Dense genotyping of immune-related susceptibility loci reveals new insights into the genetics of psoriatic arthritis

Psoriatic arthritis (PsA) is a chronic inflammatory arthritis associated with psoriasis and, despite the larger estimated heritability for PsA, the majority of genetic susceptibility loci identified to date are shared with psoriasis. Here, we present results from a case-control association study on 1,962 PsA patients and 8,923 controls using the Immunochip genotyping array. We identify eight loci passing genome-wide significance, secondary independent effects at three loci and a distinct PsA-specific variant at the IL23R locus. We report two novel loci and evidence of a novel PsA-specific association at chromosome 5q31. Imputation of classical HLA alleles, amino acids and SNPs across the MHC region highlights three independent associations to class I genes. Finally, we find an enrichment of associated variants to markers of open chromatin in CD8(+) memory primary T cells. This study identifies key insights into the genetics of PsA that could begin to explain fundamental differences between psoriasis and PsA.

IgA nephropathy and psoriatic arthritis that improved with steroid pulse therapy and mizoribine in combination with treatment for chronic tonsillitis and epipharyngitis

A 65-year-old man was admitted to our hospital with edema and renal dysfunction. He had received a diagnosis of psoriatic arthritis at 50 years of age. As a renal biopsy showed IgA nephropathy (IgAN), bilateral tonsillectomy was performed, and one course of steroid pulse therapy with an oral steroid and mizoribine were subsequently administered. The patient's proteinuria gradually reduced in association with an improvement in the renal function. In addition, the rash and arthralgia were ameliorated. In this case, adding treatment for chronic epipharyngitis accelerated the curative effects, and focal infection therapy consisting of immunosuppressive drugs was effective for both IgAN and psoriatic arthritis.

Divergent gene activation in peripheral blood and tissues of patients with rheumatoid arthritis, psoriatic arthritis and psoriasis following infliximab therapy

Objective

The immune inflammatory disorders rheumatoid arthritis (RA), psoriatic arthritis (PsA) and psoriasis (Ps) share common pathologic features and show responsiveness to anti-tumor necrosis factor (TNF) agents yet they are phenotypically distinct. The aim of this study was to examine if anti-TNF therapy is associated with divergent gene expression profiles in circulating cells and target tissues of patients with these diseases.

Methods

Peripheral blood CD14⁺ and CD14⁻ cells were isolated from 9 RA, 12 PsA and 10 Ps patients before and after infliximab (IFX) treatment. Paired synovial (n = 3, RA, PsA) and skin biopsies (n = 5, Ps) were also collected. Gene expression was analyzed by microarrays.

Results

26 out of 31 subjects responded to IFX. The transcriptional response of CD14⁺ cells to IFX was unique for the three diseases, with little overlap (<25%) in significantly changed gene lists (with PsA having the largest number of changed genes). In Ps, altered gene expression was more pronounced in lesional skin (relative to paired, healthy skin) compared to blood (relative to healthy controls). Marked suppression of up-regulated genes in affected skin was noted 2 weeks after therapy but the expression patterns differed from uninvolved skin. Divergent patterns of expression were noted between the blood cells and skin or synovial tissues in individual patients. Functions that promote cell differentiation, proliferation and apoptosis in all three diseases were enriched. RA was enriched in functions in CD14⁻ cells, PsA in CD14⁺ cells and Ps in both CD14⁺ and CD14⁻ cells, however, the specific functions showed little overlap in the 3 disorders.

Conclusion

Divergent patterns of altered gene expression are observed in RA, PsA and Ps patients in blood cells and target organs in IFX responders. Differential gene expression profiles in the blood do not correlate with those in target organs.

Optimisation of rheumatology indices: dactylitis and enthesitis in psoriatic arthritis

Outcome measures are a key part of study design and clinical assessment. Enthesitis and dactylitis are typical features of psoriatic arthritis (PsA) and the spondyloarthritides but traditionally scoring systems for enthesitis have mainly been validated in ankylosing spondylitis (AS). There are many scoring systems which are not validated used for dactylitis although newer validated scores are now available. Recently there have been advances in composite scores that include enthesitis and dactylitis to assess disease activity. These are currently being validated further and have not yet been tested in routine clinical practice.

