In vivo anti-inflammatory activities of novel cytokine IL-38 in Murphy Roths Large (MRL)/lpr mice

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.

Regulatory effect of IL-38 on NF-κB pathway in systemic lupus erythematosus

BACKGROUND

IL-38 is a newly identified cytokine that exhibits immunosuppression effects. However, there are few studies focusing on the effects and mechanisms of IL-38 in the systemic lupus erythematosus (SLE).

AIM

We investigated the effects and mechanisms of IL-38 on NF-κB signaling pathway in SLE.

METHODS

Levels of IL-38, IL-36R, IL-1RAcP, IKKα/β, NF-κB, TNF-α and anti-dsDNA antibody levels in peripheral blood of SLE patients, and in peripheral blood and kidney tissues of MRL/lpr mice, were examined with real-time PCR, ELISA, Western blot and immunohistochemistry. Pathological changes of kidney were detected with PAS staining. Recombinant human IL-38 protein and IL-38 siRNA were used to intervene the PBMCs of SLE patients and MRL/lpr mice.

RESULTS

The mRNA and protein levels of IL-38 in peripheral blood of SLE patients decreased and were positively correlated. The mRNA and protein levels of IKKα/β, NF-κB, and TNF-α increased, especially in patients with active SLE. There was a negative correlation between IL-38 and the levels of IKKα/β, NF-κB and TNF-α in SLE patients. In vitro experiments showed that the levels of IKKα/β, NF-κB and TNF-α, and anti-dsDNA antibodies decreased in PBMCs of SLE patients after treatment with human recombinant IL-38 protein. These effects were reversed after IL-38 siRNA intervention. Consistent results were obtained on IL-38, IKKα/β, NF-κB, and TNF-α in MRL/lpr lupus mice after treatment with IL-38 protein or IL-38 shRNA. Additionally, kidney function (reflected by creatinine and blood urea nitrogen), anti-dsDNA antibody, complement C3, and urinary protein levels decreased after treatment with IL-38 protein but increased after IL-38 shRNA treatment. PAS staining showed IL-38 protein treatment induced mild hyperplasia of glomerular mesangial cells and a small amount of lymphocyte infiltration. However, these were aggravated after IL-38 shRNA treatment.

CONCLUSION

IL-38 may be involved in the occurrence and development of SLE by regulating the NF-κB signaling pathway. This study only discussed the relationship between IL-38 and NF-κB, and more biological functions of IL-38 need to be further studied.

Interleukin-38 in atherosclerosis

Chronic inflammation caused by immune cells and their mediators is a characteristic of atherosclerosis. Interleukin-38 (IL-38), a member of the IL-1 family, exerts multiple anti-inflammatory effects via specific ligand-receptor interactions. Upon recognizing a specific receptor, IL-38 restrains mitogen-activated protein kinase (MAPK), nuclear factor kappa B (NK-κB), or other inflammation-related signaling pathways in inflammatory disease. Further research has shown that IL-38 also displays anti-atherosclerotic effects and reduces the occurrence and risk of cardiovascular events. On the one hand, IL-38 can regulate innate and adaptive immunity to inhibit inflammation, reduce pathological neovascularization, and inhibit apoptosis. On the other hand, it can curb obesity, reduce hyperlipidemia, and restrain insulin resistance to reduce cardiovascular disease risk. Therefore, this article expounds on the vital function of IL-38 in the development of atherosclerosis to provide a theoretical basis for further in-depth studies of IL-38 and insights on the prophylaxis and treatment of atherosclerosis.

IL-38, a potential therapeutic agent for lupus, inhibits lupus progression

BACKGROUND

Previous studies reported that IL-38 was abnormally expressed in patients with systemic lupus erythematosus (SLE). However, the involvement of IL-38 in the pathophysiology of SLE remains unknown.

METHODS

The therapeutic potential of IL-38 was tested in pristane-treated wild-type (WT) and IL-38^-/- mice. Thus, SLE was induced via pristane in WT and IL-38^-/- mice. Afterwards, the liver, spleen, and kidney of each mouse were obtained. The flow cytometric analysis of the immune cells, serologic expression of inflammatory cytokines and autoantibodies, renal histopathology, and inflammatory signaling were evaluated.

