Evaluation of classical complement pathway activation in rheumatoid arthritis: measurement of C1q-C4 complexes as novel activation products

The effect of modified Qiyuan paste on mice with low immunity and sleep deprivation by regulating GABA nerve and immune system

BACKGROUND

Low immunity and sleep disorders are prevalent suboptimal health conditions in contemporary populations, which render them susceptible to the infiltration of pathogenic factors. LJC, which has a long history in traditional Chinese medicine for nourishing the Yin and blood and calming the mind, is obtained by modifying Qiyuan paste. Dendrobium officinale Kimura et Migo has been shown to improve the immune function in sleep-deprived mice. In this study, based on the traditional Chinese medicine theory, LJC was prepared by adding D. officinale Kimura et Migo to Qiyuan paste decoction.

METHODS

Indicators of Yin deficiency syndrome, such as back temperature and grip strength, were measured in each group of mice; furthermore, behavioral tests and pentobarbital sodium-induced sleep tests were performed. An automatic biochemical analyzer, enzyme-linked immunosorbent assay kit, and other methods were used to determine routine blood parameters, serum immunoglobulin (IgG, IgA, and IgM), cont (C3, C4), acid phosphatase (ACP) and lactate dehydrogenase (LDH) levels in the spleen, serum hemolysin, and delayed-type hypersensitivity (DTH) levels. In addition, serum levels of γ-aminobutyric acid (GABA) and glutamate (Glu) were detected using high-performance liquid chromatography (HPLC). Hematoxylin-eosin staining and Nissl staining were used to assess the histological alterations in the hypothalamus tissue. Western blot and immunohistochemistry were used to detect the expressions of the GABA pathway proteins GABRA1, GAD, GAT1, and GABAT1 and those of CD4+ and CD8+ proteins in the thymus and spleen tissues.

RESULTS

The findings indicated that LJC prolonged the sleep duration, improved the pathological changes in the hippocampus, effectively upregulated the GABA content in the serum of mice, downregulated the Glu content and Glu/GABA ratio, enhanced the expressions of GABRA1, GAT1, and GAD, and decreased the expression of GABAT1 to assuage sleep disorders. Importantly, LJC alleviated the damage to the thymus and spleen tissues in the model mice and enhanced the activities of ACP and LDH in the spleen of the immunocompromised mice. Moreover, serum hemolysin levels and serum IgG, IgA, and IgM levels increased after LJC administration, which manifested as increased CD4+ content, decreased CD8+ content, and enhanced DTH response. In addition, LJC significantly increased the levels of complement C3 and C4, increased the number of white blood cells and lymphocytes, and decreased the percentage of neutrophils in the blood.

CONCLUSIONS

LJC can lead to improvements in immunocompromised mice models with insufficient sleep. The underlying mechanism may involve regulation of the GABA/Glu content and the expression levels of GABA metabolism pathway-related proteins in the brain of mice, enhancing their specific and nonspecific immune functions.

Complement factor H attenuates TNF-α-induced inflammation by upregulating EIF3C in rheumatoid arthritis

OBJECTIVE

To explore the role and underlying mechanism of Complement Factor H (CFH) in the peripheral and joint inflammation of RA patients.

METHODS

The levels of CFH in the serum and synovial fluid were determined by ELISA. The pyroptosis of monocytes was determined by western blotting and flow cytometry. The inflammation cytokine release was tested by ELISA. The cell migration and invasion ability of fibroblast-like synoviocytes (FLS) were tested by Wound healing Assay and transwell assay, respectively. The potential target of CFH was identified by RNA sequencing.

RESULTS

CFH levels were significantly elevated in the serum and synovial fluid from RA and associated with high sensitivity C-reactive protein (hs-CRP), erythrocyte sedimentation rate (ESR), and disease activity score 28 (DAS28). TNF-α could inhibit CFH expression, and CFH combined with TNF-α significantly decreased cell death, cleaved-caspase 3, gasdermin E N-terminal (GSDME-N), and inflammatory cytokines release (IL-1β and IL-6) of RA-derived monocytes. Stimulated with TNF-α increased CFH levels in RA FLS and CFH inhibits the migration, invasion, and TNF-α-induced production of inflammatory mediators, including proinflammatory cytokines (IL-6, IL-8) as well as matrix metalloproteinases (MMPs, MMP1 and MMP3) of RA FLSs. The RNA-seq results showed that CFH treatment induced upregulation of eukaryotic translation initiation factor 3 (EIF3C) in both RA monocytes and FLS. The migration of RA FLSs was promoted and the expressions of IL-6, IL-8, and MMP-3 were enhanced upon EIF3C knockdown under the stimulation of CFH combined with TNF-α.

CONCLUSION

In conclusion, we have unfolded the anti-inflammatory roles of CFH in the peripheral and joints of RA, which might provide a potential therapeutic target for RA patients.

Overview on the Link Between the Complement System and Auto-Immune Articular and Pulmonary Disease

Complement system (CS) dysregulation is a key factor in the pathogenesis of different autoimmune diseases playing a central role in many immune innate and adaptive processes. Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by ta breach of self-tolerance leading to a synovitis and extra-articular manifestations. The CS is activated in RA and seems not only to mediate direct tissue damage but also play a role in the initiation of RA pathogenetic mechanisms through interactions with citrullinated proteins. Interstitial lung disease (ILD) represents the most common extra-articular manifestation that can lead to progressive fibrosis. In this review, we focused on the evidence of CS dysregulation in RA and in ILD, and highlighted the role of the CS in both the innate and adaptive immune responses in the development of diseases, by using idiopathic pulmonary fibrosis as a model of lung disease. As a proof of concept, we dissected the evidence that several treatments used to treat RA and ILD such as glucocorticoids, pirfenidone, disease modifying antirheumatic drugs, targeted biologics such as tumor necrosis factor (TNF)-inhibitors, rituximab, tocilizumab, and nintedanib may act indirectly on the CS, suggesting that the CS might represent a potential therapeutic target in these complex diseases.