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 Arthropathy and HLA-B51: Report of 5 Cases

Psoriasis arthropathy (PsA) is a chronic inflammatory arthropathy characterized by the association of arthritis with psoriasis. Although the precise mechanisms of PsA still remain obscure, several genetic and environmental factors have been suggested to play important roles. HLA-B51 has been strongly associated with Behçet's disease; however, its association with PsA has not been documented. We describe herein five Japanese patients (4 males and 1 female) with PsA and positive for HLA-B51. The clinical forms defined by Moll and Wright revealed that the polyarticular pattern was noted in two cases, and oligoarticular, distal, and spondyloarthropathy patterns were noted in one case each. Positive rheumatoid factor was detected in one patient, and antinuclear antibody in two patients. The other HLA subclasses were A2 and A31 in 3 cases, respectively. HLA-B51 was detected in 5 out of 17 patients with PsA examined in our department; in contrast, HLA-B51 was not detected in 17 patients with psoriasis vulgaris. Our observations suggest that HLA-B51 may play a role in the pathogenesis of PsA in the Japanese population.

Treatment of severe psoriasis and psoriatic arthritis with adalimumab in an HIV-positive patient

Psoriasis in HIV-infected patients poses a distinct challenge to the dermatologist due to its increased severity, tendency to be refractory to common treatment modalities, and necessity for cautious use of immunosuppressive agents. Tumor necrosis factor-α inhibitors have been shown to be safe and effective for the treatment of psoriasis in the general population, but their role in the treatment of HIV-positive patients is still unclear. The use of the tumor necrosis factor-α inhibitor adalimumab for the treatment of psoriasis in HIV-positive patients has yet to be reported. We present the case of a 49-year-old HIV-positive man with severe plaque psoriasis who has been successfully treated with adalimumab for the past 30 months with no adverse events related to treatment.

Interleukin-17+CD8+ T cells are enriched in the joints of patients with psoriatic arthritis and correlate with disease activity and joint damage progression

OBJECTIVE

Psoriatic arthritis (PsA) is associated with HLA class I genes, in contrast to the association with HLA class II in rheumatoid arthritis (RA). Since IL-17+ cells are considered important mediators of synovial inflammation, we sought to determine whether IL-17-producing CD8+ T cells may be found in the joints of patients with PsA and whether these cells might contribute to the disease process.

METHODS

Mononuclear cells from paired samples of synovial fluid (SF) and peripheral blood (PB) from patients with PsA or patients with RA were stimulated ex vivo, and CD4- T cells were examined by flow cytometry for cytokine expression, cytotoxic markers, and frequencies of γ/δ or mucosal-associated invariant T cells. Clinical measures of arthritis activity (C-reactive protein [CRP] level, erythrocyte sedimentation rate [ESR], Disease Activity Score in 28 joints [DAS28]) and power Doppler ultrasound (PDUS) scores for the presence of active synovitis in the aspirated knee were recorded and assessed for correlations with immunologic markers.

RESULTS

Within the CD3+ T cell compartment, both IL-17+CD4- (predominantly CD8+) and IL-17+CD4+ T cells were significantly enhanced in the SF compared to the PB of patients with PsA (P = 0.0003 and P = 0.002, respectively; n = 21), whereas in patients with RA, only IL-17+CD4+ T cells were increased in the SF compared to the PB (P = 0.008; n = 14). The frequency of IL-17+CD4- T cells in PsA SF was positively correlated with the CRP level (r = 0.52, P = 0.01), ESR (r = 0.59, P = 0.004), and DAS28 (r = 0.52, P = 0.01), and was increased in patients with erosive disease (P < 0.05). In addition, the frequency of IL-17+CD4- T cells positively correlated with the PDUS score, a marker for active synovitis (r = 0.49, P = 0.04).

CONCLUSION

These results show, for the first time, that the PsA joint, but not the RA joint, is enriched for IL-17+CD8+ T cells. Moreover, the findings reveal that the levels of this T cell subset are correlated with disease activity measures and the radiographic erosion status after 2 years, suggesting a previously unrecognized contribution of these cells to the pathogenesis of PsA.

