriasis.

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.

The Impact of the 'Mis-Peptidome' on HLA Class I-Mediated Diseases: Contribution of ERAP1 and ERAP2 and Effects on the Immune Response

The strong association with the Major Histocompatibility Complex (MHC) class I genes represents a shared trait for a group of autoimmune/autoinflammatory disorders having in common immunopathogenetic basis as well as clinical features. Accordingly, the main risk factors for Ankylosing Spondylitis (AS), prototype of the Spondyloarthropathies (SpA), the Behçet's disease (BD), the Psoriasis (Ps) and the Birdshot Chorioretinopathy (BSCR) are HLA-B*27, HLA-B*51, HLA-C*06:02 and HLA-A*29:02, respectively. Despite the strength of the association, the HLA pathogenetic role in these diseases is far from being thoroughly understood. Furthermore, Genome-Wide Association Studies (GWAS) have highlighted other important susceptibility factors such as Endoplasmic Reticulum Aminopeptidase (ERAP) 1 and, less frequently, ERAP2 that refine the peptidome presented by HLA class I molecules to CD8⁺ T cells. Mass spectrometry analysis provided considerable knowledge of HLA-B*27, HLA-B*51, HLA-C*06:02 and HLA-A*29:02 immunopeptidome. However, the combined effect of several ERAP1 and ERAP2 allelic variants could generate an altered pool of peptides accounting for the "mis-immunopeptidome" that ranges from suboptimal to pathogenetic/harmful peptides able to induce non-canonical or autoreactive CD8⁺ T responses, activation of NK cells and/or garbling the classical functions of the HLA class I molecules. This review will focus on this class of epitopes as possible elicitors of atypical/harmful immune responses which can contribute to the pathogenesis of chronic inflammatory diseases.

The TNF/IL-23/IL-17 axis-Head-to-head trials comparing different biologics in psoriasis treatment

Psoriasis is a T cell-mediated disease with autoimmune characteristics modulated by genetic susceptibility along with environmental triggers. Inflammatory pathways marked with excessive production of cytokines IL-12 and IL-23, drive differentiation of pathogenic T cell responses resulting in TNF and IL-17 production. These cytokines are an integral part of the TNF/IL-23/IL-17 axis, which is responsible for maintaining inflammation in psoriatic skin. Our improved understanding of the immunopathogenesis led to the development of biological drugs in the treatment of moderate-to-severe disease. Biologics have revolutionized the management of psoriasis, highlighting the central role of TNF/IL-23/IL-17 axis in the physiopathology of the disease. Still, psoriasis usually requires long-term treatment, aiming to fully remove psoriatic lesions without experiencing adverse events. In this review, we discuss the recent findings of all 27 available head-to-head trials investigating the efficacy and safety of systemic and biologic therapies in moderate-to-severe psoriasis vulgaris, as it is thought to provide more useful knowledge than placebo intervention alone. According to our evaluation, inhibitors that specifically target IL-23 or IL-17 are clinically more beneficial than inhibitors of IL-12/IL-23 and TNF. More informative results might be obtained by comparing these more efficient biological agents to each other. In addition, newer therapies for psoriasis using small-molecule drugs may represent important advances compared to well-established biologics as these are less expensive and orally administered.

Not your average joint: Towards precision medicine in psoriatic arthritis

Precision medicine, propelled by advances in multi-omics methods and analytics, aims to revolutionize patient care by using clinically-actionable molecular markers to guide diagnostic and therapeutic decisions. We describe the applications of precision medicine in risk stratification, drug selection, and treatment response prediction in psoriatic arthritis, for which targeted, personalized approaches are steadily emerging.

Circulating CD14+HLA-DR-/low Myeloid-Derived Suppressor Cells as Potential Biomarkers for the Identification of Psoriasis TCM Blood-Heat Syndrome and Blood-Stasis Syndrome