Association of C1q gene cluster variants with rheumatoid arthritis: a pilot study

Single-nucleotide polymorphisms (SNPs) in C1q gene cluster were previously linked to autoimmunity and SLE, but data are scarce for their association with RA. In the present study, we evaluated associations of five SNPs (rs665691, rs682658, rs172378, rs292001 and rs294179) in the C1q genetic region with RA and some of its clinical and immunologic characteristics. Fifty-eight RA patients and 67 age- and gender-matched healthy controls, all Caucasian, participated in the study. They were genotyped for the five SNPs using TaqMan allelic discrimination assay, and their C1q levels were estimated by ELISA. Rheumatoid factor and anti-citrullinated peptide antibodies were measured (using latex agglutination and ELISA resp.) in the RA patients' group and relevant clinical information was collected. RA patients and healthy controls had similar frequencies of alleles and genotypes of rs665691, rs682658 and rs294179. Minor G-allele and GG genotype of rs172378 were associated with RA (OR = 2.80; 95% CI 1.62-4.81; p = 0.0002 and OR = 5.01; 95% CI 1.55-16.24; p = 0.007, resp.), as well as AA genotype of rs292001 (OR = 3.23; 95% CI 1.15-9.08; p = 0.026). C1q levels were significantly lower (still normal) in RA patients' group compared to healthy volunteers: 89 µg/ml (68-121) vs 114 µg/ml (60-169), p < 0.0001. Significant association was established between rs172378 and rs292001 and RA, in contrast to rs665691, rs682658 and rs294179. RA patients had lower C1q levels than healthy controls. Our findings correspond to the scientific knowledge so far and add additional clarity from a Bulgarian cohort.

Complement as a Therapeutic Target in Systemic Autoimmune Diseases

The complement system (CS) includes more than 50 proteins and its main function is to recognize and protect against foreign or damaged molecular components. Other homeostatic functions of CS are the elimination of apoptotic debris, neurological development, and the control of adaptive immune responses. Pathological activation plays prominent roles in the pathogenesis of most autoimmune diseases such as systemic lupus erythematosus, antiphospholipid syndrome, rheumatoid arthritis, dermatomyositis, and ANCA-associated vasculitis. In this review, we will review the main rheumatologic autoimmune processes in which complement plays a pathogenic role and its potential relevance as a therapeutic target.

Associations Between Complement Components and Vitamin D and the Physical Activities of Daily Living Among a Longevous Population in Hainan, China

Background: Vitamin D and complement components shared some common pathophysiological pathways in the musculoskeletal system, circulation, and metabolism, which were linked to physical function. It is hypothesized that serum complement components may interact with vitamin D in respect of the physical activities of daily living (PADLs). Objective: To investigate if serum complement components 3 (C3), complement components 4 (C4), and 25-hydroxyvitamin D [25(OH)D] associate with PADLs, and to examine whether the association between 25(OH)D levels and PADLs varies at different complement component levels among Chinese centenarians. Methods: This study was conducted in a group of population-based centenarians. PADLs were evaluated using the Barthel Index. Multiple regressions were used to analyze the associations among 25(OH)D, complements C3 and C4, and PADLs. Results: Among 943 participants, 672 (71.3%) had physical dependence (PD). After adjusting for potential confounders, serum 25(OH)D and C3 levels were positively correlated with PADLs, while C4 levels were negatively correlated with PADLs (Ps < 0.05). Serum 25(OH)D levels significantly interacted with both C3 (P for interaction = 0.033) and C4 (P for interaction = 0.006) levels on PADLs. At lower complement component levels, the multivariate odds ratios (ORs) of the upper tertile of vitamin D for PD were 0.32 (95% CI: 0.18-0.55) in the C3 group and 0.29 (95% CI: 0.16-0.50) in the C4 group. At higher complement component levels, the ORs in the C3 and C4 groups were not statistically significant. Conclusions: In a group of population-based Chinese centenarians, we observed that serum complement C3 and 25(OH)D levels were positively associated with PADLs, while C4 was negatively associated with PADLs. The associations between 25(OH)D levels and PADLs were more pronounced in groups with lower serum complement component levels.

Increased Nonexudative Age-Related Macular Degeneration Diagnosis Among Medicare Beneficiaries With Rheumatoid Arthritis

Purpose

AMD is the leading cause of blindness in the United States. The role of secondary inflammatory disease on AMD progression is largely unknown. Here we investigate the association between AMD and rheumatoid arthritis (RA), using MarketScan data for patients aged ≥65 years on Medicare.

Methods

Baseline data were extracted for subjects with at least two International Classification, Ninth Revision (ICD-9) diagnosis codes of RA and control subjects (no RA) and were matched at baseline by propensity score. Matched cohort data were extracted post-baseline time and examined up to 4.5 years of follow-up for ICD-9 diagnosis code AMD records. Multivariable regression models compared risk of an AMD diagnosis post-baseline for RA subjects and matched controls. Days until first AMD diagnosis between RA patients and controls was examined using survival analysis.

Results

Risk of new AMD diagnosis was elevated in RA patients (odds ratio [OR] 2.08; 95% confidence interval [CI] 1.98–2.18), with an increase in nonexudative AMD patients (P < 0.0001). Risk was elevated in female (n = 27,548) (OR 1.11; 95% CI 1.05–1.17) compared with male (n = 9704; P < 0.001) patients. The time to first AMD diagnosis was shorter for RA subjects than controls (P < 0.0001).

Conclusions

Our analysis provides support of association between RA diagnosis and increased nonexudative AMD diagnosis.

Establishment of anti-C1q monoclonal antibodies to measure serum C1q levels discriminating disease severity subsets of rheumatoid arthritis within 5 years of onset

