Lupus nephritis: the central role of nucleosomes revealed

Comparison of Clinical and Laboratory Characteristics in Lupus Nephritis vs. Non-Lupus Nephritis Patients-A Comprehensive Retrospective Analysis Based on 921 Patients

Background: Lupus nephritis (LN) is an inflammation of the kidneys that is related to systemic lupus erythematosus (SLE). This study aimed to evaluate the differences in clinical and laboratory characteristics between LN and non-LN SLE patients. Methods: We conducted a retrospective analysis of medical records collected from SLE patients treated at the University Hospital in Kraków, Poland, from 2012 to 2022. All patients met the 2019 European League Against Rheumatism and the American College of Rheumatology (EULAR/ACR) criteria for SLE. Results: Among 921 SLE patients, LN was documented in 331 (35.94%). LN patients were younger at SLE diagnosis (29 vs. 37 years; p < 0.001) and had a male proportion that was 2.09 times higher than the non-LN group (16.62% vs. 7.97%; p < 0.001). They were more often diagnosed with serositis and hematological or neurological involvement (p < 0.001 for all). Hypertension and hypercholesterolemia occurred more frequently in these patients (p < 0.001 for both). LN patients exhibited a higher frequency of anti-dsDNA, anti-histone, and anti-nucleosome antibodies (p < 0.001 for all). Conversely, the non-LN group had a 1.24-fold (95% CI: 1.03-1.50; p = 0.021) increase in the odds ratio of having positive anti-cardiolipin IgM antibody results. LN patients were more frequently treated with immunosuppressants. The risk factors for experiencing at least three LN flares included female sex, younger age at the onset of LN or SLE, LN occurring later than SLE onset, the presence of anti-nucleosome or anti-dsDNA antibodies, and certain SLE manifestations such as myalgia, arthritis, proteinuria > 3.5 g/day, and pathological urinary casts in the urine sediment. Conclusions: LN patients differ from non-LN patients in the age of SLE diagnosis, treatment modalities, and autoantibody profile and have more frequent, severe manifestations of SLE. However, we still need more prospective studies to understand the diversity of LN and its progression in SLE patients.

The role of mitochondrial damage-associated molecular patterns in acute pancreatitis

Acute pancreatitis (AP) is one of the most common gastrointestinal tract diseases with significant morbidity and mortality. Current treatments remain unspecific and supportive due to the severity and clinical course of AP, which can fluctuate rapidly and unpredictably. Mitochondria, cellular power plant to produce energy, are involved in a variety of physiological or pathological activities in human body. There is a growing evidence indicating that mitochondria damage-associated molecular patterns (mtDAMPs) play an important role in pathogenesis and progression of AP. With the pro-inflammatory properties, released mtDAMPs may damage pancreatic cells by binding with receptors, activating downstream molecules and releasing inflammatory factors. This review focuses on the possible interaction between AP and mtDAMPs, which include cytochrome c (Cyt c), mitochondrial transcription factor A (TFAM), mitochondrial DNA (mtDNA), cardiolipin (CL), adenosine triphosphate (ATP) and succinate, with focus on experimental research and potential therapeutic targets in clinical practice. Preventing or diminishing the release of mtDAMPs or targeting the mtDAMPs receptors might have a role in AP progression.

Deubiquitylating Enzymes in Cancer and Immunity

Deubiquitylating enzymes (DUBs) maintain relative homeostasis of the cellular ubiquitome by removing the post-translational modification ubiquitin moiety from substrates. Numerous DUBs have been demonstrated specificity for cleaving a certain type of ubiquitin linkage or positions within ubiquitin chains. Moreover, several DUBs perform functions through specific protein-protein interactions in a catalytically independent manner, which further expands the versatility and complexity of DUBs' functions. Dysregulation of DUBs disrupts the dynamic equilibrium of ubiquitome and causes various diseases, especially cancer and immune disorders. This review summarizes the Janus-faced roles of DUBs in cancer including proteasomal degradation, DNA repair, apoptosis, and tumor metastasis, as well as in immunity involving innate immune receptor signaling and inflammatory and autoimmune disorders. The prospects and challenges for the clinical development of DUB inhibitors are further discussed. The review provides a comprehensive understanding of the multi-faced roles of DUBs in cancer and immunity.

Impact of Corticosteroids on the Proportions of Circulating Tfh Cell Subsets in Patients With Systemic Lupus Erythematous

Objectives

This study aimed to analyze the distribution of T follicular helper (Tfh) cells in lupus patients, and the effects of steroids on circulating Tfh cells.

Methods

Circulating Tfh cell subsets were defined by multicolor flow cytometry as Tfh17, Tfh2 or Tfh1 subpopulations of CXCR5⁺CD45RA^–CD4⁺ T cells in the peripheral blood of SLE patients and healthy controls. To test the effects of corticosteroid on Tfh cells, PBMC harvested from both SLE and healthy controls were cocultured with dexamethasone, and then analyzed by Flow cytometry.

Results

The proportion of Tfh17 cells in SLE patients was increased significantly compared with healthy controls. Additionally, patients with an active disease had reduced Tfh1 subsets than those with an inactive disease and healthy controls. The frequency of Tfh2 cells was associated with the proportion of circulating plasmablasts and the amount of anti-dsDNA. Dexamethasone reduced the percentage of Tfh2 cells while increased the proportion of Tfh17 subset in gated CXCR5⁺CD45RA^–CD4⁺ T cells.

Conclusion

Our study investigated the distribution of circulating Tfh subsets in lupus patients. Corticosteroids treatment not only down-regulated the proportion of circulating Tfh cells, but also altered the distribution of Tfh subsets in vivo and in vitro.

Advances in cGAS-STING Signaling Pathway and Diseases

Pathogens can produce conserved pathogen-associated molecular patterns (PAMPs) after invading the body, which can be specifically recognized by host pattern recognition receptors (PRRs). In recent years, it has been found that cytoplasmic DNA receptors recognize exogenous DNA inducing activation of interferon 1 (IFN1), which is a rapid advance in various research areas. The cyclic GMP–AMP synthase (cGAS) stimulator of interferon gene (STING) signaling pathway is a critical natural immune pathway in cells. Early studies revealed that it plays a crucial regulatory role in pathogen infection and tumor, and it is associated with various human autoimmune diseases. Recently studies have found that activation of cGAS-STING signaling pathway is related to different organ injuries. The present review elaborates on the regulation of the cGAS-STING signaling pathway and its role in various diseases, aiming to provide a theoretical basis for immunotherapy targeting this pathway.