Psoriasis is a chronic autoimmune disease. Identification of the biomarkers responsible for Traditional Chinese Medicine (TCM) syndromes of psoriasis can help researchers recognize the different aspects of psoriasis and find novel therapeutic targets for the treatment of psoriasis. The current study investigated the levels of circulating Mo-MDSCs and Mo-MDSC-associated immune factors in the peripheral blood of psoriasis patients with different TCM syndromes. We found that the frequency of Mo-MDSCs (CD14⁺HLA-DR^−/low cells) among CD14⁺ cells from plaque psoriasis patients with blood-stasis (BS) syndrome was significantly increased when compared with healthy controls (p < 0.001) and blood-heat (BH) syndrome group (p < 0.001), respectively. However, serum IL-2, IL-4, IL-6, IL-10, IL-17A, TNF-α, IFN-γ, iNOS, Arg-1, and NO concentration showed no statistically significant difference between healthy controls and psoriasis patients as well as no significant difference between the BH and BS syndrome groups. Compared with healthy controls, the mRNA expression of Arg-1, TNF-α, ROR-γ, and PD-L1 was increased, while the mRNA expression of PD-1 and IL-10 was decreased in PBMCs from psoriasis patients. Moreover, the mRNA expression of TNF-α and FOXP3 in PBMCs showed a pronounced statistical difference between the psoriatic BH syndrome group and the BS syndrome group. Therefore, we provide evidence that the percentage of CD14⁺HLA-DR^−/low MDSC/ CD14⁺ cells and TNF-α and Foxp3 mRNA expression levels in PBMCs are potential biomarkers for distinguishing TCM BH syndrome and BS syndrome.

Adaptive and Innate Immunity in Psoriasis and Other Inflammatory Disorders

Over the past three decades, a considerable body of evidence has highlighted T cells as pivotal culprits in the pathogenesis of psoriasis. This includes the association of psoriasis with certain MHC (HLA) alleles, oligoclonal expansion of T cells in some cases, therapeutic response to T cell-directed immunomodulation, the onset of psoriasis following bone marrow transplantation, or induction of psoriasis-like inflammation by T cells in experimental animals. There is accumulating clinical and experimental evidence suggesting that both autoimmune and autoinflammatory mechanisms lie at the core of the disease. Indeed, some studies suggested antigenic functions of structural proteins, and complexes of self-DNA with cathelicidin (LL37) or melanocytic ADAMTSL5 have been proposed more recently as actual auto-antigens in some cases of psoriasis. These findings are accompanied by various immunoregulatory mechanisms, which we increasingly understand and which connect innate and adaptive immunity. Specific adaptive autoimmune responses, together with our current view of psoriasis as a systemic inflammatory disorder, raise the question of whether psoriasis may have connections to autoimmune or autoinflammatory disorders elsewhere in the body. While such associations have been suspected for many years, compelling mechanistic evidence in support of this notion is still scant. This review sets into context the current knowledge about innate and adaptive immunological processes in psoriasis and other autoimmune or autoinflammatory diseases.

The contribution of IL-17 to the development of autoimmunity in psoriasis

Psoriasis is an (auto)immune-mediated disease that manifests as widespread desquamative erythema. The TNF-α/IL-23/IL-17A axis is crucial to its pathogenesis, which is demonstrated by its excellent therapeutic response to biologics that target this axis. There is a strong association between HLA-C*0602 and psoriasis, and researchers have identified autoantigens that are restricted to this major histocompatibility class I molecule. These auto-Ags include LL-37, A disintegrin and metalloprotease domain containing thrombospondin type 1 motif-like 5 (ADAMTSL5), and keratin 17. IL-17A-producing T cells have been identified in T cell populations that are reactive to these auto-Ags. In addition, lipid Ags have surfaced as candidate auto-Ags that activate IL-17A-producing T cells in a CD1a-restricted manner. In this article, we review the candidate auto-Ags that may contribute to the activation of the IL-17A-deviated immune response in psoriasis.

2D Visualization of the Psoriasis Transcriptome Fails to Support the Existence of Dual-Secreting IL-17A/IL-22 Th17 T Cells

The present paradigm of psoriasis pathogenesis revolves around the IL-23/IL-17A axis. Dual-secreting Th17 T cells presumably are the predominant sources of the psoriasis phenotype-driving cytokines, IL-17A and IL-22. We thus conducted a meta-analysis of independently acquired RNA-seq psoriasis datasets to explore the relationship between the expression of IL17A and IL22. This analysis failed to support the existence of dual secreting IL-17A/IL-22 Th17 cells as a major source of these cytokines. However, variable relationships amongst the expression of psoriasis susceptibility genes and of IL17A, IL22, and IL23A were identified. Additionally, to shed light on gene expression relationships in psoriasis, we applied a machine learning nonlinear dimensionality reduction strategy (t-SNE) to display the entire psoriasis transcriptome as a 2-dimensonal image. This analysis revealed a variety of gene clusters, relevant to psoriasis pathophysiology but failed to support a relationship between IL17A and IL22. These results support existing theories on alternative sources of IL-17A and IL-22 in psoriasis such as a Th22 cells and non-T cell populations.