The IL-23/IL-17 axis in psoriatic arthritis

Psoriatic arthritis (PsA) is an immune-mediated chronic inflammatory disease, affecting both the skin and joints. Disease progression is associated with aberrant cytokine expression, and TNF blockade is the most successful therapy to date. However, not all patients are responsive to anti-TNF treatment, highlighting the need to better understand the cellular and molecular mechanisms that govern the disease. PsA associations with single nucleotide polymorphisms in IL23R as well as TRAF3IP2 (Act1), a molecule downstream of the IL-17 receptor (IL-17R), have linked the IL-23/IL-17 axis to disease pathology. Although both cytokines are implicated in PsA, a full picture of their cellular targets and pathogenic mechanisms has not yet emerged. In this review, we focus on the IL-23/IL-17 axis-elicited responses mediated by osteoclasts, keratinocytes and neutrophils. Expanding our understanding of the cellular and molecular mechanisms that dictate pathogenicity in PsA will contribute to developing novel treatment strategies to combat disease.

A case of inverse psoriasis successfully treated with adalimumab

Inverse psoriasis is a rare form of psoriasis characterized by the involvement of skin fold areas rather than the more common psoriatic involvement of the extensor surfaces of the extremities, trunk, and scalp. In addition, it requires a modified therapeutic approach because it is often less responsive to standard treatment regimens. Current treatment recommendations for inverse psoriasis mainly consist of topical agents, including corticosteroids, calcipotriol, and immunomodulating agents, whereas systemic medications remain insufficiently studied. Although adalimumab, a TNF-α inhibitor, has been approved for the treatment of moderate to severe plaque psoriasis, some reports indicate that TNF-α inhibitors may sometimes trigger psoriatic lesions, including inverse psoriasis. However, we present a case of inverse psoriasis and psoriatic arthritis unresponsive to standard treatment that was successfully treated with adalimumab.

Deletion of late cornified envelope genes, LCE3C_LCE3B-del, is not associated with psoriatic arthritis in Tunisian patients

A deletion of two genes from the late cornified envelope (LCE), LCE3B and LCE3C within epidermal differentiation complex on chromosome 1 was shown to be associated with both psoriasis and psoriatic arthritis (PsA) in several populations. To assess whether this deletion may contribute to the genetic predisposition to PsA in Tunisia, a total of 73 patients with PsA and 120 healthy matched controls were screened for the deletion, LCE3C_LCE3B-del, and its tag SNP, rs4112788. We also evaluated a possible relationship between PSORS1 and LCE3C_LCE3B-del through genotyping two proxy markers to HLA-C (rs12191877 and rs2073048). Our results did not provide evidence for association between the LCE3C_LCE3B-del nor the rs4112788 and the PsA. Similarly, no significant epistatic effect was observed. Our data suggest that The LCE deletion, previously identified in patients with psoriasis, is not of a major importance in the development of PsA in Tunisian patients supporting the current perception that different genetic risk factors contribute to skin and joint disease. However, these results need to be confirmed by additional large-scale studies of Tunisian PsA patients and controls.

Burden of disease: psoriasis and psoriatic arthritis

Psoriatic arthritis (PsA) increases the disease burden associated with psoriasis by further diminishing quality of life, increasing health care costs and cardiovascular risk, and potentially causing progressive joint damage. The presence of PsA influences psoriasis treatment by increasing overall disease complexity and, within the framework of current guidelines and recommendations, requiring the use of conventional disease-modifying anti-rheumatic drugs or tumor necrosis factor-α inhibitors in order to prevent progressive joint damage. Despite its important impact, PsA is still under-diagnosed in dermatology practice. Dermatologists are well positioned to recognize and treat PsA, given that it characteristically presents, on average, 10 years subsequent to the appearance of skin symptoms. Regular screening of psoriasis patients for early evident joint symptoms should be incorporated into daily dermatologic practice. Although drugs effective in PsA are available, not all patients may respond to treatment, and others may lose their initial response over time. New investigational therapies, such as inhibitors of interleukin-17A, interleukin-12/23, Janus kinase 3, or phosphodiesterase-4, may address unmet needs in psoriatic disease, with further research needed to determine the role of these agents in reducing joint damage and other comorbidities.