Positron emission tomography and single photon emission computed tomography imaging of tertiary lymphoid structures during the development of lupus nephritis

Lymphoid neogenesis occurs in tissues targeted by chronic inflammatory processes, such as infection and autoimmunity. In systemic lupus erythematosus (SLE), such structures develop within the kidneys of lupus-prone mice ((NZBXNZW)F1) and are observed in kidney biopsies taken from SLE patients with lupus nephritis (LN). The purpose of this prospective longitudinal animal study was to detect early kidney changes and tertiary lymphoid structures (TLS) using in vivo imaging. Positron emission tomography (PET) by tail vein injection of 18-F-fluoro-2-deoxy-D-glucose (¹⁸F-FDG)(PET/FDG) combined with computed tomography (CT) for anatomical localization and single photon emission computed tomography (SPECT) by intraperitoneal injection of ^99mTC labeled Albumin Nanocoll (^99mTC-Nanocoll) were performed on different disease stages of NZB/W mice (n = 40) and on aged matched control mice (BALB/c) (n = 20). By using one-way ANOVA analyses, we compared two different compartmental models for the quantitative measure of ¹⁸F-FDG uptake within the kidneys. Using a new five-compartment model, we observed that glomerular filtration of ^18FFDG in lupus-prone mice decreased significantly by disease progression measured by anti-dsDNA Ab production and before onset of proteinuria. We could not visualize TLS within the kidneys, but we were able to visualize pancreatic TLS using ^99mTC Nanocoll SPECT. Based on our findings, we conclude that the five-compartment model can be used to measure changes of FDG uptake within the kidney. However, new optimal PET/SPECT tracer administration sites together with more specific tracers in combination with magnetic resonance imaging (MRI) may make it possible to detect formation of TLS and LN before clinical manifestations.

Nucleosomal dsDNA Stimulates APOL1 Expression in Human Cultured Podocytes by Activating the cGAS/IFI16-STING Signaling Pathway

APOL1 alleles G1 and G2 are associated with faster progression to lupus nephritis (LN)-associated end-stage renal disease (LN-ESRD) in African Americans. Increased levels of type I interferons (IFNs) and nucleosome-associated double-stranded DNA (dsDNA) fragments (nsDNA) are the hallmark of this disease. Here, we identify cyclic GMP-AMP synthase (cGAS) and interferon-inducible protein 16 (IFI16) as the major DNA sensors in human immortalized podocytes. We also show that nsDNA triggers the expression of APOL1 and IFNβ via IRF3 activation through the cGAS/IFI16-STING pathway. We demonstrate that maximal APOL1 expression also requires the activation of type I IFN receptor (IFNAR) and STAT1 signaling triggered by IFNβ produced in response to nsDNA, or by exogenous IFNβ. Finally, we show that STAT1 activation is sufficient to upregulate IFI16, subsequently boosting APOL1 expression through a positive feedback mechanism. Collectively, we find that nsDNA-induced APOL1 expression is mediated by both IFNβ-independent and dependent signaling pathways triggered by activation of the cGAS/IFI16-STING pathway. We propose that simultaneous inhibition of STING and the IFNAR-STAT1 pathway may attenuate IFI16 expression, reduce IFI16-cGAS cross-talk, and prevent excessive APOL1 expression in human podocytes in response to nsDNA.

Long noncoding RNA (MEG3) in urinal exosomes functions as a biomarker for the diagnosis of Hunner-type interstitial cystitis (HIC)

BACKGROUND

Toll-like receptor-7 (TLR7) is functionally involved in the pathogenesis of Hunner-type interstitial cystitis (HIC). In addition, maternally expressed gene 3 (MEG3) is implicated in many urethral diseases. In this study, we aimed to verify the hypothesis that exosomal MEG3 in urine can be used as a novel diagnostic biomarker for HIC.

METHODS

Electron microscopy was utilized to observe the distribution of urinary exosomes between the case group and the control group. Receiver operating characteristic analysis was utilized to compare the diagnostic values of MEG3 and miR-19a-3p. Computational analysis and luciferase assay were conducted to identify the correlation between MEG3 and miR-19a-3p as well as between TLR7 and miR-19a-3p. In addition, real-time polymerase chain reaction and Western blot were performed to establish the signaling pathways implicated in the pathogenesis of HIC.

RESULTS

When age and gender distributions are excluded, urinary exosomes were equally distributed between case and control groups. The area under the curve of MEG3 was larger than that of miR-19a-3p, indicating that MEG3 has a better value in the diagnosis of HIC. In addition, patients with HIC showed elevated MEG3 expression and inhibited miR-19a-3p expression, thus establishing a negative correlation between MEG3 and miR-19a-3p. MEG3 and TLR7 were both identified as targets of miR-19a-3p, establishing a MEG3/miR-19a-3p/TLR7 signaling pathway, in which MEG3 enhances the expression of TLR7 via inhibiting the expression of miR-19a-3p.

CONCLUSION

MEG3 level was upregulated in patients with HIC. In addition, MEG3 downregulated miR-19a-3p expression while upregulating TLR7 expression. Furthermore, MEG3 contributes to the pathogenesis of HIC. Therefore, exosomal MEG3 in urine can be used as a biomarker for HIC diagnosis.

[Lupus nephritis]

Systemic lupus erythematosus is the most characteristic of auto-immune disorders that can lead to tissue damage in many organs, including kidney. Lupus nephritis occurs in 10 to 40% of lupus patients. Its clinical hallmark is the appearance of a proteinuria as soon as a 0.5 g/g or 0.5 g/d threshold, which calls for a renal histological evaluation in order to determine the lupus nephritis severity and the need for specific therapy. More than half of renal biopsies lead to the diagnosis of active lupus nephritis-class III or class IV A according to the ISN/RPS classification-that are the most severe in regards to renal prognosis and mortality. Their treatment aims to their clinical remission and to the prevention of relapse with minimal adverse effects for eventually the preservation of renal function, the prevention of other irreversible damage, and the reduction of risk of death. The remission is obtained through induction therapies of which the association of high dose steroids and cyclophosphamide is the most experienced. When this association must be challenged by the prevention of side-effect, in particular infertility, mycophenolate can be given instead of cyclophosphamide. Maintenance therapy, for the prevention of relapse, consists in mycophenolate or in azathioprine, mycophenolate being the most efficient however associated with a high risk of teratogenicity. Withdrawal of maintenance therapy is possible after two to three years in absence of high risk factors of relapse of lupus nephritis, however a reliable assessment of the risk of relapse is still lacking. Only pure membranous lupus nephritis (pure class V) associated with high level proteinuria requires specific therapies that usually associates steroids and an immunosuppressive drug. However, their choice hierarchy and even the use of less immunosuppressive strategies remain to be determined in terms of benefice over risk ratios. In spite of its trigger effect on lupus activity, pregnancy can be safe and successful if scheduled in the lowest risk periods with close multidisciplinary monitoring before, during and after. When necessary, renal replacement therapy does not require specific adaptation, renal transplantation is the best option when possible, as early as possible.

