Complement activation by both classical and alternative pathways is critical for the effector phase of arthritis

Current Challenges in Yersinia Diagnosis and Treatment

Yersinia bacteria (Yersinia enterocolitica, Yersinia pseudotuberculosis) are commonly found in nature in all climatic zones and are isolated from food (mainly raw pork, unpasteurized milk, or contaminated water), soil, and surface water, rarely from contaminated blood. Yersinia infection occurs through sick or asymptomatic carriers and contact with the feces of infected animals. The invasion of specific bacterial serotypes into the host cell is based on the type 3 secretion system (T3SS), which directly introduces many effector proteins (Yersinia outer proteins-Yops) into the host cell. The course of yersiniosis can be acute or chronic, with the predominant symptoms of acute enteritis (rarely pseudo-appendicitis or septicemia develops). Clinical and laboratory diagnosis of yersiniosis is difficult. The infection requires confirmation by isolating Yersinia bacteria from feces or other biological materials, including lymph nodes, synovial fluid, urine, bile, or blood. The detection of antibodies in blood serum or synovial fluid is useful in the diagnostic process. The treatment of yersiniosis is mainly symptomatic. Uncomplicated infections (diarrhea and abdominal pain) usually do not require antibiotic therapy, which is indicated in severe cases. Surgical intervention is undertaken in the situations of intestinal necrosis. Given the diagnostic and therapeutic difficulties, this review discusses the prevalence of Y. enterocolitica and Y. pseudotuberculosis, their mechanisms of disease induction (virulence factors and host response), clinical manifestations, diagnostic and preventive methods, and treatment strategies in the context of current knowledge and available recommendations.

Metabolic reprogramming and macrophage expansion define ACPA-negative rheumatoid arthritis: insights from single-cell RNA sequencing

Background

Anti-citrullinated peptide antibodies (ACPA)-negative (ACPA-) rheumatoid arthritis (RA) presents significant diagnostic and therapeutic challenges due to the absence of specific biomarkers, underscoring the need to elucidate its distinctive cellular and metabolic profiles for more targeted interventions.

Methods

Single-cell RNA sequencing data from peripheral blood mononuclear cells (PBMCs) and synovial tissues of patients with ACPA- and ACPA+ RA, as well as healthy controls, were analyzed. Immune cell populations were classified based on clustering and marker gene expression, with pseudotime trajectory analysis, weighted gene co-expression network analysis (WGCNA), and transcription factor network inference providing further insights. Cell-cell communication was explored using CellChat and MEBOCOST, while scFEA enabled metabolic flux estimation. A neural network model incorporating key genes was constructed to differentiate patients with ACPA- RA from healthy controls.

Results

Patients with ACPA- RA demonstrated a pronounced increase in classical monocytes in PBMCs and C1QChigh macrophages (p < 0.001 and p < 0.05). Synovial macrophages exhibited increased heterogeneity and were enriched in distinct metabolic pathways, including complement cascades and glutathione metabolism. The neural network model achieved reliable differentiation between patients with ACPA- RA and healthy controls (AUC = 0.81). CellChat analysis identified CD45 and CCL5 as key pathways facilitating macrophage-monocyte interactions in ACPA- RA, prominently involving iron-mediated metabolite communication. Metabolic flux analysis indicated elevated beta-alanine and glutathione metabolism in ACPA- RA macrophages.

Conclusion

These findings underscore that ACPA-negative rheumatoid arthritis is marked by elevated classical monocytes in circulation and metabolic reprogramming of synovial macrophages, particularly in complement cascade and glutathione metabolism pathways. By integrating single-cell RNA sequencing with machine learning, this study established a neural network model that robustly differentiates patients with ACPA- RA from healthy controls, highlighting promising diagnostic biomarkers and therapeutic targets centered on immune cell metabolism.

Role of intracellular complement activation in kidney fibrosis

Increased expression of complement C1r, C1s and C3 in kidney cells plays an important role in the pathogenesis of kidney fibrosis. Our studies suggest that activation of complement in kidney cells with increased generation of C3 and its fragments occurs by activation of classical and alternative pathways. Single nuclei RNA sequencing studies in kidney tissue from unilateral ureteral obstruction mice show that increased synthesis of complement C3 and C5 occurs primarily in renal tubular epithelial cells (proximal and distal), while increased expression of complement receptors C3ar1 and C5ar1 occurs in interstitial cells including immune cells like monocytes/macrophages suggesting compartmentalization of complement components during kidney injury. Although global deletion of C3 and macrophage ablation prevent inflammation and reduced kidney tissue scarring, the development of mice with cell-specific deletion of complement components and their regulators could bring further insights into the mechanisms by which intracellular complement activation leads to fibrosis and progressive kidney disease. LINKED ARTICLES: This article is part of a themed issue on Canonical and non-canonical functions of the complement system in health and disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.14/issuetoc.

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.

The Role of Yersinia enterocolitica O:3 Lipopolysaccharide in Collagen-Induced Arthritis

Yersinia enterocolitica O:3 is mentioned among the most common arthritogenic pathogens. Bacterial components (including lipopolysaccharide (LPS)) may persist in the joint after eradication of infection. Having an adjuvant activity, LPS may enhance production of anticollagen antibodies, involved in the pathogenesis of rheumatoid arthritis. Furthermore, its ability to activate complement contributes to the inflammation. The aim of this work was to investigate whether Yersinia LPS (coinjected with collagen) is associated with arthritis progression or other pathological effects and to elucidate the mechanism of this association. It was demonstrated that murine mannose-binding lectin C (MBL-C) recognizes the inner core heptoses of the Rd1 chemotype LPS of Yersinia. In addition, the Rd1 LPS activates the MBL-associated serine protease 1 (MASP-1) stronger than the S and Ra chemotype LPS and comparable to Klebsiella pneumoniae O:3 LPS. However, in contrast to the latter, Yersinia Rd1 LPS was associated neither with the adjuvancity nor with the enhancement of pathological changes in animal paws/impairment of motility. On the other hand, it seemed to be more hepatotoxic when compared with the other tested endotoxins, while the enlargement of inguinal lymph nodes and drop in hepatic MBL-C expression (at the mRNA level) were independent of LPS chemotype. Our data did not suggest no greater impact Y. enterocolitica O:3 on the development or severity of arthropathy related to anticollagen antibody-induced arthritis in mice, although its interaction with MBL-C and subsequent complement activation may contribute to some adverse effects.

