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Aims: Whereas intravenous administration of Toll-like receptor 4 ligand lipopolysaccharide (LPS) to human volunteers is frequently used in clinical pharmacology studies, systemic use of LPS has practical limitations. We aimed to characterize the intradermal LPS response in healthy volunteers, and as such qualify the method as local inflammation model for clinical pharmacology studies. Methods: Eighteen healthy male volunteers received 2 or 4 intradermal 5 ng LPS injections and 1 saline injection on the forearms. The LPS response was evaluated by noninvasive (perfusion, skin temperature and erythema) and invasive assessments (cellular and cytokine responses) in skin biopsy and blister exudate. Results: LPS elicited a visible response and returned to baseline at 48 hours. Erythema, perfusion and temperature were statistically significant (P Discussion: Intradermal LPS administration in humans causes an acute, localized and transient inflammatory reaction that is well-tolerated by healthy volunteers. This may be a valuable inflammation model for evaluating the pharmacological activity of anti-inflammatory investigational compounds in proof of pharmacology studies.

IntroductionThe incidence of degenerative disorders, including osteoarthritis (OA), increases rapidly in women after menopause. However, the influence of the menopause is still insufficiently investigated due to the slowness of menopausal transition. In this study, a novel human model is used in which it is expected that menopausal-related changes will occur faster. This is the Females discontinuing Oral Contraceptives Use at Menopausal age model. The ultimate aim is to link these changes to OA and other degenerative disorders, including cardiovascular diseases, diabetes, osteoporosis and tendinopathies.Methods and analysisThis is a pilot observational prospective cohort study with 2 years of follow-up. Fifty women aged 50–60 who use oral contraceptive (OC) and have the intention to stop are included. Measurements are performed once before stopping OC, and four times thereafter at 6 weeks, 6 months, 1 year and 2 years. At every time point, a questionnaire is filled in and a sample of blood is drawn. At the first and final time points, a physical examination, hand radiographs and a MRI scan of one knee are performed. The primary OA outcome is progression of the MRI Osteoarthritis Knee Score. Secondary OA outcomes are the development of clinical knee and hand OA, development of knee OA according to the MRI definition, and progression of radiographic features for hand OA. Principal component analysis will be used to assess which changes occur after stopping OC. Univariate and multivariate generalised estimating equation models will be used to test for associations between these components and OA.Ethics and disseminationThe study has been approved by the Medical Ethics Committee of the Erasmus MC University Medical Center Rotterdam (MEC-2019-0592). All participants must give informed consent before data collection. Results will be disseminated in national and international journals.Trial registration numberNL70796.078.19.

Objective: Interleukin-17A (IL-17A) and tumor necrosis factor (TNF) contribute to the pathogenesis of psoriatic arthritis (PsA). However, their functional relationship in PsA synovitis has not been fully elucidated. Additionally, although CD8+ T cells in PsA have been recognized via flow cytometry as a source of IL-17A production, it is not clear whether CD8+ T cells secrete IL-17A under more physiologically relevant conditions in the context from PsA synovitis. This study was undertaken to clarify the roles of IL-17A and TNF in the synovial fluid (SF) from patients with PsA and investigate the impact of CD8+ T cells on IL-17A production. Methods: IL-17A+ T cells were identified by flow cytometry in SF samples from 20 patients with active PsA, blood samples from 22 treatment-naive patients with PsA, and blood samples from 22 healthy donors. IL-17A+ T cells were sorted from 12 PsA SF samples and stimulated using anti-CD3/anti-CD28 or phorbol myristate acetate (PMA) and ionomycin ex vivo, alone (n = 3) or together with autologous monocytes (n = 3) or PsA fibroblast-like synoviocytes (FLS) (n = 5–6). To evaluate the differential allogeneic effects of neutralizing IL-17A and TNF, SF CD4+ T cells and PsA FLS cocultures were also used (n = 5–6). Results: Flow cytometry analyses of SF samples from patients with PsA showed IL-17A positivity for CD4+ and CD8+ T cells (IL-17A, median 0.71% [interquartile range 0.35–1.50%] in CD4+ cells; median 0.44% [interquartile range 0.17–1.86%] in CD8+ T cells). However, only CD4+ T cells secreted IL-17A after anti-CD3/anti-CD28 activation, when cultured alone and in cocultures with PsA monocytes or PsA FLS (each P < 0.05). Remarkably, CD8+ T cells only secreted IL-17A after 4- or 72-hour stimulation with PMA/ionomycin. Anti–IL-17A and anti-TNF treatments both inhibited PsA synovitis ex vivo. Neutralizing IL-17A strongly inhibited IL-6 (P < 0.05) and IL-1β (P < 0.01), while anti-TNF treatment was more potent in reducing matrix metalloproteinase 3 (MMP-3) (P < 0.05) and MMP-13. Conclusion: CD8+ T cells, in contrast to CD4+ T cells, in SF specimens obtained from PsA patients did not secrete IL-17A following T cell receptor activation. Overlapping, but distinct, effects at the level of inflammatory cytokines and MMPs were found after neutralizing IL-17A or TNF ex vivo in a human model of PsA synovitis.

Background Chronic synovial inflammation is an important hallmark of inflammatory arthritis, but the cells and mechanisms involved are incompletely understood. Previously, we have shown that CCR6+ memory T-helper (memTh) cells and synovial fibroblasts (SF) activate each other in a pro-inflammatory feedforward loop, which potentially drives persistent synovial inflammation in inflammatory arthritis. However, the CCR6+ memTh cells are a heterogeneous population, containing Th17/Th22 and Th17.1 cells. Currently, it is unclear which of these subpopulations drive SF activation and how they should be targeted. In this study, we examined the individual contribution of these CCR6+ memTh subpopulations to SF activation and examined ways to regulate their function. Methods Th17/Th22 (CXCR3−CCR4+), Th17.1 (CXCR3+CCR4−), DP (CXCR3+CCR4+), and DN (CXCR3−CCR4−) CCR6+ memTh, cells sorted from PBMC of healthy donors or treatment-naïve early rheumatoid arthritis (RA) patients, were cocultured with SF from RA patients with or without anti-IL17A, anti-IFNγ, or 1,25(OH)2D3. Cultures were analyzed by RT-PCR, ELISA, or flow cytometry. Results Th17/Th22, Th17.1, DP, and DN cells equally express RORC but differ in production of TBX21 and cytokines like IL-17A and IFNγ. Despite these differences, all the individual CCR6+ memTh subpopulations, both from healthy individuals and RA patients, were more potent in activating SF than the classical Th1 cells. SF activation was partially inhibited by blocking IL-17A, but not by inhibiting IFNγ or TBX21. However, active vitamin D inhibited the pathogenicity of all subpopulations leading to suppression of SF activation. Conclusions Human CCR6+ memTh cells contain several subpopulations that equally express RORC but differ in TBX21, IFNγ, and IL-17A expression. All individual Th17 subpopulations are more potent in activating SF than classical Th1 cells in an IFNγ-independent manner. Furthermore, our data suggest that IL-17A is not dominant in this T cell-SF activation loop but that a multiple T cell cytokine inhibitor, such as 1,25(OH)2D3, is able to suppress CCR6+ memTh subpopulation-driven SF activation.

