Cem Gabay

Interleukin-6 and chronic inflammation

Interleukin (IL)-6 is produced at the site of inflammation and plays a key role in the acute phase response as defined by a variety of clinical and biological features such as the production of acute phase proteins. IL-6 in combination with its soluble receptor sIL-6Rα, dictates the transition from acute to chonic inflammation by changing the nature of leucocyte infiltrate (from polymorphonuclear neutrophils to monocyte/macrophages). In addition, IL-6 exerts stimulatory effects on T- and B-cells, thus favoring chronic inflammatory responses. Strategies targeting IL-6 and IL-6 signaling led to effective prevention and treatment of models of rheumatoid arthritis and other chronic inflammatory diseases.

IL-1, IL-18, and IL-33 families of cytokines

Summary: The interleukin‐1 (IL‐1), IL‐18, and IL‐33 families of cytokines are related by mechanism of origin, receptor structure, and signal transduction pathways utilized. All three cytokines are synthesized as precursor molecules and cleaved by the enzyme caspase‐1 before or during release from the cell. The NALP‐3 inflammasome is of crucial importance in generating active caspase‐1. The IL‐1 family contains two agonists, IL‐1α and IL‐1β, a specific inhibitor, IL‐1 receptor antagonist (IL‐1Ra), and two receptors, the biologically active type IL‐1R and inactive type II IL‐1R. Both IL‐1RI and IL‐33R utilize the same interacting accessory protein (IL‐1RAcP). The balance between IL‐1 and IL‐1Ra is important in preventing disease in various organs, and excess production of IL‐1 has been implicated in many human diseases. The IL‐18 family also contains a specific inhibitor, the IL‐18‐binding protein (IL‐18BP), which binds IL‐18 in the fluid phase. The IL‐18 receptor is similar to the IL‐1 receptor complex, including a single ligand‐binding chain and a different interacting accessory protein. IL‐18 provides an important link between the innate and adaptive immune responses. Newly described IL‐33 binds to the orphan IL‐1 family receptor T1/ST2 and stimulates T‐helper 2 responses as well as mast cells.

Tocilizumab monotherapy versus adalimumab monotherapy for treatment of rheumatoid arthritis (ADACTA): a randomised, double-blind, controlled phase 4 trial

BACKGROUND Roughly a third of patients with rheumatoid arthritis treated with biological treatments receive them as monotherapy. Tocilizumab--an inhibitor of interleukin 6 receptor signalling--has been studied as monotherapy in several clinical trials. We assessed the efficacy and safety of tocilizumab monotherapy compared with adalimumab monotherapy for patients with rheumatoid arthritis. METHODS We did this randomised, double-blind, parallel-group, phase 4 superiority study in 76 centres in 15 countries in North and South America, Australasia, and Europe. We enrolled patients who were aged at least 18 years, had severe rheumatoid arthritis for 6 months or more, and were intolerant to methotrexate or were inappropriate for continued methotrexate treatment. Patients were randomly assigned (1:1; block size of four) to receive tocilizumab 8 mg per kg bodyweight intravenously every 4 weeks plus placebo subcutaneously every 2 weeks or adalimumab 40 mg subcutaneously every 2 weeks plus placebo intravenously every 4 weeks for 24 weeks. Investigators, patients, and sponsor personnel were masked to assignment. The primary endpoint was change in disease activity score using 28 joints (DAS28) from baseline to week 24. This trial is registered with ClinicalTrials.gov, number NCT01119859. FINDINGS We screened 452 patients and enrolled 326 patients. The intention-to-treat population contained 325 patients (163 assigned to tocilizumab, 162 assigned to adalimumab). Week 24 mean change from baseline in DAS28 was significantly greater in the tocilizumab group (-3·3) than in the adalimumab group (-1·8) patients (difference -1·5, 95% CI -1·8 to -1·1; p<0·0001). 16 of 162 (10%) patients in the adalimumab group versus 19 of 162 (12%) in the tocilizumab group had serious adverse events. More patients in the tocilizumab group than in the adalimumab group had increased LDL-cholesterol, increased alanine aminotransferase concentrations, and reduced platelet and neutrophil counts. INTERPRETATION Tocilizumab monotherapy was superior to adalimumab monotherapy for reduction of signs and symptoms of rheumatoid arthritis in patients for whom methotrexate was deemed inappropriate. The adverse event profiles of tocilizumab and adalimumab were consistent with previous findings. FUNDING F Hoffmann-La Roche.