C2 IgM Natural Antibody Enhances Inflammation and Its Use in the Recombinant Single Chain Antibody-Fused Complement Inhibitor C2-Crry to Target Therapeutics to Joints Attenuates Arthritis in Mice

Natural IgM antibodies (NAbs) have been shown to recognize injury-associated neoepitopes and to initiate pathogenic complement activation. The NAb termed C2 binds to a subset of phospholipids displayed on injured cells, and its role(s) in arthritis, as well as the potential therapeutic benefit of a C2 NAb-derived ScFv-containing protein fused to a complement inhibitor, complement receptor-related y (Crry), on joint inflammation are unknown. Our first objective was to functionally test mAb C2 binding to apoptotic cells from the joint and also evaluate its inflammation enhancing capacity in collagen antibody-induced arthritis (CAIA). The second objective was to generate and test the complement inhibitory capacity of C2-Crry fusion protein in the collagen-induced arthritis (CIA) model. The third objective was to demonstrate in vivo targeting of C2-Crry to damaged joints in mice with arthritis. The effect of C2-NAb on CAIA in C57BL/6 mice was examined by inducing a suboptimal disease. The inhibitory effect of C2-Crry in DBA/1J mice with CIA was determined by injecting 2x per week with a single dose of 0.250 mg/mouse. Clinical disease activity (CDA) was examined, and knee joints were fixed for analysis of histopathology, C3 deposition, and macrophage infiltration. In mice with suboptimal CAIA, at day 10 there was a significant (p < 0.017) 74% increase in the CDA in mice treated with C2 NAb, compared to mice treated with F632 control NAb. In mice with CIA, at day 35 there was a significant 39% (p < 0.042) decrease in the CDA in mice treated with C2-Crry. Total scores for histopathology were also 50% decreased (p < 0.0005) in CIA mice treated with C2-Crry. C3 deposition was significantly decreased in the synovium (44%; p < 0.026) and on the surface of cartilage (42%; p < 0.008) in mice treated with C2-Crry compared with PBS treated CIA mice. Furthermore, C2-Crry specifically bound to apoptotic fibroblast-like synoviocytes in vitro, and also localized in the knee joints of arthritic mice as analyzed by in vivo imaging. In summary, NAb C2 enhanced arthritis-related injury, and targeted delivery of C2-Crry to inflamed joints demonstrated disease modifying activity in a mouse model of human inflammatory arthritis.

Association Between Genetic Polymorphisms of CR2 Gene and the Risk of Steroid-Induced Osteonecrosis of the Femoral Head in the Chinese Han Male Population

Background: Multiple lines of evidence have suggested that genetic factors may contribute to steroid-induced osteonecrosis of the femoral head (SONFH). Complement receptor 2 (CR2), constituting a family of regulators of complement activation, has been recently reported to be associated with osteonecrosis of the femoral head (ONFH) in Koreans. The aim of this study was to evaluate the relationships between polymorphisms of the CR2 gene and susceptibility to SONFH in the male Han Chinese population. Materials and Methods: A total of 468 SONFH patients and 1224 healthy controls were recruited for this study. Ten tag single nucleotide polymorphisms (SNPs) located within the CR2 gene were genotyped. Genetic association analyses, including SNP and haplotypic analyses, were performed for the 10 SNPs. Furthermore, bioinformatic analyses were conducted to examine the functional consequences of SNPs shown to be significantly associated with SONFH. Results: An intronic SNP, rs311306, was identified to be significantly associated with the risk of SONFH (p = 0.0008, odds ratio = 1.44). Allelic analyses showed that the C allele of this SNP significantly elevated the risk of SONFH, which was replicated in genotypic association analyses. Moreover, a 3-SNP haplotype was significantly associated with SONFH (rs311306-rs17044576-rs3767933, p = 7.49 × 10^-8). Furthermore, bioinformatic analyses indicated limited functional consequences of SNP rs311306, but a complex interaction network was constructed for the protein encoded by the SLC44A2 gene and proteins encoded by the CD19, CD81, and C3 genes. Conclusion: Our findings shed new light on the link between the CR2 gene and SONFH in Han Chinese males, providing clues as to the nature of the mechanisms involved in the etiology of ONFH.

Investigation of the curative effects of palm vitamin E tocotrienols on autoimmune arthritis disease in vivo

The tocotrienol-rich fraction (TRF) from palm oil contains vitamin E, which possesses potent antioxidant and anti-inflammatory activities. Rheumatoid arthritis (RA) is a chronic joint inflammatory disease characterised by severe joint pain, cartilage destruction, and bone erosion owing to the effects of various pro-inflammatory mediators and cytokines. Here, we investigated the therapeutic effects of TRF in a rat model of collagen-induced arthritis (CIA). Arthritis was induced by a single intradermal injection of collagen type II in Dark Agouti (DA) rats. Rats were then treated with or without TRF by oral gavage from day 28 after the first collagen injection. Arthritic rats supplemented with TRF showed decreased articular index scores, ankle circumferences, paw volumes, and radiographic scores when compared with untreated rats. The untreated arthritic rats showed higher plasma C-reactive protein levels (p < 0.05) and production of pro-inflammatory cytokines than arthritic rats fed TRF. Moreover, there was a marked reduction in the severity of histopathological changes observed in arthritic rats treated with TRF compared with that in untreated arthritic rats. Overall, the results show that TRF had beneficial effects in this rat model of RA.

Targeting IgG in Arthritis: Disease Pathways and Therapeutic Avenues

Rheumatoid arthritis (RA) is a polygenic and multifactorial syndrome. Many complex immunological and genetic interactions are involved in the final outcome of the clinical disease. Autoantibodies (rheumatoid factors, anti-citrullinated peptide/protein antibodies) are present in RA patients' sera for a long time before the onset of clinical disease. Prior to arthritis onset, in the autoantibody response, epitope spreading, avidity maturation, and changes towards a pro-inflammatory Fc glycosylation phenotype occurs. Genetic association of epitope specific autoantibody responses and the induction of inflammation dependent and independent changes in the cartilage by pathogenic autoantibodies emphasize the crucial contribution of antibody-initiated inflammation in RA development. Targeting IgG by glyco-engineering, bacterial enzymes to specifically cleave IgG/alter N-linked Fc-glycans at Asn 297 or blocking the downstream effector pathways offers new avenues to develop novel therapeutics for arthritis treatment.

Pericytes and immune cells contribute to complement activation in tubulointerstitial fibrosis

We have examined the pathogenic role of increased complement expression and activation during kidney fibrosis. Here, we show that PDGFRβ-positive pericytes isolated from mice subjected to obstructive or folic acid injury secrete C1q. This was associated with increased production of proinflammatory cytokines, extracellular matrix components, collagens, and increased Wnt3a-mediated activation of Wnt/β-catenin signaling, which are hallmarks of myofibroblast activation. Real-time PCR, immunoblots, immunohistochemistry, and flow cytometry analysis performed in whole kidney tissue confirmed increased expression of C1q, C1r, and C1s as well as complement activation, which is measured as increased synthesis of C3 fragments predominantly in the interstitial compartment. Flow studies localized increased C1q expression to PDGFRβ-positive pericytes as well as to CD45-positive cells. Although deletion of C1qA did not prevent kidney fibrosis, global deletion of C3 reduced macrophage infiltration, reduced synthesis of C3 fragments, and reduced fibrosis. Clodronate mediated depletion of CD11bF4/80 high macrophages in UUO mice also reduced complement gene expression and reduced fibrosis. Our studies demonstrate local synthesis of complement by both PDGFRβ-positive pericytes and CD45-positive cells in kidney fibrosis. Inhibition of complement activation represents a novel therapeutic target to ameliorate fibrosis and progression of chronic kidney disease.