Interleukin 17A (IL-17A) has been put forward as a strong ally in our fight against invading pathogens across exposed epithelial surfaces by serving an antimicrobial immunosurveillance role in these tissues to protect the barrier integrity. Amongst other mechanisms that prevent tissue injury mediated by potential microbial threats and promote restoration of epithelial homeostasis, IL-17A attracts effector cells to the site of inflammation and support the host response by driving the development of ectopic lymphoid structures. Accumulating evidence now underscores an integral role of IL-17A in driving the pathophysiology and clinical manifestations in three potentially life-threatening autoimmune diseases, namely, systemic lupus erythematosus, Sjögren’s syndrome, and systemic sclerosis. Available studies provide convincing evidence that the abundance of IL-17A in target tissues and its prime source, which is T helper 17 cells (Th17) and double negative T cells (DNT), is not an innocent bystander but in fact seems to be prerequisite for organ pathology. In this regard, IL-17A has been directly implicated in critical steps of autoimmunity. This review reports on the synergistic interactions of IL-17A with other critical determinants such as B cells, neutrophils, stromal cells, and the vasculature that promote the characteristic immunopathology of these autoimmune diseases. The summary of observations provided by this review may have empowering implications for IL-17A-based strategies to prevent clinical manifestations in a broad spectrum of autoimmune conditions.

IL-23 plays an important role in the development of arthritis and the IL-23 receptor (IL-23R) is expressed on different types of T cells. However, it is not fully clear which IL-23R+ T cells are critical in driving T cell-mediated synovitis. We demonstrate, using knock-in IL-23R-GFP reporter (IL-23RGFP/+ ) mice, that CD4+ CCR6+ T cells and γδ T cells, but not CD8+ T cells, express the IL-23R(GFP). During early arthritis, IL-23R(GFP)+ CD4+ CCR6+ T cells, but not IL-23R(GFP)+ γδ T cells, were present in the inflamed joints. IL-23RGFP/+ mice were bred as homozygotes to obtain IL-23RGFP/GFP (IL-23R deficient/IL-23R-/- ) mice, which express GFP under the IL-23R promotor. Arthritis progression and joint damage were significantly milder in IL-23R-/- mice, which revealed less IL-17A+ cells in their lymphoid tissues. Surprisingly, IL-23R-/- mice had increased numbers of IL-23R(GFP)+ CD4+ CCR6+ and CCR7+ CD4+ CCR6+ T cells in their spleen compared to WT, and IL-23 suppressed CCR7 expression in vitro. However, IL-23R(GFP)+ CD4+ CCR6+ T cells were present in the synovium of IL-23R-/- mice at day 4. Finally, adoptive transfer experiments revealed that CD4+ CCR6+ T cells and not γδ T cells drive arthritis progression. These data suggest that IL-23R-dependent T cell-mediated synovitis is dependent on CD4+ CCR6+ T cells and not on γδ T cells.