Bilateral Adrenal Hemorrhage in a Patient with Antiphospholipid Syndrome during Chronic Graft-versus-host Disease

We present the case of a 56-year-old man with an upper respiratory infection followed by fatigue, hypotension, and hyponatremia. Bilateral adrenal hemorrhage was confirmed, based on T2-weighted magnetic resonance imaging. The patient had previously undergone allogeneic hematopoietic stem cell transplantation and had been diagnosed with antiphospholipid syndrome (APS) during the development of chronic graft-versus-host disease. A prompt diagnosis and steroid replacement, in addition to anticoagulant therapy, resulted in a favorable outcome. Once the diagnosis of APS has been confirmed, which might be the sign of bilateral adrenal hemorrhage, the initial manifestations of adrenal insufficiency should never be overlooked.

Broad Susceptibility of Nucleolar Proteins and Autoantigens to Complement C1 Protease Degradation

Anti-nuclear autoantibodies, which frequently target the nucleoli, are pathogenic hallmarks of systemic lupus erythematosus (SLE). Although the causes of these Abs remain broad and ill-defined, a genetic deficiency in C1 complex (C1qC1r₂C1s₂) or C4 is able to induce these Abs. Considering a recent finding that, in dead cells, nucleoli were targeted by C1q and two nucleolar autoantigens were degraded by C1r/C1s proteases, we considered that C1 could help protect against antinuclear autoimmunity by broadly degrading nucleolar proteins or autoantigens. Nucleoli were isolated to homogeneity and structurally defined. After C1 treatment, cleaved nucleolar proteins were identified by proteomic two-dimensional fluorescence difference gel electrophoresis and mass spectrometry, and further verified by Western blotting using specific Abs. The extent of nucleolar autoantigen degradation upon C1 treatment was estimated using SLE patient autoantibodies. The isolated nucleoli were broadly reactive with SLE patient autoantibodies. These nucleoli lacked significant autoproteolysis, but many nucleolar proteins and autoantigens were degraded by C1 proteases; >20 nucleolar proteins were identified as C1 cleavable. These were further validated by Western blotting using specific Abs. The broad autoantigenicity of the nucleoli may attribute to their poor autoproteolysis, causing autologous immune stimulation upon necrotic exposure. However, C1q targets at these nucleoli to cause C1 protease activation and the cleavage of many nucleolar proteins or autoantigens. This may represent one important surveillance mechanism against antinuclear autoimmunity because C1 genetic deficiency causes anti-nuclear autoantibodies and SLE disease.

The impact of biological treatments on the anti-dsDNA and anti-nucleosome tests

Background Anti-double stranded DNA antibodies are a very heterogeneous group of antibodies, quite specific for systemic lupus erythematosus. Newer technologies, such as addressable laser bead immunoassays (ALBIA), show great potential as a diagnostic application. The production of anti-double stranded DNA antibodies is often encountered in inflammatory arthritis; however, literature reports that the actual onset of drug induced lupus in patients treated with biological drugs is a rare event. False positive results for anti-double stranded DNA and anti-nucleosome antibodies detected in patients with inflammatory arthritis treated with different biologics prompted the investigation of full autoantibody profiles to evaluate each biomarker's diagnostic performance in systemic lupus erythematosus. The aim of the study was to compare the diagnostic performance of anti-double stranded DNA antibody and anti-nucleosome antibody methods and to evaluate the value of simultaneously measuring anti-double stranded DNA and anti-nucleosome antibodies, along with other anti-nuclear antibody analytes, as biomarkers for systemic lupus erythematosus, using a more appropriate control cohort including inflammatory arthritis patients with a non-clinical drug induced lupus. Methods Anti-double stranded DNA and anti-nucleosome antibody levels were evaluated in 247 patient samples: 70 systemic lupus erythematosus, 177 disease controls (including 97 inflammatory arthritis during treatment with different biologics) using the Bio-Rad BioPlex® 2200. Results Anti-nucleosome antibodies demonstrated greater clinical sensitivity and specificity than anti-double stranded DNA antibodies. At the manufacturers' cut-off range, considering the two markers as a single or combined test, the "anti-double stranded DNA test or anti-nucleosome antibodies" was the most sensitive combination (0.400) with the best negative likelihood ratio (0.62) and negative predictive value (0.803). Conclusion Anti-nucleosome antibodies are a more sensitive and specific biomarker of systemic lupus erythematosus than anti-double stranded DNA antibodies. Anti-nucleosome antibodies and anti-double stranded DNA antibodies are independent and complementary markers of systemic lupus erythematosus diagnosis and, therefore, are strongly suggested as combined tests (positive predictive value = 0.938). Moreover, the combined use of the two tests may help to overcome the decreased specificity percentage of the anti-double stranded DNA test, when considering an inflammatory arthritis cohort under biological therapies. The ALBIA method for anti-nuclear specificity detection allows a full autoantibody assessment, resulting in a much higher clinical specificity for systemic lupus erythematosus in the presence of ≥3 positive markers and significantly more positive likelihood ratio when ≥2 positive markers are present.

Molecular and Immunological Basis of Tubulo-Interstitial Injury in Lupus Nephritis: a Comprehensive Review

Lupus nephritis is an important cause of kidney failure in patients of Asian, African, or Hispanic descent. Its etiology and pathogenesis are multifactorial and remain to be elucidated. Accumulating evidence suggests that anti-double-stranded DNA (dsDNA) antibodies play a critical role in the pathogenesis, through its direct binding to cross-reactive antigens on resident renal cells or indirect binding through chromatin material to extracellular matrix components, resulting in complement activation, cell activation and proliferation, and induction of inflammatory and fibrotic processes. While tubulo-interstitial damage portends poor long-term renal prognosis, the mechanisms leading to tubulo-interstitial injury in lupus nephritis has received relatively less attention to date. Immune deposition along the tubular basement membrane is often observed in lupus nephritis and correlates with tubulo-interstitial infiltration of immune cells and interstitial fibrosis. Anti-dsDNA antibodies bind to resident renal cells, including proximal renal tubular epithelial cells, and contribute to renal inflammation and fibrosis. There is emerging evidence that epigenetic influence such as DNA methylation, histone modification, and microRNAs (miRs) also contribute to kidney fibrosis. Overexpression of miR-150 is observed in renal biopsies from patients with lupus nephritis and correlates with kidney fibrosis and chronicity score. Mycophenolate mofetil (MMF) is an established and effective standard-of-care therapy for patients with lupus nephritis. Accumulating data suggest that in addition to its immunosuppressive actions on lymphocyte proliferation, mycophenolic acid (MPA), the active metabolite of MMF, can exert a direct effect on nonimmune cells. Mediators of inflammation and fibrosis induced by anti-dsDNA antibodies in cultured proximal renal tubular epithelial cells are ameliorated by the addition of MPA, suggesting that in addition to its immunosuppressive actions, MPA may also have a beneficial effect in improving tubulo-interstitial inflammation and fibrosis through its direct action on proximal renal tubular epithelial cells.

