Rheumatoid arthritis (RA) is a systemic inflammatory autoimmune disease that leads to joint destruction and disability. Despite a significant progress in administration of biological agents for RA patients, there is still a need for improved therapy. Intravenous-immunoglobulins (IVIG) , a pooled polyspecific immunoglobulin-G (IgG) extracted from 20,000 healthy subjects, showed beneficial therapeutic effect in patients with immune-deficiency, sepsis, and autoimmune diseases. The current study aim to investigate the beneficial effect of treatment with IVIG in established collagen induced arthritis in DBA/1j mice. Murine arthritis was induced in DBA/1j mice. The treatment with IVIG started when the disease was established. The clinical score was followed twice a week until day 48. The mice were bled for plasma, the paws were H&E stained. Cytokine profile in the plasma was analyzed by Luminex technology, titers of circulating anti-collagen antibodies in the plasma was tested by ELISA. Our results show that treatment with IVIG in murine, significantly rreduced the clinical arthritis score (P<0.001). Moreover, mode of action show that IVIG significantly reduced circulating level of inflammatory cytokines (IFN, IL-1β, IL-17, IL-6, TNFα) (P<0.001), inhibit anti-collagen antibodies (P < 0.001) in the plasma of CIA mice. Importantly, histopathological examination revealed that IVIG treatment prevented the migration of inflammatory immune cells into the cartilage and synovium, reduced the extent of joint damage and preserved joint architecture. Our results proved for the first time the valuable anti-inflammatory treatment of IVIG in experimental RA. We propose IVIG therapy for a subgroup of patients with as rheumatological-related diseases.
Introduction: long-term observation of patients with ANCA-associated vasculitis (AAV) allows the identification of different longitudinal patterns of ANCA levels during follow-up. This study aimed to characterise these patterns and to determine their prognostic significance. Methods: all ANCA determinations performed in two university hospitals along a 2-year period were retrospectively reviewed. Patients were included in the analysis if they had high titers of anti-myeloperoxidase (anti-MPO) or anti-proteinase 3 (anti-PR3) antibodies at least once, they had ≥5 serial ANCA determinations, and they had AAV diagnosed by biopsy or ACR classification criteria. Patients’ time-course ANCA patterns were classified as monophasic, remitting, recurrent or persistent. Associations between ANCA patterns and prognostic variables (relapse rate and renal outcome) were analysed by univariate and multivariate statistics. Results: A total of 99 patients (55 with microscopic polyangiitis [MPA], 36 with granulomatosis with polyangiitis [GPA], and 8 with eosino¬philic granulomatosis with polyangiitis) were included. Median follow-up was 9 years. Among patients diagnosed with MPA or GPA, recurrent or persistent ANCA patterns were associated with a higher risk of clinical relapse (HR 3.7 [95% CI 1.5-9.1] and HR 2.9 [95% CI 1.1-8.0] respectively), independently of clinical diagnosis or ANCA specificity. In patients with anti-MPO antibodies, the recurrent ANCA pattern was associated with worsening renal function (OR 5.7 [95% CI 1.2-26.0]). Conclusion: Recurrent or persistent ANCA patterns are associated with a higher risk of clinical relapse. A recurrent ANCA pattern was associated with worsening renal function in anti-MPO-associated vasculitis.
The interesting report by Karagianni P et al on the finding of increased DNA methylation of H19 locus imprinting control region in saliva samples of Sjögren’s syndrome patients correlating with low complement C4 levels, may offer insights into how C4 level may be regulated in serpinopathies such as C1-inhibitor deficiency. An undetectable or low C4 level in patients with severe angioedema is a feature of C1-inhibitor deficiency (hereditary angioedema (HAE) type I with low to absent function and antigenic levels; HAE type II with point mutations in SERPING1 gene that affect the reactive centre loop affecting protein function only). However, C4 levels do not always clinically correlate with disease activity, and up to 6% patients do not have known mutations in the SERPING1 gene.