All authors: Andrea Cossarizza Hyun‐Dong Chang Andreas Radbruch Andreas Acs Dieter Adam Sabine Adam‐Klages William W. Agace Nima Aghaeepour Mübeccel Akdis Matthieu Allez Larissa Nogueira Almeida Giorgia Alvisi Graham Anderson Immanuel Andrä Francesco Annunziato Achille Anselmo Petra Bacher Cosima T. Baldari Sudipto Bari Vincenzo Barnaba Joana Barros‐Martins Luca Battistini Wolfgang Bauer Sabine Baumgart Nicole Baumgarth Dirk Baumjohann Bianka Baying Mary Bebawy Burkhard Becher Wolfgang Beisker Vladimir Benes Rudi Beyaert Alfonso Blanco Dominic A. Boardman Christian Bogdan Jessica G. Borger Giovanna Borsellino Philip E. Boulais Jolene A. Bradford Dirk Brenner Ryan R. Brinkman Anna E. S. Brooks Dirk H. Busch Martin Büscher Timothy P. Bushnell Federica Calzetti Garth Cameron Ilenia Cammarata Xuetao Cao Susanna L. Cardell Stefano Casola Marco A. Cassatella Andrea Cavani Antonio Celada Lucienne Chatenoud Pratip K. Chattopadhyay Sue Chow Eleni Christakou Luka Čičin‐Šain Mario Clerici Federico S. Colombo Laura Cook Anne Cooke Andrea M. Cooper Alexandra J. Corbett Antonio Cosma Lorenzo Cosmi Pierre G. Coulie Ana Cumano Ljiljana Cvetkovic Van Duc Dang Chantip Dang‐Heine Martin S. Davey Derek Davies Sara De Biasi Genny Del Zotto Gelo Victoriano Dela Cruz Michael Delacher Silvia Della Bella Paolo Dellabona Günnur Deniz Mark Dessing James P. Di Santo Andreas Diefenbach Francesco Dieli Andreas Dolf Thomas Dörner Regine J. Dress Diana Dudziak Michael Dustin Charles‐Antoine Dutertre Friederike Ebner Sidonia B. G. Eckle Matthias Edinger Pascale Eede Götz R.A. Ehrhardt Marcus Eich Pablo Engel Britta Engelhardt Anna Erdei Charlotte Esser Bart Everts Maximilien Evrard Christine S. Falk Todd A. Fehniger Mar Felipo‐Benavent Helen Ferry Markus Feuerer Andrew Filby Kata Filkor Simon Fillatreau Marie Follo Irmgard Förster John Foster Gemma A. Foulds Britta Frehse Paul S. Frenette Stefan Frischbutter Wolfgang Fritzsche David W. Galbraith Anastasia Gangaev Natalio Garbi Brice Gaudilliere Ricardo T. Gazzinelli Jens Geginat Wilhelm Gerner Nicholas A. Gherardin Kamran Ghoreschi Lara Gibellini Florent Ginhoux Keisuke Goda Dale I. Godfrey Christoph Goettlinger Jose M. González‐Navajas Carl S. Goodyear Andrea Gori Jane L. Grogan Daryl Grummitt Andreas Grützkau Claudia Haftmann Jonas Hahn Hamida Hammad Günter Hämmerling Leo Hansmann Goran Hansson Christopher M. Harpur Susanne Hartmann Andrea Hauser Anja E. Hauser David L. Haviland David Hedley Daniela C. Hernández Guadalupe Herrera Martin Herrmann Christoph Hess Thomas Höfer Petra Hoffmann Kristin Hogquist Tristan Holland Thomas Höllt Rikard Holmdahl Pleun Hombrink Jessica P. Houston Bimba F. Hoyer Bo Huang Fang‐Ping Huang Johanna E. Huber Jochen Huehn Michael Hundemer Christopher A. Hunter William Y. K. Hwang Anna Iannone Florian Ingelfinger Sabine M Ivison Hans‐Martin Jäck Peter K. Jani Beatriz Jávega Stipan Jonjic Toralf Kaiser Tomas Kalina Thomas Kamradt Stefan H. E. Kaufmann Baerbel Keller Steven L. C. Ketelaars Ahad Khalilnezhad Srijit Khan Jan Kisielow Paul Klenerman Jasmin Knopf Hui‐Fern Koay Katja Kobow Jay K. Kolls Wan Ting Kong Manfred Kopf Thomas Korn Katharina Kriegsmann Hendy Kristyanto Thomas Kroneis Andreas Krueger Jenny Kühne Christian Kukat Désirée Kunkel Heike Kunze‐Schumacher Tomohiro Kurosaki Christian Kurts Pia Kvistborg Immanuel Kwok Jonathan Landry Olivier Lantz Paola Lanuti Francesca LaRosa Agnès Lehuen Salomé LeibundGut‐Landmann Michael D. Leipold Leslie Y.T. Leung Megan K. Levings Andreia C. Lino Francesco Liotta Virginia Litwin Yanling Liu Hans‐Gustaf Ljunggren Michael Lohoff Giovanna Lombardi Lilly Lopez Miguel López‐Botet Amy E. Lovett‐Racke Erik Lubberts Herve Luche Burkhard Ludewig Enrico Lugli Sebastian Lunemann Holden T. Maecker Laura Maggi Orla Maguire Florian Mair Kerstin H. Mair Alberto Mantovani Rudolf A. Manz Aaron J. Marshall Alicia Martínez‐Romero Glòria Martrus Ivana Marventano Wlodzimierz Maslinski Giuseppe Matarese Anna Vittoria Mattioli Christian Maueröder Alessio Mazzoni James McCluskey Mairi McGrath Helen M. McGuire Iain B. McInnes Henrik E. Mei Fritz Melchers Susanne Melzer Dirk Mielenz Stephen D. Miller Kingston H.G. Mills Hans Minderman Jenny Mjösberg Jonni Moore Barry Moran Lorenzo Moretta Tim R. Mosmann Susann Müller Gabriele Multhoff Luis Enrique Muñoz Christian Münz Toshinori Nakayama Milena Nasi Katrin Neumann Lai Guan Ng Antonia Niedobitek Sussan Nourshargh Gabriel Núñez José‐Enrique O'Connor Aaron Ochel Anna Oja Diana Ordonez Alberto Orfao Eva Orlowski‐Oliver Wenjun Ouyang Annette Oxenius Raghavendra Palankar Isabel Panse Kovit Pattanapanyasat Malte Paulsen Dinko Pavlinic Livius Penter Pärt Peterson Christian Peth Jordi Petriz Federica Piancone Winfried F. Pickl Silvia Piconese Marcello Pinti A. Graham Pockley Malgorzata Justyna Podolska Zhiyong Poon Katharina Pracht Immo Prinz Carlo E. M. Pucillo Sally A. Quataert Linda Quatrini Kylie M. Quinn Helena Radbruch Tim R. D. J. Radstake Susann Rahmig Hans‐Peter Rahn Bartek Rajwa Gevitha Ravichandran Yotam Raz Jonathan A. Rebhahn Diether Recktenwald Dorothea Reimer Caetano Reis e Sousa Ester B.M. Remmerswaal Lisa Richter Laura G. Rico Andy Riddell Aja M. Rieger J. Paul Robinson Chiara Romagnani Anna Rubartelli Jürgen Ruland Armin Saalmüller Yvan Saeys Takashi Saito Shimon Sakaguchi Francisco Sala‐de‐Oyanguren Yvonne Samstag Sharon Sanderson Inga Sandrock Angela Santoni Ramon Bellmàs Sanz Marina Saresella Catherine Sautes‐Fridman Birgit Sawitzki Linda Schadt Alexander Scheffold Hans U. Scherer Matthias Schiemann Frank A. Schildberg Esther Schimisky Andreas Schlitzer Josephine Schlosser Stephan Schmid Steffen Schmitt Kilian Schober Daniel Schraivogel Wolfgang Schuh Thomas Schüler Reiner Schulte Axel Ronald Schulz Sebastian R. Schulz Cristiano Scottá Daniel Scott‐Algara David P. Sester T. Vincent Shankey Bruno Silva‐Santos Anna Katharina Simon Katarzyna M. Sitnik Silvano Sozzani Daniel E. Speiser Josef Spidlen Anders Stahlberg Alan M. Stall Natalie Stanley Regina Stark Christina Stehle Tobit Steinmetz Hannes Stockinger Yousuke Takahama Kiyoshi Takeda Leonard Tan Attila Tárnok Gisa Tiegs Gergely Toldi Julia Tornack Elisabetta Traggiai Mohamed Trebak Timothy I.M. Tree Joe Trotter John Trowsdale Maria Tsoumakidou Henning Ulrich Sophia Urbanczyk Willem van de Veen Maries van den Broek Edwin van der Pol Sofie Van Gassen Gert Van Isterdael René A.W. van Lier Marc Veldhoen Salvador Vento‐Asturias Paulo Vieira David Voehringer Hans‐Dieter Volk Anouk von Borstel Konrad von Volkmann Ari Waisman Rachael V. Walker Paul K. Wallace Sa A. Wang Xin M. Wang Michael D. Ward Kirsten A Ward‐Hartstonge Klaus Warnatz Gary Warnes Sarah Warth Claudia Waskow James V. Watson Carsten Watzl Leonie Wegener Thomas Weisenburger Annika Wiedemann Jürgen Wienands Anneke Wilharm Robert John Wilkinson Gerald Willimsky James B. Wing Rieke Winkelmann Thomas H. Winkler Oliver F. Wirz Alicia Wong Peter Wurst Jennie H. M. Yang Juhao Yang Maria Yazdanbakhsh Liping Yu Alice Yue Hanlin Zhang Yi Zhao Susanne Maria Ziegler Christina Zielinski Jakob Zimmermann Arturo Zychlinsky., These guidelines are a consensus work of a considerable number of members of the immunology and flow cytometry community. They provide the theory and key practical aspects of flow cytometry enabling immunologists to avoid the common errors that often undermine immunological data. Notably, there are comprehensive sections of all major immune cell types with helpful Tables detailing phenotypes in murine and human cells. The latest flow cytometry techniques and applications are also described, featuring examples of the data that can be generated and, importantly, how the data can be analysed. Furthermore, there are sections detailing tips, tricks and pitfalls to avoid, all written and peer‐reviewed by leading experts in the field, making this an essential research companion., This work was supported by the Netherlands Organisation for Scientific Research – Domain Applied and Engineering Sciences (NWO-TTW), research program VENI 15924. This work was funded by the Deutsche Forschungsgemeinschaft. European Union Innovative Medicines Initiative - Joint Undertaking - RTCure Grant Agreement 777357 and innovation program (Grant Agreement 695551).

