Elevated serum interleukin 33 is associated with autoantibody production in patients with rheumatoid arthritis

The immunomodulatory of interleukin-33 in rheumatoid arthritis: A systematic review

Rheumatoid arthritis (RA) is a systemic chronic autoimmune disease that primarily affects the joints and surrounding soft tissues, characterized by chronic inflammation and proliferation of the synovium. Various immune cells are involved in the pathophysiology of RA. The complex interplay of factors such as chronic inflammation, genetic susceptibility, dysregulation of serum antibody levels, among others, contribute to the complexity of the disease mechanism, disease activity, and treatment of RA. Recently, the cytokine storm leading to increased disease activity in RA has gained significant attention. Interleukin-33 (IL-33), a member of the IL-1 family, plays a crucial role in inflammation and immune regulation. ST2 (suppression of tumorigenicity 2 receptor), the receptor for IL-33, is widely expressed on the surface of various immune cells. When IL-33 binds to its receptor ST2, it activates downstream signaling pathways to exert immunoregulatory effects. In RA, IL-33 regulates the progression of the disease by modulating immune cells such as circulating monocytes, tissue-resident macrophages, synovial fibroblasts, mast cells, dendritic cells, neutrophils, T cells, B cells, endothelial cells, and others. We have summarized and analyzed these findings to elucidate the pathways through which IL-33 regulates RA. Furthermore, IL-33 has been detected in the synovium, serum, and synovial fluid of RA patients. Due to inconsistent research results, we conducted a meta-analysis on the association between serum IL-33, synovial fluid IL-33, and the risk of developing RA in patients. The pooled SMD was 1.29 (95% CI: 1.15-1.44), indicating that IL-33 promotes the onset and pathophysiological progression of RA. Therefore, IL-33 may serve as a biomarker for predicting the risk of developing RA and treatment outcomes. As existing drugs for RA still cannot address drug resistance in some patients, new therapeutic approaches are needed to alleviate the significant burden on RA patients and healthcare systems. In light of this, we analyzed the potential of targeting the IL-33/ST2-related signaling pathway to modulate immune cells associated with RA and alleviate inflammation. We also reviewed IL-33 and RA susceptibility-related single nucleotide polymorphisms, suggesting potential involvement of IL-33 and macrophage-related drug-resistant genes in RA resistance therapy. Our review elucidates the role of IL-33 in the pathophysiology of RA, offering new insights for the treatment of RA.

Serum alarmins and the risk of incident interstitial lung disease in rheumatoid arthritis

OBJECTIVES

To quantify associations of serum alarmins with risk of rheumatoid arthritis-associated interstitial lung disease (RA-ILD).

METHODS

Using serum collected at enrolment, three alarmins (IL-33, thymic stromal lymphopoietin [TSLP] and IL-25) were measured in a multicentre prospective RA cohort. ILD was classified using systematic medical record review. Cross-sectional associations of log-transformed (IL-33, TSLP) or quartile (IL-25) values with RA-ILD at enrolment (prevalent RA-ILD) were examined using logistic regression, while associations with incident RA-ILD developing after enrolment were examined using Cox proportional hazards. Covariates in multivariate models included age, sex, race, smoking status, RA disease activity score and anti-cyclic citrullinated antibody positivity.

RESULTS

Of 2835 study participants, 115 participants (4.1%) had prevalent RA-ILD at baseline and an additional 146 (5.1%) developed incident ILD. There were no associations between serum alarmin concentrations and prevalent ILD in unadjusted or adjusted logistic regression models. In contrast, there was a significant inverse association between IL-33 concentration and the risk of developing incident RA-ILD in unadjusted (hazard ratio [HR] 0.73 per log-fold increase; 95% CI: 0.57, 0.95; P = 0.018) and adjusted (HR 0.77; 95% CI: 0.59, 1.00; P = 0.047) models. No significant associations of TSLP or IL-25 with incident ILD were observed.

CONCLUSION

In this study, we observed a significant inverse association between serum IL-33 concentration and the risk of developing incident RA-ILD, but no associations with prevalent ILD. Additional investigation is required to better understand the mechanisms driving this relationship and how serum alarmin IL-33 assessment might contribute to clinical risk stratification in patients with RA.

Associations of MEFV gene variants, IL-33, and sST2 with the risk of Henoch-Schönlein purpura in children

Objective

Henoch-Schönlein purpura (HSP) is the most common systemic vasculitis in children. HSP is a multifactorial inflammatory disease, but its pathogenesis is still unclear. The pathogenicity of familial Mediterranean fever gene (MEFV) variants in HSP remains controversial. The objective of this study was to evaluate relationships between MEFV variants and susceptibility to HSP and their associations with clinical outcomes. We also investigated levels of IL-33 and soluble suppression of tumorigenicity 2 (sST2) in children with HSP and their clinical significance.

Methods

We selected 100 children with HSP as the case group. The control group consisted of 50 children who visited the hospital for physical health examinations. All subjects were screened for MEFV gene exon mutations, and levels of IL-33 and sST2 were measured.

Results

The frequency of MEFV variants was significantly greater in HSP patients than in healthy controls. The variant with the highest frequency was E148Q. The frequency of the C allele of the MEFV variant E148Q was 32 % in HSP patients and 18 % in controls (P-adjust = 0.04). Patients with the MEFV E148Q variant had more frequent joint involvement and recurrent purpura and higher levels of IL-33 and C-reactive protein (CRP). Levels of IL-33 and sST2 in children with HSP were significantly higher than those in the control group, and the sST2/IL-33 ratio in children with HSP was unbalanced (P-adjust <0.05). Logistic regression analysis revealed the presence of E148Q and an unbalanced sST2/IL-33 ratio to be independent risk factors for HSP.

Conclusion

The results of this study suggest that the MEFV variant E148Q is associated with HSP susceptibility in Chinese children and that carriers of the variant may have more severe clinical manifestations and greater inflammatory responses. E148Q and the sST2/IL-33 ratio may play important roles in the pathogenesis of HSP.

Circulatory levels of alarmins in patients with non-segmental vitiligo: Potential biomarkers for disease diagnosis and activity/severity assessment

Background

Non-segmental vitiligo (NSV) is an autoimmune skin disorder that is difficult to determine disease activity/severity and thus to treat. Alarmins have emerged as promising biomarkers in various diseases, so further confirmation of their potential roles in NSV would be of considerable value. With the present work, we aimed to determine the serum levels of alarmins in patients with NSV, correlate these alarmins with disease activity and severity, and analyze the predictive value of the combination of these markers.

Methods

104 NSV patients and 56 healthy controls were enrolled at the Xijing Hospital of Fourth Military Medical University between September 1, 2018, and June 30, 2019. The serum levels of alarmins (including IL-33, IL-1α, S100A9, S100A12, S100B, and HMGB1) were measured with enzyme-linked immunosorbent assays. The predictive performance of these biomarkers was evaluated with the area under the receiver operating characteristic curve (AUC), sensitivity, specificity, and other representative statistics.

Results

A total of 104 patients with NSV (mean [SD] age, 34.2 [13.0] years; 62 [59.6%] male) and 56 healthy controls (mean [SD] age, 34.8 [13.5] years; 34 [60.7%] male) were enrolled. For vitiligo diagnosis, S100B had the highest sensitivity (92.31%), whereas HMGB1 had the highest specificity (85.71%); the combination of IL-1α, S100B, S100A9, and HMGB1 increased the AUC value to 0.925, with a sensitivity of 87.50% and a specificity of 85.71%. Multivariate logistic regression analysis showed S100B (OR, 1.019; 95% CI, 1.002-1.038; P =0.03), S100A9 (OR, 1.002; 95% CI, 1.001-1.003; P<0.001), and HMGB1 (OR, 1.915; 95% CI, 1.186-3.091; P =0.008) were significantly associated with vitiligo activity. S100A9 had the highest accuracy in discriminating patients at the active stage from the stable stage, with an AUC value of 0.827. The combination of these alarmins had an AUC value of 0.860 to assess disease activity, with a sensitivity of 90.00% and a specificity of 72.97%. Furthermore, S100B (r=0.61, P <0.001), S100A9 (r=0.33, P <0.001), and HMGB1 (r = 0.51, P <0.001) levels were positively correlated with the affected body surface area (BSA) in NSV patients.

