Circulating levels of chromatin fragments are inversely correlated with anti-dsDNA antibody levels in human and murine systemic lupus erythematosus

Type I IFN in Glomerular Disease: Scarring beyond the STING

The field of nephrology has recently directed a considerable amount of attention towards the stimulator of interferon genes (STING) molecule since it appears to be a potent driver of chronic kidney disease (CKD). STING and its activator, the cyclic GMP-AMP synthase (cGAS), along with intracellular RIG-like receptors (RLRs) and toll-like receptors (TLRs), are potent inducers of type I interferon (IFN-I) expression. These cytokines have been long recognized as part of the mechanism used by the innate immune system to battle viral infections; however, their involvement in sterile inflammation remains unclear. Mounting evidence pointing to the involvement of the IFN-I pathway in sterile kidney inflammation provides potential insights into the complex interplay between the innate immune system and damage to the most sensitive segment of the nephron, the glomerulus. The STING pathway is often cited as one cause of renal disease not attributed to viral infections. Instead, this pathway can recognize and signal in response to host-derived nucleic acids, which are also recognized by RLRs and TLRs. It is still unclear, however, whether the development of renal diseases depends on subsequent IFN-I induction or other processes involved. This review aims to explore the main endogenous inducers of IFN-I in glomerular cells, to discuss what effects autocrine and paracrine signaling have on IFN-I induction, and to identify the pathways that are implicated in the development of glomerular damage.

Single-Molecule Interactions of a Monoclonal Anti-DNA Antibody with DNA

Interactions of DNA with proteins are essential for key biological processes and have both a fundamental and practical significance. In particular, DNA binding to anti-DNA antibodies is a pathogenic mechanism in autoimmune pathology, such as systemic lupus erythematosus. Here we measured at the single-molecule level binding and forced unbinding of surface-attached DNA and a monoclonal anti-DNA antibody MRL4 from a lupus erythematosus mouse. In optical trap-based force spectroscopy, a microscopic antibodycoated latex bead is trapped by a focused laser beam and repeatedly brought into contact with a DNA-coated surface. After careful discrimination of non-specific interactions, we showed that the DNA-antibody rupture force spectra had two regimes, reflecting formation of weaker (20-40 pN) and stronger (>40 pN) immune complexes that implies the existence of at least two bound states with different mechanical stability. The two-dimensional force-free off-rate for the DNA-antibody complexes was ~2.2 × 10^-3 s^-1, the transition state distance was ~0.94 nm, the apparent on-rate was ~5.26 s^-1, and the stiffness of the DNA-antibody complex was characterized by a spring constant of 0.0021 pN/nm, suggesting that the DNA-antibody complex is a relatively stable, but soft and deformable macromolecular structure. The stretching elasticity of the DNA molecules was characteristic of single-stranded DNA, suggesting preferential binding of the MRL4 antibody to one strand of DNA. Collectively, the results provide fundamental characteristics of formation and forced dissociation of DNA-antibody complexes that help to understand principles of DNA-protein interactions and shed light on the molecular basis of autoimmune diseases accompanied by formation of anti-DNA antibodies.

17-β-estradiol affects BLyS serum levels and the nephritogenic autoantibody network accelerating glomerulonephritis in NZB/WF1 mice

Systemic lupus erythematosus (SLE) is an autoimmune disease that predominantly affects fertile women, suggesting sex hormones are involved in disease pathogenesis. B lymphocyte stimulator (BLyS) has been found to be elevated in SLE patients and to drive a lupus-like syndrome in transgenic mice. Our aim was to evaluate the effects of estrogen administration on BLyS and nephritogenic anti-C1q and anti-dsDNA antibodies in lupus-prone NZB/WF1 mice. We implanted pellets releasing 17-β-estradiol (18.8 µg/day) on the back side the ear of 10 NZB/WF1 mice (group 1), and compared them with 10 mice intraperitoneally injected with PBS 200 μl twice a week (group 2), as controls. We evaluated BLyS, anti-dsDNA and anti-C1q serum levels starting one week after pellet implantation. We also analyzed time to proteinuria onset, proteinuria-free survival and overall survival. Kidneys, spleen, liver and lungs were harvested for histological analysis. Mice were bred until natural death. BLyS serum levels were higher in group 1 than in group 2 mice at each evaluation. Group 1 mice developed nephritogenic antibodies and proteinuria significantly earlier and at higher levels than controls. Direct correlation between BLyS and anti-C1q (R (2 )= 0.6962, p < 0.0001) or anti-dsDNA (R (2 )= 0.5953, p < 0.0001), and between anti-C1q and anti-dsDNA autoantibodies (R (2 )= 0.5615, p < 0.0001) were found. Proteinuria-free and global survival rates were significantly lower in group 1 than in controls. Histological analyses showed more severe abnormalities in group 1 mice. Estrogen administration is associated with increased levels of BLyS as well as of anti-C1q and anti-dsDNA antibodies, leading to accelerated glomerulonephritis and disease progression in NZB/WF1 mice.