Th17 and Th22 cells in psoriatic arthritis and psoriasis

INTRODUCTION

The aim of this study was to characterize interleukin 17 (IL-17) and interleukin 22 (IL-22) producing cells in peripheral blood (PB), skin, synovial fluid (SF) and synovial tissue (ST) in patients with psoriasis (Ps) and psoriatic arthritis (PsA).

METHODS

Flow cytometry was used to enumerate cells making IL-22 and IL-17, in skin and/or SF and PB from 11 patients with Ps and 12 patients with PsA; skin and PB of 15 healthy controls and SF from rheumatoid arthritis (RA) patients were used as controls. Expression of the interleukin 23 receptor (IL-23R) and chemokine receptors CCR4 and CCR6 was examined. Secretion of IL-17 and IL-22 was measured by ELISA. ST was analysed by immunohistochemical staining of IL-17 and IL-22.

RESULTS

Increased frequencies of IL-17+ and IL-22+ CD4+ T cells were seen in PB of patients with PsA and Ps. IL-17 secretion was significantly elevated in both PsA and Ps, whilst IL-22 secretion was higher in PsA compared to Ps and healthy controls. A higher proportion of the CD4+ cells making IL-17 or IL-22 expressed IL-23R and frequencies of IL-17+, CCR6+ and CCR4+ T cells were elevated in patients with Ps and those with PsA. In patients with PsA, CCR6+ and IL-23R + T cells numbers were elevated in SF compared to PB. Increased frequencies of IL-17+ and IL-22+ CD4+ T cells were demonstrated in Ps skin lesions. In contrast, whilst elevated frequencies of CD4+ IL-17+ cells were seen in PsA SF compared to PB, frequencies of CD4+ IL-22+ T cells were lower. Whereas IL-17 expression was equivalent in PsA, osteoarthritis (OA) and RA ST, IL-22 expression was higher in RA than either OA or PsA ST, in which IL-22 was strikingly absent.

CONCLUSIONS

Elevated frequencies of IL-17 and IL-22 producing CD4+ T cells were a feature of both Ps and PsA. However their differing distribution at disease sites, including lower frequencies of IL-22+ CD4+ T cells in SF compared to skin and PB, and lack of IL-22 expression in ST suggests that Th17 and Th22 cells have common, as well as divergent roles in the pathogenesis of Ps and PsA.

Lumbar interspinous bursitis in active polymyalgia rheumatica

OBJECTIVES

To evaluate the inflammatory involvement of lumbar interspinous bursae in patients with polymyalgia rheumatica (PMR) using magnetic resonance imaging (MRI).

METHODS

Ten consecutive, untreated new patients with PMR and pain in the shoulder and pelvic girdles were investigated. Seven patients with spondyloarthritis (4 with psoriatic spondyloarthrits, one with entheropatic spondyloarthritis, and 2 with ankylosing spondylitis) as well as 2 patients with spinal osteoarthritis and 2 patients with rheumatoid arthritis with lumbar pain served as controls. MRI of lumbar spine was performed in all PMR patients and controls. Nine patients (5 PMR patients and 4 controls) also had MRI of the thoracic spine.

RESULTS

MRI evidence of interspinous lumbar bursitis was found in 9/10 patients with PMR and in 5/11 controls. A moderate to marked (grade ≥2 on a semiquantitative 0-3 scale) lumbar bursitis occurred significantly more frequently in patients with PMR than in control patients (60% vs. 9%, p=0.020). In most of the patients and controls lumbar bursitis was found at the L3-L5 interspaces. Only 2 patients had bursitis at a different level (one patient had widespread lumbar bursitis, and one control at L2-L4). No interspinous bursitis was demonstrated by MRI of the thoracic spine in patients and controls.

CONCLUSIONS

Inflammation of lumbar bursae may be responsible for the low back pain reported by patients with PMR. The prominent inflammatory involvement of bursae including those of the lumbar spine supports the hypothesis that PMR may be a disorder affecting predominantly extra-articular synovial structures.