Conclusions

Serum S100B, S100A9, and HMGB1 might be biomarkers for diagnosing and assessing the activity/severity of NSV, either used alone or in combination.

IL-31 and IL-33 in rheumatoid arthritis patients

Objective – to investigate clinical and diagnostic significance of IL-31 and IL-33 determination in patients with rheumatoid arthritis (RA).

Material and methods. 154 patients with a reliable diagnosis of RA were examined. Serum levels of IL-31 and IL-33 were studied using multiplex xMAP technology on Bio-PlexTM 200 System analyzer (BIO-RAD, USA). The upper limit of the norm in the study of 20 healthy donor sera was (M+3σ): IL-31 – 15.08 pg/ml, IL-33 – 3.40 pg/ml.

Results. IL-31 (Me (25th; 75th percentile) – 13.75 (5.63; 308.52) and 6.10 (2.87; 8.62) pg/ml (p<0.001), IL-33 – 18.86 (7.45; 65.95) and 0.52 (0.17; 0.78) pg/ml (p><0.001) levels were observed in RA patients in comparison with the control group. An increase in IL-33 concentration (more than 3.40 pg/ml) was observed in 87.0% of patients, and IL-31 (more than 15.08 pg/ml) in 48.1% of patients with RA. An increase in IL-33 alone was observed in 42.2% (65 of 154 patients) with RA, while an isolated increase in IL-31 concentration was observed in only 2 (1.3%) patients. Simultaneous hyperproduction of IL-33 and IL-31 occurred in 69 (44.9%) patients. We revealed positive correlation of clinical and laboratory parameters of RA with cytokine concentration: SDAI correlated with IL-33 (r=0.36; p><0.05); CRP – with IL-31 (r=0.49; p><0,05) and IL-33 (r=0.40; p><0.05). Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.>< 0.001), IL-33 – 18.86 (7.45; 65.95) and 0.52 (0.17; 0.78) pg/ml (p<0.001) levels were observed in RA patients in comparison with the control group. An increase in IL-33 concentration (more than 3.40 pg/ml) was observed in 87.0% of patients, and IL-31 (more than 15.08 pg/ml) in 48.1% of patients with RA. An increase in IL-33 alone was observed in 42.2% (65 of 154 patients) with RA, while an isolated increase in IL-31 concentration was observed in only 2 (1.3%) patients. Simultaneous hyperproduction of IL-33 and IL-31 occurred in 69 (44.9%) patients. We revealed positive correlation of clinical and laboratory parameters of RA with cytokine concentration: SDAI correlated with IL-33 (r=0.36; p><0.05); CRP – with IL-31 (r=0.49; p><0,05) and IL-33 (r=0.40; p><0.05). Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.>< 0.001) levels were observed in RA patients in comparison with the control group. An increase in IL-33 concentration (more than 3.40 pg/ml) was observed in 87.0% of patients, and IL-31 (more than 15.08 pg/ml) in 48.1% of patients with RA. An increase in IL-33 alone was observed in 42.2% (65 of 154 patients) with RA, while an isolated increase in IL-31 concentration was observed in only 2 (1.3%) patients. Simultaneous hyperproduction of IL-33 and IL-31 occurred in 69 (44.9%) patients. We revealed positive correlation of clinical and laboratory parameters of RA with cytokine concentration: SDAI correlated with IL-33 (r=0.36; p<0.05); CRP – with IL-31 (r=0.49; p><0,05) and IL-33 (r=0.40; p><0.05). Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.>< 0.05); CRP – with IL-31 (r=0.49; p< ,05) and IL-33 (r=0.40; p<0.05)

Conclusion. Concentrations of IL-31 and IL-33 are elevated in RA patients and correlate with the indices of inflammatory activity of the disease.

The IL-33/ST2 Pathway in Cerebral Malaria

Interleukin-33 (IL-33) is an immunomodulatory cytokine which plays critical roles in tissue function and immune-mediated diseases. IL-33 is abundant within the brain and spinal cord tissues where it acts as a key cytokine to coordinate the exchange between the immune and central nervous system (CNS). In this review, we report the recent advances to our knowledge regarding the role of IL-33 and of its receptor ST2 in cerebral malaria, and in particular, we highlight the pivotal role that IL-33/ST2 signaling pathway could play in brain and cerebrospinal barriers permeability. IL-33 serum levels are significantly higher in children with severe Plasmodium falciparum malaria than children without complications or noninfected children. IL-33 levels are correlated with parasite load and strongly decrease with parasite clearance. We postulate that sequestration of infected erythrocytes or merozoites liberation from schizonts could amplify IL-33 production in endothelial cells, contributing either to malaria pathogenesis or recovery.

Alarmins in autoimmune diseases

Alarmins are endogenous, constitutively expressed, chemotacting and immune activating proteins or peptides released because of non-programmed cell death (i.e. infections, trauma, etc). They are considered endogenous damage-associated molecular patterns (DAMPs), able to induce a sterile inflammation. In the last years, several studies highlighted a possible role of different alarmins in the pathogenesis of various autoimmune and immune-mediated diseases. We reviewed the relevant literature about this topic, for about 160 articles. Particularly, we focused on systemic autoimmune diseases (systemic lupus erythematosus, rheumatoid arthritis, idiopathic inflammatory myopathies, ANCA-associated vasculitides, Behçet's disease) and cutaneous organ-specific autoimmune diseases (vitiligo, psoriasis, alopecia, pemphigo). Finally, we discussed about future perspectives and potential therapeutic implications of alarmins in autoimmune diseases. In fact, identification of receptors and downstream signal transducers of alarmins may lead to the identification of antagonistic inhibitors and agonists, with the capacity to modulate alarmins-related pathways and potential therapeutic applicability.

Serum IL-33 as a biomarker in different diseases: useful parameter or much need for clarification?

Interleukin-33 (IL-33), a member of the IL-1 family, is critically involved in the modulation of the activity of a diverse range of immunocompetent cells. Essential roles have been implicated in cardioprotection, in both innate and adaptive immune responses in mucosal organs, and in the maintenance of adipose tissue cells. Over the past 10 years, several studies evaluated the usability of IL-33 as a biomarker in diseases of inflammatory and noninflammatory origin. Our group is currently evaluating the predictive role of serum IL-33 in acute kidney injury (AKI). The aim of the article is to discuss selected studies on IL-33 in different diseases and its potential role as a biomarker molecule.

IL-33 in Rheumatic Diseases

Interleukin-33 (IL-33) is a nuclear factor mainly expressed in barrier epithelium, endothelial cells, and fibroblast reticular cells. Some inflammatory cells also express IL-33 under certain conditions. The important role of IL-33 in allergic reactions, helminth infection, cancer, tissue fibrosis, chronic inflammation, organ transplantation, and rheumatic immune diseases has been extensively studied in recent years. IL-33 primarily activates various circulating and tissue-resident immune cells, including mast cell, group 2 innate lymphoid cell (ILC2), regulatory T cell (Treg), T helper 2 cell (Th2), natural killer cell (NK cell), and macrophage. Therefore, IL-33 plays an immunomodulatory role and shows pleiotropic activity in different immune microenvironments. The IL-33/serum stimulation-2 (ST2) axis has been shown to have a detrimental effect on rheumatoid arthritis, systemic lupus erythematosus, and other rheumatic diseases. Interestingly, IL-33 also plays a protective role in the repair of barrier epithelium and the activation of Tregs. Therefore, the role of IL-33/ST2 depends on the underlying pathological conditions in rheumatic diseases. This review focuses on the dual role of the IL-33/ST2 axis in rheumatic diseases.

