High-mobility group box 1 inhibition alleviates lupus-like disease in BXSB mice

High mobility group box protein 1 (HMGB1) serum and urinary levels and gene polymorphism in Egyptian patients with systemic lupus erythematosus: A possible relation to lupus nephritis

Objective

The aim of this study was to evaluate the effects of the high mobility group box protein 1 (HMGB1) serum and urinary levels and gene polymorphisms on systemic lupus erythematosus (SLE) development and investigate their link to lupus nephritis (LN).

Methods

We enrolled 120 Egyptian SLE patients and 120 healthy controls. Thorough medical and clinical evaluation were carried out, and SLE disease activity index (SLEDAI) was assessed. Lupus patients were divided into two groups according to the presence of LN. Measurement of HMGB1 serum and urinary levels was done using ELISA and genotyping for HMGB1 ( rs1045411) was performed.

Results

There were statistically significantly higher HMGB1 serum and urinary levels in SLE patients ( p < 0.001). There was a marginally significant association between lupus and alleles ( p = 0.059, φ = −0.086). ‘C’ allele was marginally significant risk allele for SLE. After classifying SLE patients based on the presence or absence of LN, there was no significant difference as regard sex ( p = 0.387), age ( p = 0.208) and disease duration ( p = 0.094).However, there was a significant difference between the 2 groups in regard to the frequency of musculoskeletal manifestations ( p = 0.035), SLEDAI score ( p < 0.001), both serum ( p < 0.001) and urinary HMGB1 levels ( p < 0.001) in addition to the frequency of HMGB1 genotypes ( p = 0.003). Lupus patients with C/T-T/T HMGB1 genotypes had 3.5-times higher odds to exhibit LN.

Conclusions

Serum and urine HMGB1 measurements are helpful in the diagnosis of SLE and the prediction of LN. There is a link between HMGB1 gene variations and the risk of SLE, with evidence that the C/T-T/T HMGB1 genotype is linked to a significantly greater risk of LN in the Egyptian population.

The Role of HMGB1 in Rheumatic Diseases

HMGB1, a highly conserved non-histone nuclear protein, is widely expressed in mammalian cells. HMGB1 in the nucleus binds to the deoxyribonucleic acid (DNA) to regulate the structure of chromosomes and maintain the transcription, replication, DNA repair, and nucleosome assembly. HMGB1 is actively or passively released into the extracellular region during cells activation or necrosis. Extracellular HMGB1 as an alarmin can initiate immune response alone or combined with other substances such as nucleic acid to participate in multiple biological processes. It has been reported that HMGB1 is involved in various inflammatory responses and autoimmunity. This review article summarizes the physiological function of HMGB1, the post-translational modification of HMGB1, its interaction with different receptors, and its recent advances in rheumatic diseases and strategies for targeted therapy.

The Role of Inflammasomes in Glomerulonephritis

The inflammasome is an immune multiprotein complex that activates pro-caspase 1 in response to inflammation-inducing stimuli and it leads to IL-1β and IL-18 proinflammatory cytokine production. NLRP1 and NLRP3 inflammasomes are the best characterized and they have been related to several autoimmune diseases. It is well known that the kidney expresses inflammasome genes, which can influence the development of some glomerulonephritis, such as lupus nephritis, ANCA glomerulonephritis, IgA nephropathy and anti-GBM nephropathy. Polymorphisms of these genes have also been described to play a role in autoimmune and kidney diseases. In this review, we describe the main characteristics, activation mechanisms, regulation and functions of the different inflammasomes. Moreover, we discuss the latest findings about the role of the inflammasome in several glomerulonephritis from three different points of view: in vitro, animal and human studies.

Elevated serum free IL-18 in neuropsychiatric systemic lupus erythematosus patients with seizure disorders

BACKGROUND

Since dysregulation of total Interleukin (IL)-18 and IL-18 binding protein (IL-18BP) may participate in systemic lupus erythematosus (SLE) and contribute to the occurrence of non-autoimmune epilepsy, the aim of the current work is to investigate whether the interaction between IL-18 and IL-18BP plays any role in neuropsychiatric systemic lupus erythematosus related seizures.

