Elevated plasma level of HMGB1 is associated with disease activity and combined alterations with IFN-α and TNF-α in systemic lupus erythematosus

The role of high mobility group box-1 on the development of diabetes complications: A plausible pharmacological target

BACKGROUND

Diabetes mellitus has emerged as a pressing global concern, with a notable increase in recent years. Despite advancements in treatment, existing medications struggle to halt the progression of diabetes and its associated complications. Increasing evidence underscores inflammation as a significant driver in the onset of diabetes mellitus. Therefore, perspectives on new therapies must consider shifting focus from metabolic stress to inflammation. High mobility group box (HMGB-1), a nuclear protein regulating gene expression, gained attention as an endogenous danger signal capable of sparking inflammatory responses upon release into the extracellular environment in the late 1990s.

PURPOSE

Given the parallels between inflammatory responses and type 2 diabetes (T2D) development, this review paper explores HMGB-1's potential involvement in onset and progression of diabetes complications. Specifically, we will review and update the understanding of HMGB-1 and its inflammatory pathways in insulin resistance, diabetic nephropathy, diabetic neuropathy, and diabetic retinopathy.

CONCLUSIONS

HMGB-1 and its receptors i.e. receptor for advanced glycation end-products (RAGE) and toll-like receptors (TLRs) present promising targets for antidiabetic interventions. Ongoing and future projects in this realm hold promise for innovative approaches targeting HMGB-1-mediated inflammation to ameliorate diabetes and its complications.

Role of Platelets in Rheumatic Chronic Autoimmune Inflammatory Diseases

Platelets are essential in maintaining blood homeostasis and regulating several inflammatory processes. They constantly interact with immune cells, have immunoregulatory functions, and can affect, through immunologically active substances, endothelium, leukocytes, and other immune response components. In reverse, inflammatory and immune processes can activate platelets, which might be significant in autoimmune disease progression and arising complications. Thus, considering this interplay, targeting platelet activity may represent a new approach to treatment of autoimmune diseases. This review aims to highlight the role of platelets in the pathogenic mechanisms of the most frequent chronic autoimmune inflammatory diseases to identify gaps in current knowledge and to provide potential new targets for medical interventions.

Altered expression of miR-125a and dysregulated cytokines in systemic lupus erythematosus: Unveiling diagnostic and prognostic markers

BACKGROUND

Systemic lupus erythematosus (SLE) is a chronic autoimmune disorder impacting multiple organs, influenced by genetic factors, especially those related to the immune system. However, there is a need for new biomarkers in SLE. MicroRNA-125a (miR-125a) levels are decreased in T cells, B cells, and dendritic cells of SLE patients. MiR-125a plays a regulatory role in controlling the levels of tumor necrosis factor-alpha (TNF-α) and interleukin 12 (IL-12), which are crucial pro-inflammatory cytokines in SLE pathogenesis.

AIM

To assess the levels of miR-125a, IL-12, and TNF-α in SLE patients' plasma, evaluating their diagnostic and prognostic value.

METHODS

The study included 100 healthy individuals, 50 newly diagnosed (ND), and 50 SLE patients undergoing treatment. The patients were monitored for a duration of 24 wk to observe and record instances of relapses. MiR-125a expression was measured using real-time reverse transcription polymerase chain reaction, while ELISA kits were used to assess IL-12 and TNF-α production.

RESULTS

The results showed significantly reduced miR-125a expression in SLE patients compared to healthy individuals, with the lowest levels in ND patients. TNF-α and IL-12 expression levels were significantly elevated in SLE patients, especially in the early stages of the disease. Receiver operating characteristic curve analyses, and Cox-Mantel Log-rank tests indicated miR-125a, TNF-α, and IL-12 as proper diagnostic biomarkers for SLE. A negative correlation was found between plasma miR-125a expression and IL-12/TNF-α levels in SLE patients.

CONCLUSION

Decreased miR-125a levels may be involved in the development of SLE, while elevated levels of IL-12 and TNF-α contribute to immune dysregulation. These findings offer new diagnostic and prognostic markers for SLE. Moreover, the negative correlation observed suggests an interaction between miR-125a, TNF-α, and IL-12. Further research is necessary to uncover the underlying mechanisms that govern these relationships.

HMGB1 and Toll-like receptors: potential therapeutic targets in autoimmune diseases

HMGB1, a nucleoprotein, is expressed in almost all eukaryotic cells. During cell activation and cell death, HMGB1 can function as an alarm protein (alarmin) or damage-associated molecular pattern (DAMP) and mediate early inflammatory and immune response when it is translocated to the extracellular space. The binding of extracellular HMGB1 to Toll-like receptors (TLRs), such as TLR2 and TLR4 transforms HMGB1 into a pro-inflammatory cytokine, contributing to the occurrence and development of autoimmune diseases. TLRs, which are members of a family of pattern recognition receptors, can bind to endogenous DAMPs and activate the innate immune response. Additionally, TLRs are key signaling molecules mediating the immune response and play a critical role in the host defense against pathogens and the maintenance of immune balance. HMGB1 and TLRs are reported to be upregulated in several autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, type 1 diabetes mellitus, and autoimmune thyroid disease. The expression levels of HMGB1 and some TLRs are upregulated in tissues of patients with autoimmune diseases and animal models of autoimmune diseases. The suppression of HMGB1 and TLRs inhibits the progression of inflammation in animal models. Thus, HMGB1 and TLRs are indispensable biomarkers and important therapeutic targets for autoimmune diseases. This review provides comprehensive strategies for treating or preventing autoimmune diseases discovered in recent years.

Association between type I interferon pathway activation and clinical outcomes in rheumatic and musculoskeletal diseases: a systematic literature review informing EULAR points to consider

BACKGROUND

Type I interferons (IFN-I) contribute to a broad range of rheumatic and musculoskeletal diseases (RMDs). Compelling evidence suggests that the measurement of IFN-I pathway activation may have clinical value. Although several IFN-I pathway assays have been proposed, the exact clinical applications are unclear. We summarise the evidence on the potential clinical utility of assays measuring IFN-I pathway activation.

METHODS

A systematic literature review was conducted across three databases to evaluate the use of IFN-I assays in diagnosis and monitor disease activity, prognosis, response to treatment and responsiveness to change in several RMDs.