Origin, function and role in the development of skin diseases CLA+T-lymphocytes

The idea of CLA+T-lymphocytes, which are a special subpopulation of cells with a tropic to the skin, is given. The issues of maturation, migration and functional features of CLA+T-cells are considered. Special attention is paid to the different phenotype of memory T-cells. Modern data concerning the role of CLA+T-cells in the pathogenesis of autoimmune and allergic dermatoses, as well as malignant skin tumors are also presented. The conclusion about the necessity of further study of CLA +T-lymphocytes for detailed understanding of pathogenesis and search of variants of targeted therapy in psoriasis, atopic dermatitis, skin lymphomas and other skin diseases is made.

Autoimmunity and autoimmune co-morbidities in psoriasis

Psoriasis is characterized by widespread scaly erythematous plaques that cause significant physical and psychological burdens for the affected individuals. Accelerated inflammation driven by the tumour necrosis factor-α/interleukin-23/interleukin-17 axis is now known to be the major mechanism in the development of psoriasis. In addition, psoriasis has an autoimmune nature that manifests as autoreactive T cells and is co-morbid with other autoimmune diseases, such as autoimmune bullous diseases, vitiligo, alopecia and thyroiditis. In this article, we review the recent topics on autoimmunity and autoimmune co-morbidities in psoriasis.

Human Leukocyte Antigen-Class I Alleles and the Autoreactive T Cell Response in Psoriasis Pathogenesis

Psoriasis is a complex immune-mediated inflammatory skin disease characterized by T-cell-driven epidermal hyperplasia. It occurs on a strong genetic predisposition. The human leukocyte antigen (HLA)-class I allele HLA-C*06:02 on psoriasis susceptibility locus 1 (PSORS1 on 6p21.3) is the main psoriasis risk gene. Other HLA-class I alleles encoding HLA molecules presenting overlapping peptide repertoires show associations with psoriasis as well. Outside the major histocompatibility complex region, genome-wide association studies identified more than 60 psoriasis-associated common gene variants exerting only modest individual effects. They mainly refer to innate immune activation and the interleukin-23/T_h/c17 pathway. Given their strong risk association, explaining the role of the HLA-risk alleles is essential for elucidating psoriasis pathogenesis. Psoriasis lesions develop upon epidermal infiltration, activation, and expansion of CD8⁺ T cells. The unbiased analysis of a paradigmatic Vα3S1/Vβ13S1-T-cell receptor from a pathogenic epidermal CD8⁺ T-cell clone of an HLA-C*06:02⁺ psoriasis patient had revealed that HLA-C*06:02 directs an autoimmune response against melanocytes through autoantigen presentation, and it identified a peptide form ADAMTS-like protein 5 as an HLA-C*06:02-presented melanocyte autoantigen. These data demonstrate that psoriasis is an autoimmune disease, where the predisposing HLA-class I alleles promote organ-specific inflammation through facilitating a T-cell response against a particular skin-specific cell population. This review discusses the role of HLA-class I alleles in the pathogenic psoriatic T-cell immune response. It concludes that as a principle of T-cell driven HLA-associated inflammatory diseases proinflammatory traits promote autoimmunity in the context of certain HLA molecules that present particular autoantigens.

Psoriasis: A STAT3-Centric View

Signal Transducer and Activator of Transcription (STAT)3 has recently emerged as a key player in the development and pathogenesis of psoriasis and psoriatic-like inflammatory conditions. Indeed, STAT3 hyperactivation has been reported in virtually every cell type involved in disease initiation and maintenance, and this factor mediates the signal of most cytokines that are involved in disease pathogenesis, including the central Interleukin (IL)-23/IL-17/IL-22 axis. Despite the recent availability of effective biological agents (monoclonal antibodies) against IL-17 and IL-23, which have radically changed the current standard of disease management, the possibility of targeting either STAT3 itself or, even better, the family of upstream activators Janus kinases (JAK1, 2, 3, and TYK2) offers additional therapeutic options. Due to the oral/topical administration modality of these small molecule drugs, their lower cost, and the reduced risk of eliciting adverse immune responses, these compounds are being actively scrutinized in clinical settings. Here, we summarize the main pathological features of psoriatic conditions that provide the rationale for targeting the JAK/STAT3 axis in disease treatment.

Biomimetic nanoparticles for inflammation targeting

There have been many recent exciting developments in biomimetic nanoparticles for biomedical applications. Inflammation, a protective response involving immune cells, blood vessels, and molecular mediators directed against harmful stimuli, is closely associated with many human diseases. As a result, biomimetic nanoparticles mimicking immune cells can help achieve molecular imaging and precise drug delivery to these inflammatory sites. This review is focused on inflammation-targeting biomimetic nanoparticles and will provide an in-depth look at the design of these nanoparticles to maximize their benefits for disease diagnosis and treatment.