Mannan-Binding Lectin-Associated Serine Protease 1/3 Cleavage of Pro-Factor D into Factor D In Vivo and Attenuation of Collagen Antibody-Induced Arthritis through Their Targeted Inhibition by RNA Interference-Mediated Gene Silencing

The complement system is proposed to play an important role in the pathogenesis of rheumatoid arthritis (RA). The complement system mannan-binding lectin-associated serine proteases (MASP)-1/3 cleave pro-factor D (proDf; inactive) into Df (active), but it is unknown where this cleavage occurs and whether inhibition of MASP-1/3 is a relevant therapeutic strategy for RA. In the present study, we show that the cleavage of proDf into Df by MASP-1/3 can occur in the circulation and that inhibition of MASP-1/3 by gene silencing is sufficient to ameliorate collagen Ab-induced arthritis in mice. Specifically, to examine the cleavage of proDf into Df, MASP-1/3-producing Df-/- liver tissue (donor) was transplanted under the kidney capsule of MASP-1/3-/- (recipient) mice. Five weeks after the liver transplantation, cleaved Df was present in the circulation of MASP-1/3-/- mice. To determine the individual effects of MASP-1/3 and Df gene silencing on collagen Ab-induced arthritis, mice were injected with scrambled, MASP-1/3-targeted, or Df-targeted small interfering RNAs (siRNAs). The mRNA levels for MASP-1 and -3 decreased in the liver to 62 and 58%, respectively, in mice injected with MASP-1/3 siRNAs, and Df mRNA decreased to 53% in the adipose tissue of mice injected with Df siRNAs; additionally, circulating MASP-1/3 and Df protein levels were decreased. In mice injected with both siRNAs the clinical disease activity, histopathologic injury scores, C3 deposition, and synovial macrophage/neutrophil infiltration were significantly decreased. Thus, MASP-1/3 represent a new therapeutic target for the treatment of RA, likely through both direct effects on the lectin pathway and indirectly through the alternative pathway.

K/BxN Serum-Transfer Arthritis as a Model for Human Inflammatory Arthritis

The K/BxN serum-transfer arthritis (STA) model is a murine model in which the immunological mechanisms occurring in rheumatoid arthritis (RA) and other arthritides can be studied. To induce K/BxN STA, serum from arthritic transgenic K/BxN mice is transferred to naive mice and manifestations of arthritis occur a few days later. The inflammatory response in the model is driven by autoantibodies against the ubiquitously expressed self-antigen, glucose-6-phosphate isomerase (G6PI), leading to the formation of immune complexes that drive the activation of different innate immune cells such as neutrophils, macrophages, and possibly mast cells. The pathogenesis further involves a range of immune mediators including cytokines, chemokines, complement factors, Toll-like receptors, Fc receptors, and integrins, as well as factors involved in pain and bone erosion. Hence, even though the K/BxN STA model mimics only the effector phase of RA, it still involves a wide range of relevant disease mediators. Additionally, as a murine model for arthritis, the K/BxN STA model has some obvious advantages. First, it has a rapid and robust onset of arthritis with 100% incidence in genetically identical animals. Second, it can be induced in a wide range of strain backgrounds and can therefore also be induced in gene-deficient strains to study the specific importance of disease mediators. Even though G6PI might not be an essential autoantigen, for example, in RA, the K/BxN STA model is a useful tool to understand how autoantibodies, in general, drive the progression of arthritis by interacting with downstream components of the innate immune system. Finally, the model has also proven useful as a model wherein arthritic pain can be studied. Taken together, these features make the K/BxN STA model a relevant one for RA, and it is a potentially valuable tool, especially for the preclinical screening of new therapeutic targets for RA and perhaps other forms of inflammatory arthritis. Here, we describe the molecular and cellular pathways in the development of K/BxN STA focusing on the recent advances in the understanding of the important mechanisms. Additionally, this review provides a comparison of the K/BxN STA model to some other arthritis models.

The relative merits of therapies being developed to tackle inappropriate ('self'-directed) complement activation

The complement system is an enzyme cascade that helps defend against infection. Many complement proteins occur in serum as inactive enzyme precursors or reside on cell surfaces. Complement components have many biologic functions and their activation can eventually damage the plasma membranes of cells and some bacteria. Although a direct link between complement activation and autoimmune diseases has not been found, there is increasing evidence that complement activation significantly contributes to the pathogenesis of a large number of inflammatory diseases that may have autoimmune linkage. The inhibition of complement may therefore be very important in a variety of autoimmune diseases since their activation may be detrimental to the individual involved. However, a complete and long-term inhibition of complement may have some contra side effects such as increased susceptibility to infection. The site of complement activation will, however, determine the type of inhibitor to be used, its route of application and dosage level. Compared with conventional drugs, complement inhibitors may be the best option for treatment of autoimmune diseases. The review takes a critical look at the relative merits of therapies being developed to tackle inappropriate complement activation that are likely to result in sporadic autoimmune diseases or worsen already existing one. It covers the complement system, general aspects of complement inhibition therapy, therapeutic strategies and examples of complement inhibitors. It concludes by highlighting on the possibility that a better inhibitor of complement activation when found will help provide a formidable treatment for autoimmune diseases as well as preventing one.

Experimental models of arthritis in which pathogenesis is dependent on TNF expression

Rheumatoid arthritis (RA) is an autoimmune inflammatory disease characterized by joint damage as well as systemic manifestations. The exact cause of RA is not known. Both genetic and environmental factors are believed to contribute to the development of this disease. Increased expression of tumor necrosis factor (TNF) has been implicated in the pathogenesis of RA. Currently, the use of anti-TNF drugs is one of the most effective strategies for the treatment of RA, although therapeutic response is not observed in all patients. Furthermore, due to non-redundant protective functions of TNF, systemic anti-TNF therapy is often associated with unwanted side effects such as increased frequency of infectious diseases. Development of experimental models of arthritis in mice is necessary for studies on the mechanisms of pathogenesis of this disease and can be useful for comparative evaluation of various anti-TNF drugs. Here we provide an overview of the field and present our own data with two experimental models of autoimmune arthritis - collagen-induced arthritis and antibody-induced arthritis in C57Bl/6 and BALB/c mice, as well as in tnf-humanized mice generated on C57Bl/6 background. We show that TNF-deficient mice are resistant to the development of collagen-induced arthritis, and the use of anti-TNF therapy significantly reduces the disease symptoms. We also generated and evaluated a fluorescent detector of TNF overexpression in vivo. Overall, we have developed an experimental platform for studying the mechanisms of action of existing and newly developed anti-TNF drugs for the treatment of rheumatoid arthritis.

