Halting angiogenesis by non-viral somatic gene therapy alleviates psoriasis and murine psoriasiform skin lesions

RNA-Based Antipsoriatic Gene Therapy: An Updated Review Focusing on Evidence from Animal Models

Psoriasis presents as a complex genetic skin disorder, characterized by the interaction between infiltrated immune cells and keratinocytes. Substantial progress has been made in understanding the molecular mechanisms of both coding and non-coding genes, which has positively impacted clinical treatment approaches. Despite extensive research into the genetic aspects of psoriasis pathogenesis, fully grasping its epigenetic component remains a challenging endeavor. In response to the pressing demand for innovative treatments to alleviate inflammatory skin disorders, various novel strategies are under consideration. These include gene therapy employing antisense nucleotides, silencing RNA complexes, stem cell therapy, and antibody-based therapy. There is a pressing requirement for a psoriasis-like animal model that replicates human psoriasis to facilitate early preclinical evaluations of these novel treatments. The authors conduct a comprehensive review of various gene therapy in different psoriasis-like animal models utilized in psoriasis research. The animals included in the list underwent skin treatments such as imiquimod application, as well as genetic and biologic injections, and the results of these interventions are detailed. Animal models play a crucial role in translating drug discoveries from the laboratory to clinical practice, and these models aid in improving the reproducibility and clinical applicability of preclinical data. Numerous animal models with characteristics similar to those of human psoriasis have proven to be useful in understanding the development of psoriasis. In this review, the article focuses on RNA-based gene therapy exploration in different types of psoriasis-like animal models to improve the treatment of psoriasis.

The Experimental Animal Models in Psoriasis Research: A Comprehensive Review

Psoriasis is an autoimmune, chronic, inflammatory skin condition mediated by T cells. It differs from other inflammatory conditions by causing significant alterations in epidermal cell proliferation and differentiation that are both complicated and prominent. The lack of an appropriate animal model has significantly hindered studies into the pathogenic mechanisms of psoriasis since animals other than humans typically do not exhibit the complex phenotypic features of human psoriasis. A variety of methods, including spontaneous mutations, drug-induced mutations, genetically engineered animals, xenotransplantation models, and immunological reconstitution approaches, have all been employed to study specific characteristics in the pathogenesis of psoriasis. Although some of these approaches have been used for more than 50 years and far more models have been introduced recently, they have surprisingly not yet undergone detailed validation. Despite their limitations, these models have shown a connection between keratinocyte hyperplasia, vascular hyperplasia, and a cell-mediated immune response in the skin. The xenotransplantation of diseased or unaffected human skin onto immune-compromised recipients has also significantly aided psoriasis research. This technique has been used in a variety of ways to investigate the function of T lymphocytes and other cells, including preclinical therapeutic studies. The design of pertinent in vivo and in vitro psoriasis models is currently of utmost concern and a crucial step toward its cure. This article outlines the general approach in the development of psoriasis-related animal models, aspects of some specific models, along with their strengths and limitations.

Aldosterone Increases Vascular Permeability in Rat Skin

The aim of this study was to evaluate the effect of acute aldosterone (ALDO) administration on the vascular permeability of skin. ALDO was injected intradermally into rats, and vascular permeability was measured. Eplerenone (EPL), a selective mineralocorticoid receptor (MR) antagonist, was used. Skin biopsies were carried out for immunohistochemical (IHC) staining, and polymerase chain reactions were performed to analyze the expression of MR, 11β-hydroxysteroid dehydrogenase type 2, von Willebrand factor (vWF), vascular endothelial growth factor (VEGF), and zonula occludens 1. Our study showed the presence of MR in the rat skin vasculature for the first time. It was found that ALDO injection resulted in a more than 30% increase in vascular permeability and enhanced the endothelial exocytosis of vWF. The effect of ALDO diminished after EPL administration. An accumulation of vWF and a reduction in VEGF IHC staining were observed following chronic EPL administration. No effect of ALDO or EPL on the mRNA expression of the studied genes or skin structure was observed. The results suggest that ALDO increases vascular permeability in the skin via an MR-dependent mechanism. This effect of ALDO on skin microcirculation may have important therapeutic implications for diseases characterized by increased levels of ALDO and coexisting skin microangiopathy.