RESULTS

WT mice with pristane-induced lupus exhibited hepatomegaly, splenomegaly, severe kidney damages, increased lymphoproliferation, enhanced lymphoproliferation, and upregulated inflammatory cytokines, such as IL-6, IL-13, IL-17A, MIP-3α, IL-12p70, and IFNγ, and elevated levels of autoantibodies, such as ANA IgG, anti-dsDNA IgG, and total IgG. IL-38^-/- mice whose lupus progressed, had elevated cells of CD14⁺, CD19⁺, CD3⁺, and Th1, upregulated inflammatory cytokines and autoantibodies, and severe pathological changes in kidney. Administration of recombinant murine IL-38 to pristane-treated IL-38^-/- mice improved their renal histopathology, which depended on ERK1/2, JNK1/2, p38, NF-κB p65, and STAT5 signaling pathways.

CONCLUSION

IL-38 regulates SLE pathogenesis. Furthermore, targeting IL-38 is critical in the treatment of SLE.

IL-38 in modulating hyperlipidemia and its related cardiovascular diseases

Hyperlipidemia is confirmed to be associated with several health problems that include the combination of diabetes mellitus, obesity, and hypertension, ie, metabolic syndrome. Although the lipid-lowering therapy is an effective treatment in hyperlipidemia and its related cardiovascular diseases (CVDs), the persistence of high atherosclerotic risk is notable which could not be simply explained as a phenomenon of hyperlipidemia. Concerning on this notion, it is imperative to identify novel biomarkers which could monitor treatment and predict adverse cardiovascular events. It is demonstrated that the chronic inflammatory response caused by immune cells is a characteristic of hyperlipidemia and atherosclerosis. Notably, among several inflammatory related cytokines, interleukin 38 (IL-38), as a member of the IL-1 family, plays an important role in anti-inflammatory response by binding with its receptor which inhibits the downstream signaling pathways. In addition, IL-38 suppresses the expression of inflammatory factors mainly through the mitogen-activated protein kinase (MAPK). At the cellular level, IL-38 could inhibit the CD4 positive T lymphocyte into T-helper 17 (Th-17) lymphocyte which further enhances the immunosuppressive activity of the T-regulatory lymphocyte (T-reg) to inhibit the inflammatory response. Consistently, IL-38 is shown to be strongly correlated to development of hyperlipidemic related CVDs. In this review, the roles of IL-38 in the development of hyperlipidemia are fully summarized. Furthermore, a theoretical basis for further in-depth research of IL-38 for treatment of hyperlipidemia is also provided.

Effects of IL-38 on Macrophages and Myocardial Ischemic Injury

Macrophages play an important role in clearing necrotic myocardial tissues, myocardial ischemia-reperfusion injury, and ventricular remodeling after myocardial infarction. M1 macrophages not only participate in the inflammatory response in myocardial tissues after infarction, which causes heart damage, but also exert a protective effect on the heart during ischemia. In contrast, M2 macrophages exhibit anti-inflammatory and tissue repair properties by inducing the production of high levels of anti-inflammatory cytokines and fibro-progenitor cells. Interleukin (IL)-38, a new member of the IL-1 family, has been reported to modulate the IL-36 signaling pathway by playing a role similar to that of the IL-36 receptor antagonist, which also affects the production and secretion of macrophage-related inflammatory factors that play an anti-inflammatory role. IL-38 can relieve myocardial ischemia-reperfusion injury by promoting the differentiation of M1 macrophages into M2 macrophages, inhibit the activation of NOD-like receptor thermal protein domain-associated protein 3 (NLRP3) inflammasome, and increase the secretion of anti-inflammatory cytokines, such as IL-10 and transforming growth factor-β. The intact recombinant IL-38 can also bind to interleukin 1 receptor accessory protein-like 1 (IL-1RAPL1) to activate the c-jun N-terminal kinase/activator protein 1 (JNK/AP1) pathway and increase the production of IL-6. In addition, IL-38 regulates dendritic cell-induced cardiac regulatory T cells, thereby regulating macrophage polarization and improving ventricular remodeling after myocardial infarction. Accordingly, we speculated that IL-38 and macrophage regulation may be therapeutic targets for ameliorating myocardial ischemic injury and ventricular remodeling after myocardial infarction. However, the specific mechanism of the IL-38 action warrants further investigation.