Novel mechanisms of action of the biologicals in rheumatic diseases

Biological drugs targeting pro-inflammatory or co-stimulatory molecules or depleting lymphocyte subsets made a revolution in rheumatoid arthritis (RA) treatment. Their comparable efficacy in clinical trials raised the point of the heterogeneity of RA pathogenesis, suggesting that we are dealing with a syndrome rather than with a single disease. Several tumor necrosis factor-alpha (TNF-α) blockers are available, and a burning question is whether they are biosimilar or not. The evidence of diverse biological effects in vitro is in line with the fact that a lack of efficacy to one TNF-α agent does not imply a non-response to another one. As proteins, biologicals are potentially immunogenic. It has been recently raised that anti-drug antibodies (ADA) may affect their bioavailability and eventually the clinical efficacy through local formation of immune complexes and directly by preventing the interaction between the drug and TNF-α. Regular monitoring of drug and ADA levels appears the best way to tailor anti-TNF-α therapies. Owing to the pleiotropic characteristics of the target, anti-TNF-α blockers may affect several mechanisms beyond rheumatoid synovitis. As TNF-α plays a pivotal role in the induction of early atherosclerosis, treatment with TNF-inhibitors may modulate cholesterol handling, in particular, cholesterol efflux from macrophages. Side effects are a major issue because of the systemic TNF-α blocking action. The efficacy of an anti-C5 monoclonal antibody fused to a peptide targeting inflamed synovia in experimental arthritis opened the way for new strategies: Homing to the synovium of molecules neutralizing TNF would allow to maximize the therapeutic action avoiding the side effects.

Efficacy of parenteral administration of bee venom in experimental arthritis in the rat: a comparison with methotrexate

The use of bee venom (BV) to treat inflammation and pain in arthritis has become increasingly common. This study aimed to compare the effects of BV and methotrexate (MTX), the most used disease-modifying anti-rheumatic drug, in arthritic rats. Edema, erythema, cyanosis, hyperalgesia, reduction of the body mass gain, high circulating tumor necrosis factor alpha (TNF-α) and anti-type II collagen antibodies (AACII), and altered activity of basic (APB) and neutral (APN) aminopeptidases and dipeptidyl peptidase IV (DPPIV) are present in arthritic rats. MTX and/or BV do not affect AACII in healthy or arthritic individuals, but restores TNF-α to normal levels in arthritic rats. BV restores body mass gain to normal levels and MTX ameliorates body mass gain. BV contains DPPIV. BV restores APN in synovial fluid (SF) and in soluble fraction (S) from synovial tissue (ST), and DPPIV in solubilized membrane-bound fraction (M) from peripheral blood mononuclear cells (PBMCs). MTX restores APN of SF, as well as ameliorates APB of S-PBMCs, APN of S-ST and DPPIV of M-PBMCs. The combination therapy does not overcome the effects of BV or MTX alone on the peptidase activities. Edema is ameliorated by MTX or BV alone. MTX, but not BV, is effective in reducing hyperalgesia. Data show that anti-arthritic effects of BV at non-acupoints are not negligible when compared with MTX.

Genome-wide pathway-based association study implicates complement system in the development of Kashin-Beck disease in Han Chinese

Kashin-Beck disease (KBD) is a chronic osteochondropathy. The pathogenesis of KBD remains unknown. To identify relevant biological pathways for KBD, we conducted a genome-wide pathway-based association study (GWPAS) following by replication analysis, totally using 2743 Chinese Han adults. A modified gene set enrichment algorithm was used to detect association between KBD and 963 biological pathways. Cartilage gene expression analysis and serum complement measurement were performed to evaluate the functional relevance of identified pathway with KBD. We found that the Complement and Coagulation Cascades (CACC) pathway was significantly associated with KBD (P value=3.09×10(-5), false-discovery rate=0.042). Within the CACC pathway, the most significant association was observed at rs1656966 (P value=1.97×10(-4)) of KNG1 gene. Further replication study observed that rs1656966 (P value=0.037) was significantly associated with KBD in an independent validation sample of 1026 subjects. Gene expression analysis observed that CFD (ratio=3.39±2.68), A2M (ratio=3.67±5.63), C5 (ratio=2.65±2.52) and CD46 (ratio=2.29±137) genes of the CACC pathway were up-regulated in KBD articular cartilage compared to healthy articular cartilage. The serum level of complement C5 in KBD patients were significantly higher than that in healthy controls (P value=0.038). Our study is the first to suggest that complement system-related CACC pathway contributed to the development of KBD.

Amelioration of oxidative stress in the joint tissue may be the basis for the antiarthritic activity of Terminalia arjuna bark extract

AIM

In this study we have evaluated the antioxidant and antiarthritic activity of Terminalia arjuna bark extract (TABE) in collagen-induced arthritis (CIA) in rats.

METHODS

Arthritis was induced in rats by intradermal injection of the collagen-complete Freund's adjuvant emulsion. Right hind paw thickness was measured as a primary marker for severity of arthritis. Biochemical parameters such as tissue levels of superoxide dismutase (SOD), catalase, reduced glutathione (GSH), nitrites and thiobarbituric acid reactive substances (TBARS) were measured to determine the effect of treatment on antioxidant defenses. Articular elastase (ELA) level in the arthritic tissue was measured as a marker for neutrophil infiltration.

RESULT

Terminalia arjuna bark extract administration significantly inhibited the increase in paw thickness induced by immunization with collagen as compared to CIA-control animals. Further, it attenuated the fall in tissue SOD and GSH levels and mitigated the increase in tissue nitrites and TBARS levels as compared to CIA-control animals. Tissue ELA levels, which were significantly increased in the CIA-control animals as compared to normal animals were also significantly reduced by TABE administration.

CONCLUSION

Results of our study demonstrate the antioxidant and antiarthritic activity of TABE in CIA in rats. We believe that TABE could find clinical application in the management of rheumatoid arthritis and associated disorders.

Complement component C3: Serologic signature for osteogenesis imperfecta. Analysis of a comparative proteomic study

BACKGROUND/PURPOSE

Osteogenesis imperfecta (OI) is a disease characterized by low bone mass and bony fragility. This study investigated the serum proteomic profiles and their correlation with bone density for OI cases.

