Elevated serum interleukin-38 level at baseline predicts virological response in telbivudine-treated patients with chronic hepatitis B

Emerging functions and therapeutic targets of IL-38 in central nervous system diseases

Interleukin (IL)-38 is a newly discovered cytokine of the IL-1 family, which binds various receptors (i.e., IL-36R, IL-1 receptor accessory protein-like 1, and IL-1R1) in the central nervous system (CNS). The hallmark physiological function of IL-38 is competitive binding to IL-36R, as does the IL-36R antagonist. Emerging research has shown that IL-38 is abnormally expressed in the serum and brain tissue of patients with ischemic stroke (IS) and autism spectrum disorder (ASD), suggesting that IL-38 may play an important role in neurological diseases. Important advances include that IL-38 alleviates neuromyelitis optica disorder (NMOD) by inhibiting Th17 expression, improves IS by protecting against atherosclerosis via regulating immune cells and inflammation, and reduces IL-1β and CXCL8 release through inhibiting human microglial activity post-ASD. In contrast, IL-38 mRNA is markedly increased and is mainly expressed in phagocytes in spinal cord injury (SCI). IL-38 ablation attenuated SCI by reducing immune cell infiltration. However, the effect and underlying mechanism of IL-38 in CNS diseases remain inadequately characterized. In this review, we summarize the biological characteristics, pathophysiological role, and potential mechanisms of IL-38 in CNS diseases (e.g., NMOD, Alzheimer's disease, ASD, IS, TBI, and SCI), aiming to explore the therapeutic potential of IL-38 in the prevention and treatment of CNS diseases.

The emerging role of IL-38 in diseases: A comprehensive review

INTRODUCTION

Interleukin-38 (IL-38) is a new type of anti-inflammatory cytokine, which is mainly expressed in the immunity-related organs and is involved in various diseases including cardiovascular and cerebrovascular diseases, lung diseases, viral infectious diseases and autoimmune diseases.

AIM

This review aims to detail the biological function, receptors and signaling of IL-38, which highlights its therapeutic potential in related diseases.

CONCLUSION

This article provides a comprehensive review of the association between interleukin-38 and related diseases, using interleukin-38 as a keyword and searching the relevant literature through Pubmed and Web of science up to July 2023.

The role of IL-38 in intestinal diseases - its potential as a therapeutic target

IL-38, an anti-inflammatory cytokine, is a key regulator of homeostasis in host immunity. Intestinal immunity plays a critical role in defence against pathogenic invasion, as it is the largest surface organ and the most common entry point for micro-organisms. Dysregulated IL-38 activity is observed in several autoimmune diseases including systemic lupus erythematosus and atherosclerosis. The protective role of IL-38 is well illustrated in experimental colitis models, showing significantly worse colitis in IL-38 deficient mice, compared to wildtype mice. Moreover, exogenous IL-38 has been shown to ameliorate experimental colitis. Surprisingly, upregulated IL-38 is detected in inflamed tissue from inflammatory bowel disease patients, consistent with increased circulating cytokine levels, demonstrating the complex nature of host immunity in vivo. However, colonic IL-38 is significantly reduced in malignant tissues from patients with colorectal cancer (CRC), compared to adjacent non-cancerous tissue. Additionally, IL-38 expression in CRC correlates with 5-year survival, tumour size and differentiation, suggesting IL-38 plays a protective role during the development of CRC. IL-38 is also an independent biomarker for the prognosis of CRC, offering useful information in the management of CRC. Taken together, these data demonstrate the role of IL-38 in the maintenance of normal intestinal mucosal homeostasis, but that dysregulation of IL-38 contributes to initiation of chronic inflammatory bowel disease (resulting from persistent local inflammation), and that IL-38 provides protection during the development of colorectal cancer. Such data provide useful information for the development of novel therapeutic targets in the management of intestinal diseases for more precise medicine.

Exploratory analysis of interleukin-38 in hospitalized COVID-19 patients

INTRODUCTION

A major contributor to coronavirus disease 2019 (COVID-19) progression and severity is a dysregulated innate and adaptive immune response. Interleukin-38 (IL-38) is an IL-1 family member with broad anti-inflammatory properties, but thus far little is known about its role in viral infections. Recent studies have shown inconsistent results, as one study finding an increase in circulating IL-38 in COVID-19 patients in comparison to healthy controls, whereas two other studies report no differences in IL-38 concentrations.