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 Pathological Mechanism and Potential Application of IL-38 in Autoimmune Diseases

Interleukin-38 (IL-38), a new cytokine of interleukin-1 family (IL-1F), is expressed in the human heart, kidney, skin, etc. Recently, new evidence indicated that IL-38 is involved in the process of different autoimmune diseases. Autoimmune diseases are a cluster of diseases accompanied with tissue damage caused by autoimmune reactions, including rheumatoid arthritis (RA), psoriasis, etc. This review summarized the links between IL-38 and autoimmune diseases, as well as the latest knowledge about the function and regulatory mechanism of IL-38 in autoimmune diseases. Especially, this review focused on the differentiation of immune cells and explore future prospects, such as the application of IL-38 in new technologies. Understanding the function of IL-38 is helpful to shed light on the progress of autoimmune diseases.

Compartmentalization of interleukin 36 subfamily according to inducible and constitutive expression in the kidneys of a murine autoimmune nephritis model

The interleukin (IL) 36 subfamily belongs to the IL-1 family and is comprised of agonists (IL-36α, IL-36β, IL-36γ) and antagonists (IL-36Ra, IL-38). We previously reported IL-36α overexpression in renal tubules of chronic nephritis mice. To understand the localization status and biological relationships among each member of the IL-36 subfamily in the kidneys, MRL/MpJ-Fas^lpr/lpr mice were investigated as autoimmune nephritis models using pathology-based techniques. MRL/MpJ-Fas^lpr/lpr mice exhibited disease onset from 3 months and severe nephritis at 6-7 months (early and late stages, respectively). Briefly, IL-36γ and IL-36Ra were constitutively expressed in murine kidneys, while the expression of IL-36α, IL-36β, IL-36Ra, and IL-38 was induced in MRL/MpJ-Fas^lpr/lpr mice. IL-36α expression was significantly increased and localized to injured tubular epithelial cells (TECs). CD44⁺-activated parietal epithelial cells (PECs) also exhibited higher IL-36α-positive rates, particularly in males. IL-36β and IL-38 are expressed in interstitial plasma cells. Quantitative indices for IL-36α and IL-38 positively correlated with nephritis severity. Similar to IL-36α, IL-36Ra localized to TECs and PECs at the late stage; however, MRL/MpJ-Fas^lpr/lpr and healthy MRL/MpJ mice possessed IL-36Ra⁺ smooth muscle cells in kidney arterial tunica media at both stages. IL-36γ was constitutively expressed in renal sympathetic axons regardless of strain and stage. IL-36 receptor gene was ubiquitously expressed in the kidneys and was induced proportional to disease severity. MRL/MpJ-Fas^lpr/lpr mice kidneys possessed significantly upregulated IL-36 downstream candidates, including NF-κB- or MAPK-pathway organizing molecules. Thus, the IL-36 subfamily contributes to homeostasis and inflammation in the kidneys, and especially, an IL-36α-dominant imbalance could strongly impact nephritis deterioration.

IL-1 Family Antagonists in Mouse and Human Skin Inflammation

Interleukin (IL)-1 family cytokines initiate inflammatory responses, and shape innate and adaptive immunity. They play important roles in host defense, but excessive immune activation can also lead to the development of chronic inflammatory diseases. Dysregulated IL-1 family signaling is observed in a variety of skin disorders. In particular, IL-1 family cytokines have been linked to the pathogenesis of psoriasis and atopic dermatitis. The biological activity of pro-inflammatory IL-1 family agonists is controlled by the natural receptor antagonists IL-1Ra and IL-36Ra, as well as by the regulatory cytokines IL-37 and IL-38. These four anti-inflammatory IL-1 family members are constitutively and highly expressed at steady state in the epidermis, where keratinocytes are a major producing cell type. In this review, we provide an overview of the current knowledge concerning their regulatory roles in skin biology and inflammation and their therapeutic potential in human inflammatory skin diseases. We further highlight some common misunderstandings and less well-known observations, which persist in the field despite recent extensive interest for these cytokines.

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 overexpression prevents bleomycin-induced mouse pulmonary fibrosis

Pulmonary fibrosis is a kind of pulmonary disorder with chronic inflammation and excessive collagen deposition, and its etiology is not clear. Interleukin (IL)-38 is a new member of IL-1 family cytokines, but its role in pulmonary fibrosis has not been elucidated. In this study, a lentivirus expressing IL-38 was injected into the nasal cavity of mice with bleomycin-induced pulmonary fibrosis. We found that IL-38 overexpression reduced the body weight loss and improved the survival of mice induced by bleomycin. Furthermore, IL-38 expression attenuated the pulmonary inflammation and fibrosis damage induced by bleomycin, decreased the production of pro-inflammatory and pro-fibrotic cytokines such as IL-1β, IL-6, IL-17A, monocyte chemoattractant protein-1, and tumor necrosis factor-α, but increased the release of anti-inflammatory cytokine IL-1 receptor antagonist (IL-1Ra) in the lungs of bleomycin-challenged mice. Our data suggest that IL-38 may inhibit bleomycin-induced pulmonary inflammation and fibrosis through its anti-inflammatory effect and regulation of IL-1β/IL-1Ra balance, and IL-38 may be a new strategy for the treatment of pulmonary fibrosis.