METHODS

Data from 137 SLE patients and 30 healthy controls (HC) were consecutively collected from 2020 to 2021. Serum levels of total IL-18 and IL-18BP for all patients and HC were measured by ELISA test. Free IL-18 was calculated based on the law of mass action.

RESULTS

Among the 137 SLE patients, 103 had active disease and were classified into NPSLE (n = 50) and Non-NPSLE (n = 53) groups. Among the NPSLE patients, 16 had seizure disorders. Serum free IL-18 levels were increased in NPSLE (277.6 [150.9-428.8]pg/mL) and were correlated with disease activity (r = 0.268, p = 0.002). Moreover, serum free IL-18 levels in NPSLE patients with seizure disorders (350.9 [237.9-455.9]pg/mL) were significantly higher than the levels in those with other neuropsychiatric symptoms (237.7 [124.6-428.8] pg/mL).

CONCLUSIONS

The expression of free IL-18 was increased in neuropsychiatric systemic lupus erythematosus(NPSLE), especially in NPSLE related seizures. Also, serum levels of free IL-18 were significantly increased in active SLE patients. In this regard, free IL-18 may be involved in the pathogenesis of NPSLE related seizures and associated with disease activity.

The Effect and Regulatory Mechanism of High Mobility Group Box-1 Protein on Immune Cells in Inflammatory Diseases

High mobility group box-1 protein (HMGB1), a member of the high mobility group protein superfamily, is an abundant and ubiquitously expressed nuclear protein. Intracellular HMGB1 is released by immune and necrotic cells and secreted HMGB1 activates a range of immune cells, contributing to the excessive release of inflammatory cytokines and promoting processes such as cell migration and adhesion. Moreover, HMGB1 is a typical damage-associated molecular pattern molecule that participates in various inflammatory and immune responses. In these ways, it plays a critical role in the pathophysiology of inflammatory diseases. Herein, we review the effects of HMGB1 on various immune cell types and describe the molecular mechanisms by which it contributes to the development of inflammatory disorders. Finally, we address the therapeutic potential of targeting HMGB1.

HMGB1, anti-HMGB1 antibodies, and ratio of HMGB1/anti-HMGB1 antibodies as diagnosis indicator in fever of unknown origin

To evaluate the feasibility of serum HMGB1, anti-HMGB1 antibodies, and HMGB1/anti-HMGB1 ratio as a diagnosis indicator of initial clinical classification in patients with fever of unknown origin (FUO). Ninety-four patients with classical FUO and ninety healthy controls were enrolled in this study. The subjects’ clinical data and serum were collected. The serum concentration of HMGB1 was detected by a commercial HMGB1 ELISA kit, while the serum concentration of anti-HMGB1 antibodies were detected by an in-house built anti-HMGB1 antibodies ELISA kit and further confirmed by immunoblotting. According to the hospital diagnosis on discharge, ninety-four FUO patients were divided into four groups, Infectious disease subgroup, autoimmune disease subgroup, malignant tumor subgroup, and undetermined subgroup. The concentrations of HMGB1 in the infectious disease subgroup and autoimmune disease subgroup were higher than those in the malignant tumor subgroup, undetermined subgroup, and healthy control group. The concentration of anti-HMGB1 antibodies in autoimmune disease subtype group was higher than those in other subgroups as well as healthy control group. According to the distribution of HMGB1 and anti-HMGB1 in scatter plots of the patients with FUO, we found that the ratio of serum HMGB1/anti-HMGB1 is an ideal clinical indicator for differential diagnosis of different subtypes of FUO. The best cut-off was 0.75, and the sensitivity, specificity, and AUC were 66.67%, 87.32%, and 0.8, respectively. Correlation analysis showed that serum concentration of HMGB1 was moderately correlated with CRP in infectious diseases subgroup, and the serum concentration of anti-HMGB1 antibodies was strongly correlated with erythrocyte sedimentation rate in autoimmune disease subgroup. Our study had showed that serum HMGB1/anti-HMGB1 antibodies ratio can help clinicians identify FUO subtypes, thereby avoiding many unnecessary examinations and tests, and improving the effectiveness of clinical diagnosis and treatment of FUO.