METHODS

Here, we present an exploratory, retrospective cohort study of circulating IL-38 concentrations in hospitalized COVID-19 patients admitted to two Dutch hospitals (discovery n = 148 and validation n = 184) and age- and sex-matched healthy subjects. Plasma IL-38 concentrations were measured by enzyme-linked immunosorbent assay, disease-related proteins by proximity extension assay, and clinical data were retrieved from hospital records.

RESULTS

IL-38 concentrations were stable during hospitalization and similar to those of healthy control subjects. IL-38 was not associated with rates of intensive care unit admission or mortality. Only in men in the discovery cohort, IL-38 concentrations were positively correlated with hospitalization duration. A positive correlation between IL-38 and the inflammatory biomarker d-dimer was observed in men of the validation cohort. In women of the validation cohort, IL-38 concentrations correlated negatively with thrombocyte numbers. Furthermore, plasma IL-38 concentrations in the validation cohort correlated positively with TNF, TNFRSF9, IL-10Ra, neurotrophil 3, polymeric immunoglobulin receptor, CHL1, CD244, superoxide dismutase 2, and fatty acid binding protein 2, and negatively with SERPINA12 and cartilage oligomeric matrix protein.

CONCLUSIONS

These data indicate that IL-38 is not associated with disease outcomes in hospitalized COVID-19 patients. However, moderate correlations between IL-38 concentrations and biomarkers of disease were identified in one of two cohorts. While we demonstrate that IL-38 concentrations are not indicative of COVID-19 severity, its anti-inflammatory effects may reduce COVID-19 severity and should be experimentally investigated.

Serum interleukin-38 levels correlated with insulin resistance, liver injury and lipids in non-alcoholic fatty liver disease

Background

Insulin resistance, liver injury and dyslipidemia are reported in non-alcoholic fat liver disease (NAFLD) patients. Interleukin (IL)-38 may take part in the pathophysiology of insulin resistance. Nevertheless, the function of IL-38 in NAFLD is unknown. Herein, we determined whether serum IL-38 level might be utilised as a biochemical marker for diagnosing NAFLD.

Methods

NAFLD patients and healthy participants (n = 91 each) were enrolled. Circulating serum IL-38 levels were detected using enzyme-linked immunosorbent assay. Other metabolic and inflammatory indices related to NAFLD were also assessed.

Results

Patients with NAFLD had higher serum IL-38 levels than healthy individuals. Significantly higher serum IL-38 levels were found in patients with severe and moderate NAFLD than in patients with mild NAFLD. IL-38 showed a significant correlation with parameters of insulin resistance, inflammation, and liver enzyme in NAFLD cases. Anthropometric, insulin resistance, inflammatory parameters, lipids and frequency of NAFLD showed significant differences among the serum IL-38 level tertiles. Participants in the 2nd and 3rd tertiles of serum IL-38 levels had a greater risk of NAFLD than those in the 1st tertile. Furthermore, IL-38 ROC curve showed a high area under ROC with 0.861.

Conclusions

It is possible for serum IL-38 to be a biomarker for NAFLD.

Circulating interleukin-38 concentrations in healthy adults

Interleukin (IL)-38 is the latest discovered member of the interleukin-1 family, which has anti-inflammatory properties similar to IL-36Ra. Several studies compared circulating IL-38 concentrations in healthy and diseased populations to characterize its role in both auto-immune and inflammatory pathologies, with both higher and lower concentrations being associated with certain diseases. However, in order to use IL-38 as a biomarker, a reference range in healthy adults is needed. To establish a reference IL-38 circulating concentration, accessible data from 25 eligible studies with IL-38 concentrations in healthy adults was collected. To validate the values found in literature, we measured IL-38 concentrations by enzyme-linked immunosorbent assay (ELISA) in several cohorts from our own institute. Additionally, the effect of blood collection techniques, freeze thawing cycles, and hemolysis on IL-38 measurements was assessed. To evaluate the importance of the genetic background of individuals as confounding factor of IL-38 synthesis, we used publicly available eQTL databases with matched data on allele frequencies in individuals of different ethnicities. Mean IL-38 concentrations in the various studies were weighted by their corresponding sample size, resulting in a weighted mean, and weighted upper and lower limits were calculated by mean ± 2 SD. Differences of over 10.000-fold were found in the weighted means between studies, which could not be attributed to the blood collection method or assessment of IL-38 in plasma or serum. Although IL-38 concentrations were markedly higher in Chinese then in European population studies, we could not show an association with the genetic background. From our analysis, a reference range for circulating IL-38 in healthy adults could thus not yet be established.