RESULTS

Of 366 screened, 276 studies were selected that reported the use of assays reflecting IFN-I pathway activation for disease diagnosis (n=188), assessment of disease activity (n=122), prognosis (n=20), response to treatment (n=23) and assay responsiveness (n=59). Immunoassays, quantitative PCR (qPCR) and microarrays were reported most frequently, while systemic lupus erythematosus (SLE), rheumatoid arthritis, myositis, systemic sclerosis and primary Sjögren's syndrome were the most studied RMDs. The literature demonstrated significant heterogeneity in techniques, analytical conditions, risk of bias and application in diseases. Inadequate study designs and technical heterogeneity were the main limitations. IFN-I pathway activation was associated with disease activity and flare occurrence in SLE, but their incremental value was uncertain. IFN-I pathway activation may predict response to IFN-I targeting therapies and may predict response to different treatments.

CONCLUSIONS

Evidence indicates potential clinical value of assays measuring IFN-I pathway activation in several RMDs, but assay harmonisation and clinical validation are urged. This review informs the EULAR points to consider for the measurement and reporting of IFN-I pathway assays.

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

Background

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

Methods

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

Results

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

Conclusions

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

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.

Alarmins in autoimmune diseases

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

Extracellular HMGB1 Induced Glomerular Endothelial Cell Injury via TLR4/MyD88 Signaling Pathway in Lupus Nephritis

Previously, our study showed that HMGB1 was significantly elevated in the blood and located in the glomerular endothelium in LN patients. But whether extracellular HMGB1 is involved in the injury of glomerular endothelial cells (GECs) in LN still needs further investigation. Firstly, we detected the levels of SDC-1, VCAM-1, and proteinuria in LN patients and MRL/lpr mice and analyzed their correlations. Then, HMGB1 and TLR4/MyD88 were inhibited to observe the shedding of glycocalyx and injury of GECs in vivo and in vitro. Our results showed that HRGEC injury and SDC-1 shedding played an important role in the increase of permeability and proteinuria formation in LN. Additionally, inhibition of extracellular HMGB1 and/or downstream TLR4/MyD88/NF-κB/p65 signaling pathway also alleviated GEC monolayer permeability, reduced the shedding of the glomerular endothelial glycocalyx, improved the intercellular tight junction and cytoskeletal arrangement, and downregulated the NO level and VCAM-1 expression. These results suggested that extracellular HMGB1 might involve in GEC injury by activating the TLR4/MyD88 signaling pathway in LN, which provided novel insights and potential therapeutic target for the treatment of lupus nephritis.

High mobility group box-1 levels may be associated with disease activity of Behcet's disease

BACKGROUND

High mobility group box- 1 (HMGB- 1) is a nuclear protein acting as a proinflammatory molecule. The serum HMGB- 1 levels were found elevated in chronic inflammatory diseases. In this cross-sectional study, serum HMGB- 1 levels in Behcet's disease (BD) patients and healthy controls (HC) were studied. Also, its association with disease activity scores and clinical findings were evaluated.

METHODS

Ninety BD patients and 50 age-sex matched HC were included in the study. Disease activity scores were assessed by Behcet Disease Current Activity Form (BDCAF) and Behcet Syndrome Activity Score (BSAS). Serum HMGB- 1 levels were measured using a commercial ELISA kit. A p value of < 0.05 was considered to be statistically significant.

RESULTS

Serum HMGB- 1 levels were significantly higher in BD than in HC (43.26 pg/mL and 16.73 pg/mL; p < 0.001, respectively). Serum HMGB- 1 levels were statistically significantly associated with presence of erythema nodosum (EN) and genital ulcers in the last one month prior to recruitment (p = 0.041 and p < 0.001, respectively). BDCAF and BSAS scores were positively correlated with serum HMGB- 1 level ( p = 0.03 and p = 0.02, respectively).

DISCUSSION

HMGB - 1 may play a role in the development of BD. Also, due to its positive correlation with disease activity indices, it can be used as a novel disease activity parameter in BD.

Thalidomide and Lenalidomide for Refractory Systemic/Cutaneous Lupus Erythematosus Treatment: A Narrative Review of Literature for Clinical Practice

BACKGROUND

Thalidomide has shown exceptional results in systemic/cutaneous lupus erythematosus(SLE/CLE). Recently, lenalidomide has been also prescribed for SLE/CLE treatment. Literature regarding efficacy/adverse events for these drugs is scarce with a single systematic review and meta-analysis focused solely on thalidomide for refractory cutaneous lupus subtypes.

OBJECTIVE

We, therefore, addressed in this narrative review the efficacy/adverse effects of thalidomide and lenalidomide for SLE and CLE. In addition, we provide a specialist approach for clinical practice based on the available evidence.

RESULTS

Efficacy of thalidomide for refractory cutaneous lupus treatment was demonstrated by several studies, mostly retrospective with small sample size(≤20). The frequency of peripheral polyneuropathy is controversial varying from 15-80% with no consistent data regarding cumulative dose and length of use. Drug withdrawn results in clinical partial/complete reversibility for most cases (70%). For lenalidomide, seven studies (small sample sizes) reported its efficacy for SLE/CLE with complete/partial response in all patients with a mean time to response of 3 months. Flare rate varied from 25-75% occurring 0.5-10 months after drug withdrawn. There were no reports of polyneuropathy/worsening of previous thalidomide-induced neuropathy, but most of them did not perform nerve conduction studies. Teratogenicity risk exist for both drugs and strict precautions are required.

CONCLUSIONS

Thalidomide is very efficacious as an induction therapy for patients with severe/refractory cutaneous lupus with high risk of scarring, but its longstanding use should be avoided due to neurotoxicity. Lenalidomide is a promising drug for skin lupus treatment, particularly regarding the apparent lower frequency of nerve side effects.