[POPP syndrome: Psoriatic onychopachydermoperiostitis]

Psoriatic onychopachydermoperiostitis (POPP) syndrome characterizes a clinical variant of psoriatic arthritis originally described by Fournie et al in 1989. Both great toes are generally affected presenting with nail changes, painful swelling of the soft tissue close to the distal phalanx as well as specific radiologic changes such as periosteal reaction and bone erosions of the distal phalanges. Joint involvement is characteristically absent and classic psoriatic lesions may be associated. Painful symptoms may lead to severe functional and quality of life impairment. Traditional systemic treatment is generally frustrating. Here we report a female patient presenting POPP syndrome refractory to traditional systemic treatments and adalimumab, further presenting a favorable response to treatment with etanercept.

Nail psoriasis: a review

Nail psoriasis is common, occurring in up to half of patients with psoriasis and in 90% of patients with psoriatic arthritis. Left untreated, it may progress to debilitating nail disease, which leads to significant functional impairment. The most common clinical signs of nail psoriasis are nail plate pitting and onycholysis. Other classical signs include oil drop discoloration, subungual hyperkeratosis, and splinter hemorrhages. The modified Nail Psoriasis Severity Index (mNAPSI) can be used to grade the severity of nail psoriasis, while the Nail Psoriasis Quality of Life Scale (NPQ10) is a questionnaire that evaluates the impact of nail psoriasis on the patient's functional status and quality of life. Treatment of nail psoriasis should be individualized according to the patient's preferences, severity of nail changes, and presence of skin and/or joint involvement. Both topical and intralesional therapies are safe and effective treatment modalities for nail disease, but are limited by poor adherence and pain, respectively. Systemic therapy such as oral retinoids may be considered for widespread nail disease causing significant morbidity. Among biologic agents, tumor necrosis factor-α inhibitors and T-cell-targeted therapies such as ustekinumab may be useful for refractory severe nail psoriasis.

A multicentre study on high-frequency ultrasound evaluation of the skin and joints in patients with psoriatic arthritis treated with infliximab

OBJECTIVES

Our objective was to describe the ultrasound features of patients with PsA in joints and skin and their changes after treatment with infliximab.

METHODS

Eight hospitals recruited PsA active patients. Clinical (joint count for pain, TJC, and swelling, SJC, pain VAS, ESR, C-reactive protein and PASI) and US variables (plaque thickness, PD signal of dermal lesions, synovitis, erosions, and PD signal, assessed by 4-category ordinal scales) were independently recorded at baseline and 4, 12 and 24-week after starting treatment with infliximab. The results were analysed with paired T, Wilcoxon test, ANOVA and marginal homogeneity test.

RESULTS

Changes in 24 patients from baseline to last available data were significant for clinical variables, pain VAS, TJC and SJC as well as for ESR, CRP (all p<0.0005). Dermatological PASI changed from 14.6±14.9 to 2.1±4.1 and plaque thickness from 3.34±1.75 mm to 1.74±0.96 mm (both p<0.0005); synovitis and PD signal improved (both p<0.0005). Psoriatic plaque PD improved across the study (p<0.0005) with no signal increasing from 36.4% to 88.9% and positive PD signal decreasing from 63.6% to 11.1% of the plaques.

CONCLUSIONS

Treatment with anti-TNF-α infliximab improves the symptoms of patients with PsA at joint and psoriatic skin levels from a clinical and ultrasonographic perspective.

Adipokines in psoriatic arthritis patients: the correlations with osteoclast precursors and bone erosions