The IL-23 receptor (IL-23R) signaling pathway has pleiotropic effects on the differentiation of osteoclasts and osteoblasts, since it can inhibit or stimulate these processes via different pathways. However, the potential role of this pathway in the regulation of bone homeostasis remains elusive. Therefore, we studied the role of IL-23R signaling in physiological bone remodeling using IL-23R deficient mice. Using µCT, we demonstrate that 7-week-old IL-23R−/− mice have similar bone mass as age matched littermate control mice. In contrast, 12-week-old IL-23R−/− mice have significantly lower trabecular and cortical bone mass, shorter femurs and more fragile bones. At the age of 26 weeks, there were no differences in trabecular bone mass and femur length, but most of cortical bone mass parameters remain significantly lower in IL-23R−/− mice. In vitro osteoclast differentiation and resorption capacity of 7- and 12-week-old IL-23R−/− mice are similar to WT. However, serum levels of the bone formation marker, PINP, are significantly lower in 12-week-old IL-23R−/− mice, but similar to WT at 7 and 26 weeks. Interestingly, Il23r gene expression was not detected in in vitro cultured osteoblasts, suggesting an indirect effect of IL-23R. In conclusion, IL-23R deficiency results in temporal and long-term changes in bone growth via regulation of bone formation.

AimTo identify differentially methylated positions (DMPs) and regions (DMRs) that predict response to Methotrexate (MTX) in early rheumatoid arthritis (RA) patients.Materials and methodsDNA from baseline peripheral blood mononuclear cells was extracted from 72 RA patients. DNA methylation, quantified using the Infinium MethylationEPIC, was assessed in relation to response to MTX (combination) therapy over the first 3 months.ResultsBaseline DMPs associated with response were identified; including hits previously described in RA. Additionally, 1309 DMR regions were observed. However, none of these findings were genome-wide significant. Likewise, no specific pathways were related to response, nor could we replicate associations with previously identified DMPs.ConclusionNo baseline genome-wide significant differences were identified as biomarker for MTX (combination) therapy response; hence meta-analyses are required.

ObjectiveTo study whether glucocorticoid (GC) resistance delineates disease-relevant T helper (Th) subsets that home to the CNS of patients with early MS.MethodsThe expression of key determinants of GC sensitivity, multidrug resistance protein 1 (MDR1/ABCB1) and glucocorticoid receptor (GR/NR3C1), was investigated in proinflammatory Th subsets and compared between natalizumab-treated patients with MS and healthy individuals. Blood, CSF, and brain compartments from patients with MS were assessed for the recruitment of GC-resistant Th subsets using fluorescence-activated cell sorting (FACS), quantitative polymerase chain reaction (qPCR), immunohistochemistry, and immunofluorescence.ResultsAn MS-associated Th subset termed Th17.1 showed a distinct GC-resistant phenotype as reflected by high MDR1 and low GR expression. This expression ratio was further elevated in Th17.1 cells that accumulated in the blood of patients with MS treated with natalizumab, a drug that prevents their entry into the CNS. Proinflammatory markers C-C chemokine receptor 6, IL-23R, IFN-γ, and GM-CSF were increased in MDR1-expressing Th17.1 cells. This subset predominated the CSF of patients with early MS, which was not seen in the paired blood or in the CSF from patients with other inflammatory and noninflammatory neurologic disorders. The potential of MDR1-expressing Th17.1 cells to infiltrate brain tissue was confirmed by their presence in MS white matter lesions.ConclusionThis study reveals that GC resistance coincides with preferential CNS recruitment of pathogenic Th17.1 cells, which may hamper the long-term efficacy of GCs in early MS.

ObjectivesMethotrexate (MTX) is currently the recommended first-line therapy for treating psoriatic arthritis (PsA), despite lacking clear evidence. No estimates of efficacy of MTX in usual care and no clear MTX responsive clinical or laboratory variables are currently available. This study describes the response to MTX monotherapy in newly diagnosed patients with PsA in usual care. Second, we compared clinical variables and cytokine profiles in patients responding and not responding to MTX monotherapy.MethodsWe used data collected in the Dutch southwest Early Psoriatic Arthritis cohoRt study to select patients with PsA with oligoarthritis or polyarthritis, and at least 1 year follow-up. We analysed disease activity at 6 months of patients who started MTX monotherapy and still used MTX monotherapy 1 year after diagnosis. Cytokine profiles were determined at baseline and after 3 and 6 months with a bead-based multi-immunoassay.ResultsWe identified 219 patients of which 183 (84%) patients started MTX monotherapy within 6 months after diagnosis. 90 patients used MTX monotherapy throughout the first year of which 44 patients (24%) reached minimal disease activity(MDA) at 6 months, decreasing to 33 patients (18%) after 1 year. Non-responders had significantly higher concentrations of interleukin (IL) 23 and IL-10 before and during MTX therapy.ConclusionsOur results showed that only 18% of patients with PsA are in sustained MDA after 1 year of MTX monotherapy and non-responders more often had IL-23-driven disease. Our results indicate the need for more treat-to-target and personalised therapy strategies in PsA.