HMGB1 Activates Myeloid Dendritic Cells by Up-Regulating mTOR Pathway in Systemic Lupus Erythematosus

Research has shown that HMGB1 can activate dendritic cells (DCs), but its molecular mechanisms are not clear. In this study, we reported that the myeloid dendritic cells (mDCs) were activated in the peripheral blood of SLE patients, and the activation of mDCs was associated with the up-regulation of HMGB1 and mTOR. After stimulated by HMGB1, expression of mTOR and its substrates P70S6K and 4EBP1 in dendritic cells increased considerably (P < 0.01). The expression of HLA-DR, CD40, and CD86 on dendritic cells also significantly increased following these stimuli (P < 0.01). In addition, stimulation with HMGB1 enhanced cytokine (IL-1β, IL-6, and TNF-a) production in dendritic cells. In contrast, the HMGB1-mediated expression of HLA-DR, CD40, and CD86 on dendritic cells and production of IL-1β, IL-6, and TNF-α were reduced by rapamycin. Rapamycin can inhibit HMGB1-induced activation of mDCs and secretion of pro-inflammatory cytokines. These findings indicated that HMGB1activates mDCs by up-regulating the mTOR pathway in SLE.

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 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.

The Expression of P2X7 Receptor on Th1, Th17, and Regulatory T Cells in Patients with Systemic Lupus Erythematosus or Rheumatoid Arthritis and Its Correlations with Active Disease

P2X7 receptor (P2X7R) is highly expressed on immune cells, triggering the release of cytokines and regulating autoimmune responses. To investigate P2X7R surface expression on T helper (Th) 1, Th17, and regulatory T (Treg) cells in patients with systemic lupus erythematosus (SLE) or rheumatoid arthritis (RA) and correlations with disease activity, 29 SLE and 29 RA patients and 18 healthy controls (HCs) were enrolled. We showed that SLE and RA patients had significantly higher levels of plasma cytokines (IFN-γ, IL-1β, IL-6, IL-17A, and IL-23), frequencies of Th1 and Th17 cells, and expression of P2X7R on Th1 and Th17 than HCs, and the Th17/Treg ratio was significantly increased, whereas Treg cell levels were significantly decreased. The Ca²⁺ influx increase following BzATP stimulation was significantly higher in CD4⁺PBMCs from SLE and RA patients than in HCs. Blood levels of shed P2X7R were increased in SLE and RA patients. Furthermore, 28-joint Disease Activity Score and SLE Disease Activity Index score showed negative correlations with Treg cell levels and positive correlations with Th17/Treg ratio and Th17 cell P2X7R expression. Interestingly, Th17 cell P2X7R expression was closely correlated with IL-1β, C-reactive protein, the erythrocyte sedimentation rate, anticyclic citrullinated peptide Abs, albumin, and C4. These data indicate that increased Th17 cell P2X7R expression is functionally and positively related to disease activity and some inflammatory mediators in SLE and RA patients, and P2X7R could be critical in promoting the Th17 immune response and contributing to the complex pathogenesis of SLE and RA.

Th1, Th2, and Th17 cytokines in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the breakdown of immune tolerance leading to excessive inflammation and tissue damage. Imbalance in the levels of cytokines represents one of the multifactorial causes of SLE pathogenesis and it contributes to disease severity. Deregulated levels of T helper type 1 (Th1), type 2 (Th2), and type 17 (Th17) cytokines have been associated with autoimmune inflammation. Growing evidence has shown deregulated levels of Th1, Th2, and Th17 cytokines in SLE patients compared to healthy controls associated with disease activity and severity. In this review, we describe and discuss the levels of Th1, Th2, and Th17 cytokines in SLE patients, and clinical trials involving Th1, Th2, and Th17 cytokines in SLE patients. In particular, with the exception of IL-2, IL-4, and TGF-β1, the levels of Th1, Th2, and Th17 cytokines are increased in SLE patients associated with disease severity. Current phase II or III studies involve therapeutic antibodies targeting IFN-α and type I IFN receptor, while low-dose IL-2 therapy is assessed in phase II clinical trials.

Neutrophil extracellular traps are a source of extracellular HMGB1 in lupus nephritis: associations with clinical and histopathological features

OBJECTIVE

This study aimed to analyze the expression of the high mobility group box-1 (HMGB1) protein in neutrophil extracellular traps (NETs) of patients with lupus nephritis (LN) and its association with clinical and histopathological features of the disease.

METHODS

Twenty-three patients with biopsy-confirmed LN and 14 systemic lupus erythematosus (SLE) patients with active disease (SLE Disease Activity Index (SLEDAI) score ≥ 6) and no evidence of LN were included. Clinical and laboratory features were recorded. NETs and the expression of HMGB1 were assessed by confocal microscopy, and serum HMGB1 levels were measured by ELISA.

RESULTS

In comparison to patients without kidney disease, patients with LN had a higher expression of HMGB1 in spontaneous (57 vs. 30.4; p = 0.027) and lipopolysaccharide (LPS)-induced (55.8 vs. 24.9; p = 0.005) NETs. We found a positive correlation between serum HMGB1 and the expression of HMGB1 in LPS-induced NETs (r = 0.447, p = 0.017). The expression of HMGB1 in spontaneous NETs correlated with SLEDAI score (r = 0.514, p = 0.001), anti-dsDNA antibodies (r = 0.467, p = 0.004), the rate of glomerular filtration descent (r = 0.543, p = 0.001), and diverse histopathological components of active nephritis in the kidney biopsy, such as the activity index (r = 0.581, p = 0.004), fibrinoid necrosis (r = 0.603, p = 0.002), and cellular crescents (r = 0.486, p = 0.019).

CONCLUSIONS

In patients with SLE, NETs are a source of extracellular HMGB1. The expression of HMGB1 in NETs is higher among patients with LN, which correlates with clinical and histopathological features of active nephritis and suggest a possible role of this alarmin in the pathophysiology of kidney damage in SLE.

The non-haemostatic role of platelets in systemic lupus erythematosus

Dysregulation of lymphocyte function, accumulation of autoantibodies and defective clearance of circulating immune complexes and apoptotic cells are hallmarks of systemic lupus erythematosus (SLE). Moreover, it is now evident that an intricate interplay between the adaptive and innate immune systems contributes to the pathogenesis of SLE, ultimately resulting in chronic inflammation and organ damage. Platelets circulate in the blood and are chiefly recognized for their role in the prevention of bleeding and promotion of haemostasis; however, accumulating evidence points to a role for platelets in both adaptive and innate immunity. Through a broad repertoire of receptors, platelets respond promptly to immune complexes, complement and damage-associated molecular patterns, and represent a major reservoir of immunomodulatory molecules in the circulation. Furthermore, evidence suggests that platelets are activated in patients with SLE, and that they could contribute to the circulatory autoantigenic load through the release of microparticles and mitochondrial antigens. Herein, we highlight how platelets contribute to the immune response and review evidence implicating platelets in the pathogenesis of SLE.