An overview of the biological and multifunctional roles of IL-38 in different infectious diseases and COVID-19

Undoubtfully, the normal immune system can make a potential response to variable pathogens and neutralize or kill them depending on the type of infection through innate and acquired immunity. Cytokines have poly-peptide nature and are considered as signaling molecules that could amplify or alleviate immune responses besides their other biological functions. Interleukin 38 (IL-38) is a member of the IL-1 family cytokine that, however, its anti-inflammatory role has been observed in different autoimmune diseases like systemic lupus erythematosus (SLE), psoriasis, and Sjogren’s syndrome; there is a controversy about the cytokine pro-inflammatory function. In the current review, we skimmed IL-38 structure, signaling mechanism, and its immunological functions, IL-38-producing immune cells. Also, we argued about the role of this cytokine in viral infections including hepatitis B (HBV), hepatitis C (HCV), influenza (Flu), and COVID-19. Also, it illustrated the IL-38 protective effects on sepsis. Moreover, we explained the modulatory role of IL-38 in the COVID-19 cytokine storm.

Immunobiological Properties and Clinical Applications of Interleukin-38 for Immune-Mediated Disorders: A Systematic Review Study

Exponential growth in the usage of "cytokines" (as seroimmunobiomarkers) has facilitated more accurate prognosis, early diagnosis, novel, and efficient immunotherapeutics. Numerous studies have reported immunopathophysiological and immunopathological processes of interleukin-38 (IL-38). Therefore, in this systematic review article, the authors aimed to present an updated comprehensive overview on the immunobiological mechanisms, diagnostic, and immune gene-based therapeutic potentials of IL-38. According to our inclusion and exclusion criteria, a total of 216 articles were collected from several search engines and databases from the January 2012 to July 2021 time interval by using six main keywords. Physiologic or pathologic microenvironments, optimal dosage, and involved receptors affect the functionalities of IL-38. Alterations in serum levels of IL-38 play a major role in the immunopathogenesis of a wide array of immune-mediated disorders. IL-38 shows anti-inflammatory activities by reduction or inhibition of pro-inflammatory cytokines, supporting the therapeutic aspects of IL-38 in inflammatory autoimmune diseases. According to the importance of pre-clinical studies, it seems that manipulation of the immune system by immunomodulatory properties of IL-38 can increase the accuracy of diagnosis, and decipher optimal clinical outcomes. To promote our knowledge, more collaboration is highly recommended among laboratory scientists, internal/infectious diseases specialists, oncologists, immunologists, diseases-specific biomarkers scientists, and basic medical researchers.

Neutralization of interleukin-38 exacerbates coxsackievirus B3-induced acute myocarditis in mice

Background

Interleukin (IL)-38, a novel member of the IL-1 family, has been reported to be involved in several diseases associated with viral infection. However, the expression and functional role of IL-38 in acute viral myocarditis (AVMC) have not been investigated.

Methods

Male BALB/c mice were treated with intraperitoneal (i.p.) injection of coxsackievirus B3 (CVB3) for establishing AVMC models. On day 7 post-injection, the expression of IL-38 and IL-36R (IL-36 receptor) were measured. Mice were then treated with i.p. injection of mouse Anti-IL-38 Antibodies (Abs) for neutralization of IL-38. The survival, bodyweight loss, cardiac function, and myocarditis severity of mice were recorded. The percentages of splenic Th1 and Th17 cells, the expression levels of Th1/Th17-related master transcription factors (T-bet and RORγt) and cytokines were determined by flow cytometry, RT-qPCR, and ELISA, respectively. Cardiac viral replication was further detected.

Results

The mRNA and protein expression levels of IL-38 in myocardium and serum, as well as cardiac IL-36R mRNA levels were significantly elevated in mice with AVMC. Increased IL-38 levels were negatively correlated with the severity of AVMC. Neutralization of IL-38 exacerbated CVB3-induced AVMC, as verified by the lower survival rate, impaired cardiac function, continuous bodyweight loss, and higher values of HW/BW and cardiac pathological scores. In addition, neutralization of IL-38 suppressed Th1 cells differentiation while promoted Th17 cells differentiation, accompanied by decreased T-bet mRNA expression and increased RORγt expression. Down-regulation of IFN-γ and up-regulation of IL-17, TNF-α, and IL-6 mRNA and protein expression levels in myocardium and serum were also observed in the IL-38 neutralization group. Furthermore, neutralization of IL-38 markedly promoted cardiac viral replication.