The hair follicle-psoriasis axis: Shared regulatory mechanisms and therapeutic targets

It has long been known that there is a special affinity of psoriasis for the scalp: Here, it occurs most frequently, lesions terminate sharply in frontal skin beyond the hair line and are difficult to treat. Yet, surprisingly, scalp psoriasis only rarely causes alopecia, even though the pilosebaceous unit clearly is affected. Here, we systematically explore the peculiar, insufficiently investigated connection between psoriasis and growing (anagen) terminal scalp hair follicles (HFs), with emphasis on shared regulatory mechanism and therapeutic targets. Interestingly, several drugs and stressors that can trigger/aggravate psoriasis can inhibit hair growth (e.g. beta-blockers, chloroquine, carbamazepine, interferon-alpha, perceived stress). Instead, several anti-psoriatic agents can stimulate hair growth (e.g. cyclosporine, glucocorticoids, dithranol, UV irradiation), while skin/HF trauma (Köbner phenomenon/depilation) favours the development of psoriatic lesions and induces anagen in "quiescent" (telogen) HFs. On this basis, we propose two interconnected working models: (a) the existence of a bidirectional "hair follicle-psoriasis axis," along which keratinocytes of anagen scalp HFs secrete signals that favour the development and maintenance of psoriatic scalp lesions and respond to signals from these lesions, and (b) that anagen induction and psoriatic lesions share molecular "switch-on" mechanisms, which invite pharmacological targeting, once identified. Therefore, we advocate a novel, cross-fertilizing and integrative approach to psoriasis and hair research that systematically characterizes the "HF-psoriasis axis," focused on identification and therapeutic targeting of selected, shared signalling pathways in the future management of both, psoriasis and hair growth disorders.

Animal models of psoriasis-highlights and drawbacks

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

Aryl Hydrocarbon Receptor in Cutaneous Vascular Endothelial Cells Restricts Psoriasis Development by Negatively Regulating Neutrophil Recruitment

Vascular endothelial cells (VECs) that line the interiors of blood vessels participate in physiological and inflammatory processes. All skin cell types express the aryl hydrocarbon receptor (AhR), which is involved in the pathogenesis of psoriasis. However, the role of the cutaneous VEC AhR in the pathogenesis of psoriasis remains elusive. In the present study, we found that AhR protein expression and activation were downregulated in psoriatic VECs. Furthermore, cutaneous VEC-specific AhR-knockout (AhR^cVECs-KO) mice were established. Using imiquimod and IL-23-induced psoriasis models, we found that skin inflammation was exacerbated with excessive neutrophil recruitment in AhR^cVECs-KO mice. Furthermore, neutrophil neutralization alleviates exacerbated inflammation in imiquimod-treated AhR^cVECs-KO mice. In addition, cutaneous VECs in AhR^cVECs-KO mice exhibited increased dilation and activation compared with those in control mice. Finally, AhR-deficient microvascular endothelial cells stimulated by proinflammatory cytokines showed increased ICAM-1 expression in vivo and in vitro, which may have facilitated neutrophil recruitment. In summary, our study demonstrates that AhR in dermal VECs restricts psoriasis development by negatively regulating neutrophil recruitment, thereby providing insight into the pathogenesis of psoriasis.