Decreased serum cell-free DNA levels in rheumatoid arthritis

Purpose

Recent studies have demonstrated that serum/plasma DNA and RNA molecules in addition to proteins can serve as biomarkers. Elevated levels of these nucleic acids have been found not only in acute, but also in chronic conditions, including autoimmune diseases. The aim of this study was to assess cell-free DNA (cfDNA) levels in sera of rheumatoid arthritis (RA) patients compared to controls.

Methods

cfDNA was extracted from sera of patients with early and established RA, relapsing-remitting multiple sclerosis patients (RRMS) and healthy subjects, and its concentration was determined by quantitative PCR using two amplicons, Alu115 and β-actin205, corresponding to Alu repetitive elements and the β-actin single-copy gene, respectively. Serum DNase activity was measured by a single radial enzyme diffusion method.

Results

Reduced levels of cfDNA were observed in patients with established RA in comparison with healthy controls, early RA patients and RRMS patients. There were no significant differences in cfDNA concentration between healthy controls, early RA and RRMS patients. Total DNase activity appeared to be similar in the sera of all tested groups.

Conclusions

Our results demonstrate that cfDNA levels are strongly reduced in the sera of established RA patients, which is not caused by changes in DNase activity. Measurement of cfDNA can distinguish established RA patients from early RA patients. Thus, cfDNA may serve as a biomarker in RA.

Electronic supplementary material

The online version of this article (doi:10.1007/s13317-015-0066-6) contains supplementary material, which is available to authorized users.

The effect of cell death in the initiation of lupus nephritis

Cell death and the release of chromatin have been demonstrated to activate the immune system producing autoantibodies against nuclear antigens in patients with systemic lupus erythematosus (SLE). Apoptosis, necrosis, necroptosis, secondary necrosis, autophagy and the clearance of dying cells by phagocytosis are processes believed to have a role in tolerance avoidance, activation of autoimmune lymphocytes and tissue damage by effector cells. The released chromatin not only activates the immune system; it also acts as antigen for the autoantibodies produced, including anti-dsDNA antibodies. The subsequent immune complex formed is deposited within the basement membranes and the mesangial matrix of glomeruli. This may be considered as an initiating event in lupus nephritis. The origin of the released chromatin is still debated, and the possible mechanisms and cell sources are discussed in this study.

Single nucleotide polymorphisms in genes encoding toll-like receptors 7, 8 and 9 in Danish patients with systemic lupus erythematosus

Several studies indicate a role for toll-like receptors (TLRs) in the pathogenesis of systemic lupus erythematosus (SLE). We aimed to investigate the risk of SLE and typical clinical and serological manifestations of SLE potentially conferred by selected single nucleotide polymorphisms (SNPs) of genes encoding TLR7, TLR8, and TLR9. Using a multiplexed bead-based assay, we analyzed eight SNPs in a cohort of 142 Danish SLE patients and a gender-matched control cohort comprising 443 individuals. Our results showed an association between the rs3853839 polymorphism of TLR7 and SLE (G vs. C, P = 0.008, OR 1.60, 95 % CI 1.12-2.27 in females; P = 0.02, OR 4.50, 95 % CI 1.18-16.7 in males) confirming recent findings in other populations. Additionally, an association between the rs3764879 polymorphism of TLR8 and SLE (G vs. C, P < 0.05, OR 1.36, 95 % CI 0.99-1.86 in females; P = 0.06, OR 4.00, 95 % CI 0.90-17.3 in males) was found. None of the other investigated SNPs were associated with SLE but several SNPs were associated with clinical and serological manifestations. In summary, a previously shown association between the rs3853839 SNP of TLR7 and SLE in Asian patients was also found in Danish patients. Together with the association of several other SNPs of TLR8 and TLR9 with various clinical and serological manifestations of SLE these findings corroborate the pathogenic significance of TLRs in SLE.

MBL2 gene variants coding for mannose-binding lectin deficiency are associated with increased risk of nephritis in Danish patients with systemic lupus erythematosus

OBJECTIVES

Autoimmunity may in part result from deficiencies in the processing of apoptotic debris. As mannose-binding lectin (MBL) is involved in such processes, we hypothesized that the variants in the MBL2 gene resulting in MBL deficiency confer an increased risk of nephritis in systemic lupus erythematosus (SLE).

METHODS

A total of 171 SLE patients attending a Danish tertiary rheumatology referral center were included. Common variant alleles in exon 1 of the MBL2 gene (R52C, rs5030737; G54D, rs1800450; G57E, rs1800451) were genotyped. The normal allele and variant alleles are termed A and O, respectively. The follow-up period was defined as the time from fulfillment of the ACR 1987 classification criteria for SLE until the occurrence of an event (nephritis, end-stage renal disease (ESRD), or death) or end of follow-up. Cox regression analyses were controlled for gender, age and race.