Leptin Signaling Deficiency Impairs Humoral and Cellular Immune Responses and Attenuates Experimental Arthritis

Leptin is produced almost exclusively by adipocytes and regulates body weight at the hypothalamic level. In addition, recent studies showed that leptin plays an important role in T lymphocyte responses. To examine the role of leptin in Ag-induced arthritis, the development of joint inflammation was assessed in immunized leptin-deficient mice (ob/ob), +/?, and wild-type mice (+/+) following the administration of methylated BSA into the knees. The results showed that ob/ob mice developed less severe arthritis compared with control mice. The levels of IL-1β and TNF-α mRNA in the synovium of arthritic knees were lower in ob/ob than in +/? mice. In vitro Ag-specific T cell proliferative responses were significantly decreased in ob/ob mice with lower IFN-γ and higher IL-10 production, suggesting a shift toward a Th2-type response in ob/ob mice. The serum levels of anti-methylated BSA Abs of any isotype were significantly decreased in arthritic ob/ob mice compared with controls. Essentially identical results were obtained in db/db mice, which lack the expression of the long isoform of leptin receptor. By RT-PCR, we observed that B lymphocytes express leptin receptor mRNA, indicating that in addition to its effect on the cellular response, leptin may exert a direct effect on B cell function. In conclusion, leptin contributes to the mechanisms of joint inflammation in Ag-induced arthritis by regulating both humoral and cell-mediated immune responses.

Inhibition of interleukin-33 signaling attenuates the severity of experimental arthritis

OBJECTIVE Interleukin-33 (IL-33; or, IL-1F11) was recently identified as the ligand of the IL-1 family receptor T1/ST2. The aim of this study was to examine IL-33 production in human and mouse joints and to investigate the role of IL-33 and T1/ST2 in experimental arthritis. METHODS IL-33 expression was examined in human synovial tissue, rheumatoid arthritis (RA) synovial fibroblasts, and arthritic mouse joints. Mice with collagen-induced arthritis (CIA) were treated with blocking anti-ST2 antibody or control antibody beginning at the onset of disease. Arthritis severity was assessed by clinical and histologic scoring. Draining lymph node (LN) cell responses were examined ex vivo, and joint messenger RNA (mRNA) was used for expression profiling. RESULTS IL-33 was highly expressed in human RA synovium. In cultured synovial fibroblasts, IL-33 expression was strongly induced by IL-1beta and/or tumor necrosis factor alpha. Furthermore, IL-33 mRNA was detected in the joints of mice with CIA and increased during the early phase of the disease. Administration of a blocking anti-ST2 antibody at the onset of disease attenuated the severity of CIA and reduced joint destruction. Anti-ST2 antibody treatment was associated with a marked decrease in interferon-gamma production as well as with a more limited reduction in IL-17 production by ex vivo-stimulated draining LN cells. Finally, RANKL mRNA levels in the joint were reduced by anti-ST2 treatment. CONCLUSION IL-33 is produced locally in inflamed joints, and neutralization of IL-33 signaling has a therapeutic effect on the course of arthritis. These observations suggest that locally produced IL-33 may contribute to the pathogenesis of joint inflammation and destruction.