Interleukin-38 ameliorates poly(I:C) induced lung inflammation: therapeutic implications in respiratory viral infections

Interleukin-38 has recently been shown to have anti-inflammatory properties in lung inflammatory diseases. However, the effects of IL-38 in viral pneumonia remains unknown. In the present study, we demonstrate that circulating IL-38 concentrations together with IL-36α increased significantly in influenza and COVID-19 patients, and the level of IL-38 and IL-36α correlated negatively and positively with disease severity and inflammation, respectively. In the co-cultured human respiratory epithelial cells with macrophages to mimic lung microenvironment in vitro, IL-38 was able to alleviate inflammatory responses by inhibiting poly(I:C)-induced overproduction of pro-inflammatory cytokines and chemokines through intracellular STAT1, STAT3, p38 MAPK, ERK1/2, MEK, and NF-κB signaling pathways. Intriguingly, transcriptomic profiling revealed that IL-38 targeted genes were associated with the host innate immune response to virus. We also found that IL-38 counteracts the biological processes induced by IL-36α in the co-culture. Furthermore, the administration of recombinant IL-38 could mitigate poly I:C-induced lung injury, with reduced early accumulation of neutrophils and macrophages in bronchoalveolar lavage fluid, activation of lymphocytes, production of pro-inflammatory cytokines and chemokines and permeability of the alveolar-epithelial barrier. Taken together, our study indicates that IL-38 plays a crucial role in protection from exaggerated pulmonary inflammation during poly(I:C)-induced pneumonia, thereby providing the basis of a novel therapeutic target for respiratory viral infections.

Human recombinant interleukin-38 suppresses inflammation in mouse models of local and systemic disease

Interleukin (IL)-38 belongs to the IL-1 family and is part of the IL-36 subfamily due to its binding to the IL-36 Receptor (IL-1R6). In the current study, we assessed the anti-inflammatory properties of IL-38 in murine models of arthritis and systemic inflammation. First, the anti-inflammatory properties of mouse and human IL-38 precursors were compared to forms with a truncated N-terminus. In mouse bone marrow derived dendritic cells (BMDC), human and mouse IL-38 precursors with a truncation of the two N-terminal amino acids (3-152) suppressed LPS-induced IL-6. Recombinant human IL-38 (3-152) was further investigated for its immunomodulatory potential using four murine models of inflammatory disease: streptococcal cell wall (SCW)-induced arthritis, monosodium urate (MSU) crystal-induced arthritis, MSU crystal-induced peritonitis, and systemic endotoxemia. In each of these models IL-38 significantly reduced inflammation. In SCW and MSU crystal-induced arthritis, joint swelling, inflammatory cell influx, and synovial levels of IL-1β, IL-6, and KC were reduced by 50% or greater. These suppressive properties of IL-38 in SCW-induced arthritis were independent of the anti-inflammatory co-receptor IL-1R8, as IL-38 reduced arthritis equally in IL-1R8 deficient and WT mice. In MSU crystal-induced peritonitis, IL-38 reduced hypothermia, while plasma IL-6 and KC and peritoneal KC levels were reduced by 65-70%. In the LPS endotoxemia model, IL-38 pretreatment reduced systemic IL-6, TNFα and KC. Furthermore, in ex vivo cultured bone marrow, LPS-induced IL-6, TNFα and KC were reduced by 75-90%. Overall, IL-38 exhibits broad anti-inflammatory properties in models of systemic and local inflammation and therefore may be an effective cytokine therapy.