The IL‐23/Th17 axis has been implicated in the development of autoimmune diseases, such as rheumatoid arthritis (RA) and psoriatic arthritis (PsA). RA and PsA are heterogeneous diseases with substantial burden on patients. Increasing evidence suggests that the IL‐23 signaling pathway may be involved in the development of autoimmunity and erosive joint damage. IL‐23 can act either directly or indirectly on bone forming osteoblasts as well as on bone resorbing osteoclasts. As IL‐23 regulates the activity of cells of the bone, it is conceivable that in addition to inflammation‐mediated joint erosion, IL‐23 may play a role in physiological bone remodeling. In this review, we focus on the role of IL‐23 in autoimmune arthritis in patients and murine models, and provide an overview of IL‐23 producing and responding cells in autoimmune arthritic joints. In addition, we discuss the role of IL‐23 on bone forming osteoblasts and bone resorbing osteoclasts regarding inflammation‐mediated joint damage and bone remodeling. At last, we briefly discuss the clinical implications of targeting this pathway for joint damage and systemic bone loss in autoimmune arthritis.

Since the original identification of the T helper 17 (Th17) subset in 2005, it has become evident that these cells do not only contribute to host defence against pathogens, such as bacteria and fungi, but that they are also critically involved in the pathogenesis of many autoimmune diseases. In contrast to the classic Th1 and Th2 cells, which represent rather stably polarized subsets, Th17 cells display remarkable heterogeneity and plasticity. This has been attributed to the characteristics of the key transcription factor that guides Th17 differentiation, retinoic acid receptor-related orphan nuclear receptor gamma (RORγ). Unlike the 'master regulators' T-bet and GATA3 that orchestrate Th1 and Th2 differentiation, respectively, RORγ controls transcription at relatively few loci in Th17 cells. Moreover, its expression is not stabilized by positive feedback loops but rather influenced by environmental cues, allowing for substantial functional plasticity. Importantly, a subset of IL-17/IFNγ double-producing Th17 cells was identified in both human and mouse models. Evidence is accumulating that these IL-17/IFNγ double-producing cells are pathogenic drivers in autoimmune diseases, including rheumatoid arthritis, multiple sclerosis and inflammatory bowel disease. In addition, IL-17/IFNγ double-producing cells have been identified in disorders in which the role of autoimmunity remains unclear, such as sarcoidosis. The observed plasticity of Th17 cells towards the Th1 phenotype can be explained by extensive epigenetic priming of the IFNG locus in Th17 cells. In fact, Th17 cells display an IFNG chromatin landscape that is remarkably similar to that of Th1 cells. On the other hand, pathogenic capabilities of Th17 cells can be restrained by stimulating IL-10 production and transdifferentiation into IL-10 producing T regulatory type 1 (Tr1) cells. In this review, we discuss recent advances in our knowledge on the cellular and molecular mechanisms involved in Th17 differentiation, heterogeneity and plasticity. We focus on transcriptional regulation of the Th17 expression program, the epigenetic dynamics involved, and how genetic variants associated with autoimmunity may affect immune responses through distal gene regulatory elements. Finally, the implications of Th17 cell plasticity for the pathogenesis and treatment of human autoimmune diseases will be discussed.

textabstractBackground: Asthma is a heterogeneous disease of the airways that involves several types of granulocytic inflammation. Recently, we have shown that the activation status of myeloid cells regulated by TNFAIP3/A20 is a crucial determinant of eosinophilic or neutrophilic airway inflammation. However, whether neutrophilic inflammation observed in this model is dependent on IL-17 remains unknown. Objective: In this study, we investigated whether IL-17RA-signalling is essential for eosinophilic or neutrophilic inflammation in house dust mite (HDM)-driven airway inflammation. Methods: Tnfaip3fl/flxLyz2+/cre (Tnfaip3LysM-KO) mice were crossed to Il17raKO mice, generating Tnfaip3LysMIl17raKO mice and subjected to an HDM-driven airway inflammation model. Results: Both eosinophilic and neutrophilic inflammation observed in HDM-exposed WT and Tnfaip3LysM-KO mice respectively were unaltered in the absence of IL-17RA. Production of IL-5, IL-13 and IFN-γ by CD4+ T cells was similar between WT, Tnfaip3LysM-KO and Il17raKO mice, whereas mucus-producing cells in Tnfaip3LysM-KOIl17raKO mice were reduced compared to controls. Strikingly, spontaneous accumulation of pulmonary Th1, Th17 and γδ-17 T cells was observed in Tnfaip3LysM-KOIl17raKO mice, but not in the other genotypes. Th17 cell-associated cytokines such as GM-CSF and IL-22 were increased in the lungs of HDM-exposed Tnfaip3LysM-KOIl17raKO mice, compared to IL-17RA-sufficient controls. Moreover, neutrophilic chemo-attractants CXCL1, CXCL2, CXCL12 and Th17-promoting cytokines IL-1β and IL-6 were unaltered between Tnfaip3LysM-KO and Tnfaip3LysM-KOIl17raKO mice. Conclusion and Clinical Relevance: These findings show that neutrophilic airway inflammation induced by activated TNFAIP3/A20-deficient myeloid cells can develop in the absence of IL-17RA-signalling. Neutrophilic inflammation is likely maintained by similar quantities of pro-inflammatory cytokines IL-1β and IL-6 that can, independently of IL-17-signalling, induce the expression of neutrophil chemo-attractants.