Serum high-mobility group box 1 is correlated with interferon-α and may predict disease activity in patients with systemic lupus erythematosus

Sensing self-nucleic acids through toll-like receptors in plasmacytoid dendritic cells (pDCs), and the dysregulated type I IFN production, represent pathogenic events in the development of the autoimmune responses in systemic lupus erythematosus (SLE). Production of high-mobility group box-1 protein (HMGB1) promotes type I IFN response in pDCs. To better understand the active pathogenic mechanism of SLE, we measured serum levels of HMGB1, thrombomodulin, and cytokines (IL-1β, IL-2, IL-4, IL-5, IL-6, IL-10, IL-13, IL-17A, IL-17F, IFNα, IFNγ, TNFα) in 35 patients with SLE. Serum HMGB1 and IFNα were significantly higher in patients with active SLE (SLE Disease Activity Index (SLEDAI) score ≥ 6) compared with healthy donors or patients with inactive SLE. Furthermore, the HMGB1 levels were significantly correlated with IFNα levels. By qualitative analysis, the detection of serum IFNα or HMGB1 suggests active SLE and the presence of SLE-related arthritis, fever, and urinary abnormality out of SLEDAI manifestations. Collectively, HMGB1 and IFNα levels are biomarkers reflecting disease activity, and qualitative analysis of IFNα or HMGB1 is a useful screening test to estimate SLE severity and manifestations. Our results suggest the clinical significance of type I IFNs and HMGB1 as key molecules promoting the autoimmune process in SLE.

Platelets in Skin Autoimmune Diseases

Systemic lupus erythematosus (SLE), systemic sclerosis (SSc), and small vessel vasculitis are three autoimmune diseases frequently manifested in the skin. They share common pathogenic features, including production of autoantibodies, loss of tolerance to self-antigens, tissue necrosis and fibrosis, vasculopathy and activation of the coagulation system. Platelets occupy a central part within the coagulation cascade and are well-recognized for their hemostatic role. However, recent cumulative evidence implicates their additional and multifaceted immunoregulatory functions. Platelets express immune receptors and they store growth factors, cytokines, and chemokines in their granules enabling a significant contribution to inflammation. A plethora of activating triggers such as damage associated molecular patterns (DAMPs) released from damaged endothelial cells, immune complexes, or complement effector molecules can mediate platelet activation. Activated platelets further foster an inflammatory environment and the crosstalk with the endothelium and leukocytes by the release of immunoactive molecules and microparticles. Further insight into the pathogenic implications of platelet activation will pave the way for new therapeutic strategies targeting autoimmune diseases. In this review, we discuss the inflammatory functions of platelets and their mechanistic contribution to the pathophysiology of SSc, ANCA associated small vessel vasculitis and other autoimmune diseases affecting the skin.

Diagnostic value of serum high-mobility group box-1 in pediatric systemic lupus erythematosus

BACKGROUND

High-mobility group box-1 (HMGB1) acts as a damage-associated molecular pattern or as an alarmin and it stimulates inflammatory and immunological activities.

AIM

We sought to investigate serum HMGB1 protein expression in patients with pediatric systemic lupus erythematosus (pSLE) in relation to the disease characteristics and activity.

PATIENTS AND METHODS

This is a controlled cross-sectional study which comprised 50 children and adolescents with Systemic lupus erythematosus (SLE) and 50 age- and sex-matched healthy subjects who served as a control group. Study measurements included clinical assessment, laboratory workup for SLE (complete blood count, erythrocyte sedimentation rate, serum creatinine, creatinine clearance and 24-hour urinary protein, C3 and anti-double-stranded DNA, lupus anticoagulant and anticardiolipin antibodies) and measurement of serum HMGB1 by enzyme-linked immunosorbent assay in patients and controls.

RESULTS

Serum HMGB1 expression was significantly higher in the pSLE patients than the control group (P < 0.001). Patients with lupus nephritis (LN) had significantly higher serum HMGB1 as compared to those with normal kidneys (P < 0.04). Serum HMGB1 in LN patients correlated positively to the SLE Disease Activity Index (P < 0.0001), and 24 hours urinary proteins and negatively to creatinine clearance (P < 0.001). At a cut-off point of ≥40 µg/L, serum HMGB1 showed good diagnostic value for pSLE with sensitivity and specificity of 98% and 95%, respectively.

CONCLUSION

Serum HMGB1 seems to be a reliable biomarker for diagnosis of pSLE and monitoring disease status, especially in LN. HMBG1 might prove to be a potential therapeutic target in LN.

Autoimmune rheumatic disease IgG has differential effects upon neutrophil integrin activation that is modulated by the endothelium

The importance of neutrophils in the pathogenesis of autoimmune rheumatic diseases, such as systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA), is increasingly recognised. Generation of reactive oxygen species (ROS) and release of neutrophil extracellular traps (NETs) by activated neutrophils are both thought to contribute to pathology; although the underlying mechanisms, particularly the effects of IgG autoantibodies upon neutrophil function, are not fully understood. Therefore, we determined whether purified IgG from patients with SLE or RA have differential effects upon neutrophil activation and function. We found that SLE- and RA-IgG both bound human neutrophils but differentially regulated neutrophil function. RA- and SLE-IgG both increased PMA-induced β₁ integrin-mediated adhesion to fibronectin, whilst only SLE-IgG enhanced α_Mβ₂ integrin-mediated adhesion to fibrinogen. Interestingly, only SLE-IgG modulated neutrophil adhesion to endothelial cells. Both SLE- and RA-IgG increased ROS generation and DNA externalisation by unstimulated neutrophils. Only SLE-IgG however, drove DNA externalisation following neutrophil activation. Co-culture of neutrophils with resting endothelium prevented IgG-mediated increase of extracellular DNA, but this inhibition was overcome for SLE-IgG when the endothelium was stimulated with TNF-α. This differential pattern of neutrophil activation has implications for understanding SLE and RA pathogenesis and may highlight avenues for development of novel therapeutic strategies.