IL-33 Gene Polymorphisms as Potential Biomarkers of Disease Susceptibility and Response to TNF Inhibitors in Rheumatoid Arthritis, Ankylosing Spondylitis, and Psoriatic Arthritis Patients

Objective

Rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA) belong to inflammatory rheumatic diseases, the group of conditions of unknown etiology. However, a strong genetic component in their pathogenesis has been well established. A dysregulation of cytokine networks plays an important role in the development of inflammatory arthritis. Interleukin 33 (IL-33) is a recently identified member of the IL-1 family. To date, the significance of IL-33 in inflammatory arthritis has been poorly studied. This research aimed to investigate the potential of IL-33 gene polymorphisms to serve as biomarkers for disease susceptibility and TNF inhibitor response in RA, AS, and PsA patients.

Materials and Methods

In total, 735 patients diagnosed with RA, AS, and PsA and 229 healthy individuals were enrolled in the study. Genotyping for three single nucleotide polymorphisms (SNPs) within the IL-33 gene, namely, rs16924159 (A/G), rs10975519 (T/C), and rs7044343 (C/T), was performed using polymerase chain reaction amplification employing LightSNiP assays.

Results

In the present study, the IL-33 rs10975519 CC genotype was associated with a decreased risk of developing RA in females, while the IL-33 rs16924159 polymorphism was associated with the efficacy of anti-TNF therapy and clinical parameters for RA and AS patients. The IL-33 rs16924159 AA genotype correlated with higher disease activity and worse clinical outcomes in RA patients treated with TNF inhibitors, and AS patients carrying the IL-33 rs16924159 AA genotype had higher disease activity and a worse response to anti-TNF therapy. That indicates a deleterious role of the IL-33 rs16924159 AA genotype in the context of RA, as well as AS.

Conclusions

The obtained results suggest that IL-33 gene polymorphisms might be potential candidate biomarkers of disease susceptibility and anti-TNF treatment response in patients with inflammatory rheumatic diseases.

The Role of the IL-33/ST2 Immune Pathway in Autoimmunity: New Insights and Perspectives

Interleukin (IL)-33, a member of IL-1 cytokine family, is produced by various immune cells and acts as an alarm to alert the immune system after epithelial or endothelial cell damage during cell necrosis, infection, stress, and trauma. The biological functions of IL-33 largely depend on its ligation to the corresponding receptor, suppression of tumorigenicity 2 (ST2). The pathogenic roles of this cytokine have been implicated in several disorders, including allergic disease, cardiovascular disease, autoimmune disease, infectious disease, and cancers. However, alerted levels of IL-33 may result in either disease amelioration or progression. Genetic variations of IL33 gene may confer protective or susceptibility risk in the onset of autoimmune diseases. The purpose of this review is to discuss the involvement of IL-33 and ST2 in the pathogenesis of a variety of autoimmune disorders, such as autoimmune rheumatic, neurodegenerative, and endocrine diseases.

Association between IL-33 and other inflammatory factors in patients with rheumatoid arthritis and in fibroblast-like synoviocytes in vitro

IL-33 is a member of the IL-1 family of cytokines whose role remains controversial in rheumatoid arthritis (RA). The present study was performed to evaluate the correlation of IL-33 with other cytokines and chemokines in serum and the synovia, and to explore the nature of the association. The concentration of IL-33 in samples from 96 patients with RA was analyzed. The response of fibroblast-like synoviocytes (FLSs) to treatment with different concentrations of IL-33 was assessed in vitro. IL-33 was indicated to exhibit an association with multiple cytokines and chemokines in synovial fluid with an inverted-U-shaped trend, including IL-6, IL-1β, IL-8, MIG and IP-10, but not in the serum. Furthermore, in vitro experiments confirmed that IL-33 also exerted a U-type dose-dependent regulatory effect on FLS function. In addition, the data-points do not exactly follow the U-shaped curve fit in most cases, therefore, the applicability of this mathematical model in clinical practice is limited.

Blocking Interleukin-33 Alleviates the Joint Inflammation and Inhibits the Development of Collagen-Induced Arthritis in Mice

Rheumatoid arthritis (RA) is considered a systemic chronic inflammatory joint disease characterized by chronic synovitis and cartilage and bone destruction. Interleukin-33 (IL-33) is a proinflammatory cytokine which is highly expressed in the synovium of RA patients and the joints of mice with collagen-induced arthritis (CIA) and exacerbates CIA in mice. However, the role of the IL-33-neutralizing antibody in the murine model of CIA remains unclear. In the present study, CIA mice were given intraperitoneally with polyclonal rabbit anti-murine IL-33 antibody (anti-IL-33) or normal rabbit IgG control after the first signs of arthritis. Administration of anti-IL-33 after the onset of disease significantly reduced the severity of CIA and joint damage compared with controls treated with normal rabbit IgG. Anti-IL-33 treatment also significantly decreased the serum levels of interferon-γ(IFN-γ),IL-6, IL-12, IL-33, and tumor necrosis factor-α (TNF-α). Moreover, anti-IL-33 treatment significantly downregulated the production of IFN-γ, IL-6, IL-12, IL-33, and TNF-α in ex vivo-stimulated spleen cells. Together, our results indicate that the IL-33-neutralizing antibody may provide a therapeutic strategy for RA by inhibiting the release of proinflammatory cytokines.

Anti-inflammatory and immune-regulatory cytokines in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by a failure of spontaneous resolution of inflammation. Although the pro-inflammatory cytokines and mediators that trigger RA have been the focus of intense investigations, the regulatory and anti-inflammatory cytokines responsible for the suppression and resolution of disease in a context-dependent manner have been less well characterized. However, knowledge of the pathways that control the suppression and resolution of inflammation in RA is clinically relevant and conceptually important for understanding the pathophysiology of the disease and for the development of treatments that enable long-term remission. Cytokine-mediated processes such as the activation of T helper 2 cells by IL-4 and IL-13, the resolution of inflammation by IL-9, IL-5-induced eosinophil expansion, IL-33-mediated macrophage polarization, the production of IL-10 by regulatory B cells and IL-27-mediated suppression of lymphoid follicle formation are all involved in governing the regulation and resolution of inflammation in RA. By better understanding these immune-regulatory signalling pathways, new therapeutic strategies for RA can be envisioned that aim to balance and resolve, rather than suppress, inflammation.

Cloning and functional testing of rhesus macaque (Macaca mulatta) IL-9 and IL-33

BACKGROUND

IL-9 and IL-33 can profoundly influence immune responses. As a necessary first step toward defining their impact in the rhesus macaque model, we confirmed their endogenous expression and sequence identity and generated expression vectors for the recombinant expression of rhesus IL-9 and IL-33.

METHODS

RT-PCR and Sanger sequencing was used to define the expression and sequences for rhesus IL-9 and IL-33. The resulting recombinant cytokines were tested by ELISA and proliferation assays.

RESULTS

Full-length rhesus IL-9 and the mature form of rhesus IL-33 share 78% and 73% nucleotide similarity, respectively, with humans. Both cytokines are expressed in lymphocytes, with IL-9 expression also evident in CD4+ T cells. Recombinantly expressed rhesus IL-9 and IL-33 were each biologically active in vitro, including enhancing the proliferation of a rhesus B cell line.

CONCLUSIONS

The recombinant rhesus IL-9 and IL-33 constructs produce biologically active cytokines that can act upon rhesus B cells.

Elevated Levels of Soluble ST2 were Associated with Rheumatoid Arthritis Disease Activity and Ameliorated Inflammation in Synovial Fibroblasts

Background:

Much evidence has demonstrated that interleukin (IL)-33 plays an important role in rheumatoid arthritis (RA). However, there have been limited studies about soluble ST2, a receptor for IL-33, in RA. The aims of this study were to detect the levels of ST2 in the serum and synovial fluid of RA patients and to reveal the association of these levels with disease activity and the function of ST2 in RA.

Methods:

A total of 56 RA patients and 38 age-matched healthy controls were enrolled in this study. Synovial fluid samples were collected from another 30 RA patients and 20 osteoarthritis patients. Serum and synovial fluid levels of ST2 were measured by ELISA. In addition, the levels of ST2 in the serum of RA patients before and after therapy were detected. The function of ST2 in RA was revealed by the results of an in vitro cell assay, where recombinant ST2 proteins were used to treat peripheral blood mononuclear cells (PBMCs) and RA synovial fibroblasts (RASFs).