Innate immune sensing of viral molecular patterns is essential for development of antiviral responses. Like many viruses SARS CoV-2 has evolved strategies to circumvent innate immune detection including low CpG levels in the genome, glycosylation to shield essential elements including the receptor binding domain, RNA shielding and generation of viral proteins that actively impede anti-viral interferon responses. Together these strategies allow widespread infection and increased viral load. Despite the efforts of immune subversion SARS-CoV-2 infection does activate innate immune pathways inducing a robust type I/III interferon response, production of proinflammatory cytokines, and recruitment of neutrophils and myeloid cells. This may induce hyperinflammation or alternatively, effectively recruit adaptive immune responses that help clear the infection and prevent reinfection. The dysregulation of the renin-angiotensin system due to downregulation of angiotensin converting enzyme 2, the receptor for SARS-CoV-2, together with the activation of type I/III interferon response, and inflammasome response converge to promote free radical production and oxidative stress. This exacerbates tissue damage in the respiratory system but also leads to widespread activation of coagulation pathways leading to thrombosis. Here, we review the current knowledge of the role of the innate immune response following SARS-CoV-2 infection, much of which is based on the knowledge from SARS-CoV and other coronaviruses. Understanding how the virus subverts the initial immune response and how an aberrant innate immune response contributes to the respiratory and vascular damage in COVID-19 may help explain factors that contribute to the variety of clinical manifestations and outcome of SARS-CoV-2 infection.
Background: Bacillus Calmette-Guérin (BCG) vaccination policies of countries are postulated to have effect on the course of coronavirus disease 2019 (COVID-19) pandemic. Methods: Retrospective cross-sectional study was conducted between March 11-June 10, 2020 in a chest clinic in a state hospital in Istanbul,Turkey. Adults with diagnosis of COVID-19 pneumonia confirmed with severe acute respiratory syndrome coronavirus 2 polymerase chain reaction positivity in a nasopharyngeal sample and pulmonary infiltrates in computed chest tomography were included consecutively. Sociodemographic characteristics, body-mass index, smoking status, comorbid diseases, income rates, and BCG-vaccination status were compared between severe and mild patients with COVID-19 pneumonia. Results: Study population consisted of 123 adults (mean age, 49.7 years [standard deviation, 13.3 years]; 82 (66.7%) male). The proportion of BCG-vaccinated cases was significantly lower among severe patients than mild patients with COVID-19 pneumonia (68.5% vs 88.2%; p=.026). Mean age (54.0 ± 11.5 years vs 38.3 ±10.7 years; p <.001), diabetes rate (32.6% vs 5.9%; p=.002) and low-income (84.3% vs 52.9% p<.001) are higher in patients with severe COVID-19 pneumonia than in patients with mild COVID-19 pneumonia. Multivariate logistic regression analysis showed that increasing age (odds ratio [OR], 1.112; 95% confidence interval [CI], 1.058 – 1.169; p<.001) and low income (OR, 3.369; 95% CI, 1.074 – 10.570; p =.037) are associated with severe COVID-19 pneumonia. Conclusion: Clinical data does not support that being vaccinated with BCG is associated with disease severity in COVID-19 pneumonia. Age and low-income are the major predictors for disease severity.
Chronic Granulomatous Disease (CGD) is a rare inherited disorder in which phagocytes lack NADPH oxidase activity. The most common form is the X-linked CGD (X-CGD), caused by mutations in the CYBB gene. Clinical, functional and genetic characterizations of 16 CGD cases of male patients and their relatives were done. We classified them as suffering from different variants of CGD (X910, X91− or X91+) according to NOX2 expression and NADPH oxidase activity in neutrophils. Twelve mutations were novel (10 X910-CGD and 2 X91− -CGD). One X910-CGD was due to a new and extremely rare double missense mutation Thr208Arg-Thr503Ile. We investigated the pathological impact of each single using stable transfection of each mutated cDNA in the NOX2 knock-out PLB-985 cell line. Both mutations leading to X91−-CGD were also novel; one deletion -67delT was localized in the promoter region of CYBB, the second one c.253-1879A>G mutation activates a splicing donor site, which unveils a cryptic acceptor site, leading to the inclusion of a 124-nucleotide pseudo-exon between exons 3 and 4 and responsible for the partial loss of NOX2 expression. Both X91−-CGD mutations were characterized by a low cytochrome b558 expression and a faint NADPH oxidase activity. The functional impact of new missense mutations is discussed in the context of a new 3D-model of the dehydrogenase domain of NOX2. Our study demonstrates that low NADPH oxidase activity found in both X91−-CGD patients correlates with mild clinical forms of CGD whereas X910-CGD and X91+-CGD cases remain the most clinically severe forms.