Purpose: After the age of fifty years, the percentage of females with degenerative disorders, including osteoarthritis (OA), increases rapidly. It has been suggested that menopause, and the change in hormones during menopausal transition, influences the development of these disorders. During menopausal transition, not only the hormone levels change, but also metabolism and inflammatory responses. Investigating the influence of menopausal changes, including protein change, on the development of degenerative disorders is difficult, because these changes occur slowly. However, identifying these changes is crucial to develop novel female-specific prevention strategies and therapies for these disorders. Therefore, we propose the use of an unique and novel human model to investigate the influence of menopause on the development of degenerative disorders by modelling a “sudden menopause”, in which we expect that menopausal-related changes will occur faster: the Females discontinuing Oral Contraceptives Use at Menopausal age (FOCUM) model. This model does not have the limitations in generalizability of animal models. Nor does it have the limitations of subsequent hormonal support, malignancy and its associated treatments that are pertinent to human models with a sudden menopause caused by ovariectomy.The aim of our study is to develop the FOCUM model as a disease model for the development of OA. We want to identify when changes, especially in proteins, occur after a “sudden menopause” and which of these changes are associated with the development of OA after two years. Furthermore, we want to explore if the model can also be used to learn more about the development of cardiovascular diseases, diabetes, osteoporosis and tendinopathies. In this abstract we will report on the feasibility of our inclusion. Our aim is to include 50 female participants from the general population in and nearby Rotterdam within one year. Methods: Our study design is a pilot observational prospective cohort study with two years of follow-up. Our main questions for this pilot study are: will the inclusion of participants be feasible and what are the important time points to find changes in proteins? Females between 50 and 60 years of age, who are currently using a combined oral contraceptive and started oral contraceptive use before the age of 45, are recruited from pharmacies and (if necessary) general practices. In general, females are advised to stop oral contraceptive use at the age of 52. Females who are willing to stop oral contraceptive use at short term are invited to participate. Different measurements are performed before (T0 = 0 to 30 days) and after (T1 = 6 weeks;T2 = 6 months;T3 = 1 year;T4 = 2 years) stopping oral contraceptive use. At every time point of measurements a questionnaire is filled in, a normal photograph of both hands is taken and a sample of blood is drawn to measure hormones, proteins, glucose, cholesterol, DNA-methylation and immunological aspects of cells. At the first and final time point of measurements, also a physical examination, an radiograph of both hands, an MRI scan of one knee, a DXA-scan, and an ultrasound tissue characterization of one Achilles tendon are performed. To establish which time points of measurements are most relevant to find changes in proteins after hormone change, we will examine changes in serum levels of approximately 150 different inflammation and cardiometabolic related proteins by using the Olink-technology at different time points of measurements. At the first stage of this study, we will use the Principal Component Analysis on the change in protein levels over time. Thereafter, we will test for the association between principal components and hormone change. At the second stage of this study, we will relate these principal components to various OA outcomes. Results: In January 2020, we sent invitations to 108 local pharmacies to participate in this study. At that time, a total of 55 pharmacies were willing to participate. The participating pharmacies were asked to search in their own information system to identify all possible eligible subjects, based on age and oral contraceptive use, and to send an invitation letter in their name to these subjects. Unfortunately, due to COVID restrictions we started sending these invitation letters by the end of June 2020, four months later than planned. Until now, we have sent 534 invitations from 26 pharmacies to possible eligible subjects. A total of 107 females replied positively and gave permission to provide them more information about the study. After giving information and screening for in- and exclusion criteria, we now have 25 eligible participants who gave informed consent. Of them, 16 participants have had their first (baseline) measurements of 2,5 hours at the Erasmus MC. With the 29 participating pharmacies left, we expect to reach the targeted number of 50 inclusions by February 2021 and to report about the first stage of this study. Conclusions: At this time, we have included half of our study population. So the inclusion of 50 female participants for this study within one year seems to be feasible. By performing different measurements before and after stopping oral contraceptive use, we will be able to investigate when and which menopausal changes occur and which of these changes can be related to OA. With this model we hope to learn more about the influence of menopause on the development of OA, but also of cardiovascular diseases, diabetes, osteoporosis and tendinopathies, in order to develop new prevention strategies and therapies for these diseases.

Career situation of first and presenting author Student for a master or a PhD. Introduction Interleukin-17A (IL-17A) contributes to the pathogenesis of psoriatic arthritis (PsA) as evidenced by the success of biologics targeting IL-17 pathway in PsA patients. Both CD4+ and CD8+ T cells are reportedly producers of IL-17A in PsA with IL-17A+ CD8+ T cells specifically enriched in PsA synovial fluid (SF). However, most current findings regarding IL-17A-producing cells in PsA patients are coming from intracellular staining using flow cytometry. Objectives To confirm and compare ex vivo production of IL-17A by CD4+ and CD8+ T cells from PsA synovial fluid using flow cytometry, enzyme-linked immunosorbent assay (ELISA) and RT-qPCR. Methods Fresh SF of established PsA patients were collected and part of the cells were directly stained intracellularly for IL-17A and IFNγ after 4 hours‘ (hrs) phorbol myristate acetate and ionomycin (PMA and iono) stimulation. Blood samples of early PsA patients and age/sex-matched healthy volunteers were included as controls for PsA SF. In addition, the rest of SF cells underwent density gradient separation and mononuclear cells (SFMCs) were stored till use. CD4+ and CD8+ T cells were sorted from SFMCs, and ex vivo cultured with soluble anti-CD3/anti-CD28 (aCD3 and 28), PMA and iono or without stimulation for 4 or 72 hours. Furthermore, SF CD4+ and CD8+ T cells were co-cultured with either allogeneic PsA fibroblast-like synoviocytes (FLS) or autologous PsA CD14+ monocytes with aCD3 and 28 activation for 72 hours. Culture supernatants were tested for ELISA and cells were analyzed with intracellular staining or RT-qPCR. Results Accumulation of IL-17A+ CD8+ T cells was significantly higher in PsA SF compared to in blood of either PsA patients or healthy volunteers. Although both CD4+ and CD8+ T cells from SFMCs are IL-17A+ with flow cytometry, only CD4+ T cells produce measurable amounts of IL-17A in culture supernatants after 72 hours of aCD3 and 28 activation. Similar results were found after 3 days‘ co-culture of aCD3 and CD28 stimulated CD4+ or CD8+ T cells with PsA FLS. Also, when either co-cultured with autologous CD14+ monocytes, only CD4+ T cells showed mRNA IL-17A expression and IL-17A production. In contrast, if PMA and iono were used to stimulate CD4+ or CD8+ T cells, both produce IL-17A in supernatants after 4 or 72 hours. Conclusions Although both CD4+ and CD8+ T cells show IL-17A positivity in PsA SF with flow cytometry, the use of strong stimuli such as PMA and iono during intracellular staining may account for the IL-17A positivity in CD8+ T cells. The contribution of CD8+ T cells to IL-17A production in local PsA joints might be limited as normal TCR activation, mimicked by aCD3 and 28, didn’t induce IL-17A release in CD8+ T cells in contrast to CD4+ T cells. Disclosure of Interest None declared.