Urinary Albumin Levels are Independently Associated with Renal Lesion Severity in Patients with Lupus Nephritis and Little or No Proteinuria

Background

Systemic lupus erythematosus (SLE) leads to renal lesions, which may be clinically silent in patients with little or no proteinuria. Early detection of these lesions may improve prognosis, but early markers are controversial. This study aimed to determine renal marker proteins associated with renal lesion severity in patients with lupus nephropathy (LN) and little or no proteinuria.

Material/Methods

Patients with LN and little or no proteinuria (<0.5 g/24 hours) (n=187) that underwent kidney biopsy were grouped according to: low severity (Class I or II; n=116) versus high severity (Class III, IV, or V; n=71). Disease status was determined according to the SLE disease activity index (SLEDAI). Renal marker proteins (serum β2-macroglobulin, urinary β2-macroglobulin, albumin, IgG, and α1-macroglobulin) were measured using radioimmunoassay.

Results

Compared with the low severity group, patients in the high severity group had higher urinary albumin (11.60±8.94 versus 7.08±10.07 μg/mL, p=0.008) and urinary IgG (13.21±9.35 versus 8.74±8.90 μg/mL, p=0.007) levels. Multivariate conditional logistic regression analysis showed that urinary albumin (odds ratio (OR)=1.417, 95% confidence interval (95% CI): 1.145–1.895, p=0.001) and SLEDAI (OR=2.004, 95% CI: 1.264–3.178, p=0.003) were independently associated with severe renal lesions in these patients. Using an optimal cutoff point of urinary albumin of 7.53 μg/mL resulted in 67% sensitivity and 82% specificity for the detection of high severity renal lesions.

Conclusions

Urinary albumin levels and SLEDAI were independently associated with histological severity of renal lesions in patients with LN and little or no proteinuria. These parameters could be used to help select patients for renal biopsy.

Novel biomarkers for the assessment of paediatric systemic lupus erythematosus nephritis

The discovery of serum biomarkers specific for paediatric lupus nephritis (pLN) will facilitate the non-invasive diagnosis, follow-up and more appropriate use of treatment. The aim of this study was to explore the role of serum high-mobility group box 1 (HMGB1) protein, antibodies against nucleosomes (anti-NCS), complement factor C1q (anti-C1q) and glomerular basement membrane (anti-GBM) in pLN. Serum samples of 42 patients with paediatric systemic lupus erythematosus (pSLE) (22 with pLN and 20 without renal involvement), 15 patients with other autoimmune nephritis (AN) and 26 healthy controls (HCs) were examined using enzyme-linked immunosorbent assay (ELISA). The activity of both pSLE and pLN was assessed by the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI) tool. The levels of all four biomarkers were significantly higher in pLN compared to AN and to HCs. The anti-NCS, anti-GBM and HMGB1 serum levels were significantly higher in pLN than in pSLE without renal involvement. The anti-C1q and the HMGB1 serum levels were correlated positively with pSLE activity. The HMGB1 serum levels were also correlated positively with pLN activity. These findings suggest that serum anti-NCS, anti-GBM and HMGB1 may serve as biomarkers specific for the presence of nephritis in pSLE. HMGB1 emerged as a useful biomarker for the assessment of pLN and pSLE activity, whereas anti-C1q only of pSLE activity.

TNFα Amplifies DNaseI Expression in Renal Tubular Cells while IL-1β Promotes Nuclear DNaseI Translocation in an Endonuclease-Inactive Form

We have demonstrated that the renal endonuclease DNaseI is up-regulated in mesangial nephritis while down-regulated during progression of the disease. To determine the basis for these reciprocal DNaseI expression profiles we analyse processes accounting for an early increase in renal DNaseI expression. Main hypotheses were that i. the mesangial inflammation and secreted pro-inflammatory cytokines directly increase DNaseI protein expression in tubular cells, ii. the anti-apoptotic protein tumor necrosis factor receptor-associated protein 1 (Trap 1) is down-regulated by increased expression of DNaseI due to transcriptional interference, and iii. pro-inflammatory cytokines promote nuclear translocation of a variant of DNaseI. The latter hypothesis emerges from the fact that anti-DNaseI antibodies stained tubular cell nuclei in murine and human lupus nephritis. The present study was performed on human tubular epithelial cells stimulated with pro-inflammatory cytokines. Expression of the DNaseI and Trap 1 genes was determined by qPCR, confocal microscopy, gel zymography, western blot and by immune electron microscopy. Results from in vitro cell culture experiments were analysed for biological relevance in kidneys from (NZBxNZW)F1 mice and human patients with lupus nephritis. Central data indicate that stimulating the tubular cells with TNFα promoted increased DNaseI and reduced Trap 1 expression, while TNFα and IL-1β stimulation induced nuclear translocation of the DNaseI. TNFα-stimulation resulted in 3 distinct effects; increased DNaseI and IL-1β gene expression, and nuclear translocation of DNaseI. IL-1β-stimulation solely induced nuclear DNaseI translocation. Tubular cells stimulated with TNFα and simultaneously transfected with IL-1β siRNA resulted in increased DNaseI expression but no nuclear translocation. This demonstrates that IL-1β promotes nuclear translocation of a cytoplasmic variant of DNaseI since translocation clearly was not dependent on DNaseI gene activation. Nuclear translocated DNaseI is shown to be enzymatically inactive, which may point at a new, yet unknown function of renal DNaseI.

The Role of Damage-Associated Molecular Patterns in Human Diseases: Part I - Promoting inflammation and immunity

There is increasing interest by physicians in the impact of the innate immune system on human diseases. In particular, the role of the molecules that initiate and amplify innate immune pathways, namely damage-associated molecular patterns (DAMPs), is of interest as these molecules are involved in the pathogenesis of many human disorders. The first part of this review identifies five classes of cell stress/tissue injury-induced DAMPs that are sensed by various recognition receptor-bearing cells of the innate immune system, thereby mounting inflammation, promoting apoptosis and shaping adaptive immune responses. The DAMPs activate and orchestrate several innate immune machineries, including inflammasomes and the unfolded protein response that synergistically operates to induce inflammatory, metabolic and adaptive immune pathologies. Two examples of autoimmune diseases are discussed as they represent a typical paradigm of the intimate interplay between innate and adaptive immune responses.