Objectives: To establish anti-C1q monoclonal antibodies which can measure serum C1q levels discriminating disease severity subsets of rheumatoid arthritis (RA) within 5 years of onset.Methods: In this multi-centre, longitudinal, observational study, 122 RA patients [102 females, baseline age 58.5 years, rheumatoid factor (RF) positivity 78.7%, serum C-reactive protein (CRP) 1.2 mg/dl, and concomitant methotrexate (MTX) 4.9 mg/week (29.5%)] within 5 years of onset (disease duration 21.0 months) were enrolled from 1985 to 2000. Patients were not treated by more than 8 mg/week of MTX or biologics which may strongly affect the course of joint destruction. Disease severity at 10-15 years of onset was classified according to the number of destructed joints of overall 68 joints on plain radiographs (36 patients were mild RA group involving only peripheral joints and 86 were severe RA group involving large axial joints). Baseline serum C1q levels were evaluated by ELISA with newly developed 4 monoclonal anti-C1q antibodies, and compared between two groups as well as conventional RA disease activity markers.Results: There were no significant differences between two groups in baseline conventional RA disease activity markers such as RF, erythrocyte sedimentation rate, CRP, and matrix metalloproteinase-3. However, compared to mild RA group, severe RA group showed higher baseline serum C1q levels (μg/ml) evaluated by anti-C1q monoclonal antibodies of no.33 (104.8 ± 22.3 vs. 118.3 ± 19.3; p = .0024), no. 40 (102.6 ± 21.9 vs 121.2 ± 22.3; p = .000069), no. 54 (102.1 ± 22.5 vs. 119.3 ± 26.9; p = .00052), and no. 76 (105.6 ± 21.8 vs. 122.6 ± 26.4; p = .00043). Receiver operating characteristic curve analysis revealed that in patients with serum C1q levels of ≥110.5 μg/ml (measured by antibody no. 40), 78.9% (75/95) belonged to severe RA group.Conclusion: Measuring serum C1q levels of RA within 5 years of onset by newly developed anti-C1q antibodies may be useful in predicting the prognosis of disease severity evaluated by the extent of joint destruction.

Development of a Novel Diagnostic Biomarker Set for Rheumatoid Arthritis Using a Proteomics Approach

Background

Rheumatoid arthritis (RA) is an autoimmune disease that starts with inflammation of the synovial membrane. Studies have been conducted to develop methods for efficient diagnosis of RA and to identify the mechanisms underlying RA development. Blood samples can be useful for detecting disturbance of homeostasis in patients with RA. Nanoliquid chromatography-tandem mass spectrometry (LC-MS/MS) is an efficient proteomics approach to analyze blood sample and quantify serum proteins.

Methods

Serum samples of 18 healthy controls and 18 patients with RA were analyzed by LC-MS/MS. Selected candidate biomarkers were validated by enzyme-linked immunosorbent assay (ELISA) using sera from 43 healthy controls and 44 patients with RA.

Results

Thirty-eight proteins were significantly differentially expressed by more than 2-fold in healthy controls and patients with RA. Based on a literature survey, we selected six candidate RA biomarkers. ELISA was used to evaluate whether these proteins effectively allow distinguishing patients with RA from healthy controls and monitoring drug efficacy. SAA4, gelsolin, and vitamin D-binding protein were validated as potential biomarkers of RA for screening and drug efficacy monitoring of RA.

Conclusions

We identified a panel of three biomarkers for RA which has potential for application in RA diagnosis and drug efficacy monitoring. Further, our findings will aid in understanding the pathogenesis of RA.

C5a and C5aR are elevated in joints of rheumatoid and psoriatic arthritis patients, and C5aR blockade attenuates leukocyte migration to synovial fluid

Complement activation correlates to rheumatoid arthritis disease activity, and increased amounts of the complement split product C5a is observed in synovial fluids from rheumatoid arthritis patients. Blockade of C5a or its receptor (C5aR) is efficacious in several arthritis models. The aim of this study was to investigate the role of C5a and C5aR in human rheumatoid arthritis and psoriatic arthritis–both with respect to expression and function. Synovial fluid, blood and synovial samples were obtained from rheumatoid arthritis, psoriatic arthritis and osteoarthritis patients as a less inflammatory arthritis type, and blood from healthy subjects. Cells infiltrating synovial tissue were analysed by immunohistochemistry and flow cytometry. SF and blood were analysed for biomarkers by flow cytometry or ELISA. The effect of a blocking anti-human C5aR mAb on leukocyte migration was determined using a Boyden chamber. Appropriate statistical tests were applied for comparisons. C5aR⁺ cells were detected in most rheumatoid arthritis, in all psoriatic arthritis, but not in non-inflammatory control synovia. C5aR⁺ cells were primarily neutrophils and macrophages. C5aR⁺ macrophages were mainly found in lymphoid aggregates in close contact with T cells. C5a levels were increased in both rheumatoid arthritis and psoriatic arthritis synovial fluid compared to osteoarthritis, and in blood from rheumatoid arthritis compared to healthy subjects. Neutrophil and monocyte migration to rheumatoid arthritis synovial fluid was significantly inhibited by anti-C5aR. The data support that the C5a-C5aR axis may be driving the infiltration of inflammatory cells into the synovial fluid and synovium in both rheumatoid and psoriatic arthritis, and suggest that C5a or C5aR may be a promising treatment target in both diseases.

Fingerprinting of anti-citrullinated protein antibodies (ACPA): specificity, isotypes and subclasses

Anti-citrullinated protein antibodies (ACPA) are a family of rheumatoid arthritis (RA)-specific autoantibodies that recognize the amino acid citrulline, resulting from the post-translational modification of arginine. Peptidyl arginine deiminase, the enzyme responsible for citrullination, is present in humans in different isoforms with different tissue distribution, enzymatic activity and target specificity; nonetheless, the number of proteins citrullinated in physiological or pathological conditions is wide, but not every citrullinated protein is a target for antibodies. In pre-RA patients the immune response to citrullinated antigens is initially restricted, expands with time and, after the onset of the disease, is relatively stable. ACPA are heterogeneous in terms of not only fine specificity but also isotype and IgG subclasses usage. This heterogeneity may be relevant for the immunopathogenesis of RA, conditioning the interaction of antibodies with complement and Fc receptors.

