Psoriasis patients who are homozygous for the HLA-Cw*0602 allele have a 2.5-fold increased risk of developing psoriasis compared with Cw6 heterozygotes

Psoriasis: what we have learned from mouse models

Psoriasis is a common inflammatory skin disease of unknown etiology, for which there is no cure. This heterogeneous, cutaneous, inflammatory disorder is clinically characterized by prominent epidermal hyperplasia and a distinct inflammatory infiltrate. Crosstalk between immunocytes and keratinocytes, which results in the production of cytokines, chemokines and growth factors, is thought to mediate the disease. Given that psoriasis is only observed in humans, numerous genetic approaches to model the disease in mice have been undertaken. In this Review, we describe and critically assess the mouse models and transplantation experiments that have contributed to the discovery of novel disease-relevant pathways in psoriasis. Research performed using improved mouse models, combined with studies employing human cells, xenografts and patient material, will be key to our understanding of why such distinctive patterns of inflammation develop in patients with psoriasis. Indeed, a combination of genetic and immunological investigations will be necessary to develop both improved drugs for the treatment of psoriasis and novel curative strategies.

Genetic variations associated with psoriasis and psoriatic arthritis found by genome-wide association

Psoriasis and psoriatic arthritis are immune disorders with a complex polygenic basis. HLA-Cw6, which lies in the major histocompatibility region on chromosome 6, is considered the major genetic determinant of psoriasis. Recent genome-wide association studies have identified new variants outside of the MHC with relevance to the immunology of psoriasis. Variants in or near genes that encode subunits of cytokines (IL12B, IL23A) or cytokine receptors (IL23R) are interesting given that the gene product of IL12B, p40, is the target of a recently approved monoclonal antibody therapy for psoriasis (ustekinumab). Association with psoriasis and psoriatic arthritis has been found in TNFAIP3 and TNFIP1, ubiquitin ligases in the NF-kappaB pathway, and IL13, a Th2 cytokine. Copy number variation of human beta-defensin and late cornified envelope genes also associate with psoriasis. Many of these genetic variations also associate with immune disorders considered psoriatic co-morbidities, including Crohn's disease and diabetes.

Progress in understanding the immunopathogenesis of psoriasis

This review emphasizes how translation from bench research to clinical knowledge and vice versa has resulted in considerable progress in understanding the immunopathogenesis of psoriasis. First, the journey in understanding the pathogenic mechanisms behind psoriasis is described. The roles of different components of the adaptive and innate immune systems involved in driving the inflammatory response are explained. Discovery of new immune pathways i.e. the IL23/Th17 axis and its subsequent impact on the development of novel biological therapies is highlighted. Identification of potential targets warranting further research for future therapeutic development are also discussed.

Simple and rapid screening for HLA-Cw*06 in Polish patients with psoriasis

BACKGROUND

The human leucocyte antigen (HLA) C allele Cw*06 is currently recognized as a major disease allele at the PSORS1 locus. It has been suggested that characterization of this gene could be used as a convenient criterion for classification of psoriasis phenotypes.

AIM

To design and optimize a DNA typing procedure, suitable for identification of HLA-Cw*06 and its zygosity status verification in large-scale analyses, and to test for its robustness in a case-control study.

METHODS

PCR assays with sequence-specific primers (PCR-SSP) were used for specific detection of HLA-Cw*06. PCR with analysis of restriction fragment length polymorphism was used to distinguish between patients homozygous and heterozygous for HLA-Cw*06. Additionally, those homozygous for HLA-Cw*06 were screened for nonspecific digestion by degenerated PCR-SSP. This three-step procedure was used in the examination of 383 patients with psoriasis that developed at the age of >or= 30 years of age and of 143 healthy subjects from northern Poland.

RESULTS

A simple and rapid procedure for screening of HLA-Cw*06 was produced. A significant difference in HLA-Cw*06 frequency between patients with psoriasis and controls was seen (P = 0.02). Detailed examination of the age of disease onset among patients with psoriasis revealed that involvement of HLA-Cw*06 in the genetic background of psoriasis developing as late as the age of 45 years cannot be neglected.

CONCLUSIONS

The low cost, high-throughput capacity and requirement for small sample amounts make this procedure a useful one for HLA-Cw*06 typing in clinical practice and large population studies. We recommend that patients with psoriasis diagnosed before 45 years of age should be considered for diagnostic HLA-Cw*06 typing.