METHODS

Twenty OI patients and 20 control participants were included. Comparative serum proteomic profiles were analyzed by two-dimensional electrophoresis and tandem mass spectrometry. Serum protein levels were measured by enzyme-linked immunosorbent assay. Cutoff values and areas under the curve were estimated by the receiver operating characteristic curve. Bone mineral density data was obtained from all OI patients.

RESULTS

Candidate proteins identified by electrophoresis were complement component C3 (C3), vitamin D-binding protein (DBP), and haptoglobin (HP). Enzyme-linked immunosorbent assay validation showed that OI patients had decreased C3 and DBP and increased HP. The results were not affected by age or bisphosphonate use. Serum C3 levels significantly correlated with bone mineral density of the lumbar spine and hip. C3 had the greatest areas under the curve to distinguish OI from healthy controls.

CONCLUSION

Serum C3, DBP, and HP are emerging serologic signatures for OI. Concentrations of serum C3 correlated with the T score of OI patients. C3 had the greatest areas under the curve of the three proteins to distinguish OI from healthy controls.

Prevention of arthritis by locally synthesized recombinant antibody neutralizing complement component C5

Treatment of patients suffering from chronic diseases such as rheumatoid arthritis with recombinant antibodies is time consuming and fairly expensive and can be associated with side effects due to generalized depletion of the target molecule. We have addressed these issues by developing an alternative approach consisting of the intraarticular injection of a DNA vector encoding for the anti-C5 neutralizing recombinant miniantibody MB12/22. This method allows local production of the antibody in sufficient amount to be effective in preventing joint inflammation in a rat model of antigen-induced arthritis. Injection of the DNA vector in a right knee of normal rats resulted in the production of the minibody detected in the synovial washes by western blot with a strong signal peaking at 3 days after administration. DNA encoding for the minibody was shown for 14 days in the synovial tissue and was undetectable in the controlateral knee and in other organs. The preventive effect of this approach was evaluated in rats receiving a single injection of the vector 3 days before the induction of antigen-induced arthritis and analyzed 3 days later. The treated rats exhibited a lower increase in swelling, associated with a lower number of PMN in the articular washes and reduced deposition of C9 in synovial tissue compared to control rats. These results suggest that treating the inflamed joints with a vector that induces a local production of a neutralizing anti-C5 antibody may represent a useful strategy to inhibit in situ complement activation and to treat patients with monoarthritis. Moreover, this approach may be adopted as a novel therapeutic strategy to prevent monoarthritis as an alternative to local treatment with antibodies commonly used in this form of arthritis, with the advantages of the lower cost and the longer persistence of antibody production.

Essential role of surface-bound complement factor H in controlling immune complex-induced arthritis

Factor H (fH) is an endogenous negative regulator of the alternative pathway (AP) that binds polyanions as well as complement activation fragments C3b and C3d. The AP is both necessary and sufficient to develop collagen Ab-induced arthritis (CAIA) in mice; the mechanisms whereby normal control of the AP is overcome and injury develops are unknown. Although primarily a soluble circulating protein, fH can also bind to tissues in a manner dependent on the carboxyl-terminal domain containing short consensus repeats 19 and 20. We examined the role of fH in CAIA by blocking its binding to tissues through administration of a recombinant negative inhibitor containing short consensus repeats 19 and 20 (rfH19-20), which impairs fH function and amplifies surface AP activation in vitro. Administration of rfH19-20, but not control rfH3-5, significantly worsened clinical disease activity, histopathologic injury, and C3 deposition in the synovium and cartilage in wild-type and fH(+/-) mice. In vitro studies demonstrated that rfH19-20 increased complement activation on cartilage extracts and injured fibroblast-like synoviocytes, two major targets of complement deposition in the joint. We conclude that endogenous fH makes a significant contribution to inhibition of the AP in CAIA through binding to sites of immune complex formation and complement activation.

Genetic control of antibody production during collagen-induced arthritis development in heterogeneous stock mice

OBJECTIVE

To identify genetic factors driving pathogenic autoantibody formation in collagen-induced arthritis (CIA), a mouse model of rheumatoid arthritis (RA), in order to better understand the etiology of RA and identify possible new avenues for therapeutic intervention.

METHODS

We performed a genome-wide analysis of quantitative trait loci controlling autoantibody to type II collagen (anti-CII), anti-citrullinated protein antibody (ACPA), and rheumatoid factor (RF). To identify loci controlling autoantibody production, we induced CIA in a heterogeneous stock-derived mouse cohort, with contribution of 8 inbred mouse strains backcrossed to C57BL/10.Q. Serum samples were collected from 1,640 mice before arthritis onset and at the peak of the disease. Antibody concentrations were measured by standard enzyme-linked immunosorbent assay, and linkage analysis was performed using a linear regression-based method.

RESULTS

We identified loci controlling formation of anti-CII of different IgG isotypes (IgG1, IgG3), antibodies to major CII epitopes (C1, J1, U1), antibodies to a citrullinated CII peptide (citC1), and RF. The anti-CII, ACPA, and RF responses were all found to be controlled by distinct genes, one of the most important loci being the immunoglobulin heavy chain locus.

CONCLUSION

This comprehensive genetic analysis of autoantibody formation in CIA demonstrates an association not only of anti-CII, but interestingly also of ACPA and RF, with arthritis development in mice. These results underscore the importance of non-major histocompatibility complex genes in controlling the formation of clinically relevant autoantibodies.

Treatment of experimental arthritis by targeting synovial endothelium with a neutralizing recombinant antibody to C5

OBJECTIVE

To show that a new recombinant protein (MT07) obtained by fusing a synovial-homing peptide to a neutralizing antibody to C5 can be selectively delivered to inflamed synovium and can effectively control joint inflammation in experimental models of arthritis.

METHODS

Binding of MT07 to human, rat, and mouse synovial tissue was evaluated in vitro by immunofluorescence, and selective localization in the inflamed joints of rats was documented in vivo using time-domain optical imaging. The antiinflammatory effect of MT07 was tested in a rat model of antigen-induced arthritis (AIA) and in a mouse model of collagen antibody-induced arthritis (CAIA).

RESULTS

MT07 was able to bind to samples of inflamed synovium from humans, mice, and rats while failing to recognize uninflamed synovium as well as inflamed mouse lung or rat kidney. In vivo analysis of the biodistribution of MT07 confirmed its preferential homing to inflamed joints, with negligible inhibition of circulating C5 levels. MT07 prevented and resolved established inflammation in a rat model of AIA, as demonstrated by changes in joint swelling, polymorphonuclear cell counts in synovial washes, release of interleukin-6 and tumor necrosis factor α, and tissue damage. A similar therapeutic effect was obtained testing MT07 in a CAIA model.