Although most autoimmune diseases are considered to be CD4 T-cell or antibody-mediated, many respond to CD20-depleting antibodies that have limited influence on CD4 and plasma cells. This includes rituximab that is used in cancer, rheumatoid arthritis and off-label in a large number of other autoimmunities, notably multiple sclerosis, where ofatumumab is in late stage development and ocrelizumab is approved for use. Recently, the COVID-19 pandemic created concerns about immunosuppression in autoimmunity, leading to cessation or a delay in immunotherapy treatments. However, based on the known and emerging biology of multiple sclerosis and COVID-19, it was hypothesised that whilst B-cell depletion should not necessarily expose people to severe SARS-CoV-2-related issues, it may inhibit protective immunity following infection and vaccination. As such, drug-induced B-cell subset inhibition that controls multiple sclerosis and other autoimmunities, would not influence innate and CD8 T-cell responses, which are central to SARS-CoV-2 elimination, nor the hyper-coagulation and innate inflammation causing severe morbidity. This is supported clinically, as the majority (mortality rate n=~5/392) of SARS-CoV-2 infected, CD20-depleted people with multiple sclerosis have recovered. However, protective neutralising-antibody and vaccination responses are predicted to be blunted, until naïve B-cells repopulate, based on B-cell repopulation-kinetics and vaccination responses, from published rituximab and unpublished ocrelizumab (NCT00676715, NCT02545868) trial data, shown here. This suggests that it may be possible to undertake dose-interruption to maintain inflammatory disease control in MS and other autoimmune diseases, whilst allowing effective vaccination against SARS-CoV-29, if and when an effective vaccine is available.
Immune response variations could define successful resistance to Hepatitis C Virus (HCV) infection. Toll-like receptors (TLR)-3 are innate detectors of dsRNA viruses while bacterial and viral unmethylated CpG motifs are recognized by TLR9. We previously reported that TLR3.rs3775290 “CC” genotype was associated with HCV chronicity, while TLR9 gene played no major role in this infection. This study identified the role of TLR3.rs3775290 (c.1377C/T), TLR9.rs5743836 (-1237T→C) and TLR9.rs352140 (G2848A) gene polymorphisms in predicting the outcome of HCV-specific cell-mediated immunity (CMI) among Egyptian healthcare workers (HCWs) and patients. We enrolled 546 subjects (409 HCWs and 137 patients) divided into four groups. Group1: 265 seronegative, aviraemic subjects; group2: 25 seronegative, viraemic subjects; group3: 87 subjects with spontaneously resolved HCV infection; and group4: 169 chronic HCV HCWs and patients. All subjects were genotyped by PCR-restriction fragment length polymorphism (PCR-RFLP) analysis for the TLR3.rs3775290, TLR9.rs5743836 and TLR9.rs352140 SNPs. We, also, quantified HCV-specific CMI in 265 HCWs distributed among the four groups using an interferon gamma (IFN-γ) enzyme-linked immunospot (ELISpot) assay in response to nine HCV genotype 4a overlapping 15mer peptide pools covering the whole viral genome. No statistically significant difference was found between CMI responding subjects with different HCV states and TLR3.rs3775290 genotype or TLR9.rs352140. However, there was a significant relationship between the outcome of the HCV-specific CMI and the TLR9.rs5743836 genotype among the responding subjects (p=0.005) and the chronic HCV patients (p=0.044). In conclusion, TLR9.rs5743836 SNP; but not TLR3.rs3775290 or TLR9.rs352140 genotypes; could predict the outcome of HCV-specific CMI responses among genotype-4-infected Egyptians.
Objectives. We compared the common pathway components C3a, C5a and membrane attack complex (MAC), also known as C5b-9, and the alternative pathway components factor B and properdin in patients with ANCA-associated vasculitis (AAV) and healthy controls, and conducted a meta-analysis of the available clinical evidence for the role of complement activation in the pathogenesis of AAV. Methods. Complement components were evaluated in 59 patients with newly diagnosed or relapsing granulomatosis with polyangiitis or microscopic polyangiitis and 36 healthy volunteers. In 28 patients, testing was repeated in remission. Next, we performed a meta-analysis by searching databases to identify studies comparing complement levels in AAV patients and controls. A random-effects model was used for statistical analyses. Results. The median concentrations of MAC, C5a, C3a, and factor B were higher in active AAV patients (p<0.001). Achievement of remission was associated with reductions in C3a (p=0.005), C5a (p=0.035), and factor B levels (p=0.045), whereas MAC and properdin levels did not change. In active AAV, there were no effects of ANCA specificity, disease phenotype, previous immunosuppression, or disease severity on complement levels. A total of 1122 articles were screened, and five studies, including this report, were entered in the meta-analysis. Plasma MAC, C5a, and factor B in patients with active AAV were increased compared to patients in remission (excluding factor B) and controls. Changes in C3a were of borderline significance. Conclusion. Our findings and the results of the meta-analysis support activation of the complement system predominantly via the alternative pathway in AAV patients.
