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

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.

Association between IL-38 and inflammatory indicators in patients with bacterial pneumonia

BACKGROUND

IL-38, a recently discovered cytokine of IL-1 family, exerts immunoregulatory activities in multi-type inflammatory diseases. However, its expression level and underlying clinical importance for IL-38 in respiratory bacterial infections remain unknown.

METHODS

Thirty-five patients with bacterial pneumonia and twenty age- and gender- matched healthy individuals were enrolled in the study to determine serum IL-38 concentrations by ELISA. Then, the correlation between serum IL-38 levels and clinical features were analyzed and ROC curve was used to evaluate the potential diagnostic value for bacterial infections. In vitro, LPS-stimulated human respiratory epithelial cell model was employed to explore immunomodulatory mechanism of IL-38 in pulmonary infections.

RESULTS

Elevated serum levels of IL-38 were determined in patients with bacterial pneumonia when compared with healthy controls. In addition, serum IL-38 levels were negatively correlated with clinical inflammation parameters, including WBC count, CRP, PCT and proinflammatory IL-6 and IL-8. In vitro, we demonstrated that recombinant IL-38 was able to remarkably inhibit expression of proinflammatory IL-6, IL-8, IL-1β and TNF-α as well as adhesion molecule ICAM-1, which were partially mediated by attenuated activation of STAT3 and NF-κB signal cascades in BEAS-2B cells. Furthermore, we identified the diagnostic efficiency of IL-38 in discriminating patients with bacterial pneumonia from healthy individuals.

CONCLUSIONS

Our study indicates higher serum IL-38 levels in patients with bacterial pneumonia are involved in anti-inflammatory activities in respiratory infections revealing a critical role of IL-38 in attenuating excessive pulmonary inflammation against exogenous pathogens. More importantly, IL-38 exhibited a potential novel biomarker for bacterial pneumonia. Thus, our data may provide useful insights for both clinical and basic research for bacterial pneumonia diagnosis.

Evaluation of interleukins 37 and 38 and vitamin D status in the serum of women with Graves' disease

BACKGROUND

Graves' disease (GD) is an autoimmune thyroid disorder and recent studies have proposed a role for interleukin (IL)-37, IL-38, and vitamin D (VitD) in the pathophysiology of disease. Therefore, this study investigated the expression of IL-37, IL-38, and VitD in the serum of GD patients and correlations of their levels with some demographic and clinical characteristics.

METHODS

Serum IL-37, IL-38, and VitD levels were evaluated in 90 women with GD and 93 control women using enzyme-linked immunosorbent assay kits. Depending on therapy, six patients were newly diagnosed (ND; untreated), and 50 patients were receiving only carbimazole (CMZ), while 34 patients were also on CMZ but also received one (31 patients), two (one patient), or three (two patients) doses of radioactive iodine (RAI).

RESULTS

IL-37 levels were significantly higher in GD patients than in controls, while IL-38 and VitD levels were significantly decreased. As indicated by the area under the curve (AUC), receiver operating characteristic curve analysis demonstrated the potential of IL-37, IL-38, and VitD as biomarkers to distinguish GD patients from controls (AUC = 0.953, 0.959, and 0.793, respectively). Multinomial logistic regression analysis showed that altered levels of IL-37, IL-38, and VitD were most likely associated with the pathogenesis of GD. IL-37 was negatively correlated with IL-38 and VitD, while IL-38 and VitD were positively correlated.

CONCLUSION

Serum Il-37 levels were upregulated in women with GD, while IL-38 and VitD levels showed downregulated levels. The latter two were positively correlated while they showed a negative correlation with IL-37.

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.

Interleukin 38 alleviates aortic valve calcification by inhibition of NLRP3

Calcific aortic valve disease (CAVD) is common in people over the age of 65. Progressive valvular calcification is a characteristic of CAVD and due to chronic inflammation in aortic valve interstitial cells (AVICs) resulting in CAVD progression. IL-38 is a naturally occurring anti-inflammatory cytokine; here, we report lower levels of endogenous IL-38 in AVICs isolated from patients' CAVD valves compared to AVICs from non-CAVD valves. Recombinant IL-38 suppressed spontaneous inflammatory activity and calcium deposition in cultured AVICs. In mice, knockdown of IL-38 enhanced the production of inflammatory mediators in murine AVICs exposed to the proinflammatory stimulant matrilin-2. We also observed that in cultured AVICs matrilin-2 stimulation activated the NOD-, LRR-, and pyrin domain-containing protein 3 (NLRP3) inflammasome with procaspase-1 cleavage into active caspase-1. The addition of IL-38 to matrilin-2-treated AVICs suppressed caspase-1 activation and reduced the expression of intercellular adhesion molecule-1, vascular cell adhesion molecule-1, runt-related transcription factor 2, and alkaline phosphatase. Aged IL-38-deficient mice fed a high-fat diet exhibited aortic valve lesions compared to aged wild-type mice fed the same diet. The interleukin-1 receptor 9 (IL-1R9) is the putative receptor mediating the anti-inflammatory properties of IL-38; we observed that IL-1R9-deficient mice exhibited spontaneous aortic valve thickening and greater calcium deposition in AVICs compared to wild-type mice. These data demonstrate that IL-38 suppresses spontaneous and stimulated osteogenic activity in aortic valve via inhibition of the NLRP3 inflammasome and caspase-1. The findings of this study suggest that IL-38 has therapeutic potential for prevention of CAVD progression.