Association of complement factor B allotypes and serum biomarkers in rheumatoid arthritis patients and their relatives

The aim of the study was to investigate the allotypic variability of complement factor B (BF) in patients and relatives with rheumatoid arthritis (RA) and its association with serological biomarkers and clinical features of the disease. BF allotypes were determined by high-voltage agarose gel electrophoresis in serum samples of 180 patients with RA, 198 relatives and 98 controls from Southern Brazil. Anticyclic citrullinated peptide (anti-CCP), antimutated citrullinated vimentin (anti-MCV) and IgA-rheumatoid factor (RF) were determined by ELISA and IgM-RF by latex agglutination in all samples. No significant differences were found in the allotypic variants of BF between patients with RA, relatives and controls, nor associations with gender and age of RA onset. BF*S07 allotype was significantly associated with extra-articular manifestations (EAMs; Secondary Sjögren Syndrome, pneumonitis, rheumatoid nodules) in patients with RA (P = 0.02; OR = 6.62). Patients with phenotype BF F had lower positivity for anti-MCV biomarker (P = 0.02; OR = 0.22) and those with allotype BF*S had higher prevalence of this autoantibody (P = 0.02; OR = 3.77). An increased frequency of RF-IgA was detected in relatives of patients with RA with BF FS07 phenotype (P = 0.02; OR = 7.78). Complement BF variability did not influence the development of RA in the studied patients, but BF variants may act as markers of disease prognosis, such as development of EAMs, corroborating with the role of the alternative pathway in the pathogenesis of RA.

Fcγ and Complement Receptors and Complement Proteins in Neutrophil Activation in Rheumatoid Arthritis: Contribution to Pathogenesis and Progression and Modulation by Natural Products

Rheumatoid arthritis (RA) is a highly disabling disease that affects all structures of the joint and significantly impacts on morbidity and mortality in RA patients. RA is characterized by persistent inflammation of the synovial membrane lining the joint associated with infiltration of immune cells. Eighty to 90% of the leukocytes infiltrating the synovia are neutrophils. The specific role that neutrophils play in the onset of RA is not clear, but recent studies have evidenced that they have an important participation in joint damage and disease progression through the release of proteolytic enzymes, reactive oxygen species (ROS), cytokines, and neutrophil extracellular traps, in particular during frustrated phagocytosis of immune complexes (ICs). In addition, the local and systemic activation of the complement system contributes to the pathogenesis of RA and other IC-mediated diseases. This review discusses (i) the participation of Fcγ and complement receptors in mediating the effector functions of neutrophils in RA; (ii) the contribution of the complement system and ROS-dependent and ROS-independent mechanisms to joint damage in RA; and (iii) the use of plant extracts, dietary compounds, and isolated natural compounds in the treatment of RA, focusing on modulation of the effector functions of neutrophils and the complement system activity and/or activation.

Essential role for the lectin pathway in collagen antibody-induced arthritis revealed through use of adenovirus programming complement inhibitor MAp44 expression

Previous studies using mannose-binding lectin (MBL) and complement C4-deficient mice have suggested that the lectin pathway (LP) is not required for the development of inflammatory arthritis in the collagen Ab-induced arthritis (CAIA) model. MBL, ficolins and collectin-11 are key LP pattern recognition molecules that associate with three serine proteases-MASP-1, MASP-2, and MASP-3-and with two MBL-associated proteins designated sMAP and MBL-associated protein of 44kDA (MAp44). Recent studies have shown that MAp44, an alternatively spliced product of the MASP-1/3 gene, is a competitive inhibitor of the binding of the recognition molecules to all three MASPs. In these studies, we examined the effect of treatment of mice with adenovirus (Ad) programmed to express human MAp44 (AdhMAp44) on the development of CAIA. AdhMAp44 and Ad programming GFP (AdGFP) expression were injected i.p. in C57BL/6 wild type mice prior to the induction of CAIA. AdhMAp44 significantly reduced the clinical disease activity (CDA) score by 81% compared with mice injected with AdGFP. Similarly, histopathologic injury scores for inflammation, pannus, cartilage and bone damage, as well as C3 deposition in the cartilage and synovium, were significantly reduced by AdhMAp44 pretreatment. Mice treated with AdmMAp44, programming expression of mouse MAp44, also showed significantly decreased CDA score and histopathologic injury scores. In addition, administration of AdhMAp44 significantly diminished the severity of Ross River virus-induced arthritis, an LP-dependent model. Our study provides conclusive evidence that an intact complement LP is essential to initiate CAIA, and that MAp44 may be an appropriate treatment for inflammatory arthritis.

Genetic variants in the region of the C1q genes are associated with rheumatoid arthritis

Rodent models for arthritis implicate a role for complement in disease development and progression. In humans, complement deposition has been observed in inflamed synovia of rheumatoid arthritis (RA) patients. In this study we analysed whether genetic variants of complement component C1q predispose to RA. We genotyped single nucleotide polymorphisms (SNPs) in and around the C1q genes, C1qA, C1qB and C1qC, in a Dutch set of 845 RA cases and 1046 controls. Replication was sought in a sample set from North America (868 cases/1193 controls), and a meta-analysis was performed in a combined samples set of 8000 cases and 23 262 controls of European descent. We determined C1q serum levels in relation to C1q genotypes. In the discovery phase, five of the 13 SNPs tested in the C1q genes showed a significant association with RA. Additional analysis of the genomic area around the C1q genes revealed that the strongest associating SNPs were confined to the C1q locus. Within the C1q locus we observed no additional signal independent of the strongest associating SNP, rs292001 [odds ratio (OR) = 0·72 (0·58-0·88), P = 0·0006]. The variants of this SNP were associated with different C1q serum levels in healthy controls (P = 0·006). Interestingly, this SNP was also associated significantly in genome-wide association studies (GWAS) from the North American Rheumatoid Arthritis Consortium study, confirming the association with RA [OR = 0·83 (0·69-1·00), P = 0·043]. Combined analysis, including integrated data from six GWAS studies, provides support for the genetic association. Genetic variants in C1q are correlated with C1q levels and may be a risk for the development of RA.

Roles of adipocytes and fibroblasts in activation of the alternative pathway of complement in inflammatory arthritis in mice

The complement system is involved in mediation of joint damage in rheumatoid arthritis, with evidence suggesting activation of both the classical and alternative pathway (AP). The AP is both necessary and sufficient to mediate collagen Ab-induced arthritis, an experimental animal model of immune complex-induced joint disease. The AP in mice is dependent on MASP-1/3 cleavage of pro-factor D (pro-FD) into mature factor D (FD). The objectives of the current study were to determine the cells synthesizing MASP-1/3 and pro-FD in synovial tissue. Collagen Ab-induced arthritis was studied in wild-type C57BL/6 mice, and the localization of mRNA and protein for FD and MASP-1/3 in synovial adipose tissue (SAT) and fibroblast-like synoviocytes (FLS) was determined using various techniques, including laser capture microdissection. SAT was the sole source of mRNA for pro-FD. Cultured differentiated 3T3 adipocytes, a surrogate for SAT, produced pro-FD but no mature FD. FLS were the main source of MASP-1/3 mRNA and protein. Using cartilage microparticles (CMPs) coated with anti-collagen mAb and serum from MASP-1/3(-/-) mice as a source of factor B, pro-FD in 3T3 supernatants was cleaved into mature FD by MASP-1/3 in FLS supernatants. The mature FD was eluted from the CMP, and was not present in the supernatants from the incubation with CMP, indicating that cleavage of pro-FD into mature FD by MASP-1 occurred on the CMP. These results demonstrate that pathogenic activation of the AP can occur in the joint through immune complexes adherent to cartilage and the local production of necessary AP proteins by adipocytes and FLS.