IL-38: A novel cytokine in systemic lupus erythematosus pathogenesis

IL‐38 is a newly identified cytokine that belongs to the IL‐1 family. In our previous study, we found elevated plasma levels of IL‐38 in patients with systemic lupus erythematosus (SLE). However, the clear relationship of IL‐38 expression in plasma, peripheral blood mononuclear cells (PBMCs) and clinical and laboratory features needs elucidation. Additionally, we evaluated the possible role of IL‐38 in regulating production of inflammatory cytokines in PBMCs in vitro. A pristane‐induced murine lupus model was used to further demonstrate the effects of IL‐38 on cytokines in vivo and discuss the significance of IL‐38 in lupus development. The results showed that mRNA expression of IL‐38 in PBMCs of patients with SLE was elevated compared with volunteers, and expression of IL‐38 in both plasma and PBMCs was strongly related to clinical features, such as haematuria and proteinuria, and correlated with a SLEDAI score. Plasma levels of TNF‐α, IL‐1β, IL‐6 and IL‐23 were elevated in patients with SLE and were related to plasma levels of IL‐38. In vitro, PBMCs of patients with SLE stimulated with IL‐38 showed a decreased expression of the four inflammatory cytokines compared with PBMCs of patients without treatment. Interestingly, IL‐38 administration in lupus mice significantly reduced the development of lupus, such as reduced proteinuria, improved histological examinations of the kidneys and down‐regulated inflammatory cytokines. In conclusion, IL‐38 may suppress synthesis of pro‐inflammatory cytokines and therefore regulate lupus pathogenesis.

Interleukin-38 inhibits adipogenesis and inflammatory cytokine production in 3T3-L1 preadipocytes

Interleukin-38 (IL-38) is a novel member of the IL-1 cytokine family with anti-inflammatory activity. However, its effect on adipogenesis and inflammatory cytokines secretion of adipocytes in vitro has not been reported. To address whether IL-38 inhibits adipogenesis and inflammation in vitro, adipose precursor 3T3-L1 cells were cultured with or without IL-38. The morphology and size of lipid droplets in 3T3-L1 cells were measured by Oil red O staining. The mRNA expression levels of GATA-binding protein-3 (GATA-3), glucose transporter type 4 (GLUT4), peroxisome proliferator-associated receptor γ2, IL-1β, IL-6, and monocyte chemoattractant protein-1 (MCP-1) in 3T3-L1 cells were detected by real-time PCR, The contents of IL-6, IL-1β, and MCP-1 in 3T3-L1 cell medium supernatants were determined by enzyme-linked immunosorbent assay. IL-38 significantly decreased the number of lipid droplets in 3T3-L1 cells. IL-38 also increased GATA-3 and GLUT4 mRNA expression and inhibited IL-1β, IL-6, and MCP-1 secretion by 3T3-L1 cells. It is concluded that IL-38 can inhibit the differentiation of human adipocytes and inflammatory cytokine production by 3T3-L1 cells.

IL-38 Ameliorates Skin Inflammation and Limits IL-17 Production from γδ T Cells

Interleukin-38 (IL-38) is a cytokine of the IL-1 family with a role in chronic inflammation. However, its main cellular targets and receptors remain obscure. IL-38 is highly expressed in the skin and downregulated in psoriasis patients. We report an investigation in cellular targets of IL-38 during the progression of imiquimod-induced psoriasis. In this model, IL-38 knockout (IL-38 KO) mice show delayed disease resolution with exacerbated IL-17-mediated inflammation, which is reversed by the administration of mature IL-38 or γδ T cell-receptor-blocking antibodies. Mechanistically, X-linked IL-1 receptor accessory protein-like 1 (IL1RAPL1) is upregulated upon γδ T cell activation to feedforward-amplify IL-17 production and is required for IL-38 to suppress γδ T cell IL-17 production. Accordingly, psoriatic IL1RAPL1 KO mice show reduced inflammation and IL-17 production by γδ T cells. Our findings indicate a role for IL-38 in the regulation of γδ T cell activation through IL1RAPL1, with consequences for auto-inflammatory disease.

Anti-inflammatory mechanisms of the novel cytokine interleukin-38 in allergic asthma