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

Generalized pustular psoriasis (GPP) is the most severe psoriasis variant. Mutations in the IL-36 antagonist IL36RN, in CARD14 or AP1S3 provide genetic evidence for autoinflammatory etiology but cannot explain its pathogenesis completely. Here we demonstrate that unopposed IL-36 signaling promotes antigen-driven and likely pathogenic T-helper type 17 (Th17) responses in GPP. We observed that CD4⁺ T cells in blood and skin lesions of GPP patients were characterized by intense hyperproliferation, production of the GPP key mediator, IL-17A, and highly restricted TCR repertoires with identical T-cell clones in blood and skin lesions, indicating antigen-driven T-cell expansions. The clonally expanded CD4⁺ T cells were major producers of IL-17A. IL-36 signaling substantially enhanced TCR-mediated proliferation of CD4⁺ T cells. Moreover, GPP patients showed preferences for HLA-DRB1∗14, HLA-DQB1∗05, and HLA-DQB1∗03. We conclude that in GPP unopposed IL-36 signaling and certain HLA-class II alleles may cooperate in promoting antigen-driven Th17 responses, which in the obvious absence of exogenous triggers may reflect autoimmune reactions. This study reveals a pathogenic pathway where innate immune dysregulation promotes T-cell-mediated inflammation in GPP.

Melanocytes: Target Cells of an HLA-C*06:02-Restricted Autoimmune Response in Psoriasis

HLA-C*06:02 is the main psoriasis risk allele. By the unbiased analysis of a Vα3S1/Vβ13S1 T-cell receptor from pathogenic psoriatic CD8⁺ T cells, we had recently proven that HLA-C*06:02 directs an autoimmune response against melanocytes through autoantigen presentation in psoriasis and identified ADAMTSL5 as a melanocyte autoantigen. We concluded that psoriasis is based on a melanocyte-specific immune response and that HLA-C*06:02 may predispose to psoriasis via this newly identified autoimmune pathway. Understanding this pathway, however, requires more detailed explanation. It is based on the fact that an HLA class I-restricted autoreactive CD8⁺ T-cell response must be directed against a particular target cell type, because HLA class I molecules present peptide antigens generated from cytoplasmic (i.e., intracellular) proteins. This review summarizes the findings on the melanocyte-specific autoimmune response in the context of the immune mechanisms related to HLA function and T-cell receptor-antigen recognition. Identifying melanocytes as target cells of the psoriatic immune response now explains psoriasis as a primary autoimmune skin disease.

Psoriasis pathogenesis and the development of novel targeted immune therapies

Psoriasis is caused by a complex interplay between the immune system, psoriasis-associated susceptibility loci, autoantigens, and multiple environmental factors. Over the last 2 decades, research has unequivocally shown that psoriasis represents a bona fide T cell-mediated disease primarily driven by pathogenic T cells that produce high levels of IL-17 in response to IL-23. The discovery of the central role for the IL-23/type 17 T-cell axis in the development of psoriasis has led to a major paradigm shift in the pathogenic model for this condition. The activation and upregulation of IL-17 in prepsoriatic skin produces a "feed forward" inflammatory response in keratinocytes that is self-amplifying and drives the development of mature psoriatic plaques by inducing epidermal hyperplasia, epidermal cell proliferation, and recruitment of leukocyte subsets into the skin. Clinical trial data for mAbs against IL-17 signaling (secukinumab, ixekizumab, and brodalumab) and newer IL-23p19 antagonists (tildrakizumab, guselkumab, and risankizumab) underscore the central role of these cytokines as predominant drivers of psoriatic disease. Currently, we are witnessing a translational revolution in the treatment and management of psoriasis. Emerging bispecific antibodies offer the potential for even better disease control, whereas small-molecule drugs offer future alternatives to the use of biologics and less costly long-term disease management.

Risks for Staphylococcus aureus colonization in patients with psoriasis: a systematic review and meta-analysis