In lupus nephritis, how do extracellular DNAs trigger type I interferon secretion: Under the assistance of HMGB1-cGAS?

Systemic lupus erythematosus (SLE) is an autoimmune disease with multiple organs involved. Kidney damage is common among SLE patients. In lupus nephritis, extracellular DNA accumulation from necrosis cells and activated cells is perceived as initial step of inflammation. The up-regulated type I IFN is one pivotal cytokine causing downstream inflammation enlargement. Currently, intracellular DNA sensor cGAS signaling has been found to be related to lupus nephritis and the aberrant up-regulation of type I IFN. However, how extracellular accumulated DNA activates intracellular cGAS is still unknown. It was reported that nuclear protein HMGB1 takes part in multiple autoimmune diseases and inflammation induction. When HMGB1 is secreted to extracellular environment under certain conditions, it combines with DNA and triggers IFN-I secretion. It has been reported that HMGB1 level in renal tissue and cGAS level in peripheral blood mononuclear cells were both significantly up-regulated in SLE patients. Hence, we present a hypothesis that in lupus nephritis, the released HMGB1 helps extracellular accumulated DNA endocytosis and cGAS signaling pathway activation, followed by IFN-I secretion. We infer this is one pivotal pro-inflammation pathway in lupus nephritis progression.

Association of serum/plasma high mobility group box 1 with autoimmune diseases: A systematic review and meta-analysis

BACKGROUND

High mobility group box 1 (HMGB1) is a kind of proinflammatory mediator to stimulate the innate and adaptive immune system and participates in a number of acute and chronic inflammatory processes after sterile injury or microbial invasion. HMGB1 has been suggested to be involved in the pathogenesis of many autoimmune diseases. However, the results are contradictory or inconclusive among these findings. The aim of this study was to investigate whether serum/plasma HMGB1 levels are associated with autoimmune diseases by comparing the serum/plasma HMGB1 levels in patients with autoimmune disease and healthy controls and to further evaluate whether serum/plasma HMGB1 levels are associated with disease state.

METHODS

PubMed, Medline, and Web of science databases (up to October 1, 2017) were used to obtain all relative published literature. Study quality was assessed by the Newcastle-Ottawa scale (NOS). Pooled standard mean difference (SMD) with 95% confidence interval (CI) was calculated by fixed-effects or random-effect model analysis.

RESULTS

A total of 23 original articles of autoimmune diseases were finally included in the meta-analysis. Results revealed that the serum/plasma HMGB1 levels were increased in patients with autoimmune disease, compared to healthy controls. Subgroup analysis showed that serum/plasma HMGB1 levels in patients with active disease state were significantly higher than in those with inactive state. In addition, subgroup analysis based on disease type has indicated that the serum/plasma HMGB1 levels in patients with small vessel vasculitis, systemic lupus erythematosus, rheumatoid arthritis, ankylosing spondylitis and sjogren syndrome were significantly higher, compared to healthy controls. Further subgroup analyses by region showed that plasma/serum HMGB1 levels were higher in Asian and European patients with autoimmune diseases.

CONCLUSIONS

Serum/plasma HMGB1 levels in patients with autoimmune diseases are significantly higher than in healthy controls, and may reflect the disease activity.

The proinflammatory protein HMGB1 is a substrate of transglutaminase-2 and forms high-molecular weight complexes with autoantigens

High-mobility group box 1 (HMGB1) is a chromatin-associated protein that, in response to stress or injury, translocates from the nucleus to the extracellular milieu, where it functions as an alarmin. HMGB1's function is in part determined by the complexes (HMGB1c) it forms with other molecules. However, structural modifications in the HMGB1 polypeptide that may regulate HMGB1c formation have not been previously described. In this report, we observed high-molecular weight, denaturing-resistant HMGB1c in the plasma and peripheral blood mononuclear cells of individuals with systemic lupus erythematosus (SLE) and, to a much lesser extent, in healthy subjects. Differential HMGB1c levels were also detected in mouse tissues and cultured cells, in which these complexes were induced by endotoxin or the immunological adjuvant alum. Of note, we found that HMGB1c formation is catalyzed by the protein-cross-linking enzyme transglutaminase-2 (TG2). Cross-link site mapping and MS analysis revealed that HMGB1 can be cross-linked to TG2 as well as a number of additional proteins, including human autoantigens. These findings have significant functional implications for studies of cellular stress responses and innate immunity in SLE and other autoimmune disease.

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.

Endoplasmic reticulum stress stimulates the release of extracellular vesicles carrying danger-associated molecular pattern (DAMP) molecules

Disturbances in endoplasmic reticulum (ER) function lead to ER stress which, when severe or prolonged, may result in apoptosis. Severe ER stress has been implicated in several pathological conditions including pre-eclampsia, a multisystem disorder of pregnancy associated with the release of pro-inflammatory factors from the placenta into the maternal circulation. Here, we show that severe ER stress induced by two distinct mechanisms in BeWo choriocarcinoma cells leads to the release of extracellular vesicles (EVs) carrying pro-inflammatory damage-associated molecular pattern (DAMP) molecules. Co-treatment with the antioxidant pyrrolidine dithiocarbamate results in a reduction in ER stress-induced EV-associated DAMP release. We further demonstrate that severe ER stress is associated with changes in the expression of several stress-related proteins, notably Cited-2 and phosphorylated JNK. Together, these data indicate that severe ER stress-mediated release of EV-associated DAMPs may contribute to the heightened systemic maternal inflammatory response characteristic of pre-eclampsia and may also be relevant to other chronic inflammatory diseases which display elevated ER stress.