We elucidated the anti-inflammatory mechanisms of IL-38 in allergic asthma. Human bronchial epithelial cells and eosinophils were cocultured upon stimulation with the viral RLR ligand poly (I:C)/LyoVec or infection-related cytokine TNF-α to induce expression of cytokines/chemokines/adhesion molecules. House dust mite (HDM)-induced allergic asthma and humanized allergic asthma NOD/SCID murine models were established to assess anti-inflammatory mechanisms in vivo. IL-38 significantly inhibited induced proinflammatory IL-6, IL-1β, CCL5, and CXCL10 production, and antiviral interferon-β and intercellular adhesion molecule-1 expression in the coculture system. Mass cytometry and RNA-sequencing analysis revealed that IL-38 could antagonize the activation of the intracellular STAT1, STAT3, p38 MAPK, ERK1/2, and NF-κB pathways, and upregulate the expression of the host defense-related gene POU2AF1 and anti-allergic response gene RGS13. Intraperitoneal injection of IL-38 into HDM-induced allergic asthma mice could ameliorate airway hyperreactivity by decreasing the accumulation of eosinophils in the lungs and inhibiting the expression of the Th2-related cytokines IL-4, IL-5, and IL-13 in the bronchoalveolar lavage fluid (BALF) and lung homogenates. Histological examination indicated lung inflammation was alleviated by reductions in cell infiltration and goblet cell hyperplasia, together with reduced Th2, Th17, and innate lymphoid type 2 cell numbers but increased proportions of regulatory T cells in the lungs, spleen, and lymph nodes. IL-38 administration suppressed airway hyperreactivity and asthma-related IL-4 and IL-5 expression in humanized mice, together with significantly decreased CCR3+ eosinophil numbers in the BALF and lungs, and a reduced percentage of human CD4+CRTH2+ Th2 cells in the lungs and mediastinal lymph nodes. Together, our results demonstrated the anti-inflammatory mechanisms of IL-38 and provided a basis for the development of a regulatory cytokine-based treatment for allergic asthma.

IL-38 alleviates the inflammatory response and the degeneration of nucleus pulposus cells via inhibition of the NF-κB signaling pathway in vitro

Previous studies have suggested that the inflammatory response contributes to the onset of intervertebral disc degeneration (IVDD). Interleukin (IL)-38, a newly discovered cytokine of the IL-1 family, has been demonstrated to play an anti-inflammatory role in autoimmune diseases, such as Crohn's disease, rheumatoid arthritis and psoriasis. However, whether IL-38 participates in the pathogenesis of IVDD remains unknown. In this study, human disc tissues from IVDD patients and rat disc tissues from an IVDD model were collected to measure the expression of IL-38 in the IVDD groups and the control groups by western blot and immunohistochemical staining. To further determine the role of IL-38 in IVDD, human nucleus pulposus cells (HNPCs) were stimulated with TNF-α to generate an in vitro model of inflammation to mimic the local inflammatory environment of the lumbar disc. The inflammatory response and HNPC degeneration markers were measured after stimulation with TNF-α and IL-38. IL-38 was upregulated in both the human and rat degenerated disc tissues compared with the control tissues. In vitro, IL-38 significantly decreased the TNF-α-induced expression of IL-1β, IL-6, COX-2, MMP-13 and ADAMTS-5 in the HNPCs, and IL-38 also alleviated the TNF-α-induced reductions in type II collagen and aggrecan. Moreover, IL-38 inhibited the activation of the NF-κB signaling pathway in the HNPC-based model of inflammation by reducing the expression level of the NF-κB P-P65 protein. In conclusion, IL-38 could alleviate the inflammatory response and HNPC degeneration in vitro via the inhibition of the NF-κB signaling pathway. These results suggest that IL-38 may be a new strategy for the treatment of IVDD.

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-38 protects against sepsis by augmenting immunosuppressive activity of CD4+ CD25+ regulatory T cells

Naturally occurring CD4⁺ CD25⁺ regulatory T cells (Tregs) are required to limit immune-induced pathology and to maintain homeostasis during the early-phase of sepsis. This study aimed to investigate the role of interleukin (IL)-38, a newly described member of the IL-1 cytokine family, in mediated immune response of CD4⁺ CD25⁺ Tregs in sepsis. Here, we provide evidence that expressions of IL-38 and its receptor were detected in murine CD4⁺ CD25⁺ Tregs. Stimulation of CD4⁺ CD25⁺ Tregs with LPS markedly up-regulated the expression of IL-38. Treatment with rmIL-38 dramatically enhanced the immunosuppressive activity of CD4⁺ CD25⁺ Tregs after LPS stimulation and in septic mice induced by CLP, resulting in amplification of helper T cell (Th) 2 response and reduction in the proliferation of effector T cells. These effects were robustly abrogated when anti-IL-38 antibody was administered. Administration of rmIL-38 improved the survival rate of CLP mice. In addition, CD4⁺ CD25⁺ Tregs depletion before the onset of sepsis obviously abolished IL-38-mediated protective response. These findings suggest that IL-38 enhances the immunosuppressive activity of CD4⁺ CD25⁺ Tregs, which might contribute to the improvement of host immune function and prognosis in the setting of sepsis.