Results:

Serum-soluble ST2 levels were significantly higher in RA patients (127.14 ± 61.43 pg/ml) than those in healthy controls (78.37 ± 41.93 pg/ml, P < 0.01). Synovial fluid-soluble ST2 levels (41.90 ± 33.58 pg/ml) were much higher in RA patients than those in osteoarthritis patients (19.71 ± 16.72 pg/ml, P < 0.05). RA patients who received effective therapy for 6 months showed decreased serum-soluble ST2 levels (113.01 ± 53.90 pg/ml) compared to baseline (139.59 ± 68.36 pg/ml) (P = 0.01). RA patients with high disease activity had higher serum-soluble ST2 levels (162.02 ± 56.78 pg/ml) than those with low disease activity (94.67 ± 40.27 pg/ml, P = 0.001). Soluble ST2 did not affect IL-1β, IL-6, IL-8, or tumor necrosis factor-α (TNF-α) expression in PBMCs from RA patients. However, soluble ST2 ameliorated the expressions of IL-33 and IL-1β but not that of IL-6, IL-8, or TNF-α in resting RASFs. Interestingly, in the RASFs stimulated by TNF-α plus IL-1β, soluble ST2 showed extensive suppressive effects on the expression of IL-6, IL-8, and TNF-α.

Conclusion:

Elevated levels of ST2 in the serum and synovial fluid were associated with disease activity and ameliorated IL-33 expression and IL-33-induced inflammation in RASFs, suggesting that soluble ST2 might be a potential therapeutic candidate for RA.

IL-33 enhances the kinetics and quality of the antibody response to a DNA and protein-based HIV-1 Env vaccine

Induction of a sustained and broad antibody (Ab) response is a major goal in developing a protective HIV-1 vaccine. DNA priming alone shows reduced levels of immunogenicity; however, when combined with protein boosting is an attractive vaccination strategy for induction of humoral responses. Using the VC10014 DNA and protein-based vaccine consisting of HIV-1 envelope (Env) gp160 plasmids and trimeric gp140 proteins derived from an HIV-1 clade B infected subject who developed broadly neutralizing serum Abs, and which has been previously demonstrated to induce Tier 2 heterologous neutralizing Abs in rhesus macaques, we evaluated whether MPLA and IL-33 when administered during the DNA priming phase enhances the humoral response in mice. The addition of IL-33 during the gp160 DNA priming phase resulted in high titer gp120-specific plasma IgG after the first immunization. The IL-33 treated mice had higher plasma IgG Ab avidity, breadth, and durability after DNA and protein co-immunization with alum adjuvant as compared to MPLA and alum only treated mice. IL-33 was also associated with a significant IgM Env-specific response and expansion of peritoneal and splenic B-1b B cells. These results indicate that DNA priming in the presence of exogenous IL-33 qualitatively alters the HIV-1 Env-specific humoral response, improving the kinetics and breadth of potentially protective Ab.

Deficiency in IL-33/ST2 Axis Reshapes Mitochondrial Metabolism in Lipopolysaccharide-Stimulated Macrophages

The polarization and function of macrophages play essential roles in controlling immune responses. Interleukin (IL)-33 is a member of the IL-1 family that has been shown to influence macrophage activation and polarization, but the underlying mechanisms are not fully understood. Mitochondrial metabolism has been reported to be a central player in shaping macrophage polarization; previous studies have shown that both aerobic glycolysis and oxidative phosphorylation uniquely regulate the functions of M1 and M2 macrophages. Whether IL-33 polarizes macrophages by reshaping mitochondrial metabolism requires further investigation. In this work, we examined the mitochondrial metabolism of bone marrow-derived macrophages (BMDMs) from either wild type (WT), Il33-overexpressing, or IL-33 receptor knockout (St2^−/−) mice challenged with lipopolysaccharide (LPS). We found that after LPS stimulation, compared with WT BMDMs, St2^−/− BMDMs had reduced cytokine production and increased numbers and activity of mitochondria via the metabolism regulator peroxisome proliferator-activated receptor-C coactivator-1 α (PGC1α). This was demonstrated by increased mitochondrial DNA copy number, mitochondria counts, mitochondria fission- and fusion-related gene expression, oxygen consumption rates, and ATP production, and decreased glucose uptake, lactate production, and extracellular acidification rates. For Il33-overexpressing BMDMs, the metabolic reprogramming upon LPS stimulation was similar to WT BMDMs, and was accompanied by increased M1 macrophage activity. Our findings suggested that the pleiotropic IL-33/ST2 pathway may influence the polarization and function of macrophages by regulating mitochondrial metabolism.

Extracellular vesicles are associated with the systemic inflammation of patients with seropositive rheumatoid arthritis

Patients with rheumatoid arthritis (RA) and autoantibodies, such as rheumatoid factor and those against cyclic citrullinated peptides, are designated as seropositive and have a more severe disease with worse prognosis than seronegative RA patients. Understanding the factors that participate in systemic inflammation, in addition to articular commitment, would allow better treatment approaches for prevention of RA comorbidities and disease reactivation. We evaluated whether monocyte subsets and extracellular vesicles (EVs) could contribute to this phenomenon. Seropositive patients had higher levels of proinflammatory cytokines than those of seronegative patients and healthy controls (HCs); however, this systemic inflammatory profile was unrelated to disease activity. High frequencies of circulating EVs positive for IgG, IgM, CD41a, and citrulline, together with altered counts and receptor expression of intermediate monocytes, were associated with systemic inflammation in seropositive patients; these alterations were not observed in seronegative patients, which seem to be more similar to HCs. Additionally, the EVs from seropositive patients were able to activate mononuclear phagocytes in vitro, and induced proinflammatory cytokines that were comparable to the inflammatory response observed at the systemic level in seropositive RA patients; therefore, all of these factors may contribute to the greater disease severity that has been described in these patients.

Interleukin-33 Contributes Toward Loss of Tolerance by Promoting B-Cell-Activating Factor of the Tumor-Necrosis-Factor Family (BAFF)-Dependent Autoantibody Production

Breaking tolerance is a key event leading to autoimmunity, but the exact mechanisms responsible for this remain uncertain. Here we show that the alarmin IL-33 is able to drive the generation of autoantibodies through induction of the B cell survival factor BAFF. A temporary, short-term increase in IL-33 results in a primary (IgM) response to self-antigens. This transient DNA-specific autoantibody response was dependent on the induction of BAFF. Notably, radiation resistant cells and not myeloid cells, such as neutrophils or dendritic cells were the major source of BAFF and were critical in driving the autoantibody response. Chronic exposure to IL-33 elicited dramatic increases in BAFF levels and resulted in elevated numbers of B and T follicular helper cells as well as germinal center formation. We also observed class-switching from an IgM to an IgG DNA-specific autoantibody response. Collectively, the results provide novel insights into a potential mechanism for breaking immune-tolerance via IL-33-mediated induction of BAFF.

Prognostic Significance of Serum Interleukins and Soluble ST2 in Traditional Chinese Medicine (TCM) Syndrome-Differentiated Rheumatoid Arthritis

Backgrounds

The aim of this study was to explore the possible correlations of serum interleukins and soluble ST2 (sST2) protein with clinical features and inflammatory cytokines in rheumatoid arthritis (RA) patients, as well as to assess ability of TCM (Traditional Chinese Medicine) syndromes to differentiate RA patients and evaluate prognosis.

Material/Methods

Thirty RA patients and 25 healthy individuals were enrolled. Syndrome activity was evaluated, and lab tests were performed. Serum levels of IL-10, IL-17, IL-33, and sST2 were assessed by ELISA.

Results

Serum levels of sST2, IL-33, and pro-inflammation cytokine IL-17 were all up-regulated, while the immunosuppressive cytokine IL-10 was decreased in RA patients. Serum IL-33 level was positively associated with ESR, CRP, and RF, as well as with HAQ score, VAS score, and DAS28 scores (P<0.05). Serum sST2 level was correlated with the morning stiffness time and ESR, as well as scores of HAQ and DAS28 (P<0.05). In addition, IL-33 level was positively corelated with IL-17 (r=0.83, P<0.01) and the relative ratio of IL-10/IL-17 (r=0.904, P<0.01), and was negatively related with IL-10 (r=−0.632, P<0.01). TCM syndrome differentiation was conducted for RA patients, including the hot syndromes and cold syndromes groups. Hot syndromes RA patients had significantly more severe inflammation compared with cold syndromes patients.