HMGB1 as a therapeutic target in disease

High-mobility group box 1 (HMGB1) was initially recognized as a ubiquitous nuclear protein involved in maintaining the nucleosome integrity and facilitating gene transcription. HMGB1 has since been reevaluated to be a prototypical damage-associated molecular pattern (DAMP) protein, and together with its exogenous counterpart, pathogen-associated molecular pattern (PAMP), completes the body's alarmin system against disturbances in homeostasis. HMGB1 can be released into the extracellular matrix (ECM) by either granulocytes or necrotic cells to serve as a chemotaxis/cytokine during infection, endotoxemia, hypoxia, ischemia-reperfusion events, and cancer. Different isoforms of HMGB1 present with distinctive physiological functions in ECM-fully-reduced HMGB1 (all thiol) acts as the initial damage signal to recruit circulating myeloid cells, disulfide HMGB1 behaves as a cytokine to activate macrophages and neutrophils, and both signals are turned off when HMGB1 is terminally oxidized into the final sulfonate form. Targeting HMGB1 constitutes a favorable therapeutic strategy for inflammation and inflammatory diseases. Antagonists such as ethyl pyruvate inhibit HMGB1 by interfering with its cytoplasmic exportation, while others such as glycyrrhizin directly bind to HMGB1 and render it unavailable for its receptors. The fact that a mixture of different HMGB1 isoforms is present in the ECM poses a challenge in pinpointing the exact role of an individual antagonist. A more discriminative probe for HMGB1 may be necessary to advance our knowledge of HMGB1, HMGB1 antagonists, and inflammatory-related diseases.

Targeting HMGB1 by ethyl pyruvate ameliorates systemic lupus erythematosus and reverses the senescent phenotype of bone marrow-mesenchymal stem cells

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease involving multiple organs and systems. Mesenchymal stem cells (MSCs) from SLE patients have demonstrated defects such as impaired growth, senescence phenotype and immunomodulatory functions. Some studies have suggested the close connection between inflammation microenvironment and cellular senescence. In the current study, we detected cytokines levels in bone marrow supernatant by the quantitative proteomics analysis, and found the expression of HMGB1 was remarkably increased in bone marrow from SLE patients. Senescence associated-β-galactosidase (SA-β-gal) staining, F-actin staining and flow cytometry were used to detect the senescence of cells. After stimulation of HMGB1 in normal MSCs, the ratio of SA-β-gal positive in BM-MSCs was increased, the organization of cytoskeleton was disordered, and TLR4-NF-κB signaling was activated. Finally, Ethyl pyruvate (EP) (40 mg/kg and 100 mg/kg, three times a week), a high security HMGB1 inhibitor, was injected intraperitoneally to treat MRL/lpr mice for 8 weeks. We demonstrated that EP alleviated the clinical aspects of lupus nephritis and prolonged survival of MRL/lpr mice. In the meantime, EP reversed the senescent phenotype of BM-MSCs from MRL/lpr mice. HMGB1 could be a promising target in SLE patients, and might be one of the reasons of recurrence after MSCs transplantation.

HMGB1 in Systemic Lupus Erythematosus

The high-mobility group box 1 (HMGB1) has been shown to exert proinflammatory effects on many cells of the innate immune system. Originally identified as a nuclear protein, HMGB1 has been found to play an important role in mediating inflammation when released from apoptotic or necrotic cells as a damage-associated molecular pattern (DAMP). Systemic lupus erythematosus (SLE) is a disease of non-resolving inflammation, characterized by the presence of autoantibodies and systemic inflammation involving multiple organ systems. SLE patients have impaired clearance of apoptotic debris, which releases HMGB1 and other DAMPs extracellularly. HMGB1 activity is implicated in multiple disease phenotypes in SLE, including lupus nephritis and neuropsychiatric lupus. Elucidating the various properties of HMGB1 in SLE provides a better understanding of the disease and opens up new opportunities for designing potential therapeutics.