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 Interleukin-23/Interleukin-17 Axis Links Adaptive and Innate Immunity in Psoriasis

Research into the pathophysiology of psoriasis has shed light onto many fascinating immunological interactions and underlying genetic constellations. Most prominent among these is the crosstalk between components of the innate and the adaptive immune system and the crucial role of interleukins (IL)-23 and -17 within this network. While it is clear that IL-23 drives and maintains the differentiation of Th17 lymphocytes, many aspects of the regulation of IL-23 and IL-17 are not quite as straightforward and have been unraveled only recently. For example, we know now that Th17 cells are not the only source of IL-17 but that cells of the innate immune system also produce considerable amounts of this central effector cytokine. In addition, there is IL-23-independent production of IL-17. Besides other innate immune cells, neutrophilic granulocytes prominently contribute to IL-17-related immune regulations in psoriasis, and it appears that they employ several mechanisms including the formation of neutrophil extracellular traps. Here, we strive to put the central role of the IL-23/IL-17 axis into perspective within the crosstalk between components of the innate and the adaptive immune system. Our aim is to better understand the complex immune regulation in psoriasis, a disorder that has become a model disease for chronic inflammation.

Selenium unmasks protective iron armor: A possible defense against cutaneous inflammation and cancer

BACKGROUND

A link between selenium deficiency and inflammatory skin diseases have been noted by many, but this link is still not well understood. We have previously studied the efficacy of ceramide analogs, based on the fire ant venom Solenopsin A, against our psoriasis animal model. Treatment of animals with solenopsin analogs resulted in significantly improved skin as well as in a coordinate downregulation of selenoproteins, namely Glutathione Peroxidase 4 (GPX4). We thus hypothesize that ferroptosis may be a physiologic process that may protect the skin from both inflammatory and neoplastic processes.

METHODS

We analyze and compare gene expression profiles in the GEO database from clinical skin samples taken from healthy patients and psoriasis patients (both involved and noninvolved skin lesions). We validated the gene expression results against a second, independent, cohort from the GEO database.

RESULTS

Significant reduction in gene expression of GPX4, elevated expression of Nrf2 downstream targets, and expression profiles mirroring erastin-inhibition of Cystine/Glutamate Antiporter-System X_C activity in psoriatic skin lesions, compared to both noninvolved skin and healthy patient samples, suggest an innately inducible mechanism of ferroptosis.

CONCLUSIONS

We present data that may indicate selenoproteins, particularly GPX4, in resolving inflammation and skin cancer, including the novel hypothesis that the human organism may downregulate GPX4 and reactive oxygen (REDOX) regulating proteins in the skin as a way of resolving psoriasis and nonmelanoma skin cancer through increased reactive oxygen species. Further studies are needed to investigate ferroptosis as a possible physiologic mechanism for eliminating inflammatory and malignant tissues.

GENERAL SIGNIFICANCE

This study provides a fresh framework for understanding the seemingly contradictory effects of selenium supplementation. In addition, it offers a novel explanation of how physiologic upregulation of ferroptosis and downregulation of selenoprotein synthesis may mediate resolution of inflammation and carcinogenesis. This is of therapeutic significance.

Excessive angiogenesis associated with psoriasis as a cause for cardiovascular ischaemia

Psoriasis, a common disease affecting 2%-3% of the UK population, produces significant impairment of quality of life and is an immense burden on sufferers and their families. Psoriasis is associated with significant cardiovascular comorbidity and the metabolic syndrome. Angiogenesis, a relatively under-researched component of psoriasis, is a key factor in pathogenesis of psoriasis and also contributes to the development of atherosclerosis. Vascular endothelial growth factor (VEGF) is a well-established mediator of pathological angiogenesis which is upregulated in psoriasis. It is possible that, in patients with psoriasis, cutaneous angiogenesis may be both a marker for systemic vascular pathology and a novel therapeutic target. In this viewpoint study, the role of VEGF-mediated angiogenesis as a cause for cardiovascular events in patients with psoriasis is explored.

