NETosis is assumed to be involved in the pathogenesis of common rheumatic diseases such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), psoriatic arthritis (PsA), and ankylosing spondylitis (AS). However, the levels of circulating NETosis biomarkers and the extent of changes in these markers in specific rheumatic diseases are not fully understood. In this study, cell-free DNA (cfDNA) concentration as a non-specific marker, as well as myeloperoxidase (MPO) and citrullinated histone H3 (H3cit) as specific markers of NETosis, were investigated in SLE, RA, PsA, and AS. Analysis of covariance, accounting for sex, age and disease duration, showed that total cfDNA was elevated in SLE and AS compared with healthy subjects. Nuclear and mitochondrial cfDNA were elevated in four diseases. However, nuclear cfDNA was increased to a greater extent in SLE but mitochondrial cfDNA was higher in RA. MPO and H3cit were significantly elevated in SLE compared with other diseases, although MPO was also higher in RA. Elevated concentrations of MPO and H3cit in SLE were associated with the presence of concomitant cardiovascular diseases. The effect of biological therapy on mitochondrial cfDNA, MPO, and H3cit was also shown. The proinflammatory cytokine IL-18, implicated in the induction of NETosis, was similarly elevated in the four rheumatic diseases. Thus, the most striking signs of NETosis are found in SLE, although they are also present in RA. PsA and AS were mainly characterized by an increase in cfDNA. These data highlight characteristic changes in NETosis markers in four rheumatic diseases.

Background: Human immunodeficiency virus (HIV) infection is associated with pronounced oxidative stress, leading to the development of various virus-associated pathologies. A wealth of evidence suggests that, along with canonical enzymes of reactive oxygen species regulation, human blood contains antibodies with peroxidase, superoxide dismutase, and catalase activities. Here we show that the catalase activity of IgGs and their κκ-IgG, λλ-IgG, and κλ-IgG subfractions of HIV-infected individuals is significantly different compared to the healthy donors. Methods: Protein G-Sepharose sorbent was used to resolve IgG from blood of healthy donors and HIV-infected patients by affinity chromatography. Subfractions of κκ-IgG, λλ-IgG, and κλ-IgG were separated from IgGs samples of each group by affinity chromatography on sorbents containing immobilized antibodies to κ or λ light human chains. The IgG catalase activity level was measured spectrophotometrically by evaluating the decrease in optical density (A240) due to hydrogen peroxide decomposition. Results: The relative catalase activity of antibodies from HIV-infected patients (kcat = (1.41 ± 0.92) × 103 min-1, 95% CI: [1.01–1.81]) was statistically significant, 1.6 times higher (p = 0.014) compared to apparently healthy donors ((0.86 ± 0.49) × 103, 95% CI: [0.69–1.03]). The activity level of κκ-IgG HIV-infected patients ((0.44 ± 0.04) × 103 min-1) was 1.4 times higher than that of λλ-IgGs ((0.31 ± 0.025) × 103 min-1); the opposite was observed for κκ-IgGs from apparently healthy donors, which activity ((0.17 ± 0.015) × 103 min-1) was 3.1 times lower compared to λλ-IgGs ((0.53 ± 0.045) × 103 min-1). Conclusions: Thus, the data obtained may indicate that IgG with increased catalase activity may prevent harmful processes arising from oxidative stress in HIV-infected patients, acting as an additional natural molecular mechanism of regulation of hydrogen peroxide level.

Background/Objectives: The pathognomonic feature of systemic lupus erythematosus (SLE) is the formation of antibodies to double-stranded DNA (anti-dsDNA Abs). Cell-free DNA (cfDNA) has been suggested as one of the antigens for the generation of anti-dsDNA Abs, but the temporal changes in these biomarkers are not clear. In this study, the association of dynamic changes in total cfDNA and anti-dsDNA Abs levels in blood plasma during disease progression in a murine model of pristane-induced SLE was examined. Methods: The experimental group consisted of 12 BALB/c pristane-immunized mice; the control group included 8 PBS-treated mice. Blood samples were collected six times during the 38-week study (2 weeks before and 8, 14, 22, 28, and 36 weeks after immunization). Total cfDNA and anti-dsDNA Abs levels were determined at each time point. Results: Pristane-immunized mice showed a significant increase in the concentration of anti-dsDNA Abs. A 14-week delay in the formation of anti-dsDNA Abs was observed after an increase in the concentration of cfDNA in the experimental and control groups. Anti-dsDNA Abs and total cfDNA levels did not correlate at specific time points, but the change in cfDNA concentration from week 14 to week 28 was inversely correlated with the change in the anti-dsDNA Abs level over the same time period (R = −0.71, p = 0.009), i.e., the more the anti-dsDNA Abs level increased, the more the cfDNA concentration decreased. A direct correlation was shown between the increase in body weight of pristane-immunized mice and the increase in total cfDNA concentration in the blood from week 0 to week 14 (R = 0.6, p = 0.04). Conclusions: These findings demonstrate the dynamic nature of cfDNA and anti-dsDNA Abs levels and reciprocal dynamics of these markers in a pristane-induced mouse model of SLE.