Targeting Inflammation Driven by HMGB1

High mobility group box 1 (HMGB1) is a highly conserved, nuclear protein present in all cell types. It is a multi-facet protein exerting functions both inside and outside of cells. Extracellular HMGB1 has been extensively studied for its prototypical alarmin functions activating innate immunity, after being actively released from cells or passively released upon cell death. TLR4 and RAGE operate as the main HMGB1 receptors. Disulfide HMGB1 activates the TLR4 complex by binding to MD-2. The binding site is separate from that of LPS and it is now feasible to specifically interrupt HMGB1/TLR4 activation without compromising protective LPS/TLR4-dependent functions. Another important therapeutic strategy is established on the administration of HMGB1 antagonists precluding RAGE-mediated endocytosis of HMGB1 and HMGB1-bound molecules capable of activating intracellular cognate receptors. Here we summarize the role of HMGB1 in inflammation, with a focus on recent findings on its mission as a damage-associated molecular pattern molecule and as a therapeutic target in inflammatory diseases. Recently generated HMGB1-specific inhibitors for treatment of inflammatory conditions are discussed.

High mobility group box-1 mediates hippocampal inflammation and contributes to cognitive deficits in high-fat high-fructose diet-induced obese rats

High-fat high-sugar diet-induced obesity can lead to hippocampal inflammation and cognitive deficits, but the detailed underlying mechanism is still not clear. We aim to investigate the role of HMGB1 in hippocampal inflammatory responses and cognitive impairment in high-fat high-fructose diet (HFHFD)-induced obesity. Rats were fed with a normal control diet or an HFHFD diet for 14 weeks. In the last 6 weeks on the diets, the rats were treated with control, or an HMGB1 inhibitor glycyrrhizin, or an anti-HMGB1 neutralizing monoclonal antibody (mAb). Obesity was induced in the HFHFD-fed rats, which had higher body weight, epididymal white adipose tissue (EWAT) weight and caloric efficiency, and lower brain/body weight ratio, glucose tolerance and insulin sensitivity than the ones on normal diets. In the HFHFD-induced obese rats, the HMGB1 levels in plasma and hippocampus were increased, and the nucleus-to-cytoplasm translocation of HMGB1 was promoted. The hippocampal inflammatory responses were enhanced in the HFHFD-induced obesity, including the activation of TLR4 and NF-κB, the production of IL-1β, TNF-α and IL-6, as well as the activation of microglia and astrocytes. In addition, the hippocampal cell apoptosis and cognitive impairment were observed in the HFHFD-fed rats. The treatment with glycyrrhizin or HMGB1 mAb successfully decreased the HMGB1 levels in plasma and hippocampus, and prevented the HMGB1 translocation from the nucleus to cytoplasm. Inhibiting HMGB1 by glycyrrhizin or HMGB1 mAb suppressed the hippocampal inflammatory, alleviated the apoptosis and ameliorated the cognitive impairment in HFHFD-fed rats. These findings indicate that HMGB1 mediates the hippocampal inflammation and contributes to the cognitive deficits in HFHFD-induced obesity. Therefore, inhibition of HMGB1 may have beneficial effect in protecting against hippocampal inflammation and cognitive deficits in dietary obesity.

DNA-Mediated Interferon Signature Induction by SLE Serum Occurs in Monocytes Through Two Pathways: A Mechanism to Inhibit Both Pathways

A primary mechanism for activation of innate immunity is recognition of damage or pathogen associated molecular patterns by pattern recognition receptors (PRRs). Nucleic acid is a damage associated molecular pattern molecule that when internalized into a monocyte and recognized by intracellular nucleic acid sensing toll like receptors will cause production of type 1 interferon. The process by which DNA or RNA is delivered into the cytosol of monocytes in systemic lupus erythematosus remains incompletely understood, and therapeutic approaches to prevent DNA-mediated monocyte activation are needed. We identified two mechanisms for internalization of DNA by monocytes. IgG-bound DNA was internalized by interacting with Fc gamma receptor IIa, while high-mobility group box-1 protein-bound DNA was internalized by interacting with the receptor for advanced glycation end products. Both pathways contribute to an inflammatory phenotype in monocytes exposed to serum from patients with SLE. Moreover, both of these pathways can be inhibited by a pentapeptide, DWEYS, which is a DNA mimetope. In one instance DWEYS directly competes with DNA for antibody binding and in the other DWEYS binds high-mobility group box-1 and blocks its interaction with RAGE. Our data highlight distinct pathways involved in nucleic acid enters monocytes in SLE, and identify a potential therapeutic to prevent nucleic acid internalization in SLE.