Defects in Fas function correlate with susceptibility to systemic autoimmune diseases like autoimmune lymphoproliferative syndrome (ALPS) and systemic lupus erythematosus (SLE). C57BL/6 lpr (B6/lpr) mice are used as an animal model of ALPS and develop a mild SLE phenotype. Involvement of interleukin-17A (IL-17A) has been suggested in both phenotypes. Since IL-17 receptor A is part of the signaling pathway of many IL-17 family members we investigated the role of IL-17 receptor signaling in disease development in mice with a B6/lpr background. B6/lpr mice were crossed with IL-17 receptor A deficient (IL-17RA KO) mice and followed over time for disease development. IL-17RA KO/lpr mice presented with significantly enhanced lymphoproliferation compared with B6/lpr mice, which was characterized by dramatic lymphadenomegaly/splenomegaly and increased lymphocyte numbers, expansion of double-negative (DN) T-cells and enhanced plasma cell formation. However, the SLE phenotype was not enhanced, as anti-nuclear antibody (ANA) titers and induction of glomerulonephritis were not different. In contrast, levels of High Mobility Group Box 1 (HMGB1) and anti-HMGB1 autoantibodies were significantly increased in IL-17RA KO/lpr mice compared to B6/lpr mice. These data show that lack of IL-17RA signaling aggravates the lymphoproliferative phenotype in B6/lpr mice but does not affect the SLE phenotype.

OBJECTIVE Indoleamine 2,3-dioxygenase (IDO), the rate-limiting enzyme that converts tryptophan to kynurenine, is driven in part by type I and type II interferons (IFNs). Naive T cells are polarized into FoxP3+ Treg cells upon exposure to either IDO+ cells or kynurenine. Recent studies have suggested that the kynurenine pathway reflects a crucial interface between the immune and nervous system. The aims of the present study were to evaluate whether Treg cell levels are elevated, in conjunction with increased IDO activity, in patients with primary Sjogren's syndrome (SS) who are positive for the IFN gene expression signature, and to investigate the downstream kynurenine pathway in these patients. METHODS Serum from 71 healthy controls, 58 IFN-negative patients with primary SS, and 66 IFN-positive patients with primary SS was analyzed using high-performance liquid chromatography to measure the levels of tryptophan and kynurenine. Expression levels of messenger RNA (mRNA) for IDO and downstream enzymes in the kynurenine pathway were assessed in CD14+ monocytes using real-time quantitative polymerase chain reaction. CD4+CD45RO+ T helper memory cell populations were analyzed by flow cytometry. RESULTS Significantly increased levels of IDO activity (assessed as the kynurenine:tryptophan ratio) (P = 0.0054) and percentages of CD25(high) FoxP3+ Treg cells (P = 0.039) were observed in the serum from IFN-positive patients with primary SS, and these parameters were significantly correlated with one another (r = 0.511, P = 0.002). In circulating monocytes from IFN-positive patients with primary SS, the expression of IDO1 mRNA was up-regulated (P

IL-17A, a major proinflammatory cytokine, can be produced by a variety of leukocytes, but its exact cellular source in human inflammatory diseases remains incompletely understood. IL-17A protein is abundantly found in mast cells in human tissues, such as inflamed synovium, but surprisingly, mechanistic murine studies failed to demonstrate IL-17A production by mast cells. Here, we demonstrate that primary human tissue mast cells do not produce IL-17A themselves but actively capture exogenous IL-17A through receptor-mediated endocytosis. The exogenous IL-17A is stored in intracellular granules and can subsequently be released in a bioactive form. This novel mechanism confers to mast cells the capacity to steer IL-17A-mediated tissue inflammation by the rapid release of preformed cytokine.

Throughout life, bone is continuously remodelled. Bone is formed by osteoblasts, from mesenchymal origin, while osteoclasts induce bone resorption. This process is tightly regulated. During inflammation, several growth factors and cytokines are increased inducing osteoclast differentiation and activation, and chronic inflammation is a condition that initiates systemic bone loss. Rheumatoid arthritis (RA) is a chronic inflammatory auto-immune disease that is characterised by active synovitis and is associated with early peri-articular bone loss. Peri-articular bone loss precedes focal bone erosions, which may progress to bone destruction and disability. The incidence of generalised osteoporosis is associated with the severity of arthritis in RA and increased osteoporotic vertebral and hip fracture risk. In this review, we will give an overview of different animal models of inflammatory arthritis related to RA with focus on bone erosion and involvement of pro-inflammatory cytokines. In addition, a humanised endochondral ossification model will be discussed, which can be used in a translational approach to answer osteoimmunological questions.

Background Despite recent improvements in the treatment of rheumatoid arthritis (RA), an insufficient treatment response and the development of treatment resistance in many patients illustrates the need for new therapeutic strategies. Chronic synovial inflammation could be suppressed by targeting RA synovial fibroblast (RASF) activation by, for example, interleukin (IL)-17A-producing CCR6+ T helper memory (memTh) cells. Here, we modulated this interaction by combining the active vitamin D metabolite 1,25(OH)2D3 with dexamethasone (DEX) and explored the potential therapeutic applications. Methods CCR6+ memTh cells from peripheral blood mononuclear cells (PBMCs) of healthy donors or treatment-naive early RA patients were cultured alone or with RASF from established RA patients for 3 days and treated with or without 1,25(OH)2D3, DEX, or etanercept. Treatment effects were assessed using enzyme-linked immunosorbent assay (ELISA) and flow cytometry. Results 1,25(OH)2D3, and to lesser extent DEX, reduced production of the pro-inflammatory cytokines IL-17A, IL-22, and interferon (IFN)γ in CCR6+ memTh cells. Tumor necrosis factor (TNF)α was only inhibited by the combination of 1,25(OH)2D3 and DEX. In contrast, DEX was the strongest inhibitor of IL-6, IL-8, and tissue-destructive enzymes in RASF. As a result, 1,25(OH)2D3 and DEX additively inhibited inflammatory mediators in CCR6+ memTh-RASF cocultures. Interestingly, low doses of mainly DEX, but also 1,25(OH)2D3, combined with etanercept better suppressed synovial inflammation in this coculture model compared with etanercept alone. Conclusion This study suggests that 1,25(OH)2D3 and DEX additively inhibit synovial inflammation through targeting predominantly CCR6+ memTh cells and RASF, respectively. Furthermore, low doses of DEX and 1,25(OH)2D3 enhance the effect of TNFα blockade in inhibiting RASF activation, thus providing a basis to improve RA treatment.