The histidine transporter SLC15A4 coordinates mTOR-dependent inflammatory responses and pathogenic antibody production

SLC15A4 is a lysosome-resident, proton-coupled amino-acid transporter that moves histidine and oligopeptides from inside the lysosome to the cytosol of eukaryotic cells. SLC15A4 is required for Toll-like receptor 7 (TLR7)- and TLR9-mediated type I interferon (IFN-I) productions in plasmacytoid dendritic cells (pDCs) and is involved in the pathogenesis of certain diseases including lupus-like autoimmunity. How SLC15A4 contributes to diseases is largely unknown. Here we have shown that B cell SLC15A4 was crucial for TLR7-triggered IFN-I and autoantibody productions in a mouse lupus model. SLC15A4 loss disturbed the endolysosomal pH regulation and probably the v-ATPase integrity, and these changes were associated with disruption of the mTOR pathway, leading to failure of the IFN regulatory factor 7 (IRF7)-IFN-I regulatory circuit. Importantly, SLC15A4's transporter activity was necessary for the TLR-triggered cytokine production. Our findings revealed that SLC15A4-mediated optimization of the endolysosomal state is integral to a TLR7-triggered, mTOR-dependent IRF7-IFN-I circuit that leads to autoantibody production.

XRCC1 Arg399Gln and Arg194Trp polymorphisms and risk of systemic lupus erythematosus in an Iranian population: a pilot study

Background. Evidences are suggesting that DNA damage is implicated in development of systemic lupus erythematosus (SLE). Therefore we focused on two common XRCC1 polymorphisms (Arg399Gln and Arg194Trp) in SLE susceptibility in South East of Iran. Methods. Peripheral blood DNA was extracted from 163 SLE patients and 180 healthy controls. PCR-restriction fragment length polymorphism method was used for genotyping of XRCC1 Arg399Gln and Arg194Trp polymorphisms. Results. The frequency of Arg/Gln genotype of the XRCC1 Arg399Gln polymorphism was significantly lower in SLE patients than controls. Moreover, lower frequency of Arg/Gln genotype was found in SLE patients with malar rash compared to patients without this manifestation. No association was observed between XRCC1 Arg194Trp polymorphism and increased risk of SLE in studied population. Haplotype analysis revealed no correlation between four haplotypes of XRCC1 Arg399Gln and Arg194Trp polymorphisms and SLE risk. Conclusion. These findings suggest that XRCC1 399 Arg/Gln heterozygous genotype plays a protective role in SLE susceptibility.

The pathogenesis and diagnosis of systemic lupus erythematosus: still not resolved

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease with various clinical manifestations affecting different tissues. A characteristic feature of SLE is the presence of autoantibodies against double-stranded (ds)DNA, histones and nucleosomes, and other chromatin components. SLE is a prototype type III hypersensitivity reaction. Local deposition of anti-nuclear antibodies in complex with released chromatin induces serious inflammatory conditions by activation of the complement system. The severe renal manifestation, lupus nephritis, is classified based on histological findings in renal biopsies. Apoptotic debris, including chromatin, is present in the extracellular matrix and circulation of patients with SLE. This may be due to an aberrant process of apoptosis and/or insufficient clearance of apoptotic cells/chromatin. The non-cleared apoptotic debris may lead to activation of both the innate and adaptive immune systems. In addition, an aberrant presentation of peptides by antigen-presenting cells, disturbed selection processes for lymphocytes, and deregulated lymphocyte responses may be involved in the development of autoimmunity. In the present review, we briefly will summarize current knowledge on the pathogenesis of SLE. We will also critically discuss and challenge central issues that need to be addressed in order to fully understand the pathogenic mechanisms involved in the development of SLE and in order to have an improved diagnosis for SLE. Disappointingly, in our opinion, there are still more questions than answers for the pathogenesis, diagnosis, and treatment of SLE.

Extracellular histones in tissue injury and inflammation

Neutrophil NETosis is an important element of host defense as it catapults chromatin out of the cell to trap bacteria, which then are killed, e.g., by the chromatin's histone component. Also, during sterile inflammation TNF-alpha and other mediators trigger NETosis, which elicits cytotoxic effects on host cells. The same mechanism should apply to other forms of regulated necrosis including pyroptosis, necroptosis, ferroptosis, and cyclophilin D-mediated regulated necrosis. Beyond these toxic effects, extracellular histones also trigger thrombus formation and innate immunity by activating Toll-like receptors and the NLRP3 inflammasome. Thereby, extracellular histones contribute to the microvascular complications of sepsis, major trauma, small vessel vasculitis as well as acute liver, kidney, brain, and lung injury. Finally, histones prevent the degradation of extracellular DNA, which promotes autoimmunization, anti-nuclear antibody formation, and autoimmunity in susceptible individuals. Here, we review the current evidence on the pathogenic role of extracellular histones in disease and discuss how to target extracellular histones to improve disease outcomes.

The spectrum of anti-chromatin/nucleosome autoantibodies: independent and interdependent biomarkers of disease

Autoantibodies directed to chromatin components date back to the discovery of the LE cell and the LE cell phenomenon circa 1950, and subsequent evidence that major components of that reaction were chromatin components and histones in particular. Over time, immunoassays ranging from ELISA and line immunoassays to more modern bead-based assays incorporated histone and DNA mixtures, purified histones, and purified nucleosomes leading to a more thorough understanding of the genesis and pathogenetic relationships of antibodies to chromatin components in systemic lupus erythematosus and other autoimmune conditions. More recently, interest has focussed on other components of chromatin such as high mobility group (HMG) proteins both as targets of B cell responses and pro-inflammatory mediators. This review will focus on immunoassays that utilize chromatin components, their clinical relationships, and newer evidence implicating HMG proteins and DNA neutrophil extracellular traps (NETs) as important players in systemic autoimmune rheumatic diseases.

Clinical phenotype associations with various types of anti-dsDNA antibodies in patients with recent onset of rheumatic symptoms. Results from a multicentre observational study

Despite anti-dsDNA antibodies constitute a wide range of specificities, they are considered as the hallmark for systemic lupus erythematosus (SLE).

The pro-inflammatory potential of T cells in juvenile-onset systemic lupus erythematosus

BACKGROUND

T cells are important to systemic lupus erythematosus (SLE) disease progression. This study determined the pro-inflammatory potential of T cells within the rare condition juvenile-onset SLE (JSLE).

METHOD

IL-17A and Th1/Th2-related cytokine concentrations were measured in plasma/serum from JSLE patients (n = 19, n = 11) and HC (n = 18, n = 7). IL17A, RORC, IL23 and IL23R mRNA were measured in peripheral blood mononuclear cells (PBMCs) from JSLE and healthy controls (HC) (n = 12). Th17-associated cytokine expression was analysed in the supernatant of CD3/CD28 activated JSLE (n = 7) and HC (n = 6) PBMCs.