RESULTS

During a median follow-up of 5.7 years, nephritis developed in 94 patients, and ESRD developed in 16 of these patients. Twenty-seven patients died. The distribution of the MBL2 genotypes A/A, A/O and O/O was 58%, 35% and 7.0%, respectively. Compared to the rest, O/O patients had 2.6 times (95% CI: 1.2-5.5) higher risk of developing nephritis, and their risk of death after 10 years was 6.0 times increased (95% CI: 1.0-36). MBL serum levels below 100 ng/ml were associated with a 2.0 (95% CI: 1.2-3.4; p = 0.007) increased risk of developing nephritis. ESRD and histological class of nephritis were not associated with MBL deficiency.

CONCLUSIONS

Genetically determined MBL deficiency was associated with development of nephritis in SLE patients, but not with histological class of nephritis or ESRD.

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.

Soluble human CD83 ameliorates lupus in NZB/W F1 mice

In the present study we explored the immunomodulatory potential of prokaryotically expressed soluble CD83 in the treatment of murine lupus using the NZB/W F1 mouse model. Therefore female NZB/W F1 lupus mice were treated either with sCD83 or PBS for 4 weeks. sCD83 treated mice showed a significantly delayed onset of anti-dsDNA autoantibody production when compared with the control group. Importantly, during the treatment period with sCD83 none of the mice showed elevated levels of anti-dsDNA autoantibodies. In addition, NZB/W F1 mice which received sCD83 displayed lower concentrations of anti-histone IgG autoantibodies. Furthermore, there was no difference in total IgG antibodies, indicating a modulatory role for sCD83 in the production of self-reactive antibodies without decreasing total IgG. These results indicate that administration of sCD83 has profound immune-modulatory effects on the induction of autoantibodies in NZB/W F1 lupus mice and may thus be a promising approach to interfere with autoimmunity in SLE and other autoantibody-driven diseases.

Nucleosomes contribute to increase mesangial cell chemokine expression during the development of lupus nephritis

Nucleosomes represent a set of major autoantigens in the induction of systemic lupus erythematosus (SLE), and appear to be essential for the development of lupus nephritis. Deposition of nucleosome-containing immune complexes within the mesangial matrix and activation of mesangial cells may be important in the progression of lupus nephritis from a "sleeping" minimal change disease state to a full blown disease state. This study investigated the renal cytokine profile both in vivo during the development of the disease in (NZBxNZW)F1 (B/W) mice, and in vitro in primary B/W mesangial cells stimulated with nucleosomes, nucleosome-IgG complexes, and anti-dsDNA mAb respectively. Nucleosomes alone stimulated primary mesangial cells in a dose dependent manner. Of the chemokines produced by activated mesangial cells, CCL2, CCL7, CCL20, CXCL1, CXCL2 and CXCL5 were highly up-regulated compared to unstimulated cells. These chemokines were also increased in vivo in anti-dsDNA antibody positive and nephritic B/W kidneys, and was accompanied by infiltration of neutrophils, macrophages, T and B cells. This study provides a link between nucleosome-containing immune complexes, activation of mesangial cells, infiltration of effector cells and the development of lupus nephritis. Nucleosomes are pro-inflammatory and trigger innate immune responses, and thus are not only passive targets for autoantibodies but may play an active role in lupus pathogenesis. The removal or increased enzymatic destruction of nucleosomes, and/or the inhibition of mesangial cell activation may be possible treatment strategies in lupus nephritis.

Simultaneous positivity for anti-DNA, anti-nucleosome and anti-histone antibodies is a marker for more severe lupus nephritis

OBJECTIVE

The purpose of this study is to examine autoantibody profile of systemic lupus erythematosus (SLE) patients with lupus nephritis (LN) and to establish the correlation between the antibody reactivity and disease activity of LN.

METHODS

Autoantibodies and serological parameters were measured and analyzed in 589 SLE patients. The associations of the co-positivity of anti-dsDNA, -nucleosome and -histone antibodies (3-pos) with clinical, serological and outcome parameters were analyzed.

RESULTS

At the study entry, the prevalence for anti-dsDNA (61.52 % vs. 34.11 %, P < 0.0001), anti-nucleosome (56.09 % vs. 37.21 %, P = 0.0002) and anti-histone (49.35 % vs. 33.33 %, P = 0.0013) antibodies in patients with LN were significantly higher than that in patients without LN. Patients with 3-pos had a higher proportion of proliferative renal lesions (class III + IV). The incidence of a poor renal outcome (7.14 % vs. 2.52 %, P = 0.0174) in LN patients with 3-pos was significantly higher than those without 3-pos. Moreover, the rate of remission (73.63 % vs. 82.37 %, P = 0.0245) was significantly reduced and recurrence increased (58.90 % vs. 23.44 %, P < 0.0001) in 3-pos patients as compared to that in non 3-pos within the LN group.

CONCLUSION

Our data indicate a strong association between the 3-pos and renal disease activities, especially proliferative glomerulonephritis. The ability of 3-pos to predict renal flares may lead to major additional benefits in the follow-up of these patients.