Air pollution is associated with the development of atherosclerosis via the cooperation of CD36 and NLRP3 inflammasome in ApoE-/- mice

Previous studies have indicated that the main air pollutant fine particulate matter (≤2.5 μm; PM_2.5) exposure is associated with the development of atherosclerosis. Although the mechanism is not fully illustrated, the inflammatory responses play an important role. The present study aimed to explore whether PM_2.5-exacerbated atherosclerosis was mediated by the cooperation of cluster of differentiation 36 (CD36) and nucleotide-binding oligomerization domain-like receptor protein (NLRP3) inflammasome in apolipoprotein E^-/- (ApoE^-/-) mice. Thirty-two ApoE^-/- mice were randomly divided into two groups. One group was fed with high fat chow (HFC) for 10 weeks to establish atherosclerotic model, and the other was fed with normal chow (NC). From week 11, the mice were exposed to concentrated PM_2.5 (PM) or filtered air (FA) using Shanghai Meteorological and Environmental Animal Exposure System for 16 weeks. In both NC and HFC groups, PM_2.5 exposure induced the formation of atherosclerosis plaque. Similarly, PM mice appeared higher lipid content in the aortic root than that in the FA mice. Compared with the FA mice, PM mice appeared a decrease in high density lipoprotein-cholesterol (HDL-C) and apolipoprotein A1 along with an increase in apolipoprotein B, low density lipoprotein-cholesterol (LDL-C) and oxidized low-density lipoprotein (ox-LDL). Moreover, PM_2.5 exposure induced increase of CD36 in serum and aorta. In both NC and HFC groups, NLRP3 inflammasome activation-related indicators were activated or increased in the aorta of the PM mice when compared with the FA mice. The cooperation of CD36 and NLRP3 inflammasome activation may be the potential mechanisms linkixposed to concentrated PM_2.5 (PM) or filtered air (FA) using Shanghai Meteorological and Environmental Animal Exposure System for 16 weeks. In both NC and HFC groups, PM_2.5 exposure induced the formation of atherosclerosis plaque. Similarly, PM mice appeared higher lipid content in the aortic root than that in the FA mice. Compared with the FA mice, PM mice appeared a decrease in high density lipoprotein-cholesterol (HDL-C) and apolipoprotein A1 along with an increase in apolipoprotein B, low density lipoprotein-cholesterol (LDL-C) and oxidized low-density lipoprotein (ox-LDL). Moreover, PM_2.5 exposure induced increase of CD36 in serum and aorta. In both NC and HFC groups, NLRP3 inflammasome activation-related indicators were activated or increased in the aorta of the PM mice when compared with the FA mice. The cooperation of CD36 and NLRP3 inflammasome activation may be the potential mechanisms linking air pollution and HFC-induced atherosclerosis even in the mice with NC intake.

Extracellular HMGB1 as a therapeutic target in inflammatory diseases

INTRODUCTION

High-mobility group box 1 (HMGB1) is a ubiquitous nuclear protein that promotes inflammation when released extracellularly after cellular activation, stress, damage or death. HMGB1 operates as one of the most intriguing molecules in inflammatory disorders via recently elucidated signal and molecular transport mechanisms. Treatments based on antagonists specifically targeting extracellular HMGB1 have generated encouraging results in a wide number of experimental models of infectious and sterile inflammation. Clinical studies are still to come. Areas covered: We here summarize recent advances regarding pathways for extracellular HMGB1 release, receptor usage, and functional consequences of post-translational modifications. The review also addresses results of preclinical HMGB1-targeted therapy studies in multiple inflammatory conditions and outlines the current status of emerging clinical HMGB1-specific antagonists. Expert opinion: Blocking excessive amounts of extracellular HMGB1, particularly the disulfide isoform, offers an attractive clinical opportunity to ameliorate systemic inflammatory diseases. Therapeutic interventions to regulate intracellular HMGB1 biology must still await a deeper understanding of intracellular HMGB1 functions. Future work is needed to create more robust assays to evaluate functional bioactivity of HMGB1 antagonists. Forthcoming clinical studies would also greatly benefit from a development of antibody-based assays to quantify HMGB1 redox isoforms, presently assessed by mass spectrometry methods.