Interleukin-38 interacts with destrin/actin-depolymerizing factor in human keratinocytes

Interleukin (IL)-38 is a member of the IL-1 family of cytokines, which was proposed to exert anti-inflammatory effects. IL-38 is constitutively expressed in the skin, where keratinocytes are the main producing cells. Little information is currently available concerning IL-38 biology. Here, we investigated the subcellular localization and interaction partners of the IL-38 protein in human keratinocytes. IL-38 expression was reduced in primary keratinocytes grown in monolayer (2D) cultures. We thus used IL-38 overexpressing immortalized normal human keratinocytes (NHK/38) to study this cytokine in cell monolayers. In parallel, differentiation of primary human keratinocytes in an in vitro reconstructed human epidermis (RHE) 3D model allowed us to restore endogenous IL-38 expression. In NHK/38 cells and in RHE, IL-38 was mainly cell-associated, rather than released into culture supernatants. Intracellular IL-38 was preferentially, although not exclusively, cytoplasmic. Similarly, in normal human skin sections, IL-38 was predominantly cytoplasmic in the epidermis and essentially excluded from keratinocyte nuclei. A yeast two-hybrid screen identified destrin/actin-depolymerizing factor (DSTN) as a potential IL-38-interacting molecule. Co-immunoprecipitation and proximity ligation assay confirmed this interaction. We further observed partial co-localization of IL-38 and DSTN in NHK/38 cells. Endogenous IL-38 and DSTN were also co-expressed in all epidermal layers in RHE and in normal human skin. Finally, IL-38 partially co-localized with F-actin in NHK/38 cells, in particular along the cortical actin network and in filopodia. In conclusion, IL-38 is found predominantly in the cytoplasm of human keratinocytes, where it interacts with DSTN. The functional relevance of this interaction remains to be investigated.

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.

IL-36, IL-37, and IL-38 Cytokines in Skin and Joint Inflammation: A Comprehensive Review of Their Therapeutic Potential

The interleukin (IL)-1 family of cytokines is composed of 11 members, including the most recently discovered IL-36α, β, γ, IL-37, and IL-38. Similar to IL-1, IL-36 cytokines are initiators and amplifiers of inflammation, whereas both IL-37 and IL-38 display anti-inflammatory activities. A few studies have outlined the role played by these cytokines in several inflammatory diseases. For instance, IL-36 agonists seem to be relevant for the pathogenesis of skin psoriasis whereas, despite being expressed within the synovial tissue, their silencing or overexpression do not critically influence the course of arthritis in mice. In this review, we will focus on the state of the art of the molecular features and biological roles of IL-36, IL-37, and IL-38 in representative skin- and joint-related inflammatory diseases, namely psoriasis, rheumatoid arthritis, and psoriatic arthritis. We will then offer an overview of the therapeutic potential of targeting the IL-36 axis in these diseases, either by blocking the proinflammatory agonists or enhancing the physiologic inhibitory feedback on the inflammation mediated by the antagonists IL-37 and IL-38.

[Serum levels of interleukin-38 and interleukin-1β in the acute phase of Kawasaki disease in children]

OBJECTIVE

To study the expression of serum cytokines, interleukin-38 (IL-38) and interleukin-1β (IL-1β) in the acute phase of Kawasaki disease (KD) in children and the association of IL-38 and IL-1β with inflammatory response in the acute phase and the development of coronary artery lesion (CAL).

METHODS

A total of 40 children with KD who were hospitalized in the hospital between July 2015 and June 2016 were enrolled, with 21 children in the CAL group and 19 in the non-CAL (NCAL) group. Thirty healthy children and 19 children with infection and pyrexia, who were matched for sex and age, were enrolled as healthy control group and pyrexia control group respectively. ELISA was used to measure the serum levels of IL-38 and IL-1β in the 40 children in the acute phase of KD. Spearman's rank correlation analysis was used to investigate the correlations of IL-1β and IL-38 with interleukin-6 (IL-6), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), procalcitonin (PCT), N-terminal pro-brain natriuretic peptide (NT-proBNP), triglyceride (TG), and total cholesterol (TC).