Evidence on whether patients with psoriasis have a higher risk for staphylococcal colonization than healthy controls remains controversial. To synthesize the current literature, we performed a systematic review on the prevalence and relative risk (RR) of Staphylococcus aureus colonization in patients with psoriasis. We modified the QUADAS-2 instrument to assess the reporting quality of individual studies and applied random-effects models in meta-analysis. Overall we identified 21 eligible studies, of which 15 enrolled one or more comparison groups. The pooled prevalence of staphylococcal colonization in patients with psoriasis was 35·3% [95% confidence interval (CI) 25·0-45·6] on lesional skin and 39·2% (95% CI 33·7-44·8) in the nares. Patients with psoriasis were 4·5 times more likely to be colonized by S. aureus than healthy controls were on the skin (RR 5·54, 95% CI 3·21-9·57) and 60% more in the nares (RR 1·60, 95% CI 1·11-2·32). Cutaneous and nasal colonization by meticillin-resistant S. aureus also appeared higher in patients with psoriasis (pooled prevalence 8·6%) than in healthy controls (2·6%), yet the difference was not statistically significant (P = 0·74). In contrast, despite of a similar risk for nasal staphylococcal colonization (RR 0·67, 95% CI 0·38-1·18), patients with psoriasis were less likely to carry S. aureus on lesional skin than atopic patients (RR 0·64, 95% CI 0·40-1·02). In summarizing the current literature, we found that patients with psoriasis were at an increased risk for staphylococcal colonization compared with healthy individuals. Prospective studies on how bacterial loads correlate with disease activity can guide the clinical management of bacterial colonization while preventing the emergence of drug-resistant strains.

The molecular basis for peptide repertoire selection in the human leucocyte antigen (HLA) C*06:02 molecule

Human leukocyte antigen (HLA)-C*06:02 is identified as the allele associated with the highest risk for the development of the autoimmune skin disease psoriasis. However, the diversity and mode of peptide presentation by the HLA-C*06:02 molecule remains unclear. Here, we describe the endogenous peptide repertoire of ∼3,000 sequences for HLA-C*06:02 that defines the peptide-binding motif for this HLA allomorph. We found that HLA-C*06:02 predominantly presents nonamer peptides with dominant arginine anchors at the P2 and P7 positions and a preference for small hydrophobic residues at the C terminus (PΩ). To determine the structural basis of this selectivity, we determined crystal structures of HLA-C*06:02 in complex with two self-peptides (ARTELYRSL and ARFNDLRFV) and an analogue of a melanocyte autoantigen (ADAMTSL5, VRSRR-abu-LRL) implicated in psoriasis. These structures revealed that HLA-C*06:02 possesses a deep peptide-binding groove comprising two electronegative B- and E-pockets that coincide with the preference for P2 and P7 arginine anchors. The ADAMTSL5 autoantigen possessed a P7-Leu instead of the P7-Arg residue, but nevertheless was accommodated within the HLA-C*06:02 antigen-binding cleft. Collectively, our results provide the structural basis for understanding peptide repertoire selection in HLA-C*06:02.

Autoimmune aspects of psoriasis: Heritability and autoantigens

Chronic immune-mediated disorders (IMDs) constitute a major health burden. Understanding IMD pathogenesis is facing two major constraints: Missing heritability explaining familial clustering, and missing autoantigens. Pinpointing IMD risk genes and autoimmune targets, however, is of fundamental importance for developing novel causal therapies. The strongest association of all IMDs is seen with human leukocyte antigen (HLA) alleles. Using psoriasis as an IMD model this article reviews the pathogenic role HLA molecules may have within the polygenic predisposition of IMDs. It concludes that disease-associated HLA alleles account for both missing heritability and autoimmune mechanisms by facilitating tissue-specific autoimmune responses through autoantigen presentation.

Recent Highlights in Psoriasis Research

This article highlights recent advances in the immunology, epidemiology, and genetics/genomics of psoriasis. Advances sometimes generate more questions, and this article makes an attempt to point out where controversies might exist in the literature. Many of the articles mentioned were published in the Journal of Investigative Dermatology, but many articles from the broader scientific literature are also cited, to provide context and to add further validity for some of these key findings. Among the themes we explore are the identification of antigens in psoriasis, the co-morbidities of psoriasis, and novel integrative approaches to genome-wide association studies.

Cutaneous Expression of A Disintegrin-like and Metalloprotease domain containing Thrombospondin Type 1 motif-like 5 (ADAMTSL5) in Psoriasis goes beyond Melanocytes

A Disintegrin-like and Metalloprotease domain containing Thrombospondin type 1 motif-like 5 (ADAMTSL5) is a melanocyte-derived protein that has recently been implicated as an activating antigen for IL-17-producing T cells in psoriasis. There is a potential disconnect between the basal location of the melanocytes in the epidermis and the fact that T-cell infiltrates are seen mostly scattered in the epidermis with very large infiltrates in the dermis. Thus, we hypothesized that ADAMTSL5 may be expressed in other cells aside from melanocytes in skin. To further investigate the cutaneous expression of ADAMTSL5, we performed immunohistochemistry staining on lesional and nonlesional skin biopsies from psoriasis patients using three different commercially available antibodies. We confirmed that all ADAMTSL5 antibodies reacted with epidermal melanocytes. However, we also observed a strong expression of this protein in keratinocytes throughout the epidermis, and scattered expression in some dermal blood vessels and other perivascular dermal cells. Overall, the pattern of ADAMTSL5 expression is very similar to the infiltrating pattern of T-cells and dendritic cells in psoriasis lesions.