Background There is currently a knowledge gap on early pathogenesis prior to Rheumatoid Arthritis (RA) diagnosis. Additionally, current medication available for RA treatment has not been developed for prevention. Collagen induced arthritis (CIA) could aid in extending knowledge on early RA pathogenesis and testing the preventive effects of medicines. Objectives In this study we sought a marker that can differentiate mice prior to clinically manifest disease into their future CIA status with the aim to facilitate research into early disease processes and preventive treatment strategies. Methods Blood was obtained at time points prior (days 12 and 19) and after clinically manifest disease (days 27 and 35) during CIA. Antibodies against bovine and mouse collagen type II (mCII) were measured from plasma by ELISA. CD4+CCR6+ memory Th cells as well as other T cell types were determined in blood. Cytokines and chemokines were detected in plasma by Luminex. Mice were divided into CIA negative and CIA positive groups based on CIA score reached on day 35. Results Antibodies against mCII of the IgG2a isotype differed prior to clinically manifest disease but are not suitable as a differentiation marker. CD4+CCR6+ memory Th cells in blood differed only at day 35. The same holds for IL-6, TNFα and CXCL2. In contrast, CXCL1 differed prior to clinically manifest disease with an AUC significantly better (p=0.003) than random. Conclusions Here we identified CXCL1 as a marker that can differentiate mice prior to clinically manifest disease into CIA positive and CIA negative mice. This might help facilitate research into early disease processes and preventive pre-clinical treatment strategies. Disclosure of Interest None declared

Background Although treatment of rheumatoid arthritis (RA) has significantly improved during the past decades, many patients do not adequately respond or become resistant to current treatments. It is currently unknown why some patients respond well and others do not, and how the response rate could be improved. Vitamin D has strong immunomodulatory properties and it has been shown RA patients have a lower serum 25(OH)D level than healthy individuals. Moreover, vitamin D levels are correlated with disease severity. 1 2 Interestingly, in vitro studies have shown that vitamin D augments the suppressive effects of etanercept in a simplified model for synovial inflammation. 3 This suggests that vitamin D could improve the therapeutic response to etanercept in RA patients. Objectives To investigate if etanercept response is related to serum vitamin D (25(OH)D) levels in RA patients. Methods For this study, data were used from the tREACH trial, a multicenter stratified single blinded randomised clinical trial. RA patients, according to the 2010 classification criteria, who started with etanercept within the first 12 months of the study were included in the analysis. Serum vitamin D (25(OH)D) levels were determined at the start of treatment (Tstart) and 3 months later using the LIAISON 25 OH Vitamin D TOTAL assay. Correlation coefficients between vitamin D levels and the disease activity score (DAS) were calculated. Treatment response was determined with the EULAR response criteria, and difference in response rates was assessed using Chi-Square tests. Results 91 patients started etanercept in the first 12 months of the study, of which 24 did not have serum for 25(OH)D measurements at both start of treatment and three months later. Therefore, a total of 67 patients was included in this study, of which 82% was female. At baseline, 45 (67%) and 48 (73%) were positive for rheumatoid factor and anti-citrullinated protein antibodies, respectively. DAS after etanercept treatment was weakly inversely correlated with serum 25(OH)D after treatment (r=-0.29, p=0.02) and the change in 25(OH)D during treatment (r=-0.25, p=0.04). After correcting for DAS and serum 25(OH)D at the start of treatment the aforementioned correlations were still found. Importantly, EULAR response rate was significantly lower in patients who were vitamin d-deficient at the start of treatment (34.6% vs 59.4%) and in patients with decreasing 25(OH)D levels during treatment (39.2% vs 57.7%) (figure 1). Conclusions RA patients with a serum 25(OH)D level below 50 nmol/L at the start of etanercept treatment or a decreasing level during treatment have a lower EULAR response rate. Therefore, increasing serum 25(OH)D level in vitamin D deficient patients may be important to achieve optimal effects of TNFα blocking therapy. References [1] Lee YH, Bae SC. Clin Exp Rheumatol2016;34(5):827–33. [2] Lin J, Liu J, Davies ML, et al. PLoS One2016;11(1):e0146351. [3] van Hamburg JP, Asmawidjaja PS, Davelaar N, et al. Ann Rheum Dis2012;71(4):606–12. Disclosure of Interest None declared

Background IL-17RD is a member of the IL-17 receptor family. In contrast to the other IL-17 receptors, IL-17RA, -RB, -RC and -RE, little is known about the ligand and function of IL-17RD. Recently, IL-17RD has been described to negatively regulate a selection of IL-17A responsive genes. IL-17RD is therefore proposed to limit IL-17A signalling. Objectives In this study we examined IL-17RD expression in multiple cells types and its role in the development of collagen induced arthritis. Methods Human synovial fibroblasts from Rheumatoid Arthritis (RA) patients were stimulated with tumour necrosis factor α (TNFα), interleukin 1 β (IL-1β) or IL-17A for multiple time points. IL-17RD expression levels were measured via qPCR. Collagen induced arthritis (CIA) was induced in IL-17RD knockout mice and wildtype littermates. At days 1 and 21, mice were immunised intradermally with chicken collagen type II in complete Freund’s adjuvant (CFA). Mice were scored 3 times a week for clinical disease defined as swollen joints with a maximum score of 8. Due to ethical reasons, mice were removed from the experiments when they reached a score of 6. CD4+ memory T cells, CD8+ memory T cells, CD19+ B cells and monocytes were isolated from WT spleens and analysed for IL-17RD expression. Blood neutrophil migration assays were performed in vitro using WT and IL-17RD deficient (IL-17RD KO) mouse synovial fibroblasts. Results Human synovial fibroblasts from RA patients have baseline expression of IL-17RD. Upon stimulation with TNFα a significant downregulation of IL-17RD expression was measured from 24 hours onwards. IL1β stimulation had a similar effect as TNFα on IL-17RD expression. Lack of IL-17RD did not result in differences in CIA severity, but the incidence of CIA was reduced. IL-17RD is mainly expressed in synovial fibroblasts. IL-17RD KO synovial fibroblasts attract less neutrophils likely by lower production of neutrophil attractants. Conclusions An inflammatory environment causes synovial fibroblasts to downregulate IL-17RD expression. Lack of IL-17RD reduces the incidence CIA, which is an IL-17-driven model. The decrease in CIA incidence is likely explained via the reduced attraction of neutrophils to the site of inflammation. Disclosure of Interest None declared

Despite recent improvements in the treatment of rheumatoid arthritis (RA), an insufficient treatment response and the development of treatment resistance in many patients illustrates the need for new therapeutic strategies. Chronic synovial inflammation could be suppressed by targeting RA synovial fibroblast (RASF) activation by, for example, interleukin (IL)-17A-producing CCR6CCR61,25(OH)This study suggests that 1,25(OH)