Interleukin-33 Is Biologically Active Independently of Caspase-1 Cleavage

The new interleukin (IL)-1 family cytokine IL-33 is synthesized as a 30-kDa precursor. Like pro-IL-1β, human pro-IL-33 was reported to be cleaved by caspase-1 to generate an 18-kDa fragment, which is sufficient to activate signaling by the IL-33 receptor T1/ST2. However, the proposed caspase-1 cleavage site is poorly conserved between species. In addition, it is not clear whether caspase-1 cleavage of pro-IL-33 occurs in vivo and whether, as for IL-1β, this cleavage is a prerequisite for IL-33 secretion and bioactivity. In this study, we further investigated caspase-1 cleavage of mouse and human pro-IL-33 and assessed the potential bioactivity of the IL-33 precursor. We observed the generation of a 20-kDa IL-33 fragment in cell lysates, which was enhanced by incubation with caspase-1. However, in vitro assays of mouse and human pro-IL-33 indicated that IL-33 is not a direct substrate for this enzyme. Consistently, caspase-1 activation in THP-1 cells induced cleavage of pro-IL-1β but not of pro-IL-33, and activated THP-1 cells released full-length pro-IL-33 into culture supernatants. Finally, addition of full-length pro-IL-33 induced T1/ST2-dependent IL-6 secretion in mast cells. However, we observed in situ processing of pro-IL-33 in mast cell cultures, and it remains to be determined whether full-length pro-IL-33 itself indeed represents the bioactive species. In conclusion, our data indicate that pro-IL-33 is not a direct substrate for caspase-1. In addition, our results clearly show that caspase-1 cleavage is not required for pro-IL-33 secretion and bioactivity, highlighting major differences between IL-1β and IL-33.

CD14 Is an Acute-Phase Protein

The origin of soluble CD14 (sCD14) in the circulation is uncertain. To examine whether CD14 could be an acute-phase protein (APP), the levels of sCD14, IL-6, and C-reactive protein were determined by ELISA in serum and synovial fluid (SF) of patients with various arthropathies, and the regulation of CD14 synthesis was examined in liver cells. In patients with crystal-mediated or immunologically mediated arthritis (rheumatoid arthritis), serum levels of sCD14 were higher than or similar to those found in infection-mediated arthritis (reactive arthritis), precluding a relation with bacteria exposure. Levels of sCD14 were similar in SF and serum, and did not correlate with the number of SF leukocytes, excluding an important source from leukocyte membrane-bound CD14, by protease-mediated shedding. In contrast, serum levels of sCD14 in patients correlated with those of C-reactive protein, a classical APP, and IL-6, a cytokine known to regulate the synthesis of APP in the liver. Serum levels of sCD14 also correlated with disease activity in rheumatoid arthritis and reactive arthritis patients. IL-6 stimulated the production of CD14 by HepG2 hepatoma cells. By real-time PCR, the inducibility of CD14 by IL-6 was also observed at the mRNA level both in HepG2 cells and human primary hepatocytes. These in vitro results were confirmed by in vivo studies in IL-6−/− mice injected with turpentine, an experimental model of acute-phase response. Liver levels of CD14 mRNA increased in IL-6+/+, but not in IL-6−/− mice. These results indicate that sCD14 can be considered as a type 2 APP.

EULAR recommendations for terminology and research in individuals at risk of rheumatoid arthritis: report from the Study Group for Risk Factors for Rheumatoid Arthritis

The Study Group for Risk Factors for Rheumatoid Arthritis was established by the EULAR Standing Committee on Investigative Rheumatology to facilitate research into the preclinical and earliest clinically apparent phases of rheumatoid arthritis (RA). This report describes the recommendation for terminology to be used to define specific subgroups during different phases of disease, and defines the priorities for research in this area. Terminology was discussed by way of a three-stage structured process: A provisional list of descriptors for each of the possible phases preceding the diagnosis of RA were circulated to members of the study group for review and feedback. Anonymised comments from the members on this list were fed back to participants before a 2-day meeting. 18 participants met to discuss these data, agree terminologies and prioritise important research questions. The study group recommended that, in prospective studies, individuals without RA are described as having: genetic risk factors for RA; environmental risk factors for RA; systemic autoimmunity associated with RA; symptoms without clinical arthritis; unclassified arthritis; which may be used in a combinatorial manner. It was recommended that the prefix ‘pre-RA with:’ could be used before any/any combination of the five points above but only to describe retrospectively a phase that an individual had progressed through once it was known that they have developed RA. An approach to dating disease onset was recommended. In addition, important areas for research were proposed, including research of other tissues in which an adaptive immune response may be initiated, and the identification of additional risk factors and biomarkers for the development of RA, its progression and the development of extra-articular features. These recommendations provide guidance on approaches to describe phases before the development of RA that will facilitate communication between researchers and comparisons between studies. A number of research questions have been defined, requiring new cohorts to be established and new techniques to be developed to image and collect material from different sites.