Decreasing graft rejection and increasing graft and patient survival are great challenges facing liver transplantation (LT). Different T-cell subsets participates in the acute cellular rejection (ACR) of the allograft. Cell-mediated immunity markers of the recipient could help to understand the mechanisms underlying acute rejection. This study aimed to analyse CD4+CD154+ and CD8+CD154+ T-cells in a cohort of adult liver patients undergoing LT to determine the influence on ACR using multiparametric flow cytometry functional assay. Thiry patients were immunologically monitored at baseline and during 1 year post-transplant. Two groups were established, with (ACR) and without (NACR) acute cellular rejection. Leukocyte, total lymphocyte, percentages of CD4+CD154+ and CD8+CD154+ T-cells, HLA mismatch between recipient-donor and their relation with ACR as well as the acute rejection frequencies were analysed. T-cells were stimulated with concanavalin A (Con-A) and surface antigens were analysed by FACS analysis. A high percentage of CD4+CD154+ T-cells (p=0.001) and a low percentage of CD8+CD154+ T-cells (p=0.002) at baseline were statistically significant in ACR. A receiver operating characteristic analysis determined the cut-off values capable to stratify patients at high risk of ACR with high sensitivity and specificity for CD4+CD154+ (p=0.001) and CD8+CD154+ T-cells (p=0.002). In logistic regression analysis, CD4+CD154+, CD8+CD154+ and HLA mismatch were confirmed as independent risk factors to ACR. Post-transplant percentages of both T-cell subsets were significantly higher in ACR, despite variations compare to pre-transplant. These findings support the selection of candidates for LT based on the pre-transplant percentages of CD4+CD154+ and CD8+CD154+ T-cells in parallel with other transplant factors
Although increasing evidence demonstrates the association between intestinal dysbiosis and pancreatic diseases, such as chronic pancreatitis and pancreatic cancer, it remains largely unknown whether intestinal dysbiosis is involved in the immunopathogenesis of autoimmune pancreatitis (AIP). Recently, we found that intestinal dysbiosis mediates experimental AIP via the activation of plasmacytoid dendritic cells (pDCs), which can produce IFN-α and IL-33. However, candidate pathobionts for type 1 AIP have not been identified. In this study, we tried to identify pathobionts associated with type 1 AIP. Fecal samples were obtained from type 1 AIP patients before and after prednisolone (PSL) treatment and subjected to 16S ribosomal RNA sequencing to evaluate the composition of intestinal bacteria. Induction of remission by PSL was associated with the complete disappearance of Klebsiella species from feces, in two of the three analyzed patients with type 1 AIP. To assess the pathogenicity of Klebsiella species, mild experimental AIP was induced in MRL/MpJ mice by repeated injections of 10 μg of polyinosinic-polycytidylic acid (poly (I:C)) in combination with oral administration of heat-killed Klebsiella pneumoniae. The AIP pathology score was significantly higher in MRL/MpJ mice that received both oral administration of heat-killed K. pneumoniae and intraperitoneal injections of poly (I:C) than in those administered with either agent alone. Pancreatic accumulation of pDCs capable of producing large amounts of IFN-α and IL-33 was also significantly higher in mice that received both treatments. These data suggest that intestinal colonization by K. pneumoniae may play a pathogenic role in AIP.
The aim of this multicenter retrospective study was to evaluate the incidence of hyperprogressive disease after treatment with pembrolizumab as a second-line treatment in patients (n=167) with non-small-cell lung cancer (NSCLC) with metastatic disease whose tumors expressed programmed death-ligand-1 in ≥1% and to search for factors associated with its development. All patients received platinum-containing chemotherapy as a first-line treatment. The neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR), and their derivations were retrospectively analyzed. The psoas major muscle area (PMMA) was calculated at the L3 position on computed tomography before chemotherapy and immunotherapy. Patients with ∆PMMA≥10% were considered to have sarcopenia (low muscle mass). We also performed multinomial logistic regression to estimate the effects of hematological biomarkers and ∆PMMA on the response to immunotherapy. Hyperprogressors (HPs) had significantly higher NLRs, PLRs and ∆PMMA levels than the other patients. Moreover, in multivariate regression analysis, higher levels of ∆PMMA were associated with a decreased likelihood of being a progressor (P) (OR, 0.81; 95% CI, 0.65-0.99; p=0.047) or a nonprogressor (NP) (OR, 0.76; 95% CI, 0.62-0.94; p=0.012) vs an HP. In multivariate analysis, higher NLRs tended to decrease the likelihood of being a P vs an HP (OR, 0.66; 95% CI, 0.42-1.06; p=0.09) and significantly decrease the likelihood of being an NP vs an HP (OR, 0.44; 95% CI, 0.28-0.69; p<0.0001). Our data suggest that a high pre-immunotherapy NLR and the presence of sarcopenia are potential risk factors for the development of hyperprogressive disease.