[Autoimmune reactions in psoriasis : Spotlight]

BACKGROUND

Psoriasis is a human leukocyte antigen (HLA)-associated T‑cell-mediated disorder.

OBJECTIVES

The role of the main psoriasis risk allele HLA-C*06:02 in disease manifestation and the mechanisms which activate the pathogenic T‑cell response in the skin of psoriasis patients remained elusive.

MATERIALS AND METHODS

Key to the immune pathogenesis of psoriasis was the analysis of the specificity of the infiltrating lesional psoriatic CD8(+) T cells

RESULTS AND CONCLUSION

Analyses of the lesional psoriatic T‑cell reactivity demonstrate that psoriasis is an autoimmune disease. It is based on an autoimmune response against melanocytes which is preferentially mediated by HLA-C*06:02 through autoantigen presentation. Here we discuss the mechanisms of this autoimmune response in the context of the polygenic psoriatic predisposition.

Melanocyte antigen triggers autoimmunity in human psoriasis

Psoriasis vulgaris is a common T cell-mediated inflammatory skin disease with a suspected autoimmune pathogenesis. The human leukocyte antigen (HLA) class I allele, HLA-C*06:02, is the main psoriasis risk gene. Epidermal CD8(+) T cells are essential for psoriasis development. Functional implications of HLA-C*06:02 and mechanisms of lesional T cell activation in psoriasis, however, remained elusive. Here we identify melanocytes as skin-specific target cells of an HLA-C*06:02-restricted psoriatic T cell response. We found that a Vα3S1/Vβ13S1 T cell receptor (TCR), which we had reconstituted from an epidermal CD8(+) T cell clone of an HLA-C*06:02-positive psoriasis patient specifically recognizes HLA-C*06:02-positive melanocytes. Through peptide library screening, we identified ADAMTS-like protein 5 (ADAMTSL5) as an HLA-C*06:02-presented melanocytic autoantigen of the Vα3S1/Vβ13S1 TCR. Consistent with the Vα3S1/Vβ13S1-TCR reactivity, we observed numerous CD8(+) T cells in psoriasis lesions attacking melanocytes, the only epidermal cells expressing ADAMTSL5. Furthermore, ADAMTSL5 stimulation induced the psoriasis signature cytokine, IL-17A, in CD8(+) T cells from psoriasis patients only, supporting a role as psoriatic autoantigen. This unbiased analysis of a TCR obtained directly from tissue-infiltrating CD8(+) T cells reveals that in psoriasis HLA-C*06:02 directs an autoimmune response against melanocytes through autoantigen presentation. We propose that HLA-C*06:02 may predispose to psoriasis via this newly identified autoimmune pathway.

Kv1.3 in psoriatic disease: PAP-1, a small molecule inhibitor of Kv1.3 is effective in the SCID mouse psoriasis--xenograft model

Kv1.3 channels regulate the activation/proliferation of effector memory T cells and thus play a critical role in the pathogenesis of autoimmune diseases. Using a combination of immunohistochemistry, confocal microscopy, flow cytometry and electrophysiology methods we observed a significant enrichment of activated Kv1.3(+) memory T cells in psoriasis plaques and synovial fluid from patients with psoriasis/psoriatic arthritis (PsA) compared to non-lesional psoriatic skin, normal skin or peripheral blood lympho-mononuclear cells. In in vitro studies performed with lesional mononuclear cells or T cells derived from skin and joints of psoriatic disease, the small molecule Kv1.3 blocker PAP-1 dose-dependently inhibited proliferation and suppressed IL-2 and IFN-γ production. To further substantiate the pathologic role of Kv1.3 high TEM cells in psoriatic disease we tested whether PAP-1 is able to improve psoriatic disease pathology in the SCID mouse-psoriasis skin xenograft model. Following four weeks of daily treatment with 2% PAP-1 ointment we noticed about 50% reduction in the epidermal thickness (rete peg length) and the number of CD3(+) lymphocytes/mm(2) of dermis decreased by 85%. Vehicle treated and untreated plaques in contrast remained unchanged and showed no reduction in epidermis thickness and infiltrating CD3(+) T cells and HLA-DR(+) T cells. Based on these results we propose the development of Kv1.3 targeted topical immunotherapy for psoriasis and possibly for other inflammatory skin conditions, where effector memory T cells are involved in the pathogenesis.