Multiple Loci within the major histocompatibility complex confer risk of psoriasis

Psoriasis is a common inflammatory skin disease characterized by thickened scaly red plaques. Previously we have performed a genome-wide association study (GWAS) on psoriasis with 1,359 cases and 1,400 controls, which were genotyped for 447,249 SNPs. The most significant finding was for SNP rs12191877, which is in tight linkage disequilibrium with HLA-Cw*0602, the consensus risk allele for psoriasis. However, it is not known whether there are other psoriasis loci within the MHC in addition to HLA-C. In the present study, we searched for additional susceptibility loci within the human leukocyte antigen (HLA) region through in-depth analyses of the GWAS data; then, we followed up our findings in an independent Han Chinese 1,139 psoriasis cases and 1,132 controls. Using the phased CEPH dataset as a reference, we imputed the HLA-Cw*0602 in all samples with high accuracy. The association of the imputed HLA-Cw*0602 dosage with disease was much stronger than that of the most significantly associated SNP, rs12191877. Adjusting for HLA-Cw*0602, there were two remaining association signals: one demonstrated by rs2073048 (p = 2×10⁻⁶, OR = 0.66), located within c6orf10, a potential downstream effecter of TNF-alpha, and one indicated by rs13437088 (p = 9×10⁻⁶, OR = 1.3), located 30 kb centromeric of HLA-B and 16 kb telomeric of MICA. When HLA-Cw*0602, rs2073048, and rs13437088 were all included in a logistic regression model, each of them was significantly associated with disease (p = 3×10⁻⁴⁷, 6×10⁻⁸, and 3×10⁻⁷, respectively). Both putative loci were also significantly associated in the Han Chinese samples after controlling for the imputed HLA-Cw*0602. A detailed analysis of HLA-B in both populations demonstrated that HLA-B*57 was associated with an increased risk of psoriasis and HLA-B*40 a decreased risk, independently of HLA-Cw*0602 and the C6orf10 locus, suggesting the potential pathogenic involvement of HLA-B. These results demonstrate that there are at least two additional loci within the MHC conferring risk of psoriasis.

Psoriasis (Ps) is a chronic inflammatory disease of the skin, affecting approximately 2% of Europeans. The HLA-C gene, located within the major histocompatibility complex (MHC) region on chromosome 6, is the major genetic determinant of psoriasis. However, multiple susceptibility genes within MHC are also hypothesized. Recently, we carried out a genome-wide association scan (GWAS) on psoriasis with 1,359 patients and 1,400 healthy controls, which identified seven psoriasis loci in the human genome and confirmed the effect of HLA-C. This dataset contains densely distributed genetic variations, single nucleotide polymorphisms (SNPs), which were then further analyzed in search for additional susceptibility genes within the MHC region. Using the SNP data, we imputed in all samples the HLA-C risk allele with high accuracy. Adjusting for the HLA-C, two additional loci, one near C6orf10 and one near HLA-B/MICA, have significant associations with psoriasis, which were also observed in an independent Han Chinese dataset, suggesting that within the MHC there are at least three genes moderating susceptibility to psoriasis.

A study of the killer cell immunoglobulin-like receptor gene KIR2DS1 in a Caucasoid Brazilian population with psoriasis vulgaris

Psoriasis is a chronic inflammatory skin disease whose pathogenesis and genetic background remain unclear. Considering that previous studies have suggested an association of psoriasis vulgaris (PV) and killer cell immunoglobulin-like receptors (KIRs), we typed 15 KIR genes and human leukocyte antigen (HLA)-Cw in 79 Brazilian Caucasoid patients with PV and 110 healthy controls by polymerase chain reaction (PCR) using sequence-specific oligonucleotides and sequence-specific primers. We did not observe a relevant increase in the frequency of the activating KIR2DS1 gene in the PV group [KIR2DS1, 46 of 79 cases (58.2%) vs 40 of 110 controls (36.4%)]. However, an association of KIR2DS1 with Cw*0602+ in 26.5% of PV patients was observed, while it was present in only 5.4% of controls. These results suggest that activating KIR2DS1 gene may not confer susceptibility to PV, and an association of KIR2DS1 gene with the HLA-Cw*0602+ was observed in these patients.