Electropermeabilization of Inner and Outer Cell Membranes with Microsecond Pulsed Electric Fields: Quantitative Study with Calcium Ions

Microsecond pulsed electric fields (μsPEF) permeabilize the plasma membrane (PM) and are widely used in research, medicine and biotechnology. For internal membranes permeabilization, nanosecond pulsed electric fields (nsPEF) are applied but this technology is complex to use. Here we report that the endoplasmic reticulum (ER) membrane can also be electropermeabilized by one 100 µs pulse without affecting the cell viability. Indeed, using Ca2+ as a permeabilization marker, we observed cytosolic Ca2+ peaks in two different cell types after one 100 µs pulse in a medium without Ca2+. Thapsigargin abolished these Ca2+ peaks demonstrating that the calcium is released from the ER. Moreover, IP3R and RyR inhibitors did not modify these peaks showing that they are due to the electropermeabilization of the ER membrane and not to ER Ca2+ channels activation. Finally, the comparison of the two cell types suggests that the PM and the ER permeabilization thresholds are affected by the sizes of the cell and the ER. In conclusion, this study demonstrates that µsPEF, which are easier to control than nsPEF, can permeabilize internal membranes. Besides, μsPEF interaction with either the PM or ER, can be an efficient tool to modulate the cytosolic calcium concentration and study Ca2+ roles in cell physiology.

Advances in Non-Viral DNA Vectors for Gene Therapy

Uses of viral vectors have thus far eclipsed uses of non-viral vectors for gene therapy delivery in the clinic. Viral vectors, however, have certain issues involving genome integration, the inability to be delivered repeatedly, and possible host rejection. Fortunately, development of non-viral DNA vectors has progressed steadily, especially in plasmid vector length reduction, now allowing these tools to fill in specifically where viral or other non-viral vectors may not be the best options. In this review, we examine the improvements made to non-viral DNA gene therapy vectors, highlight opportunities for their further development, address therapeutic needs for which their use is the logical choice, and discuss their future expansion into the clinic.

Psoriasis

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

A Low Protein Binding Cationic Poly(2-oxazoline) as Non-Viral Vector

Developing safe and efficient non-viral gene delivery systems remains a major challenge. We present a new cationic poly(2-oxazoline) (CPOx) block copolymer for gene therapy that was synthesized by sequential polymerization of non-ionic 2-methyl-2-oxazoline and a new 2-oxazoline monomer, 2-(N-methyl, N-Boc-amino)-methyl-2-oxazoline, followed by deprotection of the pendant secondary amine groups. Upon mixing with plasmid DNA (pDNA), CPOx forms small (diameter ≈80 nm) and narrowly dispersed polyplexes (PDI <0.2), which are stable upon dilution in saline and against thermal challenge. These polyplexes exhibited low plasma protein binding and very low cytotoxicity in vitro compared to the polyplexes of pDNA and poly(ethylene glycol)-b-poly(L-lysine) (PEG-b-PLL). CPOx/pDNA polyplexes at N/P = 5 bound considerably less plasma protein compared to polyplexes of PEG-b-PLL at the same N/P ratio. This is a unique aspect of the developed polyplexes emphasizing their potential for systemic delivery in vivo. The transfection efficiency of the polyplexes in B16 murine melanoma cells was low after 4 h, but increased significantly for 10 h exposure time, indicative of slow internalization of polyplexes. Addition of Pluronic P85 boosted the transfection using CPOx/pDNA polyplexes considerably. The low protein binding of CPOx/pDNA polyplexes is particularly interesting for the future development of targeted gene delivery.