RESULTS

The serum level of IL-38 in the children in the acute phase of KD was significantly lower than that in the healthy control group (P<0.05), but significantly higher than that in the pyrexia control group (P<0.05). There was no significant difference in the level of IL-38 between the CAL and NCAL groups (P>0.05). The children in the acute phase of KD had a significantly higher level of IL-1β than the healthy control group (P<0.05), while there was no significant difference between this group and the pyrexia control group (P>0.05). There was also no significant difference in the level of IL-1β between the CAL and NCAL groups (P>0.05). Serum IL-1β and IL-38 levels were not correlated with serum levels of CRP, ESR, PCT, IL-6, and NT-ProBNP or blood lipids (TG and TC) (P>0.05).

CONCLUSIONS

IL-38 is involved in an inflammatory response in the acute phase of KD and may exert an anti-inflammatory effect, which is opposite to the effect of IL-1β to promote inflammatory response. However, there is no significant correlation between these two cytokines and the development of CAL in KD.

Role of Interleukin-38 in Chronic Inflammatory Diseases: A Comprehensive Review

Interleukin (IL)-38 is the newest member of the IL-1 family. It can bind to several receptors, regulate the generation, function of inflammatory cytokines through the downstream signaling pathways. IL-38 is expressed in several tissues, such as placenta, heart, and brain. It is involved in a wide variety of diseases, including chronic inflammatory diseases. In this review, we discuss the expression and biological functions of IL-38, especially the role in rheumatic autoimmune diseases. Collection of the information may improve the understanding of IL-38, and may give potential for theoretical basis for clinical trials and drug development in the future.

The severity of imiquimod-induced mouse skin inflammation is independent of endogenous IL-38 expression

The IL-1 cytokine family includes eleven members, among which Il-36α, β and γ, IL-36Ra and IL-38. The IL-36 cytokines are involved in the pathogenesis of psoriasis. IL-38 is also expressed in the skin and was previously proposed to act as an IL-36 antagonist. In this study, we thus examined expression and function of Il-38 in a mouse model of imiquimod (IMQ)-induced skin inflammation. Il-38 mRNA was detected in the epidermis and in primary mouse keratinocytes, but not in dermal fibroblasts. At the peak of IMQ-induced inflammation, skin Il-38 mRNA levels were reduced, whereas Il-36ra mRNA expression increased. The severity of IMQ-induced skin inflammation, as assessed by recording ear thickness and histological changes, was similar in Il-38 KO and WT littermate control mice, while, in contrast, Il-36ra-deficient mice displayed more severe skin pathology than their WT littermates. Il-38-deficiency had no impact on IMQ-induced expression of proinflammatory mediators in the skin in vivo, on the basal expression of various cytokines or chemokines by cultured primary keratinocytes and dermal fibroblasts in vitro, or on the response of these cells to Il-36β. Finally, after cessation of topical IMQ application, the resolution of skin inflammation was also not altered in Il-38 KO mice. In conclusion, Il-38-deficiency did not impact the development or resolution of IMQ-induced skin inflammation. Our observations further suggest that endogenous Il-38 does not exert Il-36 inhibitory activity in this model, or in cultured skin cells. A potential anti-inflammatory function of Il-38 in mouse skin thus still remains to be demonstrated.

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.

Overview of the IL-1 family in innate inflammation and acquired immunity

The interleukin-1 (IL-1) family of cytokines and receptors is unique in immunology because the IL-1 family and Toll-like receptor (TLR) families share similar functions. More than any other cytokine family, the IL-1 family is primarily associated with innate immunity. More than 95% of living organisms use innate immune mechanisms for survival whereas less than 5% depend on T- and B-cell functions. Innate immunity is manifested by inflammation, which can function as a mechanism of host defense but when uncontrolled is detrimental to survival. Each member of the IL-1 receptor and TLR family contains the cytoplasmic Toll-IL-1-Receptor (TIR) domain. The 50 amino acid TIR domains are highly homologous with the Toll protein in Drosophila. The TIR domain is nearly the same and present in each TLR and each IL-1 receptor family. Whereas IL-1 family cytokine members trigger innate inflammation via IL-1 family of receptors, TLRs trigger inflammation via bacteria, microbial products, viruses, nucleic acids, and damage-associated molecular patterns (DAMPs). In fact, IL-1 family member IL-1a and IL-33 also function as DAMPs. Although the inflammatory properties of the IL-1 family dominate in innate immunity, IL-1 family member can play a role in acquired immunity. This overview is a condensed update of the IL-1 family of cytokines and receptors.