Genetik der Psoriasis

Psoriasis ist eine chronische, entzündliche Hauterkrankung mit einer multifaktoriellen Vererbung. Als wichtigster Risikofaktor gilt derzeit das HLA-CW0602-Allel [bzw. ein Faktor in starkem LD („linkage disequilibrium“)], das insbesondere für die frühere Manifestationsform (< 40. Lebensjahr) prädisponiert und u. a. einen Einfluss auf die Schwere des Verlaufs hat. Durch genomweite Kopplungsanalysen konnten bisher 11 weitere Suszeptibilitätsloci, jedoch nur wenige Kandidatengene identifiziert werden, alle mit vergleichsweise geringem relativem Risiko (Odds-Ratio, OR). Weitere Aspekte der komplexen Ätiopathogenese dieser Erkrankung konnten in immunologischen Ansätzen, aufgrund von Therapieerfolgen mit Antikörpern gegen immunrelevante Moleküle und bei kandidatengenorientierten Assoziationsstudien aufgeklärt werden. Die pathophysiologischen und genetischen Befunde konvergieren zunehmend und zeichnen die Psoriasis als Erkrankung eines fehlgesteuerten immunologischen Regulationsprozesses zwischen Keratinozyten und Zellen des angeborenen und erworbenen Immunsystems aus.

Observations of Psoriasis in the Absence of Therapeutic Intervention Identifies Two Unappreciated Morphologic Variants, Thin-Plaque and Thick-Plaque Psoriasis, and their Associated Phenotypes

Psoriatic plaque thickness is a clinical measure of psoriasis severity. We have observed that patients tend to revert to a baseline thickness of psoriatic plaques when in an untreated state, and hypothesized that other features of psoriasis could associate with this trait. Data prospectively collected on 500 participants in the Utah Psoriasis Initiative were used for the study. In response to a question assessing plaque thickness when disease was at its worst, 144 (28.8%) reported thick plaques, 123 (24.6%) reported thin plaques, and 233 (46.6%) reported intermediate thickness. For patients with "worst-ever" disease at enrollment (n=122), there was significant correlation of thickness between assessment by the patient and the physician (r=0.448, P-value 0.01). Thick plaques associated with male gender, increased body mass index, nail disease, psoriatic arthritis, larger plaques, more body sites, and greater total body surface area affected. Thin plaques associated with eczema, guttate psoriasis, and skin cancer. We suggest that this is preliminary evidence that plaque thickness is an easily measured trait that associates with other clinical features of psoriasis, and that stratification on this phenotype may be useful in further defining the genetic basis of this disease.

Distinct clinical differences between HLA-Cw*0602 positive and negative psoriasis patients--an analysis of 1019 HLA-C- and HLA-B-typed patients

A major susceptibility gene for psoriasis is located in the major histocompatibility complex class I region on chromosome 6 very close to the HLA-Cw6 gene. We collected a cohort of 1,019 patients with chronic plaque psoriasis. The patients were typed for HLA-C and HLA-B. A total of 654 (64.2%) were HLA-Cw*0602 positive but 365 (35.8%) carried other HLA-C alleles. We confirmed that HLA-Cw*0602 positive patients have younger age of onset (17.5 vs 24.3 years, P<10(-10)), higher incidence of guttate and the eruptive type of psoriasis (P<0.0001), more frequent exacerbations with throat infections (P=0.01), higher incidence of the Koebner's phenomenon (P=0.01), and more extensive disease (P=0.03). A striking new finding was a diverging pattern of disease severity in HLA-Cw*0602 positive and negative patients depending on the age of onset of the disease (P=0.0006). HLA-Cw*0602 positive women also had more frequent remissions during pregnancy (P<0.0001). All types of nail changes were, however, more common in the Cw*0602 negative patients (P=0.003) and they more often had multiple types of nail lesions (P<0.0001). The three ancestral haplotypes of Cw*0602 all conferred an increase in odds ratio but showed no difference in any of the clinical features studied. Our findings indicate that the genetic factor on chromosome 6 has a strong influence on the phenotype of the disease, and underline that differences in clinical features of psoriasis may be to a large extent genetically determined.

Antígenos de histocompatibilidade humanos e dermatologia: da pesquisa para a prática clínica

A participação do sistema de histocompatibilidade humano (HLA: human leukocyte antigens) na patogênese das doenças auto-imunes é bem conhecida. Situado no braço curto do cromossomo 6, o sistema HLA se destaca por seu polimorfismo e por sua capacidade de conferir susceptibilidade ou proteção a diferentes enfermidades. Em Dermatologia, esse sistema desempenha papel importante na patogenia e história natural de várias doenças. A força e o tipo de associação variam com a dermatose e, algumas vezes, com o grupo étnico-racial estudado. O surgimento de métodos moleculares para tipificação dos alelos HLA e as recentes atualizações de sua nomenclatura têm contribuído para o melhor entendimento desse sistema. Infelizmente, essas informações não têm sido veiculadas de maneira adequada na literatura clínica, o que dificulta o entendimento da associação do HLA com as doenças cutâneas. Nesta revisão, são discutidos alguns aspectos do sistema HLA, métodos de detecção, nomenclatura e sua associação com vitiligo, pênfigo, psoríase, lúpus eritematoso, escabiose, leishmaniose cutânea, hanseníase, paracoccidioidomicose e dermatite atópica.