RESULTS

JSLE plasma IL-17A level (21.5 ± 5.2 pg/ml) was higher compared to HC (7.2 ± 2.5 pg/ml, p = 0.028). No differences were found in Th1/Th2 cytokines levels. IL = 17A (p = 0.022), IL-6 (p = 0.028) and IL-21 (p = 0.003) concentrations were increased in supernatants from activated JSLE PBMCs. IL-17 F (p = 0.50) and IL-22 (p = 0.43) were also increased but were not statistically significant. IL17A and IL23 mRNA was significantly higher in JSLE PBMCs (p = 0.018 and p = 0.01).

CONCLUSION

JSLE T cells have an increased ability to secrete Th17 associated cytokines once activated, which could contribute to the pro-inflammatory disease phenotype seen in these patients.

Association between XRCC3 Thr241Met SNP and systemic lupus erythematosus in Han Chinese patients in Taiwan, and a meta-analysis of healthy populations

BACKGROUND

X-ray repair cross-complementing group 3 (XRCC3) plays a crucial role in mammalian DNA repair processes. The polymorphism of XRCC3, rs861539 (Thr > Met at codon 241), is common in populations worldwide. This study analyzed the relationship between this functional single nucleotide polymorphism and systemic lupus erythematosus (SLE) in the Han Chinese population in Taiwan (HC-TW).

METHODS

Genotyping was performed using polymerase chain reaction restriction fragment length polymorphism on 163 SLE patients and 191 healthy participants in the control group.

RESULTS

The data showed that the genotype frequency at codon 241 did not differ significantly between the SLE patients and the healthy participants in the control group; however, the allele frequency analysis indicated a significant difference between these groups. In addition, we used the genotype and allele frequencies of 191 healthy HC-TW participants for comparison with HapMap populations. The results indicated a significant difference of XRCC3 Thr241Met allele and genotype frequencies between the HC-TW population and HapMap populations, except for the other Han Chinese populations. A prior study showed that Thr241 > Met substitution in XRCC3 protein was positive as damaging and functional consequences as well.

CONCLUSION

This is the first study to demonstrate the difference of XRCC3 Thr241 > Met variant between the HC-TW population and HapMap population.

Delivering Oxidation Resistance-1 (OXR1) to Mouse Kidney by Genetic Modified Mesenchymal Stem Cells Exhibited Enhanced Protection against Nephrotoxic Serum Induced Renal Injury and Lupus Nephritis

OBJECTIVE

To elucidate the role of oxidation resistance 1 (OXR1) gene. Oxidative stress plays a pivotal role in pathogenesis of immune-mediated nephritis. Recently we identified oxidation resistance 1 (OXR1) is conventionally expressed in eukaryotes and has an ability to prevent oxidative damage caused by various oxidative stresses. However the protective effect of OXR1 in immune-associated inflammatory response and oxidative damage is not clear and will be investigated in this study.

METHODS

We utilized mesenchymal stem cells (MSCs) as vehicles to carry OXR1 into the injured kidneys of nephritis model mice and investigated the influence of OXR1 on glomerulonephritis. Human OXR1 gene was integrated into genome of MSCs via lentiviral vector, and established hOXR1-MSC cell line which still maintains the differentiation property. 129/svj mice with anti-glomerular basement membrane (GBM) challenge and spontaneous lupus mice B6.Sle1.Sle2.Sle3 were injected with hOXR1-MSCs (i.v. injection) to evaluate the function of hOXR1. Immunohistochemistry was used to appraise the renal pathology and Tunel staining was applied to detect cell apoptosis.

RESULTS

Compared with control mice, hOXR1-MSCs administration showed significantly decreased blood urea nitrogen (BUN), proteinuria and ameliorated renal pathological damage. hOXR1-MSCs transplantation significantly reduced macrophage and T lymphocyte infiltration by inhibiting the expression of CCL2, CCL7, IL-1β, IL-6 and NFκB in mouse kidney. Moreover, hOXR1-MSCs prevented hydrogen peroxide (H₂O₂)-induced oxidative stress and its implantation reduced nitric oxide (NO) in mouse serum and urine to inhibit tubular cell apoptosis.

CONCLUSION

OXR1-MSCs transplantation may exert a certain protective effect on nephritis by suppressing inflammation and oxidative stress.

Human polyomaviruses in disease and cancer

Today the human polyomavirus (HPyV) family consists of 10 members, BK virus (BKV) and JC virus (JCV) isolated 40 years ago and the more recently identified KI virus (KIPyV), WU virus (WUPyV), Merkel cell polyomavirus (MCPyV), HPyV6, HPyV7, trichodysplasia spinulosa virus (TSPyV), HPyV9 and MWPyV. Serological studies suggest that HPyVs subclinically infect the general population with rates ranging from 35% to 90%. However, significant disease is only observed in patients with impaired immune functions. Thus, BKV has been linked to hemorrhagic cystitis (HC) after allogeneic hematopoietic stem cell transplantation and PyV-associated nephropathy (PyVAN) after kidney transplantation; JCV to progressive multifocal leukoencephalopathy (PML) in HIV-AIDS, hematological diseases and in autoimmune diseases treated with certain lymphocyte-specific antibodies. KIPyV and WUPyV have been found in the respiratory tract, HPyV6 and 7 in the skin, and HPyV9 in serum and skin, and MWPyV in stools and skin, but so far none of these PyVs have been linked to any disease. TSPyV, on the other hand, was identified in trichodysplasia spinulosa, a rare skin disease characterized by virus-induced lytic as well as proliferative tumor-like features that is observed in immune-suppressed transplant patients. In contrast to all the other HPyVs so far, MCPyV is unique in its association with a cancer, Merkel cell carcinoma, which is a rare skin cancer arising in the elderly and chronically immunosuppressed individuals. The discovery of the new HPyVs has revived interest in the Polyomaviridae and their association to human disease and cancer. In this review, we summarize knowledge about this expanding family of human pathogens.