Psoriasis

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

Keratin 17 as a therapeutic target for the treatment of psoriasis

Keratin 17 (K17) is the only ectopically expressed keratin in psoriatic lesional epidermis. This review focuses mainly on reports that have addressed the mechanism of K17 up-regulation and its biological role in psoriasis. In addition to IFN-γ, IL-17A and IL-22, which are derived from Th17 and Th22 cells, could up-regulate K17 mRNA and protein levels in keratinocytes in a dose-dependent manner. Moreover, these effects are partially blocked with STAT1- and STAT3-specific inhibitors, as well as small interfering RNA (siRNA) targeting STAT1 and STAT3. On the other hand, the HLA DRB1*04 and/or *07 positive patients show significant T cell responses to two peptides from K17 protein selected on the basis of predicted HLA DRB1*04 and/or *07 bindings. One peptide contains the ALEEAN sequence, while the other peptide has an amino acid sequence that has not been previously reported. Analysis of these processes led us to propose the existence of a K17/T cells/cytokine autoimmune loop, in which ectopically expressed K17 impacts on the maintenance of psoriasis by activating autoreactive T cells. Furthermore, it has been found that altered peptide ligands, which are produced through single alanine residue substitutions at a critical TCR contact position, abolish the T cell proliferation and IFN-γ production induced by K17 pathogenic peptides. K17-specific antisense ODNs and RNAi suppress K17 mRNA and protein expression in psoriatic skin in vivo, which coincides with marked clinical and histological improvement. These findings highlight K17 as an attractive target for novel therapies aimed at curtailing psoriasis driven by chronic inflammation.

New insights of T cells in the pathogenesis of psoriasis

Psoriasis is one of the most common immune-mediated chronic, inflammatory skin diseases characterized by hyperproliferative keratinocytes and infiltration of T cells, dendritic cells, macrophages and neutrophils. Although the pathogenesis of psoriasis is not fully understood, there is ample evidence suggesting that the dysregulation of immune cells in the skin, particularly T cells, plays a critical role in psoriasis development. In this review, we mainly focus on the pathogenic T cells and discuss how these T cells are activated and involved in the disease pathogenesis. Newly identified 'professional' IL-17-producing dermal γδ T cells and their potential role in psoriasis will also be included. Finally, we will briefly summarize the recent progress on the T cell and its related cytokine-targeted therapy for psoriasis treatment.

Analysis of the paired TCR α- and β-chains of single human T cells

Analysis of the paired i.e. matching TCR α- and β-chain rearrangements of single human T cells is required for a precise investigation of clonal diversity, tissue distribution and specificity of protective and pathologic T-cell mediated immune responses. Here we describe a multiplex RT-PCR based technology, which for the first time allows for an unbiased analysis of the complete sequences of both α- and β-chains of TCR from single T cells. We validated our technology by the analysis of the pathologic T-cell infiltrates from tissue lesions of two T-cell mediated autoimmune diseases, psoriasis vulgaris (PV) and multiple sclerosis (MS). In both disorders we could detect various T cell clones as defined by multiple T cells with identical α- and β-chain rearrangements distributed across the tissue lesions. In PV, single cell TCR analysis of lesional T cells identified clonal CD8⁺ T cell expansions that predominated in the epidermis of psoriatic plaques. An MS brain lesion contained two dominant CD8⁺ T-cell clones that extended over the white and grey matter and meninges. In both diseases several clonally expanded T cells carried dual TCRs composed of one Vβ and two different Vα-chain rearrangements. These results show that our technology is an efficient instrument to analyse αβ-T cell responses with single cell resolution in man. It should facilitate essential new insights into the mechanisms of protective and pathologic immunity in many human T-cell mediated conditions and allow for resurrecting functional TCRs from any αβ-T cell of choice that can be used for investigating their specificity.

Bacterial agents in spondyloarthritis: a destiny from diversity?

The spondyloarthritides (SpAs) are a group of diseases that share clinical, radiographic and laboratory features; these arthritides also display a tendency for family aggregation. Given the intimate relationship that these types of arthritis share, it suggests that the SpAs might share a common aetiology. Of all the SpAs, the role of bacteria is most clearly defined in reactive arthritis. Tremendous recent insights into the pathophysiology of reactive arthritis have been made, demonstrating that the causative bacteria play a much more complex role than previously thought. The bacteria that are proven to cause reactive arthritis, one of the five types of SpA, will be reviewed and their role in the pathophysiology of reactive arthritis will be examined. The speculative data suggesting links between various other bacteria and the other types of SpAs will be critically analysed. Although these data are not definitive, when viewed using the paradigm that the SpAs might actually represent a common end point from several diverse starting points, they are provocative, suggesting that bacteria might, indeed, be aetiological for the entire group of SpAs.