CONCLUSION

Our findings show that the novel recombinant molecule MT07 has the unique ability to selectively target inflamed joints and to exert local control of the inflammatory process by neutralizing the complement system without interfering with circulating C5 levels. We believe that this approach can be extended to other antiinflammatory drugs currently used to treat patients with rheumatoid arthritis.

Lack of the lectin-like domain of thrombomodulin worsens Shiga toxin-associated hemolytic uremic syndrome in mice

Shiga toxin (Stx)-producing Escherichia coli is a primary cause of diarrhea-associated hemolytic uremic syndrome (HUS), a disorder of thrombocytopenia, microangiopathic hemolytic anemia, and acute renal failure. The pathophysiology of renal microvascular thrombosis in Stx-HUS is still ill-defined. Based on evidence that abnormalities in thrombomodulin (TM), an anticoagulant endothelial glycoprotein that modulates complement and inflammation, predispose to atypical HUS, we assessed whether impaired TM function may adversely affect evolution of Stx-HUS. Disease was induced by coinjection of Stx2/LPS in wild-type mice (TM(wt/wt)) and mice that lack the lectin-like domain of TM (TM(LeD/LeD)), which is critical for its anti-inflammatory and cytoprotective properties. After Stx2/LPS, TM(LeD/LeD) mice exhibited more severe thrombocytopenia and renal dysfunction than TM(wt/wt) mice. Lack of lectin-like domain of TM resulted in a stronger inflammatory reaction after Stx2/LPS with more neutrophils and monocytes/macrophages infiltrating the kidney, associated with PECAM-1 and chemokine upregulation. After Stx2/LPS, intraglomerular fibrin(ogen) deposits were detected earlier in TM(LeD/LeD) than in TM(wt/wt) mice. More abundant fibrin(ogen) deposits were also found in brain and lungs. Under basal conditions, TM(LeD/LeD) mice exhibited excess glomerular C3 deposits, indicating impaired complement regulation in the kidney that could lead to local accumulation of proinflammatory products. TM(LeD/LeD) mice with HUS had a higher mortality rate than TM(wt/wt) mice. If applicable to humans, these findings raise the possibility that genetic or acquired TM defects might have an impact on the severity of microangiopathic lesions after exposure to Stx-producing E. coli infections and raise the potential for using soluble TM in the treatment of Stx-HUS.

Cartilage oligomeric matrix protein specific antibodies are pathogenic

Introduction

Cartilage oligomeric matrix protein (COMP) is a major non-collagenous component of cartilage. Earlier, we developed a new mouse model for rheumatoid arthritis using COMP. This study was undertaken to investigate the epitope specificity and immunopathogenicity of COMP-specific monoclonal antibodies (mAbs).

Methods

B cell immunodominant regions on the COMP molecule were measured with a novel enzyme-linked immunosorbent assay using mammalian expressed full-length mouse COMP as well as a panel of recombinant mouse COMP fragments. 18 mAbs specific to COMP were generated and the pathogenicity of mAbs was investigated by passive transfer experiments.

Results

B cell immunodominant epitopes were localized within 4 antigenic domains of the COMP but with preferential response to the epidermal growth factor (EGF)-like domain. Some of our anti-COMP mAbs showed interactions with the native form of COMP, which is present in cartilage and synovium. Passive transfer of COMP-specific mAbs enhanced arthritis when co-administrated with a sub-arthritogenic dose of a mAb specific to collagen type II. Interestingly, we found that a combination of 5 COMP mAbs was capable of inducing arthritis in naive mice.

Conclusions

We have identified the specificities of mAbs to COMP and their contribution to the development of arthritis. These findings will further improve our understanding of the autoantibody mediated immunopathologies occurring widely in rheumatoid arthritis (RA), as well as in other autoimmune disorders.

Abrogated RANKL expression in properdin-deficient mice is associated with better outcome from collagen-antibody-induced arthritis

Introduction

Properdin amplifies the alternative pathway of complement activation. In the present study, we evaluated its role in the development of collagen antibody-induced arthritis (CAIA).

Methods

Arthritis was induced by intraperitoneal injection of a collagen antibody cocktail into properdin-deficient (KO) and wild-type (WT) C57BL/6 mice. Symptoms of disease were evaluated daily. The degree of joint damage was assessed histologically and with immunostaining for bone-resorption markers. Phenotypes of cell populations, their receptor expression, and intracellular cytokine production were determined with flow cytometry. Osteoclast differentiation of bone marrow (BM) precursors was evaluated by staining for tartrate-resistant acid phosphatase (TRAP).

Results

Properdin-deficient mice developed less severe CAIA than did WT mice. They showed significantly improved clinical scores and downregulated expression of bone-resorption markers in the joints at day 10 of disease. The frequencies of Ly6G⁺CD11b⁺ cells were fewer in BM, blood, and synovial fluid (SF) of KO than of WT CAIA mice. The receptor activator of nuclear factor κB ligand (RANKL) was downregulated on arthritic KO neutrophils from BM and the periphery. Decreased C5a amounts in KO SF contributed to lower frequencies of CD5aR⁺-bearing neutrophils. In blood, surface C5aR was detected on KO Ly6G⁺ cells as a result of low receptor engagement. Circulating CD4⁺ T cells had an altered ability to produce interleukin (IL)-17 and interferon (IFN)-γ and to express RANKL. In KO CAIA mice, decreased frequencies of CD4⁺ T cells in the spleen were related to low CD86 expression on Ly6G^highCD11b⁺ cells. Arthritic KO T cells spontaneously secreted IFN-γ but not IL-17 and IL-6, and responded to restimulation with less-vigorous cytokine production in comparison to WT cells. Fewer TRAP-positive mature osteoclasts were found in KO BM cell cultures.

Conclusions

Our data show that the active involvement of properdin in arthritis is related to an increased proinflammatory cytokine production and RANKL expression on immune cells and to a stimulation of the RANKL-dependent osteoclast differentiation.