Background. Anti-citrullinated protein/peptide antibodies (ACPA) play important roles in the pathogenesis of rheumatoid arthritis (RA). ACPA-positive (ACPA+) and ACPA-negative (ACPA-) RA were suggested to be different disease subsets with distinct differences in genetic variation and clinical outcomes. The aims of the present study were to compare gene expression profiles in ACPA+ and ACPA- RA and identify novel candidate gene signatures that might serve as therapeutic targets. Methods. Comprehensive transcriptome analysis of peripheral blood mononuclear cells (PBMCs) from ACPA+ and ACPA- RA patients, and healthy controls was performed via RNA sequencing. A validation cohort was used to further investigate differentially expressed genes via PCR and ELISA. Spearman’s correlation test was used to evaluate the correlation of differentially expressed genes and the clinical and laboratory data of the patients. The role of differentially expressed genes in osteoclastogenesis was further investigated. Results. Expression of C-X-C motif chemokine ligand 2 (CXCL2) was significantly increased in ACPA+ RA than in ACPA- RA, which was validated in PBMCs and serum. CXCL2 promoted the migration of CD14+ monocytes and increased osteoclastogenesis in RA patients. RAW264.7 macrophages were used to investigate specific mechanisms, and the results suggested that CXCL2 stimulated osteoclastogenesis via ERK MAPK and NFκB pathways. Conclusion. CXCL2 was highly expressed in ACPA+ RA than in ACPA- RA. CXCL2 promoted osteoclastogenesis and was related to bone erosion in RA, which suggest that the blockade of CXCL2 might be a novel strategy for the treatment of RA.
Tuberculosis (TB) is one of the top 10 causes of mortality worldwide from a single infectious agent and has significant implications for global health. In 2018, 1.5 million people died from TB worldwide and 440,000 of those were from India. The WHO End-TB strategy aims to reduce TB deaths by 95% and new TB cases by 90% by 2035, with a call for more basic research on TB pathogenesis and immunity. A major hurdle in the development of effective TB vaccines and therapies is the absence of defined immune-correlates of protection. In this context, the role of regulatory T cells (Treg), which are essential for maintaining immune homeostasis, is even less understood. This review aims to address this knowledge gap by providing an overview of the emerging patterns of Treg function in TB. The review also provides a comprehensive critical analysis of the key features of Treg cells in TB; highlights the importance of a balanced immune response as being important in TB and discusses the importance of probing not just Treg frequency but also qualitative aspects of Treg function as part of a comprehensive search for novel TB treatments.
Growing evidence shows that a homozygous 6.7-kb deletion of the novel anti-inflammatory molecule leukocyte immunoglobulin like receptor A3 (LILRA3) is associated with many autoimmune disorders. However, its effects on pathogenesis of inflammatory bowel disease (IBD) have not been clarified yet. LILRA3 is mainly expressed in monocytes, whereas its effects on biological behaviors of monocytes have not been systematically reported. To investigate the association between LILRA3 polymorphism and IBD susceptibility, LILRA3 polymorphism was assessed in 378 IBD patients and 509 healthy controls in our study, quantitative real-time PCR (qRT-PCR), western blot and immunohistochemistry (IHC) were employed to detect the LILRA3 expression in IBD patient blood and intestinal samples. Despite no association of the polymorphism with IBD development was found, LILRA3 expression was markedly increased in IBD patients compared with healthy controls. Human U937 monocyte cell line was employed to establish LILRA3-overexpressing cells and the effects of LILRA3 on the biological behaviors of U937 cells were systematically explored. We found that overexpression of LILRA3 in monocytes led to significant decreases in secretion of interferon-γ (IFN-γ), tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6). Additionally, LILRA3 abated monocyte migration by reducing the expression of several chemokines and enhanced monocyte phagocytosis by increasing CD36 expression. Furthermore, LILRA3 promoted monocyte proliferation through a combination of Akt and MEK/Erk signaling pathways. We report for the first time that LILRA3 is related to IBD and functions as an anti-inflammatory modulator in U937 cells.