Interactions of the complement system with molecules of extracellular matrix: relevance for joint diseases

Rheumatoid arthritis (RA) is a highly disabling disease affecting all structures of the joint. Understanding the pathology behind the development of RA is essential for developing targeted therapeutic strategies as well as for developing novel markers to predict disease onset. Several molecules normally hidden within the cartilage tissue are exposed to complement components in the synovial fluid upon cartilage breakdown. Some of these have been shown to activate complement and toll-like receptors, which may enhance an already existing inflammatory response, thereby worsening the course of disease. Other cartilage-resident molecules have in contrast shown to possess complement-inhibitory properties. Knowledge about mechanisms behind pathological complement activation in the joints will hopefully lead to methods which allow us to distinguish patients with pathological complement activation from those where other inflammatory pathways are predominant. This will help to elucidate which patients will benefit from complement inhibitory therapies, which are thought to aid a specific subset of patients or patients at a certain stage of disease. Future challenges are to target the complement inhibition specifically to the joints to minimize systemic complement blockade.

Mannose binding lectin is required for alphavirus-induced arthritis/myositis

Mosquito-borne alphaviruses such as chikungunya virus and Ross River virus (RRV) are emerging pathogens capable of causing large-scale epidemics of virus-induced arthritis and myositis. The pathology of RRV-induced disease in both humans and mice is associated with induction of the host inflammatory response within the muscle and joints, and prior studies have demonstrated that the host complement system contributes to development of disease. In this study, we have used a mouse model of RRV-induced disease to identify and characterize which complement activation pathways mediate disease progression after infection, and we have identified the mannose binding lectin (MBL) pathway, but not the classical or alternative complement activation pathways, as essential for development of RRV-induced disease. MBL deposition was enhanced in RRV infected muscle tissue from wild type mice and RRV infected MBL deficient mice exhibited reduced disease, tissue damage, and complement deposition compared to wild-type mice. In contrast, mice deficient for key components of the classical or alternative complement activation pathways still developed severe RRV-induced disease. Further characterization of MBL deficient mice demonstrated that similar to C3^−/− mice, viral replication and inflammatory cell recruitment were equivalent to wild type animals, suggesting that RRV-mediated induction of complement dependent immune pathology is largely MBL dependent. Consistent with these findings, human patients diagnosed with RRV disease had elevated serum MBL levels compared to healthy controls, and MBL levels in the serum and synovial fluid correlated with severity of disease. These findings demonstrate a role for MBL in promoting RRV-induced disease in both mice and humans and suggest that the MBL pathway of complement activation may be an effective target for therapeutic intervention for humans suffering from RRV-induced arthritis and myositis.

Arthritogenic alphaviruses such as Ross River virus (RRV) and chikungunya virus are transmitted to humans by mosquitoes and cause epidemics of debilitating infectious arthritis and myositis in various areas around the world. Studies in humans and mice indicate that the host inflammatory response is critical for development of RRV-induced arthritis and myositis, and the host complement system, a component of the host inflammatory response, plays an essential role in the development of RRV-induced disease through activation of complement receptor 3 (CR3)-bearing inflammatory cells. Of the three main complement activation pathways, only the lectin pathway activated by mannose binding lectin (MBL) was essential for RRV-induced complement activation, tissue destruction, and disease. Furthermore, we found that levels of MBL were elevated in human patients suffering from RRV-induced polyarthritis and MBL levels correlated with disease severity. Taken together, our data implicates a role for MBL in mediating RRV-induced disease in both humans and mice, and suggests that therapeutic targeting of MBL may be an effective strategy for disease treatment in humans.

Serum COMP-C3b complexes in rheumatic diseases and relation to anti-TNF-α treatment

INTRODUCTION

Cartilage oligomeric matrix protein (COMP) is found at elevated concentrations in sera of patients with joint diseases such as rheumatoid arthritis (RA) and osteoarthritis (OA). We recently showed that COMP activates complement via the alternative pathway and that COMP-C3b complexes are present in sera of RA patients, but not in healthy controls. We now set out to elaborate on the information provided by this marker in a variety of diseases and larger patient cohorts.

METHODS

COMP-C3b levels in sera were measured by using an enzyme-linked immunosorbent assay (ELISA) capturing COMP and detecting C3b. Serum COMP was measured by using ELISA.

RESULTS

COMP-C3b levels were significantly elevated in patients with RA as well as in systemic lupus erythematosus (SLE), compared with healthy controls. SLE patients with arthritis had significantly higher COMP-C3b levels than did those without. COMP-C3b was furthermore elevated in patients with ankylosing spondylitis (AS), psoriatic arthritis (PsA), reactive arthritis, systemic sclerosis, and OA. COMP-C3b did not correlate with COMP in any of the patient groups. COMP-C3b correlated with disease activity in RA, but not in other diseases. COMP-C3b levels in RA patients decreased on treatment with tumor necrosis factor (TNF)-α inhibitors, whereas the levels increased in patients with AS or PsA. The changes of COMP-C3b did not parallel the changes of C-reactive protein (CRP).

CONCLUSIONS

COMP-C3b levels are elevated in several rheumatologic diseases and correlate with inflammatory measures in RA. COMP-C3b levels in RA decrease during TNF-α inhibition differently from those of CRP, suggesting that formation of COMP-C3b relates to disease features not reflected by general inflammation measures.