Inflammation as "common soil" of the multifactorial diseases

Inflammation is classically recognized as an essential step for the control of microbial invasion or tissue injury as well as for the maintenance of tissue homeostasis under a variety of noxious conditions. One of the most intriguing aspect of studying inflammation is the plurality of the inflammatory mediators that are continuously discovered (microRNAs, adipokines, inflammasomes and the danger signals, etc.) and their effects on target tissues. Several studies have demonstrated that inflammatory response represents the "common soil" of the multifactorial diseases, encompassing both chronic inflammatory rheumatic disorders and a wide variety of conditions including type 2 diabetes, cardiovascular and neurodegenerative diseases, obesity, cancer, asthma, and ageing. While the inflammatory response observed in the rheumatic disorders seems to be triggered by infection and injury, i.e. the main inducers of inflammation, in the other conditions mentioned it appears to be supported by tissue malfunction or homeostatic imbalance. In the present review, we discuss the data emerged from research on inflammatory mediators sustaining multifactorial diseases.

Ezrin, maspin, peroxiredoxin 2, and heat shock protein 27: potential targets of a streptococcal-induced autoimmune response in psoriasis

Psoriasis is an HLA-Cw6-associated T cell-mediated autoimmune disease of the skin that is often triggered by streptococcal angina. To identify keratinocyte proteins, which may become psoriatic autoantigens as the result of an immune response against streptococci, rabbits were immunized with heat-killed Streptococcus pyogenes. Streptococcal immunization induced Ab formation against various human keratinocyte proteins. Sera from psoriasis patients reacted against several of these proteins as well. Common serologic reactivities of rabbits and patients included the proteins ezrin, maspin, peroxiredoxin 2 (PRDX2), heat shock protein (hsp)27, and keratin 6. When used for stimulation of blood lymphocytes, ezrin, maspin, PRDX2, and hsp27 induced increased T cell activation in psoriasis patients, which was particularly evident for HLA-Cw6(+) individuals. Ag-specific T cell lines generated with these proteins consisted predominantly of CD8(+) T cells and used TCR beta-chain rearrangements, which were highly homologous to those expanded within the corresponding skin lesion. Several immunodominant epitopes on the different proteins could be defined according to sequence alignments with the whole genome of S. pyogenes. Our data indicate that maspin, ezrin, PRDX2, hsp27, and potentially keratin 6 could act as autoantigens of a streptococcal-induced autoimmune response and represent targets of the exaggerated T cell response in psoriasis. Additionally, ezrin and hsp27 might constitute antigenic links between psoriasis and inflammatory bowel disease, uveitis, or arteriosclerosis, which are clinically associated.

Molecular dissection of psoriasis: integrating genetics and biology

Psoriasis is a common and debilitating disease of the skin, nails, and joints, with an acknowledged but complex genetic basis. Early genome-wide linkage studies of psoriasis focused on segregation of microsatellite markers in families; however, the only locus consistently identified resided in the major histocompatibility complex. Subsequently, several groups mapped this locus to the vicinity of HLA-C, and two groups have reported HLA-Cw6 itself to be the major susceptibility allele. More recently, the development of millions of single-nucleotide polymorphisms, coupled with the development of high-throughput genotyping platforms and a comprehensive map of human haplotypes, has made possible a genome-wide association approach using cases and controls rather than families. Taking advantage of these developments, we participated in a collaborative genome-wide association study of psoriasis involving thousands of cases and controls. Initial analysis of these data revealed and/or confirmed association between psoriasis and seven genetic loci-HLA-C, IL12B, IL23R, IL23A, IL4/IL13, TNFAIP3, and TNIP1-and ongoing studies are revealing additional loci. Here, we review the epidemiology, immunopathology, and genetics of psoriasis, and present a disease model integrating its genetics and immunology.

Psoriasis--as an autoimmune disease caused by molecular mimicry

Psoriasis is strongly associated with streptococcal throat infection, and patients have increased occurrence of such infections. Psoriatic lesional T cells are oligoclonal, and T cells recognizing determinants common to streptococcal M-protein and keratin have been detected in patients' blood. We propose that CD8(+) T cells in psoriatic epidermis respond mainly to such determinants, whereas CD4(+) T cells in the dermis preferentially recognize determinants on the streptococcal peptidoglycan that might itself act as an adjuvant. The streptococcal association might reflect the concurrence of superantigen production promoting skin-homing of tonsil T cells, M-protein mimicking keratin determinants, and adjuvant effects of the peptidoglycan. Accordingly, improvement of psoriasis after tonsillectomy should be associated with fewer T cells that recognize keratin and streptococcal determinants.