Significant bone remodeling with disordered osteoclastogenesis has been implicated in the pathogenesis of psoriatic arthritis (PsA). And there is a high prevalence of the metabolic syndrome (MS) in PsA patients. Adipokines, especially leptin and adiponectin, have recently been reported to be involved in the development and regulation of some autoimmune diseases. In this study, we examined the alternation of circulating osteoclastogenesis related cytokines [tumor necrosis factor-α (TNF-α), osteoprotegerin (OPG) and receptor activator of nuclear factor-κB ligand (RANKL)] and adipokines (leptin, adiponectin, resistin, chemerin, omentin) in PsA patients, and analysed the correlations between these factors and osteoclast precursors numbers, radiographic damage scores, and disease activity index. 41 PsA patients, 20 psoriasis patients, and 24 healthy controls were recruited. Blood samples were obtained for detecting the levels of TNF-α, OPG, RANKL and the adipokines. The numbers of osteoclast precursors (OCs) in peripheral blood were assessed. Radiographs of affected joints in PsA patients were scored for erosion, joint-space narrowing, osteolysis, and new bone formation. Compared with healthy controls, patients with PsA had higher TNF-α, RANKL, OCs, leptin and omentin but lower adiponectin and chemerin. Increased serum levels of TNF-α, RANKL, leptin, and omentin were positively correlated with OCs numbers. In contrast, serum adiponectin levels were decreased in PsA patients and negatively correlated with OCs numbers. TNF-α, RANKL and leptin were positively correlated with Psoriatic Arthritis Joint Activity Index (PsAJAI). Only TNF-α was positively correlated with radiographic damage scores. Our data demonstrated that systemic expression of soluble mediators of osteoclastogenesis and adipokines were disordered in PsA. Certain adipokines were elevated in the circulation of patients with PsA and might contribute to pathogenesis of arthritis. Prospective studies will be of interest to determine the pluripotent effects of adipokines on osteoclastogenesis in chronic inflammatory rheumatic diseases. Future studies may lead to novel therapeutic strategies.

Predictors of functional impairment and pain in erosive osteoarthritis of the interphalangeal joints: comparison with controlled inflammatory arthritis

OBJECTIVE

To compare levels of pain and functional limitation in patients with erosive osteoarthritis (OA) of the interphalangeal finger joints with those in patients with nonerosive OA and patients with controlled inflammatory arthritis affecting the hands, and to explore predictors of functional impairment in erosive OA.

METHODS

A cross-sectional study including 270 patients with OA of the hands who were referred to rheumatology clinics was performed. A group of patients with inflammatory arthritis (rheumatoid arthritis or psoriatic arthritis) with a low Disease Activity Score in 28 joints (<3.2; n = 79) was examined. Levels of functional impairment (measured by the Functional Index for Hand OA [FIHOA] and Australian/Canadian OA Hand Index [AUSCAN]) and pain were compared between the groups. Predictors of functional impairment in erosive OA were evaluated by generalized linear models.

RESULTS

Of 270 patients with hand OA, 167 (61.9%) were classified as having erosive OA. Despite a higher percentage of patients taking analgesics (almost 60%), patients with erosive OA had worse functional outcome and pain scores than patients with controlled inflammatory arthritis or nonerosive OA. Pain scores remained significantly higher in patients with erosive OA after correction for potential confounders. FIHOA and AUSCAN function scores showed a trend toward more disability in patients with erosive OA. Female sex and the number of radiographic affected joints (consisting of joints in the erosive and remodeled radiographic phases) were the strongest predictors of functional impairment in erosive OA. Whether the carpometacarpal joints were affected did not influence functional status in patients with erosive OA.

CONCLUSION

Our findings indicate that patients with erosive OA have more functional impairment and significantly more pain compared to patients with controlled inflammatory arthritis affecting the hands. This highlights the significant clinical burden of erosive OA and warrants the search for new treatment strategies.

Osteoporosis and psoriatic arthritis

Osteoporosis (OP) is a skeletal disorder characterized by compromised bone strength that predisposes to an increased risk of fracture. The prevalence of OP in the general population is very high as established in several studies, and OP represents one of the possible aspects of bone involvement in arthritis. In psoriatic arthritis this involvement is particularly complex because it affects not only mechanisms of bone loss but also of bone formation. We will discuss these aspects and the available epidemiological data.

Th17 and interleukin 23 in the pathogenesis of psoriatic arthritis and spondyloarthritis

Psoriatic arthritis and spondyloarthritis (SpA) are complex immune-mediated diseases affecting peripheral and axial joints. T cells have been considered fundamental in triggering the disease and maintaining the process in the chronic phase. The recent discovery of the CD4+ Th17 lymphocyte subset and the interleukin 23/interleukin 17 axis has further contributed to the definition of unknown pathways, challenging previous models and the role of Th1/Th2 T cells in immune mediated diseases, including SpA.