Conclusions

IL-33 is a possible index for monitoring disease activity and inflammation condition in RA. IL-33 contributes to RA pathogenesis through unbalancing IL-10 and IL-17. In terms of TCM, hot syndromes RA presented more serious inflammation and more active disease activity, indicating a poorer prognosis.

Effects of Tocilizumab Therapy on Serum Interleukin-33 and Interleukin-6 Levels in Patients With Rheumatoid Arthritis

Objectives

This study aims to examine the effects of tocilizumab therapy on serum levels of interleukin (IL)-33 and IL-6 in rheumatoid arthritis (RA) patients.

Patients and methods

Interleukin-33 and IL-6 levels in serum samples from 83 RA patients (10 males, 73 females; mean age 51.9 years; range, 26 to 77 years) and 12 healthy controls (2 males, 10 females; mean age 52.2 years; range, 39 to 62 years) were compared by cross-sectional, case control analysis. Of the RA patients, 40 received 24 weeks of tocilizumab therapy and were assigned to the prospective cohort. These 40 patients were then divided into two subgroups as responders and non-responders according to the American College of Rheumatology (ACR) 20. The remaining 43 RA patients did not receive tocilizumab therapy. Serum cytokine levels were analyzed at baseline and after 24 weeks of tocilizumab therapy in these patients.

Results

Interleukin-33 and IL-6 concentrations were significantly higher in RA patients than in healthy controls (p<0.001 for both). Serum IL-33 levels in RA patients showed a significant correlation with rheumatoid factor titer (r=0.660, p<0.001), and IL-6 levels showed a significant correlation with high-sensitivity C-reactive protein levels (Spearman's rank correlation coefficient=0.482, p<0.001). Serum IL-33 levels decreased significantly after 24 weeks of tocilizumab therapy (p<0.001); this was particularly marked in ACR20 responders (p<0.001). However, the decrease in non-responders was not significant (p=0.066). Changes in serum IL-6 levels after 24 weeks of tocilizumab therapy were not significant in either ACR20 responders or non-responders.

Conclusion

Serum IL-33 levels in RA patients receiving tocilizumab therapy decreased significantly, particularly in ACR20 responders. Thus, IL-33 may be a useful marker for monitoring responses to tocilizumab therapy.

IL-33 promotes the egress of group 2 innate lymphoid cells from the bone marrow

ILC2s are potent mucosal effector cells that participate in type 2 inflammatory responses. Stier et al. demonstrate that IL-33 negatively regulates CXCR4, mediating the egress of ILC2 lineage cells from the bone marrow for potential hematogenous trafficking.

Group 2 innate lymphoid cells (ILC2s) are effector cells within the mucosa and key participants in type 2 immune responses in the context of allergic inflammation and infection. ILC2s develop in the bone marrow from common lymphoid progenitor cells, but little is known about how ILC2s egress from the bone marrow for hematogenous trafficking. In this study, we identified a critical role for IL-33, a hallmark peripheral ILC2-activating cytokine, in promoting the egress of ILC2 lineage cells from the bone marrow. Mice lacking IL-33 signaling had normal development of ILC2s but retained significantly more ILC2 progenitors in the bone marrow via augmented expression of CXCR4. Intravenous injection of IL-33 or pulmonary fungal allergen challenge mobilized ILC2 progenitors to exit the bone marrow. Finally, IL-33 enhanced ILC2 trafficking to the lungs in a parabiosis mouse model of tissue disruption and repopulation. Collectively, these data demonstrate that IL-33 plays a critical role in promoting ILC2 egress from the bone marrow.

IL-33-ST2 Axis in Liver Disease: Progression and Challenge

The new member of the IL-1 family, interleukin-33 (IL-33), participates in the progression of a variety of diseases through binding with its receptor ST2. Recently, much clinical evidence and experimental data have indicated that IL-33 is associated with various liver diseases. This review primarily addresses the relationship between IL-33 and several hepatic diseases. IL-33 can alleviate high-fat diet- (HFD-) induced hepatic steatosis and insulin resistance, and IL-33 acts as an alarmin, which quickly triggers the immune system to respond to virus invasion and toxic damage to the liver. However, when liver injury is chronic, IL-33 promotes Th2 reactions and hepatic stellate cell (HSC) activity, facilitating progression to liver fibrosis. The complicated functions of IL-33 should be considered before its clinical application.

Hypoxia-inducible factor-1α: a promising therapeutic target for autoimmune diseases

INTRODUCTION

Hypoxia-inducible factor-1α (HIF-1α) plays a crucial role in both innate and adaptive immunity. Emerging evidence indicates that HIF-1α is associated with the inflammation and pathologic activities of autoimmune diseases. Areas covered: Considering that the types of autoimmune diseases are complicated and various, this review aims to cover the typical kinds of autoimmune diseases, discuss the molecular mechanisms, biological functions and expression of HIF-1α in these diseases, and further explore its therapeutic potential. Expert opinion: Inflammation and hypoxia are interdependent. HIF-1α as a key regulator of hypoxia, exerts a crucial role in the balance between Th17 and Treg, and involves in the inflammation and pathologic activities of autoimmune diseases. Although there are many challenges remaining to be overcome, targeting HIF-1α could be a promising strategy for autoimmune diseases therapies.

Serum Levels of Interleukin 33 and Soluble ST2 Are Associated with the Extent of Disease Activity and Cutaneous Manifestations in Patients with Active Adult-onset Still's Disease

OBJECTIVE

Interleukin 33 (IL-33), a member of the IL-1 family and a ligand of the orphan receptor ST2, plays key roles in innate and adaptive immunity. We examined the associations between IL-33/ST2 levels and clinical manifestations of patients with active adult-onset Still's disease (AOSD).

METHODS

Blood samples were collected from 40 patients with active AOSD, 28 patients with rheumatoid arthritis (RA), and 27 healthy controls (HC). The serum levels of IL-33 and soluble ST2 were determined using ELISA. Expression levels of IL-33 and ST2 in biopsy specimens obtained from 34 AOSD patients with rash were immunohistochemically investigated.

RESULTS

IL-33 levels of patients with AOSD were higher than those of patients with RA and HC. Soluble ST2 levels of patients with AOSD were higher than those of HC, but not of patients with RA. Serum IL-33 levels correlated with systemic score, erythrocyte sedimentation rate, ferritin levels, and aspartate transaminase levels. However, serum soluble ST2 levels correlated only with ferritin levels. The numbers of inflammatory cells expressing IL-33 and ST2 were elevated in skin lesions of patients with AOSD compared to HC, but did not differ from those of the skin lesions of eczema or psoriasis.

CONCLUSION

We found significantly higher serum IL-33 and soluble ST2 levels in patients with active AOSD. Results indicate that the IL-33/ST2 signaling pathway may play a role in the pathogenesis of the acute inflammation and skin manifestations associated with AOSD.

Interleukin-33 as a marker of disease activity in rheumatoid factor positive polyarticular juvenile idiopathic arthritis

OBJECTIVE

To investigate clinical usefulness of serum interleukin (IL)-33 levels as an indicator of disease activity in juvenile idiopathic arthritis (JIA).

METHODS

We measured serum levels of IL-33 in 39 patients with JIA, including 7 patients with rheumatoid factor positive poly-JIA (RF + poly-JIA), 8 patients with RF negative poly-JIA (RF-poly-JIA), 20 patients with oligoarticular JIA (Oligo-JIA), 4 patients with enthesitis-related arthritis (ERA) and 30 age-matched healthy controls. Furthermore, we determined their correlation with measures of disease activity.