Highest clinical effectiveness of rituximab in autoantibody-positive patients with rheumatoid arthritis and in those for whom no more than one previous TNF antagonist has failed: pooled data from 10 European registries

Objective To assess the 6-month effectiveness of the first rituximab (RTX) course in rheumatoid arthritis (RA) and to identify possible predictors of response. Method 10 European registries submitted anonymised datasets (baseline, 3- and 6-month follow-up) from patients with RA who had started RTX, and datasets were pooled and analysed. Heterogeneity between countries was analysed by analysis of variance. Predictors of response were identified by logistic regression. Results 2019 patients were included (mean age/disease duration 53.8/12.1 years, 80.3% female, 85.6% rheumatoid factor (RF) positive and 76.8% (456/594 patients) anti-cyclic citrullinated peptide antibodies (anti-CCP) positive). For these patients an average of 2.7 disease-modifying antirheumatic drugs (DMARDs) (range 0–10) had failed, and RTX was given as the first biological agent in 36.6% of patients. There was significant heterogeneity between countries for several baseline characteristics, including the number of previous biological agents. Disease Activity Score based on 28 joint counts (DAS28) decreased from 5.8±1.4 at baseline to 4.2±1.4 at 6 months (p<0.0001) and 22.2%/42.5% achieved European League Against Rheumatism (EULAR) good/moderate response. Larger 6-month improvement in DAS28 was observed in RF-positive and anti-CCP-positive versus seronegative patients. The following predictors of EULAR good response at 6 months were identified in a multivariate analysis: anti-CCP positivity (OR=2.86, p=0.003), number of previous DMARDs (OR=0.84, p=0.06), ≤1 previous biological agents (OR=1.89, p=0.04), baseline DAS28 level (OR=0.74, p=0.003). Conclusion In this large observational cohort of patients with RA treated with RTX, seropositive patients achieved significantly greater reductions in DAS28 at 6 months than seronegative patients. Effectiveness was best when RTX was used as the first biological agent or after failure of no more than one anti-tumour necrosis factor agent.

Interleukin-33 biology with potential insights into human diseases

Interleukin (IL)-33 is a member of the IL-1 family of cytokines. IL-33 is a nuclear protein that is also released into the extracellular space, and thus acts as a dual-function molecule, as does IL-1α. Extracellular IL-33 binds to the cell-surface receptor ST2, leading to the activation of intracellular signaling pathways similar to those used by IL-1. Unlike conventional cytokines, IL-33 might be secreted via unconventional pathways, and can be released upon cell injury as an alarmin. IL-33 is expressed in cells that are in contact with the environment, and acts as an early inducer of inflammation. Its production is then upregulated in inflamed tissues, thus contributing to the further amplification of inflammatory responses. Studies of IL-33-deficient mice will provide more information on intracellular functions of this cytokine. A large body of evidence supports the pathogenic role of IL-33 in asthma and possibly other inflammatory airway conditions. Furthermore, IL-33 has been shown to be involved in experimental models of arthritis and potentially has a pathogenic role in ulcerative colitis and fibrotic conditions, suggesting that IL-33 antagonists might be of interest for the treatment of asthma, rheumatoid arthritis and ulcerative colitis. However, IL-33 also appears to exert important functions in host defense against pathogens and to display cardioprotective properties, which might have implications for the clinical use of IL-33 blockade.