Angiogenesis and lymphangiogenesis in inflammatory skin disorders

Angiogenesis, the growth of new blood vessels from pre-existing vessels, occurs physiologically in wound healing, during inflammatory diseases, and in tumor growth. Lymphangiogenesis can be activated in inflammation and tumor metastasis. The family of vascular endothelial growth factors (VEGFs) and angiopoietins are essential for angiogenesis and lymphangiogenesis. The angiogenic process is tightly regulated by VEGFs, angiopoietins, and endogenous inhibitors. VEGFs and angiopoietins exert their effects by activating specific receptors present on blood and lymphatic endothelial cells. There is now compelling evidence that cells of innate and adaptive immunity (macrophages, mast cells, neutrophils, eosinophils, lymphocytes) are a major source of angiogenic and lymphangiogenic factors. Chronic inflammatory skin diseases such as psoriasis and atopic dermatitis are characterized by altered angiogenesis, lymphangiogenesis, or both. Also such acute inflammatory skin disorders as urticaria, ultraviolet B-induced damage, and angioedema are associated with changes in angiogenic factors. In systemic sclerosis there is a switch from proangiogenic to antiangiogenic factors that play a role in the defective vascular process of this disorder. As yet, there are no clinical trials showing that canonical VEGF/VEGF receptor-targeted strategies can modulate inflammatory skin diseases. Novel strategies targeting other angiogenic/lymphangiogenic pathways should also be investigated.

Inositoylated platelet-activating factor (Ino-C2-PAF) modulates dynamic lymphocyte-endothelial cell interactions and alleviates psoriasis-like skin inflammation in two complementary mouse models

Psoriasis, a tumor necrosis factor alpha (TNFα)-governed inflammatory disorder with prominent dysregulation of cutaneous vascular functions, has evolved into a model disorder for studying anti-inflammatory therapies. We present experimental in vitro and in vivo data on 1-O-octadecyl-2-O-(2-(myo-inositolyl)-ethyl)-sn-glycero-3-(R/S)-phosphatidyl-choline (Ino-C2-PAF), the lead compound of a class of synthetic glycosylated phospholipids, in anti-inflammatory therapy. Ino-C2-PAF strongly induced apoptosis only in TNFα-stimulated, but not in untreated human vascular endothelial cells. Moreover, TNFα-induced endothelial adhesion molecules that mediated the rolling and firm adhesion of leukocytes (vascular cell adhesion protein-1 (VCAM-1), E-selectin, and ICAM-1) were selectively downregulated by Ino-C2-PAF. Similarly, expression of L-selectin, VCAM-1 receptor α4β1 integrin , and lymphocyte function-associated antigen-1 on human peripheral blood mononuclear cells was reduced without induction of apoptosis. Functionally, these changes were accompanied by significant impairment of rolling and adhesion of human peripheral blood lymphocytes on TNFα-activated endothelial cells in a dynamic flow chamber system. When the therapeutic potential of Ino-C2-PAF was assessed in two complementary mouse models of psoriasis, K5.hTGFβ1 transgenic and JunB/c-Jun-deficient mice, Ino-C2-PAF led to significant alleviation of the clinical symptoms and normalized the pathological cutaneous changes including vascularization. There were no overt adverse effects. These findings suggested that Ino-C2-PAF is a potential candidate in the therapy of inflammatory skin diseases that include abnormal vascular functions.

Skin electroporation for transdermal drug delivery: the influence of the order of different square wave electric pulses

Electroporation can be used as an active enhancement method for intra- and transdermal drug delivery. Differences in response of skin to electric pulses depend on their amplitude, duration and number and have been a point of interest in the past. While protocols consisting of the same repetitive, mostly exponentially decaying pulses have been used before, this study is focused on comparing different combinations of square wave short high voltage (HV) and longer low voltage (LV) electroporation pulses. Our in vitro experimental results show that longer LV pulses significantly increase subsequent passive transport of calcein through dermatomed pig skin, while short HV pulses alone result in negligible calcein passive transdermal transport. Surprisingly, when the long LV pulses are preceded by short duration HV pulses, the total calcein transported is reduced significantly. This result is explained using a theoretical physics based model of individual local transport region (LTR) evolution during the applied LV pulse. The theoretical model shows that HV pulses alter the structure of the stratum corneum in such a way that when the LV pulses are applied, insufficient thermal energy is generated to initiate LTR expansion. Together, the experimental results and theoretical predictions show that the total pulse energy alone cannot account for total solute transport: that the order of the types of pulses administered must also be considered. Our findings open a direction for further improvement of the method using new protocols.