High Mobility Group Box-1 (HMGb1): Current Wisdom and Advancement as a Potential Drug Target

High mobility group box-1 (HMGb1) protein, a nuclear non-histone protein that is released or secreted from the cell in response to damage or stress, is a sentinel for the immune system that plays a critical role in cell survival/death pathways. This review highlights key features of the endogenous danger-associated molecular pattern (DAMP) protein, HMGb1 in the innate inflammatory response along with various cofactors and receptors that regulate its downstream effects. The evidence demonstrating increased levels of HMGb1 in human inflammatory diseases and conditions is presented, along with a summary of current small molecule or peptide-like antagonists proven to specifically target HMGb1. Additionally, we delineate the measures needed toward validating this protein as a clinically relevant biomarker or bioindicator and as a relevant drug target.

Glycyrrhizin, a Direct HMGB1 Antagonist, Ameliorates Inflammatory Infiltration in a Model of Autoimmune Thyroiditis via Inhibition of TLR2-HMGB1 Signaling

BACKGROUND

High mobility group box-1 (HMGB1), a non-histone protein, plays an important role in autoimmune diseases. However, the significance of HMGB1 in the pathogenesis of autoimmune thyroiditis has not been reported. The purpose of this study was to explore whether HMGB1 participates in the pathogenesis of autoimmune thyroiditis, and whether glycyrrhizin (GL), a direct inhibitor of HMGB1, attenuates the severity of thyroid inflammatory infiltration in a murine model of autoimmune thyroiditis.

METHODS

A total of 80 male NOD.H-2^h4 mice were randomly divided into a control or iodine supplement (NaI) group at four weeks of age, and the control group was fed with regular water, whereas the NaI group was supplied with 0.005% sodium iodine water. Another 24 male NOD.H-2^h4 mice were also randomized into three groups (eight mice per group) as follows: control, NaI, and GL treatment after iodine supplementation (NaI + GL). The NOD.H-2^h4 mice were fed with 0.005% sodium iodide water for eight weeks to enhance autoimmune thyroiditis. After iodine treatment, the mice received intraperitoneal injections of GL for four weeks. The severity of lymphocytic infiltration in the thyroid gland was measured by histopathological studies. The serum levels of HMGB1, tumor necrosis factor alpha, interleukin (IL)-6, IL-1β, and thyroglobulin antibody titers were measured using an enzyme-linked immunosorbent assay. HMGB1 expression was measured by immunohistochemical staining and real-time polymerase chain reaction. TLR2, HMGB1, MyD88, and nuclear transcription factor κB were measured by Western blot.

RESULTS

The mRNA expression of HMGB1 was significantly higher at 8 and 16 weeks in the NaI group than it was in the control group. Serum levels of thyroglobulin antibodies, HMGB1, tumor necrosis factor alpha, IL-6, and IL-1β were significantly increased in the NaI group, but they were dramatically attenuated with GL injection. The prevalence of thyroiditis and the infiltration of lymphocytes were significantly decreased in the NaI + GL group. GL administration also significantly reduced the protein expression of TLR2, MyD88, HMGB1 and nuclear transcription factor κB in the thyroid gland and attenuated the severity of thyroiditis.

CONCLUSION

HMGB1 may play a crucial role in autoimmune thyroiditis by causing inflammatory infiltration, thus increasing the severity of autoimmune thyroiditis. GL effectively attenuated thyroiditis in the iodine-induced NOD.H-2^h4 mice via a molecular mechanism related to the inhibition of TLR2-HMGB1 signaling.

High-mobility group box 1 in multiple sclerosis

This study is one in series determining the potential of RAGE axis (receptor for advanced glycation end products, isoforms, ligands) as a biomarker in multiple sclerosis (MS). We evaluated serum levels of RAGE ligand, the high-mobility group box (HMGB)1 in MS patients, and assessed the correlation between HMGB1 serum levels and the use of disease-modifying drugs (DMDs), and between HMGB1 serum levels and indicators of MS disease severity. HMGB1 serum levels were compared between 96 (23 males) MS patients and 34 age- and gender-matched healthy controls (HCs) using enzyme-linked immunosorbent assays. DMD-naïve MS patients had significantly higher HMGB1 serum levels compared with DMD-treated (P = 0.04) and compared with HCs (P = 0.01). HMGB1 serum levels were not significantly different between total MS patients (DMD-naïve plus DMD-treated) and HCs (P = 0.09). DMD-naïve MS patients in clinical relapse tended to have lower HMGB1 serum levels than clinically stable RRMS patients (P = 0.07). HMGB1 serum levels showed 0.65 area under the curve (95 % CI 0.55-0.95) sensitivity/specificity for MS clinical relapse. The role of HMGB1 in MS disease pathology and DMD modulation of this protein warrant further investigations.

Microparticles in the blood of patients with systemic lupus erythematosus (SLE): phenotypic characterization and clinical associations

Systemic lupus erythematosus (SLE) is a prototypic autoimmune disease characterized by circulating autoantibodies and the formation of immune complexes. In these responses, the selecting self-antigens likely derive from the remains of dead and dying cells, as well as from disturbances in clearance. During cell death/activation, microparticles (MPs) can be released to the circulation. Previous MP studies in SLE have been limited in size and differ regarding numbers and phenotypes. Therefore, to characterize MPs more completely, we investigated 280 SLE patients and 280 individually matched controls. MPs were measured with flow cytometry and phenotyped according to phosphatidylserine expression (PS⁺/PS⁻), cellular origin and inflammatory markers. MPs, regardless of phenotype, are 2–10 times more abundant in SLE blood compared to controls. PS⁻ MPs predominated in SLE, but not in controls (66% vs. 42%). Selectively in SLE, PS⁻ MPs were more numerous in females and smokers. MP numbers decreased with declining renal function, but no clear association with disease activity was observed. The striking abundance of MPs, especially PS⁻ MPs, suggests a generalized disturbance in SLE. MPs may be regarded as “liquid biopsies” to assess the production and clearance of dead, dying and activated cells, i.e. pivotal events for SLE pathogenesis.

High mobility group box 1 skews macrophage polarization and negatively influences phagocytosis of apoptotic cells

OBJECTIVES

Decreased phagocytosis of apoptotic cells plays an important role in the pathogenesis of SLE. This can lead to secondary necrosis and release of nuclear proteins, such as high mobility group box 1 (HMGB1). We hypothesized that increased HMGB1 levels, as present in SLE, skew macrophage differentiation towards M1-like phenotypes and thereby diminish uptake of apoptotic cells. The aim of this study was to investigate the effect of HMGB1 on macrophage polarization and on phagocytic capacity of differentiated macrophages.