Conclusions

Neutralization of IL-38 exacerbates CVB3-induced AVMC in mice, which may be attributable to the imbalance of Th1/Th17 cells and increased CVB3 replication. Thus, IL-38 can be considered as a potential therapeutic target for AVMC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01687-w.

The interleukin-1 cytokine family members: Role in cancer pathogenesis and potential therapeutic applications in cancer immunotherapy

The interleukin-1 (IL-1) family is one of the first described cytokine families and consists of eight cytokines (IL-1β, IL-1α, IL-18, IL-33, IL-36α, IL-36β, IL-36γ and IL-37) and three receptor antagonists (IL-1Ra, IL-36Ra and IL-38). The family members are known to play an essential role in inflammation. The importance of inflammation in cancer has been well established in the past decades. This review sets out to give an overview of the role of each IL-1 family member in cancer pathogenesis and show their potential as potential anticancer drug candidates. First, the molecular structure is described. Next, both the pro- and anti-tumoral properties are highlighted. Additionally, a critical interpretation of current literature is given. To conclude, the IL-1 family is a toolbox with a collection of powerful tools that can be considered as potential drugs or drug targets.

Biology of interleukin-38 and its role in chronic inflammatory diseases

Interleukin (IL)-38 is the tenth member of the IL-1 cytokine family. IL-38 shares high similarity with IL-36Ra and IL-1Ra and can bind to their receptors, thus exerting an anti-inflammatory effect. Despite the lack of a signal peptide, IL-38 can be released from several cell types, but its maturation process remains obscure. The role of IL-38 in numerous inflammatory diseases, especially in autoimmune diseases, has been extensively studied. In this review, we discuss the characteristics, biological functions and pathways of IL-38, as well as its role in several chronic inflammatory diseases. Better understanding the role of IL-38 will pave the way for clinical treatments in the near future.

Interleukin-38 is elevated in inflammatory bowel diseases and suppresses intestinal inflammation

There has been no report investigating the role of IL-38 in inflammatory bowel diseases (IBD). Therefore, we investigated the expression of IL-38 in IBD patients and its role in regulating intestinal inflammation. The levels of IL-38 were significantly elevated in the intestine of IBD patients and DSS-induced colitis mice. Immunofluorescence analysis revealed that B cell, not macrophage or T cell, was the source of IL-38 in the intestine. We found that rIL-38 treatment significantly attenuated DSS-induced colitis, including alleviation of weight loss, disease activity index, macroscopic changes and histological damage of colon, along with lower levels of IL-1β and TNF-α. In vitro, rIL-38 significantly decreased the expression of proinflammatory cytokines in LPS-stimulated RAW 264.7 cells and BMDM. This is the first study suggesting that IL-38 may have a protective effect in IBD, which inhibits the production of proinflammatory cytokines from macrophages. IL-38 may represent a promising therapeutic strategy in IBD.

Interleukin 30 to Interleukin 40

Cytokines are important molecules that regulate the ontogeny and function of the immune system. They are small secreted proteins usually produced upon activation of cells of the immune system, including lymphocytes and myeloid cells. Many cytokines have been described, and several have been recognized as pivotal players in immune responses and in human disease. In fact, several anticytokine antibodies have proven effective therapeutics, especially in various autoimmune diseases. In the last 15 years, new cytokines have been described, and many remain poorly understood. Among the most recent cytokines discovered are interleukins-30 (IL-30) to IL-40. Several of these are members of other cytokine superfamilies, including several IL-1 superfamily members (IL-33, IL-36, IL-37, and IL-38) as well as several new members of the IL-12 family (IL-30, IL-35, and IL-39). The rest (IL-31, IL-32, IL-34, and IL-40) are encoded by genes that do not belong to any cytokine superfamily. Our aim of this review was to present a concise version of the information available on these novel cytokines to facilitate their understanding by members of the immunological community.

Interleukin 38 Protects Against Lethal Sepsis

Background

Interleukin 38 (IL-38) is the most recently characterized cytokine of the interleukin 1 family. However, its role in sepsis remains unknown.