Peroxiredoxins (PRXs) are intracellular antioxidative enzymes but work as inflammatory amplifiers under the extracellular condition. To date, the function of PRXs in the pathogenesis of multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD) is not fully understood. The aim of this study was to investigate whether PRXs play a role in the pathogenesis of MS and NMOSD. We analyzed levels of PRXs (PRX1, PRX5, and PRX6) in the CSF and serum of 16 patients with MS, 16 patients with NMOSD, and 15 patients with other neurological disorders (ONDs). We identified potential correlations between significantly elevated PRXs levels and the clinical variables in patients with MS and NMOSD. Additionally, pathological analyses of PRXs (PRX1-6) in the central nervous system were performed using the experimental autoimmune encephalomyelitis (EAE), animal model of MS. We found that serum levels of PRX5 and PRX6 in patients with MS and NMOSD were higher compared with those in patients with ONDs (p < 0.05). Furthermore, high levels of PRX5 and PRX6 were partly associated with blood–brain barrier dysfunction and disease duration in NMOSD patients. No significant elevation was found in CSF PRXs levels of MS and NMOSD. Spinal cords from EAE mice showed remarkable PRX5 staining, especially in CD45+ infiltrating cells. In conclusion, PRX5 and PRX6 may play a role in the pathogeneses of MS and NMOSD.
Background: Cladribine (CdA), an oral prodrug approved for the treatment of relapsing multiple sclerosis, selectively depletes lymphocytes. CdA passes the blood-brain barrier suggesting a potential effect on CNS resident cells. Objective: We examined, if CdA modifies the phenotype and function of naïve and activated primary mouse microglia, when applied in different concentrations including 0.1-1 µM that putatively overlaps human CSF concentrations. Methods: Primary microglia cultures without stimulation or in the presence of proinflammatory lipopolysaccharide (LPS) or anti-inflammatory IL-4 were co-treated with different concentrations of CdA for 24 hours. Viability was assessed by MTT assay. Phagocytotic ability and morphology were examined by flow cytometry, and random migration by IncuCyte Zoom and TrackMate. Change in gene expression was examined by qPCR, and protein secretion by Meso Scale Discovery. Results: LPS and IL-4 upregulated deoxycytidine kinase (DCK) expression. Only activated microglia were affected by CdA, and this was unrelated to viability. CdA 0.1-1 µM significantly reduced granularity, phagocytotic ability and random migration of activated microglia. CdA 10 µM increased the IL-4-induced gene expression of Arg1 and LPS-induced expression of IL-1beta, TNF, iNOS, and Arg1, but protein secretion remained unaffected. CdA 10 µM potentiated the increased expression of anti-inflammatory TNFR2 but not TNFR1 induced by LPS. Conclusion: Microglia acquire a less activated phenotype when treated with 0.1–1 µM CdA that putatively overlaps human CSF concentrations. This may be related to the upregulated gene expression of DCK upon activation and suggests a potential alternative mechanism of CdA with direct effect on CNS resident cells.
Properdin is the only one positive regulator of the complement system. In this study, we characterize the prevalence, functional consequences and disease associations of autoantibodies against properdin in a cohort of patients with autoimmune disease systemic lupus erythematosus (SLE), suffering from lupus nephritis (LN). We detected autoantibodies against properdin in plasma of 22.5% of the LN patients (16/71) by ELISA. The binding of these autoantibodies to properdin was dose-dependent and was validated by surface plasmon resonance. Higher levels of anti-properdin were related to high levels of anti-dsDNA and ANA and to low concentrations of C3 and C4 in patients and also with histological signs of LN activity and chronicity. The high negative predictive value (NPV) of anti-properdin and anti-dsDNA combination suggested that patients who are both negative for anti-properdin and anti-dsDNA will not have severe nephritis. IgG from anti- properdin positive patients’ plasma increased the C3b deposition on late apoptotic cells by flow cytometry. Nevertheless, these IgGs did not modify substantially the binding of properdin to C3b, the C3 convertase C3bBb and the pro-convertase C3bB, evaluated by surface plasmon resonance. In conclusion, anti- properdin autoantibodies exist in LN patients. They have weak but relevant functional consequences, which could have pathological significance.