METHODS

SLE patients with quiescent disease (SLEDAI ⩽4) and healthy controls (HCs) were included. Monocytes and differentiated M1 and M2 macrophages were assessed for expression of M1 and M2 markers and for phagocytic capacity. HMGB1 was added during differentiation and during phagocytosis.

RESULTS

Expression of CD86 (M1) was not different, whereas CD163 (M2) was significantly lower on SLE monocytes. After differentiation, no differences regarding surface receptor expression and phagocytic capacity were observed between M1 and M2 macrophages from SLE patients and HCs. Addition of HMGB1 during M2 differentiation resulted in high IL-6 and TNF-α mRNA expression and reduced phagocytic capacity of apoptotic cells. Furthermore, adding HMGB1 to apoptotic Jurkat cells diminished phagocytosis of these cells.

CONCLUSION

Circulating monocytes from SLE patients display an M1-like phenotype compared with HCs, but in vitro differentiation abolishes this difference. HMGB1 skews differentiation of M2-like macrophages towards an M1-like phenotype and, subsequently, reduces phagocytosis of apoptotic cells. These data imply that the phenotype of monocytes or macrophages is determined by their environment, such as the presence of cytokines and HMGB1.

HMGB1, IL-1α, IL-33 and S100 proteins: dual-function alarmins

Our immune system is based on the close collaboration of the innate and adaptive immune systems for the rapid detection of any threats to the host. Recognition of pathogen-derived molecules is entrusted to specific germline-encoded signaling receptors. The same receptors have now also emerged as efficient detectors of misplaced or altered self-molecules that signal tissue damage and cell death following, for example, disruption of the blood supply and subsequent hypoxia. Many types of endogenous molecules have been shown to provoke such sterile inflammatory states when released from dying cells. However, a group of proteins referred to as alarmins have both intracellular and extracellular functions which have been the subject of intense research. Indeed, alarmins can either exert beneficial cell housekeeping functions, leading to tissue repair, or provoke deleterious uncontrolled inflammation. This group of proteins includes the high-mobility group box 1 protein (HMGB1), interleukin (IL)-1α, IL-33 and the Ca²⁺-binding S100 proteins. These dual-function proteins share conserved regulatory mechanisms, such as secretory routes, post-translational modifications and enzymatic processing, that govern their extracellular functions in time and space. Release of alarmins from mesenchymal cells is a highly relevant mechanism by which immune cells can be alerted of tissue damage, and alarmins play a key role in the development of acute or chronic inflammatory diseases and in cancer development.

Resolution of Inflammation: What Controls Its Onset?

An effective resolution program may be able to prevent the progression from non-resolving acute inflammation to persistent chronic inflammation. It has now become evident that coordinated resolution programs initiate shortly after inflammatory responses begin. In this context, several mechanisms provide the fine-tuning of inflammation and create a favorable environment for the resolution phase to take place and for homeostasis to return. In this review, we focus on the events required for an effective transition from the proinflammatory phase to the onset and establishment of resolution. We suggest that several mediators that promote the inflammatory phase of inflammation can simultaneously initiate a program for active resolution. Indeed, several events enact a decrease in the local chemokine concentration, a reduction which is essential to inhibit further infiltration of neutrophils into the tissue. Interestingly, although neutrophils are cells that characteristically participate in the active phase of inflammation, they also contribute to the onset of resolution. Further understanding of the molecular mechanisms that initiate resolution may be instrumental to develop pro-resolution strategies to treat complex chronic inflammatory diseases, in humans. The efforts to develop strategies based on resolution of inflammation have shaped a new area of pharmacology referred to as "resolution pharmacology."

Resolution of Inflammation: What Controls Its Onset?

An effective resolution program may be able to prevent the progression from non-resolving acute inflammation to persistent chronic inflammation. It has now become evident that coordinated resolution programs initiate shortly after inflammatory responses begin. In this context, several mechanisms provide the fine-tuning of inflammation and create a favorable environment for the resolution phase to take place and for homeostasis to return. In this review, we focus on the events required for an effective transition from the proinflammatory phase to the onset and establishment of resolution. We suggest that several mediators that promote the inflammatory phase of inflammation can simultaneously initiate a program for active resolution. Indeed, several events enact a decrease in the local chemokine concentration, a reduction which is essential to inhibit further infiltration of neutrophils into the tissue. Interestingly, although neutrophils are cells that characteristically participate in the active phase of inflammation, they also contribute to the onset of resolution. Further understanding of the molecular mechanisms that initiate resolution may be instrumental to develop pro-resolution strategies to treat complex chronic inflammatory diseases, in humans. The efforts to develop strategies based on resolution of inflammation have shaped a new area of pharmacology referred to as “resolution pharmacology.”

Clearance Deficiency and Cell Death Pathways: A Model for the Pathogenesis of SLE

Alterations of cell death pathways, including apoptosis and the neutrophil specific kind of death called NETosis, can represent a potential source of autoantigens. Defects in the clearance of apoptotic cells may be responsible for the initiation of systemic autoimmunity in several chronic inflammatory diseases, including systemic lupus erythematosus (SLE). Autoantigens are released mainly from secondary necrotic cells because of a defective clearance of apoptotic cells or an inefficient degradation of DNA-containing neutrophil extracellular traps (NETs). These modified autoantigens are presented by follicular dendritic cells to autoreactive B cells in germinal centers of secondary lymphoid organs. This results in the loss of self-tolerance and production of autoantibodies, a unifying feature of SLE. Immune complexes (IC) are formed from autoantibodies bound to uncleared cellular debris in blood or tissues. Clearance of IC by blood phagocytes, macrophages, and dendritic cells leads to proinflammatory cytokine secretion. In particular, plasmacytoid dendritic cells produce high amounts of interferon-α upon IC uptake, thereby contributing to the interferon signature of patients with SLE. The clearance of antinuclear IC via Fc-gamma receptors is considered a central event in amplifying inflammatory immune responses in SLE. Along with this, the accumulation of cell remnants represents an initiating event of the etiology, while the subsequent generation of autoantibodies against nuclear antigens (including NETs) results in the perpetuation of inflammation and tissue damage in patients with SLE. Here, we discuss the implications of defective clearance of apoptotic cells and NETs in the development of clinical manifestations in SLE.