Mammalian DNA is an endogenous danger signal that stimulates local synthesis and release of complement factor B

Complement factor B plays a critical role in ischemic tissue injury and autoimmunity. Factor B is dynamically synthesized and released by cells outside of the liver, but the molecules that trigger local factor B synthesis and release during endogenous tissue injury have not been identified. We determined that factor B is upregulated early after cold ischemia-reperfusion in mice, using a heterotopic heart transplant model. These data suggested upregulation of factor B by damage-associated molecular patterns (DAMPs), but multiple common DAMPs did not induce factor B in RAW264.7 mouse macrophages. However, exogenous DNA induced factor B mRNA and protein expression in RAW cells in vitro, as well as in peritoneal and alveolar macrophages in vivo. To determine the cellular mechanisms involved in DNA-induced factor B upregulation we then investigated the role of multiple known DNA receptors or binding partners. We stimulated peritoneal macrophages from wild-type (WT), toll-like receptor 9 (TLR9)-deficient, receptor for advanced glycation end products (RAGE)⁻/⁻ and myeloid differentiation factor 88 (MyD88)⁻/⁻ mice, or mouse macrophages deficient in high-mobility group box proteins (HMGBs), DNA-dependent activator of interferon-regulatory factors (DAI) or absent in melanoma 2 (AIM2), with DNA in the presence or absence of lipofection reagent. Reverse transcription-polymerase chain reaction, Western blotting and immunocytochemical analysis were employed for analysis. Synthesis of factor B was independent of TLR9, RAGE, DAI and AIM2, but was dependent on HMGBs, MyD88, p38 and NF-κB. Our data therefore show that mammalian DNA is an endogenous molecule that stimulates factor B synthesis and release from macrophages via HMGBs, MyD88, p38 and NF-κB signaling. This activation of the immune system likely contributes to damage following sterile injury such as hemorrhagic shock and ischemia-reperfusion.

Regulatory T cell-mediated control of autoantibody-induced inflammation

Autoimmune inflammation including autoantibody-induced inflammation is responsible for the lethal organ damage. Autoantibody-induced inflammation can be separated in two components, autoantibody production, and local inflammatory responses. Accumulating evidence has suggested that regulatory T cells (Treg) control both antibody production and the numbers and functions of effector cells such as innate cells and T helper cells. Autoantibodies are produced by both the follicular and extrafollicular pathways. Recently, follicular regulatory T cells (T(FR)) and Qa-1 restricted CD8(+) Treg were identified as populations that are capable of suppressing follicular T helper cell (T(FH))-mediated antibody production. In local inflammation, CD4(+)CD25(+)Foxp3(+) Treg have the capacity to control inflammation by suppressing cytokine production in T helper cells. Although complement proteins contribute to autoantibody-induced local inflammation by activating innate cells, Treg including CD4(+)CD25(+)Foxp3(+) Treg are able to suppress innate cells, chiefly via IL-10 production. IL-10-secreting T cells such as T regulatory type I (Tr1) and Tr1-like cells might also play roles in the control of Th17 and innate cells. Therefore, several kinds of Tregs have the potential to control autoimmune inflammation by suppressing both autoantibody production and the local inflammatory responses induced by autoantibodies.

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.

Role of C3a receptors, C5a receptors, and complement protein C6 deficiency in collagen antibody-induced arthritis in mice

The complement system, especially the alternative pathway, plays essential roles in the induction of injury in collagen Ab-induced arthritis (CAIA) in mice. The goal of the current study was to directly compare the roles of receptors for C3a and C5a, as well as the membrane attack complex, as effector mechanisms in the pathogenesis of CAIA. Clinical disease activity in C3aR(-/-), C5aR(-/-), and C6-deficient (C6-def) mice was decreased by 52, 94, and 65%, respectively, as compared with wild-type mice. Decreases in histopathologic injury as well as in IgG and C3 deposition paralleled the clinical disease activity. A decrease in the percentage of synovial neutrophils was observed in C3aR(-/-), C5aR(-/-), and C6-def mice, and a decrease in macrophages was observed in C3aR(-/-) and C5aR(-/-), but not in C6-def, mice. Synovial mRNA obtained by laser capture microdissection exhibited a decrease in TNF-α in C5aR(-/-) mice and in IL-1β in both C5aR(-/-) and C6-def mice, whereas C3aR(-/-) mice demonstrated no change in either cytokine. Our findings show that absent C3aR-, C5aR-, or membrane attack complex-initiated effector mechanisms each decrease susceptibility to CAIA, with clinical effects most pronounced in C5aR-deficient mice. Although the absence of C3aR, C5aR, or C6 led to differential deficiencies in effector mechanisms, decreased proximal joint IgG and C3 deposition was common to all three genotypes in comparison with wild-type mice. These data suggest the existence of positive-feedback amplification pathways downstream of all three effectors that promote additional IgG deposition and C3 activation in the joint.

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.

Basic aminopeptidase activity is an emerging biomarker in collagen-induced rheumatoid arthritis

The objective of this study was to investigate the catalytic activity of basic aminopeptidase (APB) and its association with periarticular edema and circulating tumor necrosis factor (TNF)-alpha and type II collagen (CII) antibodies (AACII) in a rat model of rheumatoid arthritis (RA) induced by CII (CIA). Edema does not occur in part of CII-treated, even when AACII is higher than in control. TNF-alpha is detectable only in edematous CII-treated. APB in synovial membrane is predominantly a membrane-bound activity also present in soluble form and with higher activity in edematous than in non-edematous CII-treated or control. Synovial fluid and blood plasma have lower APB in non-edematous than in edematous CII-treated or control. In peripheral blood mononuclear cells (PBMCs) the highest levels of APB are found in soluble form in control and in membrane-bound form in non-edematous CII-treated. CII treatment distinguishes two categories of rats: one with arthritic edema, high AACII, detectable TNF-alpha, high soluble and membrane-bound APB in synovial membrane and low APB in the soluble fraction of PBMCs, and another without edema and with high AACII, undetectable TNF-alpha, low APB in the synovial fluid and blood plasma and high APB in the membrane-bound fraction of PBMCs. Data suggest that APB and CIA are strongly related.

A recombinant vaccine effectively induces c5a-specific neutralizing antibodies and prevents arthritis

Objectives

To develop and validate a recombinant vaccine to attenuate inflammation in arthritis by sustained neutralization of the anaphylatoxin C5a.

Methods

We constructed and expressed fusion protein of C5a and maltose binding protein. Efficacy of specific C5a neutralization was tested using the fusion protein as vaccine in three different arthritis mouse models: collagen induced arthritis (CIA), chronic relapsing CIA and collagen antibody induced arthritis (CAIA). Levels of anti-C5a antibodies and anti-collagen type II were measured by ELISA. C5a neutralization assay was done using a rat basophilic leukemia cell-line transfected with the human C5aR. Complement activity was determined using a hemolytic assay and joint morphology was assessed by histology.

Results

Vaccination of mice with MBP-C5a led to significant reduction of arthritis incidence and severity but not anti-collagen antibody synthesis. Histology of the MBP-C5a and control (MBP or PBS) vaccinated mice paws confirmed the vaccination effect. Sera from the vaccinated mice developed C5a-specific neutralizing antibodies, however C5 activation and formation of the membrane attack complex by C5b were not significantly altered.

Conclusions

Exploitation of host immune response to generate sustained C5a neutralizing antibodies without significantly compromising C5/C5b activity is a useful strategy for developing an effective vaccine for antibody mediated and C5a dependent inflammatory diseases. Further developing of such a therapeutic vaccine would be more optimal and cost effective to attenuate inflammation without affecting host immunity.