Curcumin attenuates lupus nephritis upon interaction with regulatory T cells in New Zealand Black/White mice

Curcumin has been used in Asian traditional medicine for its medicinal properties. Recent studies have demonstrated that curcumin has antioxidant, anti-tumour and anti-inflammatory activities. The aim of the present study is to investigate the effects of curcumin on established lupus nephritis (LN) in New Zealand Black/White (NZB/W) F1 female mice, in particular, its interaction with regulatory T (Treg) cells. Starting at 18 weeks of age, mice were fed a standard diet or a diet containing 1 % curcumin until the end of the study. The proteinuria level and the serum levels of IgG1, IgG2a and anti-double-stranded DNA (dsDNA) IgG antibodies were measured. Additionally, IgG immune complex deposition in the glomeruli and renal inflammation were compared between curcumin-treated mice and control mice. Curcumin decreased the proteinuria level and serum levels of IgG1, IgG2a and anti-dsDNA IgG antibodies in NZB/W F1 female mice. IgG immune complex deposition in the glomeruli was reduced in curcumin-treated mice. Furthermore, renal inflammation was also decreased after curcumin treatment. Interestingly, these therapeutic effects of curcumin disappeared after Treg depletion by anti-CD25 antibody injection. Curcumin exerted a protective effect against LN in NZB/W F1 mice. We speculate that the protective effects of curcumin in LN may involve, at least in part, its interaction with Treg cells.

Role of Structure-Based Changes due to Somatic Mutation in Highly Homologous DNA-Binding and DNA-Hydrolyzing Autoantibodies Exemplified by A23P Substitution in the VH Domain

Anti-DNA autoantibodies are responsible for tissue injury in lupus. A subset of DNA-specific antibodies capable of DNA cleavage can be even more harmful after entering the living cells by destroying nuclear DNA. Origins of anti-DNA autoantibodies are not fully understood, and the mechanism of induction of DNA-cleaving activity remains speculative. The autoantibody BV04-01 derived from lupus-prone mouse is the only DNA-hydrolyzing immunoglobulin with known 3D structure. Identification and analysis of antibodies homologous to BV04-01 may help to understand molecular bases and origins of DNA-cleaving activity of autoantibodies. BLAST search identified murine anti-DNA autoantibody MRL-4 with sequences of variable region genes highly homologous to those of autoantibody BV04-01. Despite significant homology to BV04-01, not only MRL-4 had no DNA-cleaving activity, but also reversion of its unusual P23 mutation to the germline alanine resulted in a dramatic loss of affinity to DNA. Contrary to this effect, transfer of the P23 mutation to the BV04-01 has resulted in a significant drop in DNA binding and almost complete loss of catalytic activity. In the present paper we analyzed the properties of two homologous autoantibodies and mutants thereof and discussed the implications of unusual somatic mutations for the development of autoantibodies with DNA-binding and DNA-hydrolyzing activity.

Heparin exerts a dual effect on murine lupus nephritis by enhancing enzymatic chromatin degradation and preventing chromatin binding in glomerular membranes

OBJECTIVE

Association of nucleosome-IgG immune complexes with glomerular basement membranes (GBMs) is an important event in the development of lupus nephritis. Preventing this binding and/or increasing nuclease sensitivity of nucleosomes may be viable strategies for the prevention of the disease. Theoretically, heparin may alter nucleosomal structure and increase sensitivity to proteinases and nucleases, and may also inhibit binding of nucleosomes and nucleosome-IgG complexes to basement membrane structures. The aim of this study was to investigate whether and eventually how heparin prevents murine lupus nephritis.

METHODS

Surface plasmon resonance was used to analyze if heparin inhibits binding of nucleosomes to laminin and collagen. The effect of heparin on nuclease- and proteinase-mediated degradation of nucleosomes was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and agarose gel electrophoresis. In vitro results were compared with analyses in vivo in heparin-treated (NZB × NZW)F(1) mice. Anti-double-stranded DNA antibody production, deposition of nucleosome-IgG complexes in GBMs, and development of proteinuria were monitored, and circulating chromatin fragments were quantified using quantitative polymerase chain reaction.

RESULTS

In vitro studies demonstrated that heparin increased enzymatic degradation of nucleosomes and almost completely inhibited binding of nucleosomes to laminin and collagen. (NZB × NZW)F(1) mice treated with heparin demonstrated delayed or no antibody production and higher variation of circulating chromatin levels compared with untreated control mice. This effect was accompanied by highly reduced nucleosome-IgG complexes in GBMs and delayed development of nephritis.

CONCLUSION

Increasing the degradation of nucleosomes, reducing their immunogenicity, and preventing binding of nucleosome-IgG complexes in glomeruli together provide an alternative basis for the treatment of lupus nephritis.

Dangers within: DAMP responses to damage and cell death in kidney disease

The response to exogenous pathogens leads to activation of innate immunity through the release of pathogen-associated molecular patterns (PAMPs) and their binding to pattern recognition receptors. A classic example is septic shock where Toll receptor 4 recognizes PAMPs. Although well accepted, this concept does not explain the activation of innate immunity and inflammation occurs with transplantation, autoimmunity, or trauma. Increasingly recognized is that endogenous molecules released by dying cells (damage-associated molecular patterns; DAMPs) activate cellular receptors leading to downstream inflammation. Thus endogenous danger signals and exogenous PAMPs elicit similar responses through seemingly similar mechanisms. Also emerging is our understanding that normal repair processes benefit from dampening the immune response to these endogenous danger molecules. Here we focus on the role of DAMPs and their putative receptors in the pathogenesis of acute and chronic kidney diseases.

Development of self-reactive germinal center B cells and plasma cells in autoimmune Fc gammaRIIB-deficient mice

The leukemogenic effects of Myc drive recurrent trisomy in a mouse model of acute myeloid leukemia.

Abnormalities in expression levels of the IgG inhibitory Fc gamma receptor IIB (FcγRIIB) are associated with the development of immunoglobulin (Ig) G serum autoantibodies and systemic autoimmunity in mice and humans. We used Ig gene cloning from single isolated B cells to examine the checkpoints that regulate development of autoreactive germinal center (GC) B cells and plasma cells in FcγRIIB-deficient mice. We found that loss of FcγRIIB was associated with an increase in poly- and autoreactive IgG⁺ GC B cells, including hallmark anti-nuclear antibody–expressing cells that possess characteristic Ig gene features and cells producing kidney-reactive autoantibodies. In the absence of FcγRIIB, autoreactive B cells actively participated in GC reactions and somatic mutations contributed to the generation of highly autoreactive IgG antibodies. In contrast, the frequency of autoreactive IgG⁺ B cells was much lower in spleen and bone marrow plasma cells, suggesting the existence of an FcγRIIB-independent checkpoint for autoreactivity between the GC and the plasma cell compartment.