Association study of C1qA polymorphisms with systemic lupus erythematosus in a Han population

Objective: The aim of this study was to evaluate the association of single nucleotide polymorphisms (SNPs) in the C1qA gene region with systemic lupus erythematosus (SLE) in a Chinese Han population. Methods: Chinese SLE patients ( n = 748) and ethnically- and geographically-matched healthy controls ( n = 750) were genotyped for the C1qA region SNPs, rs172378 and rs665691, by using the Sequenom MassArray system. Results: The Chinese Han SLE patients and controls had statistically similar frequencies of alleles, genotypes, and haplotypes of C1qA polymorphisms. Moreover, no association signal was detected on different genetic models (additive, dominant, and recessive) or in SLE subgroups stratified by various clinical manifestations. Conclusions: The C1qA SNPs, rs172378 and rs665691, confer no genetic predisposition to SLE in a Chinese Han population.

Arthrogenicity of type II collagen monoclonal antibodies associated with complement activation and antigen affinity

Background

The collagen antibody-induced arthritis (CAIA) model, which employs a cocktail of monoclonal antibodies (mAbs) to type II collagen (CII), has been widely used for studying the pathogenesis of autoimmune arthritis. In this model, not all mAbs to CII are capable of inducing arthritis because one of the initial events is the formation of collagen-antibody immune complexes on the cartilage surface or in the synovium, and subsequent activation of the complement by the complexes induces arthritis, suggesting that a combination of mAbs showing strong ability to bind mouse CII and activate the complement may effectively induce arthritis in mice. In the present study, we examined the relationship between the induction of arthritis by the combination of IgG2a (CII-6 and C2A-12), IgG2b (CII-3, C2B-14 and C2B-16) and IgM (CM-5) subclones of monoclonal antibodies (mAb) of anti-bovine or chicken CII and the ability of mAbs to activate complement and bind mouse CII.

Methods

DBA/1J mice were injected with several combinations of mAbs followed by lipopolysaccharide. Furthermore, the ability of mAbs to activate the complement and bind mouse CII was examined by ELISA.

Results

First, DBA/1J mice were injected with the combined 4 mAbs (CII-3, CII-6, C2B-14, and CM-5) followed by lipopolysaccharide, resulting in moderate arthritis. Excluding one of the mAbs, i.e., using only CII-3, CII-6, and C2B-14, induced greater inflammation of the joints. Next, adding C2A-12 but not C2B-16 to these 3 mAbs produced more severe arthritis. A combination of five clones, consisting of all 5 mAbs, was less effective. Histologically, mice given the newly developed 4-clone cocktail had marked proliferation of synovial tissues, massive infiltration by inflammatory cells, and severe destruction of cartilage and bone. Furthermore, 4 of the 6 clones (CII-3, CII-6, C2B-14, and C2A-12) showed not only a strong cross-reaction with mouse CII but also marked activation of the complement in vitro.

Conclusion

The combination of 4 mAbs showing strong abilities to activate the complement and bind mouse CII effectively induced arthritis in DBA/1J mice. This in vitro system may be useful for the selection of mAbs associated with the development of arthritis.

Suppression of antibody-mediated arthritis in mice by Fab fragments of the mediating antibodies

BACKGROUND AND PURPOSE

Fab fragments (Fabs) of antibodies maintain the ability to bind specific antigens, but lack the binding site for complement as well as the site for binding to receptors on effector cells, such as macrophages that play an important role in inflammation. In the present study, we investigated whether Fabs specific for ovalbumin (OVA) were specifically able to suppress anti-OVA antibody-mediated arthritis (AOA-MA) in mice.

EXPERIMENTAL APPROACH

AOA-MA was induced by i.v. injection of purified anti-OVA antibodies into naïve mice followed by intra-articular (left ankle) challenge with the antigen. Anti-OVA Fabs prepared by digestion of anti-OVA antibodies with papain were injected i.v. immediately after administration of the intact antibodies. Normal Fabs were used as a control. Arthritis was assessed by thickness of the joints (caliper) and by histology of paw sections, stained with haematoxylin and eosin.

KEY RESULTS

AOA-MA was markedly suppressed by anti-OVA Fabs, but not by control Fabs. Histologically, mice treated with control Fabs showed marked oedema of synovial tissues with a large number of inflammatory cells including neutrophils, whereas animals given anti-OVA Fabs had mild oedema of the synovium and sparse infiltration of such cells. The antigen-specific suppression of joint inflammation by anti-OVA Fabs was associated with reduced consumption of complement. In vitro studies showed that anti-OVA Fabs significantly blocked the binding of intact anti-OVA antibodies to OVA.

CONCLUSIONS AND IMPLICATIONS

Antibody-mediated arthritis appears to be specifically down-regulated by Fabs that competitively inhibit the binding of antibodies to antigens.

Complement system and rheumatoid arthritis: relationships with autoantibodies, serological, clinical features, and anti-TNF treatment

Autoantibodies (rheumatoid factor, RF; anti-citrullinated-protein antibodies, ACPA) and complement system are involved in rheumatoid arthritis (RA). ACPA and anti-TNF agents are capable of in vitro modulating complement activity. We investigated the relationships between complement, autoantibodies, and anti-TNF treatment in vivo. One-hundred fourteen RA patients (89F/25M), diagnosed according to 1987 ACR criteria, and 30 healthy controls were enrolled. Serological analysis included ESR, CRP, complement C3, C4 and CH50, RF and ACPA (ELISA, cut-off>20 U/ml). Split-products (SP) of C3 and B were studied by immunoelectrophoresis/counterimmunoelectrophoresis. Seventy-six patients started anti-TNF treatment and were studied at baseline and after 22 weeks. Disease activity was measured with DAS28 and response to therapy with EULAR criteria. At baseline, RA patients showed significantly higher levels of C3 and C4 than controls (C3 127.9±26.5 vs 110±25 mg/dl, P=0.0012; C4 29.7±10.2 vs 22.7±8.3mg/dl, P=0.0003). No differences in C3, C4 and CH50 levels were observed between ACPA+ (n=76) and ACPA- (n=38) patients. After 22 weeks of anti-TNF, C3, C4 and RF were significantly reduced (P<0.003, <0.005 and <0.04, respectively) and RF changes showed negative correlation with CH50. SP of C3 and B were observed neither at baseline nor after 22 weeks. DAS28 significantly improved after 22 weeks. Patients showing higher baseline C3 or lower reduction of C3 levels after 22 weeks had a worse EULAR outcome (X2=22.793, P<0.001). RF levels seem to correlate with complement CH50. The presence of high levels of C3 in RA patients may reflect a pro-inflammatory status and represent a negative prognostic factor for anti-TNF therapy.