RESULTS

Serum IL-33 levels in patients with RF + poly-JIA were significantly elevated compared to those in patients with RF-poly-JIA, oligo-JIA and HC. Serum IL-33 levels in patients with RF-poly-JIA, oligo-JIA and ERA were not elevated compared to those in HC. Serum IL-33 levels in RF + poly-JIA patients normalized in remission phase. Serum IL-33 levels correlated positively with RF in patients with RF + poly-JIA.

CONCLUSIONS

These results indicate that serum IL-33 levels in RF + poly-JIA patients correlated with disease activity, suggesting a potential role of IL-33 as a promising indicator of disease activity.

IL-33 neutralization suppresses lupus disease in lupus-prone mice

IL-33 is a new member of the IL-1 family that plays a role in inflammation. In this study, we evaluated the potential of IL-33 inhibition as a treatment for systemic lupus erythematosus (SLE) using the lupus-prone model MRL/lpr mice and the underlying mechanisms of action. We treated mice with anti-mouse IL-33 antibody (anti-IL-33Ab) via intraperitoneal injection every other day from week 14 until week 20 for 6 weeks. A control group received the same amount of IgG control. Renal damage and mouse survival were compared. Cytokines, antibodies, immune complex, Tregs, myeloid-derived suppressor cells (MDSCs), and Th17 cells were also analyzed. Correlations between serum IL-33 and SLE disease activity index in human SLE were also investigated. MRL/lpr mice treated with anti-IL-33Ab showed reduced proteinuria and reduced serum anti-dsDNA levels. Nephritis, immune complex deposits, and the circulating antibodies and immune complex besides the mortality were significantly reduced by anti-IL-33Ab. Anti-IL-33Ab remarkably increased Tregs and MDSCs and reduced the Th17 cells and IL-1β, IL-6, and IL-17 levels in MRL/lpr mice. These results suggest that IL-33 inhibition may inhibit SLE via expansion of Tregs and MDSCs and inhibition of Th17 cells and proinflammatory responses, indicating that blockade of IL-33 has a protective effect on SLE.

IL-33 and soluble ST2 levels as novel predictors for remission and progression of carotid plaque in early rheumatoid arthritis: A prospective study

OBJECTIVES

To study the association between the baseline IL-33 and soluble ST2 (sST2) levels with disease remission and progression of carotid atherosclerosis in early rheumatoid arthritis (ERA) patients.

METHODS

A total of 98 ERA patients were enrolled. Disease activity and the presence of carotid plaque were evaluated at baseline and 12 months later. Plasma IL-33 and sST2 levels were determined using enzyme-linked immunosorbent assay kits.

RESULTS

Baseline IL-33 and sST2 levels were associated with inflammatory markers and cardiovascular (CV) risk factors. Overall, 44(45%), 18(18%), and 21(21%) patients achieved remission based on 28-joint disease activity score (DAS28), Boolean, and simplified disease activity score (SDAI) criteria at 12 months, respectively. Patients with detectable IL-33 at baseline were less likely to achieve DAS28 (P = 0.010) and SDAI remission (P = 0.021), while a lower baseline sST2 level was able to predict DAS28, Boolean, and SDAI remission (P = 0.005, 0.001, and <0.001, respectively). Using multivariate analysis, a lower baseline sST2 level independently predict Boolean (OR = 0.789; P = 0.005) and SDAI remission (0.812; P = 0.008). Regarding carotid atherosclerosis, 9/98(9.2%) patients had plaque progression at 12 months. Baseline IL-33 was detectable in 8/9(89%) and 42/83(51%) of patients with and without plaque progression respectively (P = 0.029). Baseline detectable IL-33 was an independent predictor for plaque progression after adjusting for traditional CV risk factors (P = 0.017).

CONCLUSIONS

Lower baseline sST2 levels independently predict disease remission and baseline detectable IL-33 independently predicts carotid plaque progression in ERA patients. This study suggests that inflammation induced by the IL-33/ST2 axis may play a significant role in the development of cardiovascular disease in RA.

Severe neutrophil-dominated inflammation and enhanced myelopoiesis in IL-33-overexpressing CMV/IL33 mice

IL-33 is a cytokine of the IL-1 family, which signals through the ST2 receptor. Previous studies emphasized a role for IL-33 in shaping innate and adaptive immune responses. IL-33 was also reported to modulate myelopoiesis and myeloid cell activity. In this article, we describe IL-33-overexpressing CMV/IL33 and LysM/IL33 mice, which display an inflammatory phenotype associated with growth retardation and paw swelling. The phenotype of CMV/IL33 mice is dependent on activation of the ST2 receptor and is characterized by extensive neutrophil infiltration into different organs, including the paws. Local or systemic levels of proinflammatory mediators such as IL-1β, Cxcl-1, G-CSF, and IL-6 are increased. CMV/IL-33 mice also suffer from anemia, thrombocytosis, and a marked dysregulation of myelopoiesis, leading to an important increase in myeloid cell production or accumulation in bone marrow (BM), spleen, and peripheral blood. Consistently, recombinant IL-33 induced proliferation of myeloid lineage cells in BM-derived granulocyte cultures, whereas IL-33 knockout mice exhibited minor deficiencies in spleen and BM myeloid cell populations. Our observations reveal a neutrophil-dominated inflammatory phenotype in IL-33-overexpressing CMV/IL33 and LysM/IL33 mice, and highlight important regulatory effects of IL-33 on myelopoiesis in vitro and in vivo, where excessive IL-33 signaling can translate into the occurrence of a myeloproliferative disorder.

Role of IL-33 and its receptor in T cell-mediated autoimmune diseases

Interleukin-33 (IL-33) is a new cytokine of interleukin-1 family, whose specific receptor is ST2. IL-33 exerts its functions via its target cells and plays different roles in diseases. ST2 deletion and exclusion of IL-33/ST2 axis are accompanied by enhanced susceptibility to dominantly T cell-mediated organ-specific autoimmune diseases. It has been reported that IL-33/ST2 pathway plays a key role in host defense and immune regulation in inflammatory and infectious diseases. This review focuses on new findings in the roles of IL-33 and ST2 in several kinds of T cell-mediated autoimmune diseases.

Immune-mediated experimental arthritis in IL-33 deficient mice

Previous work suggested implication of the interleukin (IL)-1 family cytokine IL-33, signaling through its receptor ST2, in the pathogenesis of human and mouse arthritis. In this study, we directly investigated the role of endogenous IL-33 in antigen-induced arthritis (AIA) and collagen-induced arthritis (CIA) using IL-33 KO mice. AIA was induced by injection of methylated bovine serum albumin (mBSA) into knee joints of previously immunized mice. CIA was induced by immunization with bovine type II collagen. Disease severity was evaluated by clinical and histological scoring and cellular immune responses were assessed in cultured draining lymph node cells. Our results indicate that the development of AIA or CIA, as assessed by clinical or histological evaluation, is not impaired in IL-33 deficient mice. We did not observe any consistent modifications in humoral or cellular immune responses in IL-33 KO mice, although IL-33 deficiency enhanced antigen-specific IFN-γ production, proliferation or IgG2a titers in some experiments, suggesting that endogenous IL-33 may contribute to shaping the adaptive immune response. In conclusion, our data suggest that IL-33 plays a modifying rather than a pivotal role in disease development in two models of immune-mediated arthritis.

Genetic variant in IL33 is associated with susceptibility to rheumatoid arthritis

INTRODUCTION

Interleukin (IL)-33 is a proinflammatory cytokine contributing to the pathogenesis of rheumatoid arthritis (RA). The gene encoding IL-33 may serve as a genetic factor and be associated with the risk of RA. To investigate the potential association between IL33 and RA, we performed a case-control study based on Chinese Han population.

METHODS

A three-stage case-control study was performed. Two tag single-nucleotide polymorphisms (SNPs) (rs7044343 and rs10975514), mapping to the IL33 gene, were first genotyped in the discovery population. We further genotyped rs7044343 and rs10975514 in the validation and replication population. The associations between the two tag SNPs and phenotypic subgroups of RA and levels of serum IL-33 were assessed with a logistic regression model.