Tick-borne encephalitis (TBE) is a neuroinvasive flavivirus infection with a wide spectrum of clinical manifestations whose molecular mechanisms remain insufficiently characterized. MiRNAs regulate pro-inflammatory cytokine production; therefore, changes in their profiles across different forms of TBE may determine the nature of the cytokine response. The aim of this work was to identify the specific features of the circulating miRNA and cytokine profiles in different clinical forms of TBE, as well as to analyze the correlations between them. The study included patients with febrile, meningeal, and encephalitic forms of TBE, patients with inflammatory rheumatic diseases (IRD), and healthy donors. Plasma concentrations of eight miRNAs (miR-25-3p, miR-29a-3p, miR-92a-3p, miR-146a-5p, miR-146b-5p, miR-181a-5p, miR-486-3p, and miR-766-3p) were measured by stem-loop real-time RT-PCR. Cytokine concentrations (IL-1β, IL-2, IL-8, IL-18, TNF-α) were measured by ELISA. Kendall’s rank correlation test was used for the correlation analysis. In all forms of TBE, a distinct circulating miRNA signature emerges (↑ miR-25-3p, miR-146b-5p, ↑ miR-766-3p, and ↓ miR-29a-3p), which is associated with an acute antiviral response and is not specific to chronic autoimmune inflammation. Several miRNAs (miR-29a-3p, miR-92a-3p, miR-146b-5p, and miR-486-3p) showed opposite changes in TBE and IRD, pointing to fundamentally different mechanisms of immune regulation in acute neuroinfection and systemic autoimmune pathology. Several statistical associations between circulating miRNA and pro-inflammatory cytokine levels were identified. TNF-α levels positively correlated with miR-146b-5p and negatively with miR-25-3p, while IL-2 positively correlated with miR-25-3p. In the encephalitic form of TBE, IL-1β positively correlated with miR-146b-5p and miR-92a-3p. The present study is of a pilot nature. The miRNA and cytokine patterns identified here were based on a small sample size and should therefore be regarded as preliminary. Once confirmed, these signatures may provide a basis for the differential diagnosis of TBE and the development of prognostic biomarkers of disease severity.

Antinuclear antibodies, especially anti-DNA antibodies, are known to be a hallmark of systemic lupus erythematosus (SLE) and represent a diverse pool of autoantibodies with different origins, antigenic properties, and physicochemical features. Antibodies with catalytic properties have been found among the antibody repertoire in SLE, but the specific features and clinical associations of such antibodies have not been sufficiently studied. This study showed that chromatographically purified IgG from the serum of SLE patients effectively hydrolyzed DNA and DNA-associated proteins such as histones and high-mobility group box 1 (HMGB1) compared to healthy individuals. Remarkably, the level of hydrolysis of DNA and DNA-associated proteins was closely correlated. At the same time, these antibodies did not hydrolyze the control protein, tumor necrosis factor-α (TNFα), which does not possess DNA-binding properties. IgG DNase activity levels varied significantly, so patients were divided into high- and low-activity subgroups using the DBSCAN algorithm, with the difference between median values being greater than 49 times. The subgroup with high IgG DNase activity was characterized by an increase in anti-DNA antibodies (p < 0.04) than the subgroup with low activity, which had a shorter duration of the disease (p = 0.03) and was more often characterized by a subacute rather than a non-chronic course of the disease (p = 0.048). High catalase-like activity of IgG was also detected in SLE. Thus, the antibody pool in SLE contains not only high-affinity antinuclear autoantibodies but also catalytic antibodies capable of hydrolyzing DNA and DNA-associated proteins. These findings expand our understanding of the heterogeneity of the repertoire of catalytic autoantibodies among SLE patients.