Innate immunity and rheumatoid arthritis

Innate immunity, with macrophages playing a central role, is critically important in the pathogenesis of RA. Although environmental insults such as smoking have been implicated in the initiation of rheumatoid arthritis (RA) in patients who express the shared epitope, the understanding of the role of innate immunity in the pathogenesis of this disease is also expanding. As the understanding continues to expand, enticing targets for new therapeutic interventions continue to be identified. This article focuses on cells of myelomonocytic origin, their receptors, and factors that interact with them.

The complement cascade as a mediator of tissue growth and regeneration

Recent evidence has demonstrated that the complement cascade is involved in a variety of physiologic and pathophysiologic processes in addition to its role as an immune effector. Research in a variety of organ systems has shown that complement proteins are direct participants in maintenance of cellular turnover, healing, proliferation and regeneration. As a physiologic housekeeper, complement proteins maintain tissue integrity in the absence of inflammation by disposing of cellular debris and waste, a process critical to the prevention of autoimmune disease. Developmentally, complement proteins influence pathways including hematopoietic stem cell engraftment, bone growth, and angiogenesis. They also provide a potent stimulus for cellular proliferation including regeneration of the limb and eye in animal models, and liver proliferation following injury. Here, we describe the complement cascade as a mediator of tissue growth and regeneration.

Anti-cyclic citrullinated peptide antibodies from rheumatoid arthritis patients activate complement via both the classical and alternative pathways

OBJECTIVE

It has been suggested that anti-citrullinated protein antibodies (ACPAs) play an important role in the pathogenesis of rheumatoid arthritis (RA). To exert their pathologic effects, ACPAs must recruit immune effector mechanisms such as activation of the complement system. Mouse models of RA have shown that, surprisingly, arthritogenic antibodies activate the alternative pathway of complement rather than the expected classical pathway. This study was undertaken to investigate whether human anti-cyclic citrullinated peptide (anti-CCP) antibodies activate the complement system in vitro and, if so, which pathways of complement activation are used.

METHODS

We set up novel assays to analyze complement activation by anti-CCP antibodies, using cyclic citrullinated peptide-coated plates, specific buffers, and normal and complement-deficient sera as a source of complement.

RESULTS

Anti-CCP antibodies activated complement in a dose-dependent manner via the classical pathway of complement, and, surprisingly, via the alternative pathway of complement. The lectin pathway was not activated by anti-CCP antibodies. Complement activation proceeded in vitro up to the formation of the membrane attack complex, indicating that all activation steps, including the release of C5a, took place.

CONCLUSION

Our findings indicate that anti-CCP antibodies activate the complement system in vitro via the classical and alternative pathways but not via the lectin pathway. These findings are relevant for the design of interventions aimed at inhibition of complement-mediated damage in RA.

Immune Complexes and Complement in Serum and Synovial Fluid of Rheumatoid Arthritis Patients

Rheumatoid arthritis (RA) is predominantly an intraarticular inflammatory and autoimmune disease that involves different autoantibodies and effector mechanisms. The aim of the study was to determine the utility of Circulating Immune Complexes (CIC) and complement components (C3c, C4) as possible markers for the disease activity in laboratory diagnostics. In a cross-section study 59 patients, according to the clinical criteria, were categorized into two groups: group with moderate (MA, n=24), and group with severe activity (SA, n=35) of RA. The concentration of CIC, C3c and C4 in sera (S) and synovial fluids (SF) was examined by an immunonephelometric method in both groups and compared with values in the control group (n=15) of patients with lesions of the menisci. Obtained results showed that there was no statistical significance in the values of C3c and C4, in both biological fluids, among all tested groups. Significant differences were found in the levels of CIC in both fluids, while testing the parameters (× ± SD, IU/mL) in the sera of groups with SA and MA of RA: 7.43 ± 13.40; 3.01 ± 2.92 (p<0.05) and SF: 13.47 ± 21.1, 5.33 ± 7.53 (p<0.001), respectively. These differences were higher between the group with SA and CG. Results for the concentrations of CIC were significantly higher in SF compared to sera: in the RA group with SA by 77% and group with MA by about 82%. These data could provide a confirmation of the hypothesis about local, intraarticular autoantibodies and subsequent CIC production. It can be concluded that the examination of CIC concentration in serum, and where it is possible in SF, is a useful marker of disease activity in RA patients, in contrast to the tested components of the complement. This statement does not exclude their consumption within immune effector mechanisms, but elicits the possibility that lower molecular fragments (C3d, C4d), as well as the novel activation products, could be better disease activity markers in RA patients.

The soluble terminal complement complex (SC5b-9) up-regulates osteoprotegerin expression and release by endothelial cells: implications in rheumatoid arthritis

OBJECTIVE

Complement activation products contribute to a large number of inflammatory diseases, including RA. We have investigated whether osteoprotegerin (OPG) may concur with the soluble terminal complement complex (SC5b-9) to the inflammatory cascade characterizing RA.

METHODS

Levels of SC5b-9 and OPG in the plasma and SF of patients with active RA were determined by ELISA. The presence of SC5b-9 and OPG in RA synovial lesions was analysed by immunohistochemistry. Cultured endothelial cells were used for in vitro leucocyte/endothelial cell adhesion assays. In addition, endothelial cells were exposed to SC5b-9 in order to evaluate the effects on the production of OPG protein, as well as the activation of the OPG promoter.

RESULTS

Patients affected by active RA are characterized by elevated levels of both SC5b-9 and OPG in plasma and/or SF. Of note, we have observed a co-localization of SC5b-9 and OPG in endothelial cells of post-capillary venules of RA synovial lesions. Data on endothelial cell cultures showed that exposure to SC5b-9 induced the up-regulation of OPG expression/release, stimulating the transcriptional activity of the OPG promoter, and synergized with TNF-alpha in up-regulating OPG production.