Methods

Circulating IL-38 levels were measured in 2 cohorts of adult and pediatric patients with sepsis. Using 2 murine models of lipopolysaccharide (LPS)-induced endotoxemia and cecal ligation and puncture (CLP)-induced sepsis, the effects of IL-38 on survival, inflammation, tissue injury, and bacterial clearance were assessed.

Results

Serum IL-38 concentrations were significantly elevated in adult and pediatric patients with sepsis relative to corresponding healthy adult and pediatric controls, respectively. An increased IL-38 level negatively correlated with the number of blood leukocytes and with the level of inflammatory cytokines, including interleukin 6 (IL-6) and tumor necrosis factor α (TNF-α) in clinical sepsis. Anti-IL-38 antibody impaired survival and while recombinant IL-38 improved survival in the 2 murine models of LPS-induced endotoxemia and CLP-induced sepsis. IL-38 administration decreased the inflammatory response, as reflected by lower levels of cytokines and chemokines (including IL-6, TNF-α, interleukin 10, interleukin 17, interleukin 27, CXCL1, and CCL2), and less damage to tissues (including lung, liver, and kidney) in CLP-induced sepsis. Furthermore, IL-38 augmented bacterial clearance in CLP-induced polymicrobial sepsis.

Conclusions

These findings suggest that IL-38 attenuates sepsis by decreasing inflammation and increasing bacterial clearance, thus providing a novel tool for antisepsis therapy.

IL-38: A New Player in Inflammatory Autoimmune Disorders

Interleukin (IL)-38, a newly discovered IL-1 family cytokine, is expressed in several tissues and secreted by various cells. IL-38 has recently been reported to exert an anti-inflammatory function by binding to several receptors, including interleukin-36 receptor (IL-36R), interleukin-1 receptor accessory protein-like 1 (IL-1RAPL1), and interleukin-1 receptor 1 (IL-1R1) to block binding with other pro-inflammatory cytokines and inhibit subsequent signaling pathways; thereby regulating the differentiation and function of T cells, peripheral blood mononuclear cells, macrophages, and dendritic cells. Inflammatory autoimmune diseases, which are common immune-mediated inflammatory syndromes, are characterized by an imbalance between T helper cells (Ths), especially Th1s and Th17s, and regulatory T cells (Tregs). Recent findings have shown that abnormal expression of IL-38 in inflammatory autoimmune diseases, such as rheumatoid arthritis, psoriatic arthritis, systemic lupus erythematosus, primary Sjogren’s syndrome, psoriasis, inflammatory bowel disease, hidradenitis suppurativa, ankylosing spondylitis, and glaucoma, involves Th1s, Th17s, and Tregs. In this review, the expression, regulation, and biological function of IL-38 are discussed, as are the roles of IL-38 in various inflammatory autoimmune disorders. Current data support that the IL-38/IL-36R and/or IL-38/IL-1RAPL1 axis primarily play an anti-inflammatory role in the development and resolution of inflammatory autoimmune diseases and indicate a possible therapeutic benefit of IL-38 in these diseases.

Is Interleukin-38 a key player cytokine in atherosclerosis immune gene therapy?

Atherosclerosis, a chronic inflammatory disease of the arteries associated with lipids and other metabolic alterations is a leading cause of death all around the world and its rate is raising as a result of unhealthy lifestyles. Reports by World Health Organization indicate that 31% of all death occurrences are due to heart attacks and strokes. Today, the most common medicines for treating atherosclerosis are statins which are HMG-coA reductase inhibitors. Beside their benefits in treating atherosclerosis, some side effects have been reported as well. Thus, therapeutic methods based on statins should be evaluated to result in more beneficial effects. Since atherosclerosis is an inflammatory disorder, an anti-inflammatory component can decrease the impact of this disease. Interleukin-38, a newly discovered anti-inflammatory cytokine, which acts as an Interleukin-36 receptor antagonist can block Nuclear Factor KB and Activator protein-1 signaling pathways, and block atherogenic core formation accordingly. This novel proposed immune gene therapy can be applied to atherosclerosis treatment in a trial study. In this hypothesis, Interleukin-38 gene is transferred into bone marrow Mesenchymal Stem Cells of atherosclerotic mouse model Apo E-/- via an adenoviral vector. It is expected that Interleukin-38 gene expression by Mesenchymal Stem Cells can efficiently remedy atherosclerosis without the side effects of statins.