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.

Lupus erythematosus revisited

Lupus erythematosus (LE) is a multifactorial autoimmune disease with clinical manifestations of differing severity. The exact pathomechanisms and interactions resulting in the inflammatory and immunological processes of this heterogeneous disease remain elusive. Approaches in the understanding of the pathomechanisms revealed that the clinical expression of LE is predisposed by susceptibility genes and that various environmental factors are responsible for an abnormal immune response. Several studies demonstrated that ultraviolet (UV) light is one of the major factors in the pathogenesis of the disease. Standardized photoprovocation in patients with LE has been shown to be a safe and efficient model for evaluating the underlying pathomechanisms which lead to the production of autoantibodies and immune complexes. In particular, interferons were defined as important players in the early activation of the immune system and were observed to play a specific role in the immunological interface between the innate and the adaptive immune system. Abnormalities or disturbances in the different processes of cell death, such as apoptosis or necrosis, have also been recognized as crucial in the pathogenesis of LE. Although each process is different and characterized by unique features, the processes are interrelated and result in a complex disease.

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.

Circulating HMGB1 and RAGE as Clinical Biomarkers in Malignant and Autoimmune Diseases

High molecular group box 1 (HMGB1) is a highly conserved member of the HMG-box-family; abundantly expressed in almost all human cells and released in apoptosis; necrosis or by activated immune cells. Once in the extracellular space, HMGB1 can act as a danger associated molecular pattern (DAMP), thus stimulating or inhibiting certain functions of the immune system; depending on the “combinatorial cocktail” of the surrounding milieu. HMGB1 exerts its various functions through binding to a multitude of membrane-bound receptors such as TLR-2; -4 and -9; IL-1 and RAGE (receptor for advanced glycation end products); partly complex-bound with intracellular fragments like nucleosomes. Soluble RAGE in the extracellular space, however, acts as a decoy receptor by binding to HMGB1 and inhibiting its effects. This review aims to outline today’s knowledge of structure, intra- and extracellular functions including mechanisms of release and finally the clinical relevance of HMGB1 and RAGE as clinical biomarkers in therapy monitoring, prediction and prognosis of malignant and autoimmune disease.

HMGB1 Promotes Systemic Lupus Erythematosus by Enhancing Macrophage Inflammatory Response

Background/Purpose. HMGB1, which may act as a proinflammatory mediator, has been proposed to contribute to the pathogenesis of multiple chronic inflammatory and autoimmune diseases including systemic lupus erythematosus (SLE); however, the precise mechanism of HMGB1 in the pathogenic process of SLE remains obscure. Method. The expression of HMGB1 was measured by ELISA and western blot. The ELISA was also applied to detect proinflammatory cytokines levels. Furthermore, nephritic pathology was evaluated by H&E staining of renal tissues. Results. In this study, we found that HMGB1 levels were significantly increased and correlated with SLE disease activity in both clinical patients and murine model. Furthermore, gain- and loss-of-function analysis showed that HMGB1 exacerbated the severity of SLE. Of note, the HMGB1 levels were found to be associated with the levels of proinflammatory cytokines such as TNF-α and IL-6 in SLE patients. Further study demonstrated that increased HMGB1 expression deteriorated the severity of SLE via enhancing macrophage inflammatory response. Moreover, we found that receptor of advanced glycation end products played a critical role in HMGB1-mediated macrophage inflammatory response. Conclusion. These findings suggested that HMGB1 might be a risk factor for SLE, and manipulation of HMGB1 signaling might provide a therapeutic strategy for SLE.

C1q-mediated repression of human monocytes is regulated by leukocyte-associated Ig-like receptor 1 (LAIR-1)

Systemic lupus erythematosus (SLE) is a chronic autoimmune disease characterized by abnormal function of both the innate and the adaptive immune system, leading to a loss of tolerance to self-antigens. Monocytes are a key component of the innate immune system and are efficient producers of multiple cytokines. In SLE, inappropriate activation of monocytes is thought to contribute to the loss of self-tolerance. In this study, we demonstrate that type 1 interferon (IFN) production by CpG-challenged monocytes can be suppressed by C1q through activating leukocyte-associated Ig-like receptor-1 (LAIR-1), which contains immunoreceptor tyrosine-based inhibition motifs (ITIMs). The phosphorylation of LAIR-1 and the interaction of LAIR-1 with SH2 domain-containing protein tyrosine phosphatase-1 (SHP-1) were enhanced after LAIR-1 engagement by C1q. Moreover, engagement of LAIR-1 by C1q inhibited nuclear translocation of interferon regulatory factor (IRF)-3 and IRF5 in CpG-stimulated monocytes. These data suggest a model in which LAIR-1 engagement by C1q helps maintain monocyte tolerance, specifically with respect to Toll-like receptor-9-mediated monocyte activation.

Heparin inhibits the inflammatory response induced by LPS and HMGB1 by blocking the binding of HMGB1 to the surface of macrophages

High mobility group box 1 protein (HMGB1), a nuclear non-histone DNA-binding protein, is secreted extracellularly during inflammation and is a late mediator of inflammatory responses. The pro-inflammatory activity of recombinant HMGB1 proteins is dependent upon the formation of complexes with other mediators, such as lipopolysaccharide (LPS). This study investigated the influence of heparin on LPS+HMGB1-mediated inflammatory responses in cultured macrophages and a murine sepsis model. HMGB1 promoted the phosphorylation of p38 and ERK1/2. HMGB1 enhanced the induction of the pro-inflammatory cytokine, TNF-α, by LPS in macrophages. Heparin blocked the binding of HMGB1 to the surface of macrophages, and suppressed the phosphorylation of p38 and ERK1/2, but not JNK; TNF-α secretion was also decreased. However, heparin alone did not affect LPS-induced production of TNF-α. Heparin reduced lethality in mice exposed to LPS+HMGB1. To conclude, heparin inhibited LPS-induced HMGB1-amplified inflammatory responses by blocking HMGB1 binding to macrophage surfaces. Heparin could be used therapeutically as an effective inhibitor of HMGB1-associated inflammation.