Vascular normalization as a therapeutic strategy for malignant and nonmalignant disease

Pathological angiogenesis-driven by an imbalance of pro- and antiangiogenic signaling-is a hallmark of many diseases, both malignant and benign. Unlike in the healthy adult in which angiogenesis is tightly regulated, such diseases are characterized by uncontrolled new vessel formation, resulting in a microvascular network characterized by vessel immaturity, with profound structural and functional abnormalities. The consequence of these abnormalities is further modification of the microenvironment, often serving to fuel disease progression and attenuate response to conventional therapies. In this article, we present the "vascular normalization" hypothesis, which states that antiangiogenic therapy, by restoring the balance between pro- and antiangiogenic signaling, can induce a more structurally and functionally normal vasculature in a variety of diseases. We present the preclinical and clinical evidence supporting this concept and discuss how it has contributed to successful treatment of both solid tumors and several benign conditions.

Angiogenic and inflammatory properties of psoriatic arthritis

Psoriatic arthritis (PsA) is a chronic inflammatory arthropathy associated with psoriasis and included in seronegative spondyloarthropathy. PsA has several unique characteristics different from rheumatoid arthritis (RA), such as enthesopathy, dactylitis, and abnormal bone remodeling. As compared with synovitis of RA (pannus), proliferation of PsA synovium is mild and characterized by hypervascularity and increased infiltration of polymorphonuclear leukocytes in the synovial tissues. Angiogenesis plays a crucial role in cutaneous psoriasis, and several angiogenic factors such as vascular endothelial growth factor, interleukin-8, angiopoietin, tumor necrosis factor- α and transforming growth factor-β, are suggested to play an important role also in the pathophysiology of PsA. Further, IL-17 has various functions such as upregulation of proinflammatory cytokines, attraction of neutrophils, stimulation of keratinocytes, endothelial cell migration, and osteoclast formation via RANKL from activated synovial fibroblasts. Thus, IL-17 may be important in angiogenesis, fibrogenesis, and osteoclastogenesis in PsA. In this paper, roles of angiogenesis in the psoriatic synovium are discussed, which may strengthen the understanding of the pathogenesis of PsA.

Involvement of IL-9 in Th17-associated inflammation and angiogenesis of psoriasis

It is thought that a Th1/Th17-weighted immune response plays a predominant role in the pathogenesis of psoriasis. Our findings now indicate a link between IL-9, a Th2 and Th9 cytokine, and Th17 pathway in psoriasis. In K5.hTGF-β1 transgenic mice, exhibiting a psoriasis-like phenotype, we found increased IL-9R and IL-9 expression in the skin and intradermal IL-9 injection induced Th17-related inflammation. IL-9 also promoted angiogenesis and VEGF and CD31 overexpression in mice in vivo and increased tube formation of human endothelial cells in vitro. Injecting anti-IL-9 antibody into K5.hTGF-β1 transgenic mice not only diminished inflammation (including skin infiltration by T cells, monocytes/macrophages, and mast cells) and angiogenesis but also delayed the psoriasis-like skin phenotype. Notably, injection of anti-psoriatic acting anti-IL-17 antibody reduced skin IL-9 mRNA and serum IL-9 protein levels in K5.hTGF-β1 transgenic mice and prevented IL-9-induced epidermal hyperplasia and inflammation of the skin of wild type mice. In addition, we observed that IL-9R expression in lesional skin from psoriasis patients was markedly higher than in healthy skin from control subjects. Moreover, IL-9 significantly enhanced IL-17A production by cultured human peripheral blood mononuclear cells or CD4+ T cells, especially in psoriasis patients. Thus, IL-9 may play a role in the development of psoriatic lesions through Th17-associated inflammation and angiogenesis.