CONCLUSIONS

Our findings demonstrate that SC5b-9 induces OPG production by endothelial cells and we propose that the SC5b-9-mediated up-regulation of OPG may be an important mechanism whereby complement contributes in promoting and/or enhancing the inflammation in RA.

Crosstalk between the alpha2beta1 integrin and c-met/HGF-R regulates innate immunity

Data from several investigators suggest that the alpha2beta1 integrin, a receptor for collagens, laminins, decorin, E-cadherin, matrix metalloproteinase-1, endorepellin, and several viruses, is required for innate immunity and regulation of autoimmune/allergic disorders. We demonstrated that the innate immune response to Listeria monocytogenes required alpha2beta1 integrin expression by peritoneal mast cells (PMCs). Ligation of the alpha2beta1 integrin by C1q contained in immune complexes comprised of Listeria and antibody was required for PMC activation in vitro and in vivo. However, ligation of the alpha2beta1 integrin alone was insufficient to activate cytokine secretion, suggesting that one or more additional signals emanating from a coreceptor were required for PMC activation. Here, we demonstrate that C1q, but neither other complement proteins nor FcRgamma, is required for early innate immune response to Listeria. The binding of Listeria's Internalin B (InlB) to hepatocyte growth factor receptor (HGF-R)/c-met provides the costimulatory function required for PMC activation. Either HGF or Listeria InlB bound to c-met and either C1q or type I collagen bound to alpha2beta1 integrin stimulates PMC activation. These findings suggest that crosstalk between c-met and the alpha2beta1 integrin may contribute to mast-cell activation in autoimmune and inflammatory disorders.

Selective therapeutic control of C5a and the terminal complement complex by anti-C5 single-chain Fv in an experimental model of antigen-induced arthritis in rats

OBJECTIVE

To determine the role of the terminal complement complex (TCC) in the development of experimental antigen-induced arthritis (AIA) and the therapeutic effects of human anti-C5 single-chain Fv (scFv).

METHODS

Two different anti-C5 scFv, one that inhibits both release of C5a and assembly of the TCC (TS-A 12/22) and another that selectively blocks formation of the TCC (TS-A 8), were injected at the onset of AIA. The effects of these scFv on disease severity were evaluated for up to 21 days and compared with the effects of injection of an unrelated scFv. AIA was also established in C6-deficient and C6-sufficient PVG rats to obtain further information on the role of the TCC in this model.

RESULTS

TS-A 12/22 and TS-A 8 proved to be equally effective in reducing joint swelling, cell counts and tumor necrosis factor alpha levels in synovial lavage fluids, and the degree of histomorphologic changes compared with the effects of the unrelated scFv. TS-A 12/22 and TS-A 8 prevented the deposition of C9 but not that of C3, confirming the ability of the 2 scFv to neutralize C5. Administration of the 2 anti-C5 scFv after AIA onset also reduced disease severity. In C6-deficient rats with AIA, disease activity was reduced markedly compared with that in C6-sufficient rats.

CONCLUSION

These 2 human anti-C5 scFv could represent potential therapeutic reagents to be used in patients with rheumatoid arthritis. In addition, the finding that TS-A 8 was as effective as TS-A 12/22 in reducing disease severity suggests that the TCC is mainly responsible for the joint inflammation and damage observed in AIA.

Rheumatoid arthritis and the complement system

Complement activation contributes to a pathological process in a number of autoimmune and inflammatory diseases, including rheumatoid arthritis (RA). In this review we summarize current knowledge of complement contribution to RA, based on clinical observations in patients and in vivo animal models, as well as on experiments in vitro aiming at elucidation of underlying molecular mechanisms. There is strong evidence that both the classical and the alternative pathways of complement are pathologically activated during RA as well as in animal models for RA. The classical pathway can be initiated by several triggers present in the inflamed joint such as deposited autoantibodies, dying cells, and exposed cartilage proteins such as fibromodulin. B cells producing autoantibodies, which in turn form immune complexes, contribute to RA pathogenesis partly via activation of complement. It appears that anaphylatoxin C5a is the main product of complement activation responsible for tissue damage in RA although deposition of membrane attack complex as well as opsonization with fragments of C3b are also important. Success of complement inhibition in the experimental models described so far encourages novel therapeutic approaches to the treatment of human RA.

Candidate inhibitors of porcine complement

Therapeutic complement inhibition is a promising strategy for treatment of a number of diseases as judged from rodent studies. The species distance from rodents to humans may limit the clinical relevance of these studies. The pig is an alternative animal for studies of human diseases like sepsis and ischemia/reperfusion injury. However, available complement inhibitors for use in pigs are scarce. The aim of the present study was to investigate and compare the efficacy of selected candidate inhibitors of porcine complement in vitro for possible future application in vivo. Sera from three different pigs were each incubated with three different activators of the complement system (zymosan, heat-aggregated immunoglobulin G (HAIGG) and Escherichia coli). Three groups of complement inhibitor candidates were tested: serine protease inhibitors (FUT-175 and C1-inhibitor), monoclonal antibodies (anti-factor B (fB) and anti-factor D (fD)) and a recombinant regulatory protein (vaccinia virus complement control protein (VCP)). Read-out was the terminal C5b-9 complement complex (TCC). The serine protease inhibitors FUT-175 and C1-inhibitor dose-dependently inhibited TCC formation in zymosan-, HAIGG- and E. coli-activated porcine sera, but with different efficacy. Complete inhibition of TCC was obtained using 0.2 mg/mL FUT-175, but required 16 mg/mL of C1-inhibitor. The monoclonal anti-fB and -fD antibodies both inhibited TCC formation dose-dependently, but in different ways. Anti-fB at high dose (1 mg/mL) completely inhibited TCC formation in sera activated with zymosan and virtually completely in sera activated with HAIGG, but not in sera activated with E. coli. Anti-fD inhibited all three activators at low dose (0.05 mg/mL), and approximately 50% TCC reduction was obtained. The recombinant complement regulatory protein VCP efficiently and dose-dependently inhibited TCC formation with a complete inhibition found at 0.05 mg/mL for all three activators. All candidates tested inhibited porcine complement activation, but in different ways and to different degrees. Of the complement-specific candidates, VCP inhibited all activators completely at low doses.