RESULTS

In the discovery population, the CC genotype of rs7044343 was associated with RA patients (odds ratio (OR) = 0.777, 95% confidence interval (CI), 0.611 to 0.988; P = 0.040). After anti-citrullinated peptide antibody (ACPA) stratification, the CC genotype of rs7044343 was also shown to be a protective genotype in RA without ACPA (OR = 0.610; 95% CI, 0.379 to 0.982; P = 0.042). In the validation population and replication population, the association between rs7044343 and RA, especially ACPA-negative RA, was still significant. A meta-analysis of discovery, validation, and replication panels confirmed the association between CC genotype of rs7044343 and RA (Pcombined = 0.0004; ORcombined = 0.77; 95% CI, 0.67 to 0.89). No evidence was found for heterogeneity between three sample sets (Phet = 0.99; I² = 0%). Similar results were also obtained in ACPA-negative RA (Pcombined = 0.0002; ORcombined = 0.57; 95% CI, 0.43 to 0.77). No association was detected between rs10975514 polymorphism and RA susceptibility in the discovery and validation population. The serum levels of IL-33 were significantly lower in the patients with the rs7044343 CC genotype.

CONCLUSION

The CC genotype of rs7044343 in IL33 is associated with RA patients and downregulates IL-33 expression in RA.

Emerging role of interleukin-33 in autoimmune diseases

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family. It predominantly induces type 2 immune responses and thus is protective against atherosclerosis and nematode infections but contributes to allergic airway inflammation. Interleukin-33 also plays a pivotal role in the development of many autoimmune diseases through mechanisms that are still not fully understood. In this review, we focus on the recent advances in understanding of the expression and function of IL-33 in some autoimmune disorders, aiming to provide insight into its potential role in disease development.

IL-33 enhances proliferation and invasiveness of decidual stromal cells by up-regulation of CCL2/CCR2 via NF-κB and ERK1/2 signaling

Interleukin (IL)-33, a newly described member of the IL-1 family, has been reported to facilitate primary tumor progression and metastatic dissemination. However, its biological function on decidual stromal cells (DSCs) remains unclear. In this study, we tested the hypothesis whether IL-33 promotes proliferation and invasion of DSCs, and the possible mechanism. IL-33 and its orphan receptor ST2 was found to be co-expressed by DSCs in human first-trimester pregnancy. Addition of IL-33, enhanced the proliferation and invasion of DSCs in a dosage-dependent manner, concomitantly with increasing expression of proliferation relative gene (PCNA, survivin) and invasion relative gene (titin, MMP2). Blocking IL-33/ST2 signaling by soluble sST2 apparently abolished the stimulatory effect on the proliferation, invasiveness and related gene expression in DSCs. We also demonstrated that chemokines CCL2/CCR2 was significantly increased with IL-33 administration. Moreover, inhibition of CCL2/CCR2 activation using CCL2 neutralizing antibody or CCR2 blocker prevented IL-33-stimulated proliferation and invasiveness capacity of DSCs. Increasing phosphorylation of nuclear factor NF-κB p65 and extracellular signal-regulated kinases ERK1/2 after treatment with IL-33 was confirmed by western blotting. And the IL-33-induced CCL2/CCR2 expression was abrogated by treatment with the NF-κB inhibitor BAY 11-7082 or ERK1/2 inhibitor U0126. Finally, we showed that decreased IL-33/ST2 expression was observed in DSCs from spontaneous abortion compared with normal pregnancy at both gene and protein levels. This study provides evidence for the molecular mechanism of IL-33 in promoting proliferation and invasiveness of DSCs by up-regulation of CCL2/CCR2 via NF-κB and ERK1/2 signal pathways and thus contributes insight to the potential of IL-33 involved in successful pregnancy via inducing DSCs mitosis and invasion.

Differences in synovial fluid cytokine levels but not in synovial tissue cell infiltrate between anti-citrullinated peptide/protein antibody-positive and -negative rheumatoid arthritis patients

Introduction

Comparative data on synovial cell infiltrate and cytokine levels in anti citrullinated peptide/protein antibody (ACPA)-positive and ACPA negative rheumatoid arthritis (RA) patients are scarce. Our aim was to analyze synovial cell infiltrate and synovial fluid (SF) levels of cytokines in patients with RA according to the presence or absence of ACPA in serum.

Methods

A cross-sectional study in a single center including consecutive RA patients was performed. Patients were defined as 'ACPA negative' if serum was negative to two different ACPAs [second generation commercial anti-cyclic citrullinated peptide antibodies (CCP2) and chimeric fibrin/filaggrin citrullinated antibodies]. Parallel synovial tissue (ST) biopsies and SF were obtained by knee arthroscopy. Synovial cell infiltrate and endothelial cells were analyzed by immunohistochemistry and SF levels of Th1, Th2, Th17 and pro-inflammatory cytokines by Quantibody(R) Human Array.

Results

A total of 83 patients underwent arthroscopy, with a mean age of 55.9 ± 12 years, and mean disease duration of 45 months (interquartile range, IQR 10.8 to 122). 62% were female and 77% were ACPA positive. No significant differences were found in clinical variables, acute phase reactants, synovial cell infiltrate or lymphoid neogenesis (LN) between ACPA positive and negative patients. However ACPA positive patients had significantly higher levels of IL-1β, IL-10, IL-17 F and CC chemokine ligand 20 (CCL-20) than ACPA negative patients.

Conclusions

In our cohort of patients with RA no significant differences were found in synovial cell infiltrate or synovial LN according to ACPA status. However, ACPA positive patients had higher levels of T-cell derived and pro-inflammatory cytokines than ACPA negative patients. As systemic and local inflammation was similar in the two groups, these findings support a distinct synovial physiopathology.

Increased IL-33 in synovial fluid and paired serum is associated with disease activity and autoantibodies in rheumatoid arthritis

OBJECTIVES

IL-33, a newly found cytokine which is involved in joint inflammation, could be blocked by a decoy receptor-sST2. The expression and correlation of IL-33 and sST2 in rheumatoid arthritis (RA) are of great interest.

METHODS

Synovial fluid (SF) was obtained from 120 RA and 30 osteoarthritis (OA) patients, and paired sera were collected from 54 of these RA patients. The levels of IL-33 and sST2 were measured by ELISA.

RESULTS

SF IL-33 was significantly higher in RA than in OA, which was correlated with disease activity score 28, erythrocyte sedimentation rate, rheumatoid factor (RF)-IgM, RF-IgG, glucose phosphate isomerase (GPI), and immunoglobulin. Serum IL-33 was correlated positively with SF IL-33 in RA. Furthermore, it was correlated with RF-IgM and GPI. sST2 was partly detectable in RA (13 out of 54, 24.1%), while not in OA. Serum sST2 in RA had no significant correlation with serum IL-33 or SF IL-33. However, SFs from both RA and OA patients did not express sST2.

CONCLUSIONS

This study supported that IL-33 played an important role in the local pathogenesis of RA. Considering the tight correlation between IL-33 and clinical features, it may become a new target of local treatment.

Hypoxia-inducible factor-1α and interleukin 33 form a regulatory circuit to perpetuate the inflammation in rheumatoid arthritis

Hyperplasia of synovial fibroblasts, infiltration with inflammatory cytokines, and tissue hypoxia are the major characteristics of rheumatoid arthritis (RA). Interleukin 33 (IL-33) is a newly identified inflammatory cytokine exacerbating the disease severity of RA. Hypoxia-inducible factor-1α (HIF-1α) showed increased expression in RA synovium and could regulate a number of inflammatory cytokine productions. Nevertheless, its correlation with IL-33 remains largely unknown. Here, we showed that elevated levels of IL-33 were demonstrated in RA patient synovial fluids, with upregulated expression of HIF-1α and IL-33 in the synovial fibroblasts. Knocking down HIF-1α compromised IL-33 expression in rheumatoid arthritis synovial fibroblasts (RASF), while enforcing HIF-1α expression in RASF substantially upregulated IL-33 levels. HIF-1α promoted the activation of the signalling pathways controlling IL-33 production, particularly the p38 and ERK pathways. Moreover, we showed for the first time that IL-33 in turn could induce more HIF-1α expression in RASF, thus forming a HIF-1α/IL-33 regulatory circuit that would perpetuate the inflammatory process in RA. Targeting this pathological pathway and HIF-1α may provide new therapeutic strategies for overcoming the persistent and chronic inflammatory disease.