HLA-C locus alleles distribution in patients from northern Poland with psoriatic arthritis - preliminary report

The aim of the study was to compare the frequency of human leucocyte antigen-C (HLA-C) locus alleles in patients with psoriatic arthritis and in healthy controls in the same ethnic group in Poland, and to correlate them with age of onset of psoriatic skin changes and joints symptoms. HLA-C locus alleles of 41 patients and 80 controls were determined by a polymerase chain reaction (PCR) low-resolution method. The Cw*06 allele occurred more frequently (P adjusted for multiple comparison = 0.004) in patients with psoriatic arthritis than in controls. Patients who carried the HLA-Cw*06 allele had a significantly earlier mean age of onset of both psoriasis (P = 0.01) and arthritis (P = 0.008) compared with Cw*06-negative patients. Our results confirm the association between Cw*06 allele and psoriatic arthritis in the northern Poland population and suggest that the HLA-Cw*06 may determine not only the disease susceptibility, but also the age of onset of psoriatic arthritis.

Distinct HLA-C/KIR genotype profile associates with guttate psoriasis

Psoriasis is a multifactorial disease with a strong genetic background. It associates strongly to HLA-Cw*0602. HLA-C interacts with killer immunoglobulin-like receptors (KIR) on natural killer (NK) and some natural killer-T (NKT) cells. KIR's function is triggered by specific binding to HLA ligands, which depends on the amino acid 80 of the MHC class I alpha-chain. This permits classifying all HLA-C alleles into two functional groups: asparagine (N80) or lysine (K80) carrying alleles. Psoriasis patients recruited at disease onset were categorized as guttate, vulgaris without arthropathy and vulgaris with arthropathy plus skin lesions. Patients and carefully matched controls were genotyped for position 80 of HLA-C and for KIR. Based on possible HLA/KIR combinations, individuals were classified according to expected NK/NKT cell responses: balanced (B), excess inhibition (EI), excess activation (EA), or undetermined (U). HLA-Cw6 and position 80 genotyping associated strongly to disease, whereas KIR2DS1 associated weakly. Individuals of the U and EI classes were more common among guttate psoriasis patients, which related to HLA-Cw*0602 status. These results suggest that different levels for NK/NKT cell activation thresholds, not only reduction, contribute to immune deregulation in psoriasis. In the guttate phenotype, balanced HLA-C/KIR interactions might be altered by the presence of concomitant streptococcal infections.

Molecular diversity of HLA-Cw alleles in the Maratha community of Mumbai, Maharashtra, western India

Recent advances suggest a significant role for the HLA-C locus as a target of alloreactions after bone marrow transplantation. The biological importance of products of the HLA-C locus, both as transplant antigens and as ligands for natural killer (NK) cells, is well established. A total of 10 different serologically defined HLA-Cw antigen specificities (Cw1-Cw10) are encoded by the C locus; however, there are now 151 different alleles that can be identified by molecular methods. Serological definition of Cw alleles therefore includes 20-50% blanks, which cannot be detected by the available antisera. We used the molecular method of polymerase chain reaction (PCR)-based sequence-specific amplification and probe hybridization to define Cw alleles in 91 individuals from the Maratha community, and compared the data with data for 92 serologically typed Maratha individuals from India. We identified Cw*12, Cw*14, Cw*15, Cw*16 and Cw*18, along with the serologically identified Cw*01, Cw*02, Cw*03, Cw*04, Cw*06 and Cw*07 alleles. The HLA-Cw blank allele frequency in the Maratha was reduced from 0.5706 to 0.00. Furthermore, by using a molecular technique, it was possible to identify novel allele subtypes, such as Cw*0104, Cw*0203 and Cw*0707, and a high frequency of Cw* 1801 in the Maratha community compared with other Indian and world populations. Our results will have clinical implications in related and unrelated HLA-matched bone marrow transplantation in India.