Simultaneous detection of anti-C1q and anti-double stranded DNA autoantibodies in lupus nephritis: predictive value for renal flares

Clinical difficulties in predicting systemic lupus erythematosus (SLE) renal flares are still encountered. Biological markers such as autoantibodies (aAbs) may be of major interest for clinicians in the follow-up of SLE patients. The aim of our study was to investigate the clinical utility of one of these biological markers, anti-C1q aAbs, in predicting renal flares of SLE nephritis in comparison with the 'gold standard' anti-double stranded DNA (anti-dsDNA) aAbs. Anti-C1q aAbs and anti-dsDNA aAbs were analysed through a longitudinal retrospective study of 23 SLE patients presenting with one or more renal flares. Anti-C1q and/or anti-dsDNA aAbs were found in 20 (87%) of 23 patients, of whom 16 (69%) displayed both. Thirty-three renal flares occurred during the course of the study, and anti-C1q aAbs and anti-dsDNA aAbs were positive in 25 (76%) and 24 (73%) of these flares respectively. The sensitivity of anti-C1q and/or anti-dsDNA aAbs in predicting renal flares reached 85%. The specificity of anti-C1q aAbs was 84%, of anti-dsDNA aAbs 77% and of both aAbs 97%. Positive and negative predictive values were as follows: 56% and 70% for anti-C1q aAbs, 53% and 72% for anti-dsDNA aAbs. The combination of both aAbs had the highest positive predictive value (69%), whereas absence of both aAbs was associated with the highest negative predictive value (74%). In conclusion, our results confirm that anti-C1q aAbs are present in a significant percentage of SLE patients with active renal involvement, suggesting that these aAbs could be a useful additional marker. The presence of anti-C1q and anti-dsDNA aAbs was associated with a high risk of renal flare, whereas the absence of both aAbs excluded such an event. These data confirm that systematic detection of anti-C1q and anti-dsDNA aAbs is of interest for the follow-up in SLE patients with renal involvement.

Renal Dnase1 enzyme activity and protein expression is selectively shut down in murine and human membranoproliferative lupus nephritis

Background

Deposition of chromatin-IgG complexes within glomerular membranes is a key event in the pathogenesis of lupus nephritis. We recently reported an acquired loss of renal Dnase1 expression linked to transformation from mild to severe membranoproliferative lupus nephritis in (NZBxNZW)F1 mice. As this may represent a basic mechanism in the progression of lupus nephritis, several aspects of Dnase1 expression in lupus nephritis were analyzed.

Methodology/Principal Findings

Total nuclease activity and Dnase1 expression and activity was evaluated using in situ and in vitro analyses of kidneys and sera from (NZBxNZW)F1 mice of different ages, and from age-matched healthy controls. Immunofluorescence staining for Dnase1 was performed on kidney biopsies from (NZBxNZW)F1 mice as well as from human SLE patients and controls. Reduced serum Dnase1 activity was observed in both mesangial and end-stage lupus nephritis. A selective reduction in renal Dnase1 activity was seen in mice with massive deposition of chromatin-containing immune complexes in glomerular capillary walls. Mice with mild mesangial nephritis showed normal renal Dnase1 activity. Similar differences were seen when comparing human kidneys with severe and mild lupus nephritis. Dnase1 was diffusely expressed within the kidney in normal and mildly affected kidneys, whereas upon progression towards end-stage renal disease, Dnase1 was down-regulated in all renal compartments. This demonstrates that the changes associated with development of severe nephritis in the murine model are also relevant to human lupus nephritis.

Conclusions/Significance

Reduction in renal Dnase1 expression and activity is limited to mice and SLE patients with signs of membranoproliferative nephritis, and may be a critical event in the development of severe forms of lupus nephritis. Reduced Dnase1 activity reflects loss in the expression of the protein and not inhibition of enzyme activity.

Nuclease deficiencies promote end-stage lupus nephritis but not nephritogenic autoimmunity in (NZB × NZW) F1 mice

New information has profoundly improved our insight into the processes that account for lupus nephritis. This review summarizes the data proving that secondary necrotic chromatin fragments are generated and retained in kidneys at time-points when the major renal nuclease Dnase-1 is selectively and severely downregulated. Second, we discuss data, which may indicate that nuclease deficiencies are not associated with autoimmunity to chromatin. Secondary to downregulation of renal Dnase-1, large chromatin fragment-immunoglobulin G complexes are accumulated in glomerular basement membranes of patients producing anti-chromatin autoantibodies. Exposure of chromatin in situ in glomeruli is the factor that renders anti-chromatin (anti-dsDNA and anti-nucleosome) antibodies nephritogenic. Without exposed chromatin, they circulate as non-pathogenic antibodies. This shows that acquired loss of renal Dnase-1 enzyme activity is a dominant event responsible for the progression of lupus nephritis into end-stage disease. Before the loss of Dnase-1, lupus-prone (NZB × NZW) F1 mice develop mild or silent nephritis with mesangial immune complex deposits, which correlates solely with onset of anti-dsDNA antibody production. The principal cellular and molecular requirements needed to produce these autoantibodies have been explained experimentally, but the mechanism(s) accounting for them in vivo in context of lupus nephritis have not yet been determined. However, published data show that defects in nucleases operational in apoptotic or necrotic cell death are not associated with the induction of nephritogenic anti-dsDNA autoantibodies. The data discussed in this study explain how an unusual exposure of chromatin may be a central factor in the evolution of lupus nephritis in (NZB x NZW) F1 mice, but not in promoting nephritogenic chromatin-specific autoimmunity.

Pure anti-dsDNA mAbs need chromatin structures to promote glomerular mesangial deposits in BALB/c mice

The glomerular targets for nephritogenic antibodies have been identified as membrane-associated chromatin fragments. The processes responsible for their deposition are poorly understood. To determine early events in antibody-mediated nephritis, we injected highly pure anti-dsDNA mAbs into BALB/c mice. Mice receiving one dose of anti-dsDNA mAbs were sacrificed 6 or 24 h later. No direct binding of mAbs to glomerular membranes or to the mesangial matrix was observed by immune electron microscopy. In contrast, repeated injections of the same antibodies over 4 weeks resulted in deposition of electron dense structures predominantly in the mesangial matrix. These structures contained mAbs and chromatin fragments as determined by co-localization immune electron microscopy. Biotinylated anti-dsDNA mAbs, injected into nephritic (NZB x NZW)F1 or MRL(lpr/lpr) mice were detected in newly formed electron dense structures within glomerular capillary membranes. There were no correlation between mAb affinity for DNA, as determined by surface plasmon resonance analyses, and ability to bind chromatin fragments in vivo. No direct binding of mAbs to inherent membrane antigens was observed. Quantification of DNA in sera before and after one single injection of antibodies revealed increased DNA levels at 6 h after injection of anti-dsDNA mAb, and lower levels after 24 h. Repeated injections of anti-dsDNA caused an increase in circulating DNA. These results indicate that availability of chromatin fragments, presumable in circulation, is important for glomerular mesangial matrix deposition of anti-dsDNA antibody-containing immune complexes in context of lupus nephritis.