Association of High Mobility Group Box Chromosomal Protein 1 and Receptor for Advanced Glycation End Products Serum Concentrations With Extraglandular Involvement and Disease Activity in Sjögren's Syndrome

OBJECTIVE

To assess serum levels of high mobility group box chromosomal protein 1 (HMGB-1) and the soluble receptor for advanced glycation end products (sRAGE) in patients with Sjögren's syndrome (SS) and explore correlations with disease activity.

METHODS

Thirty-nine patients with SS and 21 healthy controls were included in this cross-sectional study. Clinical and laboratory values were obtained from all patients. Disease activity was assessed using the European League Against Rheumatism SS Disease Activity Index (ESSDAI). Serum samples were collected and HMGB-1 and sRAGE levels were measured using enzyme-linked immunosorbent assay (ELISA), and HMGB-1 concentrations were semiquantified by Western blotting.

RESULTS

In ELISA, HMGB-1 serum levels did not differ between healthy controls and patients with SS (P = 0.783). When measured by semiquantitative Western blotting, HMGB-1 levels were increased in patients with SS compared to healthy controls (P = 0.012). HMGB-1 serum levels detected by Western blotting were higher in patients with extraglandular manifestations (P = 0.003) and were correlated with ESSDAI disease activity (r = 0.544, P < 0.0001). Furthermore, sRAGE was elevated in the sera of patients with SS (P = 0.003) compared to healthy controls and was also correlated with the ESSDAI (r = 0.545, P = 0.002).

CONCLUSION

Serum levels of total HMGB-1 and sRAGE were elevated in patients with SS compared to healthy controls and correlated with disease activity as measured by the ESSDAI. Patients with extraglandular involvement had high serum levels of HMGB-1.

Anti-high Mobility Group Box 1 Antibody Ameliorates Albuminuria in MRL/lpr Lupus-Prone Mice

We evaluated the efficacy of a neutralizing anti-high mobility group box 1 (HMGB1) monoclonal antibody in MRL/lpr lupus-prone mice. The anti-HMGB1 monoclonal antibody (5 mg/kg weight) or class-matched control immunoglobulin G2a (IgG2a) was administered intravenously twice a week for 4-15 weeks. Urine albumin was monitored, and histological evaluation of the kidneys was conducted at 16 weeks. Lymphadenopathies were evaluated by 1-(2'-deoxy-2'-[¹⁸F]fluoro-β-D-arabinofuranosyl)cytosine ([¹⁸F]FAC) positron emission tomography/computed tomography (PET/CT) at 12 weeks. Following 4-week treatment, [¹⁸F]FAC-PET/CT showed similar accumulation in cervical and axillary lymph nodes at 12 weeks of age. However, anti-HMGB1 monoclonal antibody sufficiently inhibited the increase in albuminuria compared to an isotype control following 15-week treatment. Complement deposition was also improved; however, there were no significant differences in IgG deposition and renal pathological scores between the two groups. Anti-double-stranded DNA (dsDNA) antibody titers and cytokine and chemokine levels were also unaltered. Although there were no significant differences in glomerular macrophage infiltration, neutrophil infiltration was significantly decreased by the anti-HMGB1 monoclonal antibody. Antagonizing HMGB1 treatment suppressed HMGB1 translocation from nuclei in the kidney and suppressed neutrophil extracellular traps. The anti-HMGB1 monoclonal antibody demonstrated therapeutic potential against albuminuria in lupus nephritis by inhibiting neutrophil recruitment and neutrophil extracellular traps.

Autoantibodies to box A of high mobility group box 1 in systemic lupus erythematosus