Fine mapping of the psoriasis susceptibility gene PSORS1: a reassessment of risk associated with a putative risk haplotype lacking HLA-Cw6

Human leukocyte antigen (HLA)-Cw6 has long been associated with psoriasis, and PSORS1 (psoriasis susceptibility 1), a major gene for psoriasis susceptibility, has been mapped to its vicinity. A previous analysis identified multiple risk haplotypes carrying HLA-Cw6 and one haplotype (cluster 17, HLA-Cw8-B65) that appeared to carry risk for psoriasis but did not carry HLA-Cw6. This haplotype was very similar to other risk haplotypes for at least 60 kb telomeric to HLA-C, suggesting identity by descent with the remaining risk chromosomes. The association, however, between psoriasis and this haplotype as assessed by the transmission/disequilibrium test (TDT) was of borderline significance (p-value 0.048). In order to better assess the risk associated with cluster 17, a multicenter collaboration typed additional subjects for a single marker (M6S161) for which one allele (249 bp) was found only on cluster 17. The new sample included 1275 pedigrees as well as 300 cases and 913 controls. Transmission of this allele to affected individuals was examined using the TDT and the pedigree disequilibrium test (PDT), and case-control samples were analyzed by a trend test across genotype categories. By all methods, the newly acquired genotypes failed to confirm the association originally reported, despite adequate power. In contrast, the 248 bp allele, which is found on all HLA-Cw6-positive risk haplotypes as well as several non-risk haplotypes, shows significant excess transmission for all cohorts. Taken together, these results indicate that cluster 17 does not carry a psoriasis-susceptibility allele, and expand the PSORS1 risk interval to approximately 300 kb.

Recent insights into the immunopathogenesis of psoriasis provide new therapeutic opportunities

Chronic and excessive inflammation in skin and joints causes significant morbidity in psoriasis patients. As a prevalent T lymphocyte-mediated disorder, psoriasis, as well as the side effects associated with its treatment, affects patients globally. In this review, recent progress is discussed in the areas of genetics, the immunological synapse, the untangling of the cytokine web and signaling pathways, xenotransplantation models, and the growing use of selectively targeted therapies. Since psoriasis is currently incurable, new management strategies are proposed to replace previous serendipitous approaches. Such strategic transition from serendipity to the use of novel selective agents aimed at defined targets in psoriatic lesions is moving rapidly from research benches to the bedsides of patients with this chronic and debilitating disease.

Recent insights into the immunopathogenesis of psoriasis provide new therapeutic opportunities

Chronic and excessive inflammation in skin and joints causes significant morbidity in psoriasis patients. As a prevalent T lymphocyte-mediated disorder, psoriasis, as well as the side effects associated with its treatment, affects patients globally. In this review, recent progress is discussed in the areas of genetics, the immunological synapse, the untangling of the cytokine web and signaling pathways, xenotransplantation models, and the growing use of selectively targeted therapies. Since psoriasis is currently incurable, new management strategies are proposed to replace previous serendipitous approaches. Such strategic transition from serendipity to the use of novel selective agents aimed at defined targets in psoriatic lesions is moving rapidly from research benches to the bedsides of patients with this chronic and debilitating disease.

Immunopathogenic mechanisms in psoriasis

Psoriasis is a common autoimmune skin disease characterized by T cell-mediated hyperproliferation of keratinocytes. The disease has a strong but complex genetic background with a concordance of approximately 60% in monozygotic twins, and recent linkage and high resolution association studies indicate that HLA-Cw*0602 is itself a major susceptibility allele for psoriasis. Patients carrying this allele have been shown to have different clinical features and earlier age of disease onset, and patients homozygous for this allele have about 2.5 times higher disease risk than heterozygotes. Published data indicate that CD8+ T cells may play a major effector role in psoriasis. Epidermal infiltration of predominantly oligoclonal CD8+ T cells, and probably also of CD4+ T cells in the dermis, is a striking feature of chronic psoriasis lesions, indicating that these cells are responding to specific antigens. We argue that CD4+ T cells are essential for initiating and maintaining the pathogenic process of psoriasis but that cross-primed CD8+ T cells are the main effector cells responding to antigens in the HLA-Cw*0602 binding pocket of keratinocytes. It is further proposed that CD8+ T cells are involved in the control of the Th1 polarization, which is observed in psoriasis lesions, through a complex interplay between CD4+, CD8+ T cells and cross-presenting dendritic cells. It is also suggested that spontaneous remissions or fluctuations in disease activity may be determined by a balance within the lesions between effector and suppressor CD4+ and CD8+ T cells.