Dysregulation of immunity in COVID-19 and SLE

The immune response plays a crucial role in preventing diseases, such as infections. There are two types of immune responses, specific and innate immunity, each of which consists of two components: cellular immunity and humoral immunity. Dysfunction in any immune system component increases the risk of developing certain diseases. Systemic lupus erythematosus (SLE), an autoimmune disease in the human body, develops an immune response against its own components. In these patients, due to underlying immune system disorders and receipt of immunosuppressive drugs, the susceptibility to infections is higher than in the general population and is the single largest cause of mortality in this group. COVID-19 infection, which first appeared in late 2019, has caused several concerns in patients with SLE. However, there is no strong proof of additional risk of developing COVID-19 in patients with SLE, and in some cases, studies have shown less severity of the disease in these individuals. This review paper discusses the immune disorders in SLE and COVID-19.

GDF-15: A Potential Biomarker and Therapeutic Target in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a rheumatic disease. Growth differentiation factor 15 (GDF-15) is a member of transforming growth factor-β superfamily. To date, association of GDF-15 with SLE pathogenesis is not clarified. This study discussed GDF-15 serum levels and gene polymorphisms in SLE patients and lupus mouse model further demonstrated the role of GDF-15 in lupus development. We conducted two independent case-control studies for SLE patients. One is to evaluate serum levels of GDF-15 in 54 SLE patients and 90 healthy controls, and the other one is to analyze gene polymorphisms of GDF-15 in 289 SLE patients and 525 healthy controls. Serum levels of GDF-15 were detected by ELISA. GDF-15 gene polymorphisms (rs1055150, rs1058587, rs1059519, rs1059369, rs1227731, rs4808793, and rs16982345) were genotyped by the Kompetitive Allele-Specific PCR (KASP) method. Addition of recombinant GDF-15 into pristane-induced lupus mice evaluated histological and serological changes. Results showed that serum levels of GDF-15 were overexpressed in SLE patients and associated with disease activity. Polymorphisms rs1055150, rs1059369, rs1059519, and rs4808793 of GDF-15 gene were related to SLE risk. Lupus mice showed splenomegaly, severe histological scores, and high levels of autoantibodies [antinuclear antibodies (ANA) and total immunoglobulin G (IgG)], whereas administration of GDF-15 into lupus mice reduced the histological changes. Percentages of CD8⁺, CD11b⁺, CD19⁺, CD11C⁺ cells, T_H2 cells, and pro-inflammatory cytokines (IL-1β, IL-2, IL-4, IL-21, and IL-22) were reduced after GDF-15 treatment in lupus mice. In conclusion, GDF-15 was related to lupus pathogenesis and inhibited lupus development.

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.

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.

Low serum interleukin-38 levels in patients with Graves' disease and Hashimoto's thyroiditis

Background

Autoimmune thyroid disease (AITD) mainly includes Graves’ disease (GD) and Hashimoto's thyroiditis (HT), which is caused by individual genetics, autoimmune dysfunction, and a variety of external environmental factors. Interleukin (IL)‐38 is involved in a wide range of autoimmune diseases, but little is known about IL‐38 expression in AITD.

Methods

Fifty patients with GD, 50 with HT, and 50 healthy controls (HC) were enrolled in this study. Basic information of the participants was obtained through a physical examination. Immunological data were obtained by an automatic chemiluminescence immunoanalyzer. C‐reactive protein (CRP) concentrations and the white blood cell count were measured. Serum IL‐38 levels were determined by an enzyme‐linked immunosorbent assay.

Results

Serum IL‐38 levels were significantly lower in the GD and HT groups than in the HC group (both p < 0.01). Serum CRP concentrations were significantly lower in the HT group than in the HC group (p < 0.05). Receiver operating characteristic curve analysis showed that the area under the curve was 0.7736 (p < 0.01) for IL‐38 and 0.7972 (p < 0.01) for IL‐38 combined with CRP in the GD group. In the HT group, the area under the curve was 0.7276 (p < 0.01) for IL‐38 and 0.7300 for IL‐38 combined with CRP (p < 0.01).

Conclusions

The results suggest that serum IL‐38 level is a potential new diagnostic biomarker in patients with GD and HT.

Interleukin 38 serum level is increased in patients with vitiligo, correlated with disease severity, and associated with signs of disease activity

BACKGROUND

Vitiligo is an acquired cutaneous depigmenting disease caused by a T helper (Th) 1-cytotoxic T cells driven autoimmune attack against melanocytes, in which Th17 is also involved. Interleukin (IL)-38 belongs to the IL-1 family of cytokines and suppresses Th1 and Th17 activation. IL-38 protein and mRNA levels have been found to be elevated in various autoimmune disorders and correlated with disease severity and activity, including psoriasis, systemic sclerosis, rheumatoid arthritis, and atopic dermatitis. No previous studies have been performed to investigate the expression of IL-38 in patients with vitiligo.