The enigmatic role of IL-38 in inflammatory diseases

IL-38 is the most recently discovered cytokine of the IL-1 family and is considered a potential inhibitor of the IL-1 and Toll-like receptor families. IL-38 exerts anti-inflammatory properties, especially on macrophages, by inhibiting secretion of pro-inflammatory cytokines, leading to reduced T-lymphocyte TH17 maturation. IL-38 has been studied most extensively in the context of chronic inflammatory diseases, particularly arthritis, where it is considered an attractive new drug candidate. IL-38 research has entered a new phase, with the realization that IL-38 is important in the pathophysiology of TH17 dependent-diseases (psoriasis, psoriatic arthritis and ankylosing spondylitis). In this review, we provide a critical evaluation of several controversial issues concerning IL-38 function and regulation. There is effectively contrasting data regarding IL-38: it is produced in conditions such as apoptosis, necrosis or inflammation, but data is lacking regarding IL-38 processing and biological function. Furthermore, the receptor for IL-38 has yet to be identified, although three candidate receptors - IL-1R1, IL-36R and IL-1RAPL1-have been proposed. Future studies will hopefully uncover new aspects of this enigmatic cytokine.

Toward cure chronic hepatitis B infection and hepatocellular carcinoma prevention: Lessons learned from nucleos(t)ide analogues therapy

Nucleos(t)ide analogues (NAs) could successfully suppress hepatitis B virus (HBV) replication in patients with chronic hepatitis B (CHB). However, due to probable development of drug resistance or low/delayed response, these treatments may not be satisfactory. In addition to the HBV DNA polymerase inhibiting activity, these drugs could lead to changes in cytokines profiles. It is important to monitor these changes so that they could be used as target of treatment. Evaluating the previously reported immune responses due to NAs treatments, it was concluded that interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), interleukin-4 (IL-4), and IL-12 increase after the treatment. This will be followed by the improved capacity of immune cells for eliminating HBV. In contrast, regulatory responses including IL-10 and transforming growth factor-beta (TGF-β) significantly decreased as the result of NAs therapy. Unexpectedly, T helper (Th) 17-associated cytokines also decreased significantly. These results could be used to employ the new strategies to suppress viral replication, minimize HBV DNA levels, inducing hepatitis B e antigen (HBeAg) seroconversion or even hepatitis B surface antigen (HBsAg) seroclearance. In order to accomplish these goals, extended treatment with high dose of both IL-12 and IFN in combination with high barrier to resistance NA might significantly improve the HBsAg seroclearance rate. Considering the danger of emerging aberrant immune responses, determining the optimum dosage as well as close monitoring of patients during the treatment is strongly advised. In order to make HBV immunotherapy practical, further studies are needed to confirm these results.

IL-38 overexpression induces anti-inflammatory effects in mice arthritis models and in human macrophages in vitro

OBJECTIVES

Interleukin (IL)-38 is a newly characterised cytokine that belongs to the IL-1 family. This cytokine is expressed in the rheumatoid arthritis (RA) synovial tissue and IL-38 deficient mice have exacerbated arthritis. Here, we analysed the effect of IL-38 overexpression in the joints of arthritic mice, in human macrophages and synovial fibroblasts in vitro.

METHODS

Articular injections of an adeno-associated virus (AAV) 2/8 encoding IL-38 were performed in collagen-induced arthritis (CIA), K/BxN serum transfer-induced arthritis (STIA) and antigen-induced arthritis (AIA) in mice. The effect of IL-38 overexpression was evaluated through clinical scores, immunohistochemistry, microCT, Luminex and RT-qPCR analysis. THP-1 macrophages were transduced with a lentiviral vector to overexpress IL-38.

RESULTS

Clinical inflammatory scores were significantly decreased after AAV IL-38 injection in joints of mice with CIA and STIA, but not AIA. This decrease was accompanied by reduced macrophage infiltration and a decreased expression of Th17 cytokines (IL-17, IL-23, IL-22) and TNFα. However, IL-38 overexpression had no effect on cartilage or bone destruction. In vitro, the THP-1 monocytic cell line expressed less IL-6, TNFα and IL-23 after IL-38 overexpression. Conditioned media from these cells, containing released IL-38, also exert an anti-inflammatory effect on human primary macrophages and synovial fibroblasts from patients with RA.

CONCLUSIONS

This study shows for the first time that IL-38 overexpression attenuates the severity of experimental arthritis. IL-38 may exert its anti-inflammatory effects by decreasing the production of proinflammatory cytokines by macrophages and synovial fibroblasts. This effect can lead to the development of novel treatment strategies in arthritis.