Serum level of interleukin-33 and soluble ST2 and their association with disease activity in patients with Behcet's disease

Interleukin (IL)-33 is an important mediator of innate immunity. Behcet's disease (BD) is an autoinflammatory disorder characterized by hyperactivity of the innate immune response. We measured serum levels of IL-33 and its receptor soluble ST2 (sST2) in patients with BD to investigate their association with disease activity. Serum levels of both IL-33 and sST2 were higher in patients with BD compared with those in normal controls (IL-33: 594.48±175.04 pg/mL in BD and 224.23±56.64 pg/mL in normal controls [P=0.048], sST2: 99.01±15.92 pg/mL in BD and 23.56±3.25 pg/mL in normal controls [P<0.001]). IL-33 and sST2 expression in skin tissue, as shown by immunohistochemistry, was higher in patients with BD compared with that in the normal controls. Serum sST2 level correlated significantly with the BD currently active form (BDCAF), Iranian BD dynamic activity measure (IBDDAM), erythrocyte sedimentation rate and C-reactive protein. Multiple linear regression showed that serum sST2 was an independent factor associated with IBBDAM (regression coefficient, 0.374; P=0.004), and BDCAF (regression coefficient, 0.236; P=0.047). These results demonstrate that IL-33 and sST2 are highly expressed in patients with BD and that serum sST2 is an independent factor associated with IBDDAM and BDCAF, suggesting a potential role for sST2 as a surrogate marker of disease activity in patients with BD.

Potential contribution of interleukin-33 to the development of interstitial lung disease in patients with primary Sjogren's Syndrome

OBJECTIVE

To determine whether interleukin (IL)-33 and soluble ST2 (sST2) are associated with primary Sjogren's Syndrome (pSS).

METHODS

Serum levels of IL-33 and sST2 in 110 pSS patients and 78 healthy controls were measured by enzyme-linked immunosorbent assay (ELISA). Immunoglobulins, rheumatoid factors (RF), antinuclear antibody (ANA), anti-SSA/RO-52 antibody, anti-SSB antibody and erythrocyte sedimentation rate (ESR) were measured by standard laboratory techniques. Interstitial lung disease (ILD) was identified on high-resolution computed tomography (HRCT). Disease activity in pSS was scored with the European League Against Rheumatism Sjogren's Syndrome Disease Activity Index (ESSDAI).

RESULTS

Serum levels of IL-33 and sST2 were significantly elevated in pSS patients, especially in patients with ILD. There was significant positive correlation between IL-33 and RF, anti-SSB antibody.

CONCLUSION

IL-33/sST2 may be involved in the pathogenesis of pSS and partly contribute to the ILD in pSS patients.

IL-33 in rheumatoid arthritis: potential role in pathogenesis and therapy

Rheumatoid arthritis (RA) is characterized by chronic inflammatory disease, including synovial proliferation and excessive pro-inflammatory cytokines production, leading to cartilage and bone destruction. Cytokine-mediated immunity plays an important role in the pathogenesis of various autoimmune diseases such as RA. Recently, the IL-1 family member IL-33, was recognized to perform as an inflammatory cytokine, exerted profound effects in human RA and experimental inflammatory arthritis. Furthermore, inhibition of IL-33 signaling proposed a potential therapeutic approach. In this review, we summarize recent advances on the pathological roles of IL-33 in RA and discuss the therapeutic significance of these new findings.

Profibrotic interleukin-33 is correlated with uterine leiomyoma tumour burden

STUDY QUESTION

Are interleukin-33 (IL-33) serum levels higher in women with uterine leiomyoma compared with controls without leiomyoma?

SUMMARY ANSWER

Serum IL-33 is elevated in women with uterine leiomyoma and correlated with features of uterine leiomyoma tumour burden, namely fibroid number, size and weight.

WHAT IS KNOWN ALREADY

Uterine leiomyomas are the most common benign tumours in premenopausal women associated with major tissue fibrosis. IL-33 is a cytokine involved in fibrotic disorders. The potential role of IL-33 in leiomyoma has not been reported before.

STUDY DESIGN, SIZE, DURATION

This is a prospective laboratory study conducted in a tertiary-care university hospital between January 2005 and December 2010. We investigated non-pregnant, 42-year-old patients (n = 151) during surgery for a benign gynaecological condition.

PARTICIPANTS/MATERIALS, SETTING, METHODS

After complete surgical exploration of the abdominopelvic cavity, 59 women with histologically proved uterine leiomyoma and 92 leiomyoma-free control women were enrolled. Women with endometriosis or past history of ovarian malignancy and borderline tumours were not included. The control group included women with benign ovarian cysts, paratubal cysts or tubal defects without any evidence of uterine leiomyoma. For each patient, a structured questionnaire was completed during a face-to-face interview conducted by the surgeon during the month preceding surgery. Serum samples were obtained in the month preceding the surgical procedures according to the menstrual phase or hormonal therapy. IL-33 was measured in sera by enzyme-linked immunosorbent assay, and correlation of IL-33 concentration with the extent and severity of the disease was investigated.

MAIN RESULTS AND THE ROLE OF CHANCE

IL-33 was detected in 32 (54.2%) women with leiomyoma and 18 (19.6%) controls (P < 0.001). Serum IL-33 was higher in women with leiomyoma (median, 140.1 pg/ml; range, 7.5-2247.7) than in controls (median, 27.8 pg/ml; range, 7.5-71.6; P = 0.002). We found positive correlations between serum IL-33 concentration and leiomyoma features, such as fibroid weight (r = 0.630; P = 0.001) and size (r = 0.511; P = 0.018) and the number of fibroids (r = 0.503; P = 0.003).

LIMITATIONS, REASONS FOR CAUTION

There was a possible selection bias due to inclusion of only surgical patients. Therefore our control group consisted of women who underwent surgery for benign gynaecological conditions. This may lead to biases stemming from the fact that certain of these conditions, such as tubal infertility or ovarian cysts, might be associated with altered serum IL-33 levels.

WIDER IMPLICATIONS OF THE FINDINGS

We demonstrate for the first time that elevated serum IL-33 levels are associated with the existence of uterine leiomyoma. However, even if an association does not constitute proof of cause and effect, investigating the mechanisms that underlie fibrogenesis associated with leiomyomas is a step towards understanding this enigmatic disease. This study opens the doors to future, more mechanistics studies to establish the exact role of IL-33 in uterine leiomyomas pathogenesis.

STUDY FUNDING/COMPETING INTEREST(S)

No funding, no conflict of interest.

Soluble ST2 as a marker of disease activity in systemic juvenile idiopathic arthritis

To assess the role of interleukin (IL)-33 and ST2, the receptor for IL-33, in the pathogenesis of systemic juvenile idiopathic arthritis (s-JIA), we sequentially measured the serum levels of IL-33 and soluble ST2 (sST2) in patients with s-JIA and determined their correlation with measures of disease activity and severity. Twenty-four patients with s-JIA, 5 with rheumatoid factor positive polyarticular JIA (RF+poly-JIA), and 20 age-matched healthy controls (HCs) were analyzed. IL-33 and sST2 levels were quantified in serum by enzyme-linked immunosorbent assays. Serum IL-33 levels in most patients with active s-JIA were below the lowest detection limit. Serum IL-33 levels in patients with RF+poly-JIA were significantly higher than those in patients with s-JIA and HC. Serum sST2 levels in patients during the active phase of s-JIA were much higher than those in patients with poly-JIA and HC. Serum sST2 levels in patients with s-JIA were significantly elevated even in the inactive phase, when other clinical parameters were normalized. Serum sST2 levels correlated positively with the clinical parameters of disease activity. These findings indicate that ST2 may be an important mediator in s-JIA. Serum sST2 levels in patients with s-JIA correlated with disease activity, suggesting a potential role as a promising indicator of disease activity.