AIM

To evaluate IL-38 serum level in patients with vitiligo compared to healthy controls (Hcs) and examine the association between IL-38 level and severity and activity of vitiligo.

PATIENTS AND METHODS

The study comprised 21 patients with vitiligo and 21 Hcs. Vitiligo severity and activity were evaluated via Vitiligo Extent Score (VES) and Vitiligo Disease Activity (VIDA) Score, respectively. IL-38 serum level was evaluated by enzyme-linked immunosorbent assay.

RESULTS

Vitiligo patients had significantly higher serum level of IL-38 than Hcs (p < 0.001). This level was significantly higher among patients with signs of vitiligo activity (p = 0.048), correlated positively with VES (p < 0.001), and correlated negatively with the age of patients (p = 0.001) and the age of disease onset (p = 0.022).

CONCLUSION

IL-38 serum level was higher in patients with vitiligo than in Hcs and was related to vitiligo severity and signs of activity.

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.

Cytokines as Biomarkers in Systemic Lupus Erythematosus: Value for Diagnosis and Drug Therapy

Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease. The disease is characterized by activation and dysregulation of both the innate and the adaptive immune systems. The autoimmune response targets self-molecules including cell nuclei, double stranded DNA and other intra and extracellular structures. Multiple susceptibility genes within the immune system have been identified, as well as disturbances in different immune pathways. SLE may affect different organs and organ systems, and organ involvement is diverse among individuals. A universal understanding of pathophysiological mechanism of the disease, as well as directed therapies, are still missing. Cytokines are immunomodulating molecules produced by cells of the immune system. Interferons (IFNs) are a broad group of cytokines, primarily produced by the innate immune system. The IFN system has been observed to be dysregulated in SLE, and therefore IFNs have been extensively studied with a hope to understand the disease mechanisms and identify novel targeted therapies. In several autoimmune diseases identification and subsequent blockade of specific cytokines has led to successful therapies, for example tumor necrosis factor-alpha (TNF-α) inhibition in rheumatoid arthritis. Authors of this review have sought corresponding developments in SLE. In the current review, we cover the actual knowledge on IFNs and other studied cytokines as biomarkers and treatment targets in SLE.

Roles of IL-1 and IL-10 family cytokines in the progression of systemic lupus erythematosus: Friends or foes?

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease of unknown etiology that can affect nearly every organ system in the body. Besides genetic and environmental factors, unbalanced pro-inflammatory and anti-inflammatory cytokines contribute to immune dysregulation, trigger an inflammatory response, and induce tissue and organ damage. Inflammatory responses in SLE can be promoted and/or maintained by the availability of cytokines that are overproduced systemically and/or in local tissues. Several key cytokines have been considered potential targets for the reduction of chronic inflammation in SLE. Recent studies indicated that dysregulated production of several cytokines, including those of the IL-1 family and IL-10 family, orchestrate immune activation and self-tolerance, play critical roles in the pathogenesis of SLE. Among IL-1 family cytokines, IL-1, IL-18, IL-33, IL-36, IL-37, and IL-38 had been the most thoroughly investigated in SLE. Additionally, IL-10 family cytokines, IL-10, IL-20, IL-22, IL-26, IL-28, and IL-29 are dysregulated in SLE. Therefore, a better understanding of the initiation and progression of SLE may provide suitable novel targets for therapeutic intervention. In this review, we discuss the involvement of inflammation in the pathogenesis of SLE, with a focus on IL-1 family and IL-10 family cytokines, and highlight pathophysiological approaches and therapeutic potential for treating SLE.

Lack of Association between Serum Interleukin-23 and Interleukin-27 Levels and Disease Activity in Patients with Active Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a chronic systemic autoimmune disease characterized by the production of multiple autoantibodies, resulting in tissue and organ damage. Recent studies have revealed that interleukin-23 (IL-23) and interleukin-27 (IL-27) may be therapeutically relevant in selected SLE manifestations. This study aimed to identify associations between serum IL-27 and IL-23 levels and disease activity in Polish patients with different manifestations of SLE: neuropsychiatric lupus (NPSLE), and lupus nephritis (LN). Associations between interleukin levels and oligo-specific antibodies against double-stranded DNA (dsDNA), dose of glucocorticoids, and type of treatment were also analyzed. An enzyme-linked immunosorbent assay was used to assess anti-dsDNA antibodies and analyze the serum concentration of IL-27 and IL-23 from 72 patients aged 19-74 years with confirmed active SLE. Disease activity was measured using the Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI 2-K). No significant correlations between interleukin levels and SLEDAI score, anti-dsDNA, corticosteroid dose, or type of treatment were noted. Patients with NPSLE and LN presented the highest median scores of SLEDAI.

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-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.