Autoantibodies to nuclear structures are a hallmark of systemic lupus erythematosus (SLE), including autoantibodies to nuclear protein high mobility group box 1 (HMGB1). HMGB1 consists of three separate domains: box A, box B and an acidic tail. Recombinant box A acts as a competitive antagonist for HMGB1 and might be an interesting treatment option in SLE. However, antibodies to box A might interfere. Therefore, levels of anti-box A were examined in SLE patients in association with disease activity and clinical parameters. Serum anti-box A was measured in 86 SLE patients and 44 age- and sex-matched healthy controls (HC). Serum samples of 28 patients with primary Sjögren's syndrome and 32 patients with rheumatoid arthritis were included as disease controls. Anti-HMGB1 and anti-box B levels were also measured by enzyme-linked immunosorbent assay during quiescent disease [SLE Disease Activity Index (SLEDAI) ≤ 4, n = 47] and active disease (SLEDAI ≥ 5, n = 39). Anti-box A levels in active SLE patients were higher compared to quiescent patients, and were increased significantly compared to HC and disease controls. Anti-box A levels correlated positively with SLEDAI and anti-dsDNA levels and negatively with complement C3 levels. Increased levels of anti-box A antibodies were present in the majority of patients with nephritic (73%) and non-nephritic exacerbations (71%). Antibodies to the box A domain of HMGB1 might be an interesting new biomarker, as these had a high specificity for SLE and were associated with disease activity. Longitudinal studies should be performed to evaluate whether these antibodies perform better in predicting an exacerbation, especially non-nephritic exacerbations.

Treatment with Anti-HMGB1 Monoclonal Antibody Does Not Affect Lupus Nephritis in MRL/lpr Mice

High mobility group box 1 (HMGB1) is a nuclear DNA binding protein that acts as an alarmin when secreted. HMGB1 is increased in systemic lupus erythematosus and might represent a potential therapeutic target. We investigated whether treatment with an anti-HMGB1 antibody affects the development of lupus nephritis in MRL/lpr mice. Seven-week-old MRL/lpr mice were injected intraperitoneally twice weekly for 10 wks with 50 μg monoclonal anti-HMGB1 (2G7, mouse IgG2b) (n = 12) or control antibody (n = 11). Control MRL/MPJ mice (n = 10) were left untreated. Every 2 wks, blood was drawn and urine was collected at wk 7, 11 and 17. Mice were sacrificed at 17 wks for complete disease evaluation. Plasma HMGB1 and anti-HMGB1 levels were increased in MRL/lpr mice compared with control MRL/MPJ mice. There were no differences in albuminuria, urine HMGB1 and plasma levels of complement C3, anti-dsDNA and proinflammatory cytokines between untreated and treated mice at any time point. Lupus nephritis of mice treated with anti-HMGB1 monoclonal antibody (mAb) was classified as class III (n = 3) and class IV (n = 9), while mice treated with control mAb were classified as class II (n = 4), class III (n = 2) and class IV (n = 5). IgG and C3 deposits in kidneys were similar in mice treated with anti-HMGB1 mAb or control mAb. In conclusion, treatment with monoclonal anti-HMGB-1 antibody 2G7 does not affect development of lupus nephritis, disease progression or proinflammatory cytokine levels in MRL/lpr mice. This result indicates that blocking of HMGB1 by this neutralizing antibody does not affect lupus nephritis in MRL/lpr mice.

Targeting the inflammasome in rheumatic diseases

Activation of the inflammasome, a protein complex responsible for many cellular functions, including the activation of the proinflammatory cytokines interleukin (IL)-1β and IL-18, has been identified as a key participant in many rheumatic diseases including autoimmune, inflammatory, and autoinflammatory syndromes. This review will discuss the recent advances in understanding the role of this complex in various rheumatic diseases. Furthermore, it will focus on available therapies, which directly and indirectly target the inflammasome and its downstream cytokines to quiet inflammation and possibly dampen autoimmune processes.

Antibodies against High Mobility Group Box protein-1 (HMGB1) versus other anti-nuclear antibody fine-specificities and disease activity in systemic lupus erythematosus

Introduction

The non-histone nuclear protein high mobility group box protein-1 (HMGB1) is typically associated with nucleosomes, but may shuttle between the nucleus and the cytoplasm, and under some conditions also be released extracellularly and participate in systemic inflammation. Monoclonal HMGB1-targeting antibodies can ameliorate murine polyarthritis and lupus-like disease. Interestingly, autoantibodies against HMGB1 have also been described in patients with systemic lupus erythematosus (SLE), but their clinical implications remain elusive. The main aims of this study were to detect serum anti-HMGB1 antibodies in patients with SLE and relate them to other types of antinuclear antibodies (ANA), and to disease activity.

Methods

188 Swedish SLE patients meeting the 1982 American College of Rheumatology classification criteria and/or the 2012 Systemic Lupus International Collaborating Clinics classification criteria participated in the study. Anti-HMGB1 antibody levels were analysed in patient and control (n = 112) sera by an in-house ELISA using recombinant histidine-tagged HMGB1. SLE sera were also analysed for ANA by immunofluorescence (IF) microscopy (IF-ANA) using fixed HEp-2 cells, and by a line-blot assay for antigen fine-specificities. To quantify antibodies to double-stranded DNA, a fluoroenzyme-immunoassay was employed.

Results

At inclusion, 23 % of the SLE patients were anti-HMGB1 antibody positive compared to 5 % of the controls. Anti-HMGB1 antibodies occurred in 49 % of the IF-ANA positive SLE patients, and in 34 % of IF-ANA negative cases (p = 0.004). Levels of anti-HMGB1 antibodies correlated with anti-dsDNA antibody levels (r = 0.49; p < 0.001). Significant, but less pronounced correlations were found regarding anti-HMGB1 and SLE disease activity index (SLEDAI-2K: r = 0.15; p = 0.04), classical complement function (r = -0.24; p = 0.002) and complement protein C4 (r = -0.23; p = 0.002). Average anti-HMGB1 antibody levels were significantly higher among patients with homogenous ± other IF-ANA staining patterns (median 180 AU) compared to IF-ANA negative cases (median 83 AU) (p = 0.004). Rabbit anti-HMGB1 antibodies gave rise to cytoplasmic, but not nuclear, staining of HEp-2 cells.

Conclusions

We confirm that anti-HMGB1 antibodies are common in SLE and correlate with disease activity variables. Although anti-HMGB1 antibodies measured by ELISA often coincide with nuclear IF-ANA staining, our results indicate that anti-HMGB1 antibodies do not give rise to nuclear staining of the predominantly used commercial HEp-2 cell slides.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0856-2) contains supplementary material, which is available to authorized users.

The inflammasome and lupus: another innate immune mechanism contributing to disease pathogenesis?

PURPOSE OF REVIEW

The role of innate immunity in systemic lupus erythematosus (SLE) has been a rapidly expanding area of research over the last decade. Included in this rubric is the concept that activation of the inflammasome, a molecular complex that activates caspase-1 and in turn the cytokines IL-1β and IL-18, is important in lupus pathogenesis. This review will summarize the recent discoveries exploring the role of the inflammasome machinery in SLE.

RECENT FINDINGS

Immune complexes can activate the NLRP3 inflammasome, and SLE-derived macrophages are hyper-responsive to innate immune stimuli, leading to enhanced activation of the inflammasome and production of inflammatory cytokines. Work in several murine models suggests an important role for the NLRP3 inflammasome in mediating lupus nephritis. Caspase-1, the central enzyme of the inflammasome, is essential for the development of type I interferon responses, autoantibody production, and nephritis in the pristane model of lupus. The absence of melanoma 2 inflammasome may have protective and pathogenic roles in SLE.

SUMMARY

Recent evidence suggests that the inflammasome machinery is dysregulated in SLE, plays an important role in promotion of organ damage, and may mediate cross-talk between environmental triggers and the development of lupus. Further research should focus on whether inhibition of inflammasome components may serve as a viable target for therapeutic development in SLE.

Molecular mechanism and therapeutic modulation of high mobility group box 1 release and action: an updated review

High mobility group box 1 (HMGB1) is an evolutionarily conserved protein, and is constitutively expressed in virtually all types of cells. Infection and injury converge on common inflammatory responses that are mediated by HMGB1 secreted from immunologically activated immune cells or passively released from pathologically damaged cells. Herein we review the emerging molecular mechanisms underlying the regulation of pathogen-associated molecular patterns (PAMPs)-induced HMGB1 secretion, and summarize many HMGB1-targeting therapeutic strategies for the treatment of infection- and injury-elicited inflammatory diseases. It may well be possible to develop strategies that specifically attenuate damage-associated molecular patterns (DAMPs)-mediated inflammatory responses without compromising the PAMPs-mediated innate immunity for the clinical management of infection- and injury-elicited inflammatory diseases.