Efficient osteoclast differentiation requires local complement activation

Previous studies using blocking antibodies suggested that bone marrow (BM)-derived C3 is required for efficient osteoclast (OC) differentiation, and that C3 receptors are involved in this process. However, the detailed underlying mechanism and the possible involvement of other complement receptors remain unclear. In this report, we found that C3(-/-) BM cells exhibited lower RANKL/OPG expression ratios, produced smaller amounts of macrophage colony-stimulating factor and interleukin-6 (IL-6), and generated significantly fewer OCs than wild-type (WT) BM cells. During differentiation, in addition to C3, WT BM cells locally produced all other complement components required to activate C3 and to generate C3a/C5a through the alter-native pathway, which is required for efficient OC differentiation. Abrogating C3aR/C5aR activity either genetically or pharmaceutically suppressed OC generation, while stimulating WT or C3(-/-) BM cells with exogenous C3a and/or C5a augmented OC differentiation. Furthermore, supplementation with IL-6 rescued OC generation from C3(-/-) BM cells, and neutralizing antibodies to IL-6 abolished the stimulatory effects of C3a/C5a on OC differentiation. These data indicate that during OC differentiation, BM cells locally produce components, which are activated through the alternative pathway to regulate OC differentiation. In addition to C3 receptors, C3aR/C5aR also regulate OC differentiation, at least in part, by modulating local IL-6 production.

Deletion of either CD55 or CD97 ameliorates arthritis in mouse models

OBJECTIVE

CD55 (decay-accelerating factor) is best known for its role in the negative regulation of the complement system. Indeed, lack of this molecule leads to disease aggravation in many autoimmune disease models. However, CD55 is abundantly present on fibroblast-like synoviocytes and is also a ligand of the adhesion-class heptahelical receptor CD97, which is expressed by infiltrating macrophages. Treatment with antibodies to CD97 ameliorates the collagen-induced model of rheumatoid arthritis (RA) in DBA/1 mice, but the net contribution of CD55 is unknown. This study was undertaken to investigate the role of CD55 in experimental RA.

METHODS

Arthritis was induced in wild-type, CD55(-/-), and CD97(-/-) mice using collagen-induced and K/BxN serum-transfer models. Incidence of arthritis was monitored over time, and disease activity was assessed by clinical and immunohistochemical evaluation.

RESULTS

In contrast to observations in many inflammatory disease models, lack of CD55 resulted in decreased arthritis in experimental models of RA. Consistent with the previously reported effects of anti-CD97 antibody treatment, CD97(-/-) mice had reduced arthritis activity compared with wild-type controls.

CONCLUSION

Our findings indicate that the lack of CD55 or CD97 in 2 different models of arthritis increases resistance to the disease. These findings provide insight into a role for CD55 interaction with CD97 in the pathogenesis of RA and suggest that therapeutic strategies that disrupt CD55/CD97 may be clinically beneficial.

The role of properdin in murine zymosan-induced arthritis

Using properdin-deficient and wild-type mice, we have investigated the role of properdin in development and progression of zymosan-induced arthritis. At the initial phase of local, zymosan-induced inflammation, properdin-deficient and wild-type mice showed bone erosion, proteoglycan loss and cell infiltration. Compared to wild-type, properdin-deficient mice had reduced C5a and IL-6 but similar synovial TNF-alpha and sRANKL levels. Both groups showed a systemic immune response. Elevated IFN-gamma production and STAT1 signaling in splenocytes and a shift to Th1 response in popliteal lymph nodes were observed in properdin-deficient mice. Properdin-deficient mice had significantly less circulating zymosan-specific IgG antibodies than wild-type. In the chronic phase, the lack of properdin resulted in significant proteoglycan loss in the joints and lower cartilageneous STAT1 expression. The level of synovial C5a on day 30 was comparable in both groups, but C5aR staining was more apparent in the joints of properdin-deficient mice. Our data show that properdin is an important player in processes involved in inflammatory joint degradation.

Transgenic mice expressing human FcgammaRIIa have enhanced sensitivity to induced autoimmune arthritis as well as elevated Th17 cells

The major human Fc receptor, huFcgammaRIIa, is implicated in the development of autoimmune arthritis in humans but until recently has not been studied in mouse models. We evaluated potential roles of FcgammaRIIa by using transgenic mice expressing the receptor. We examined two models of induced autoimmune arthritis pristane-induced arthritis (PIA) and collagen-induced arthritis (CIA) as well as the anti-collagen-II antibody-induced arthritis (CAIA) model. In the induced arthritis models PIA and CIA, the transgenic mice developed a more severe arthritis than the other arthritis-prone SJL or DBA1 mice. Interestingly, anti-collagen-II antibodies were elevated in PIA in the susceptible mice. In the CIA model, the highly susceptible transgenic mouse had IgG subclass levels equivalent to the unaffected and disease resistant C57BL/6 mouse strain implying that the FcgammaRIIa lowers the threshold of IgG dependent leukocyte activation. This is consistent with the greatly enhanced sensitivity of the FcgammaRIIa transgenic mice to CAIA which clearly indicates a role for the receptor at least at the inflammatory effector cell level. Other roles for huFcgammaRIIa or other gene products in the development of autoimmunity cannot be ruled out however, especially as the mice exhibited elevated Th1 or Th17 CD4 T cells in the draining lymph nodes.

Complement activation pathways in murine immune complex-induced arthritis and in C3a and C5a generation in vitro

The alternative pathway (AP) of complement alone is capable of mediating immune complex-induced arthritis in the collagen antibody-induced arthritis (CAIA) model in mice. Whether the classical pathway (CP) or lectin pathway (LP) alone can mediate CAIA is not known. Using mice genetically deficient in different complement components, our results reported herein establish that the CP and LP alone are each incapable of mediating CAIA. A lower level or absence of C3 and/or C5 activation by the CP may be possible explanations for the importance of the AP in CAIA and in many murine models of disease. In addition, other investigators have reported that CP C5 convertase activity is absent in mouse sera. To address these questions, we employed an in vitro system of adherent immunoglobulin (Ig)G-induced complement activation using plates coated with murine anti-collagen monoclonal antibody (mAb). These experiments used complement-deficient mouse sera and wild-type mouse or normal human sera under conditions inactivating either the CP (Ca(++) deficiency) or the AP (mAb inhibitory to factor B). Robust generation of both C3a and C5a by either the AP or CP alone were observed with both mouse and human sera, although there were some small differences between the species of sera. We conclude that neither the CP nor LP alone is capable of mediating CAIA in vivo and that mouse sera exhibits a high level of IgG-induced C5a generation in vitro through either the CP or AP.

Targeted inhibition of the complement alternative pathway with complement receptor 2 and factor H attenuates collagen antibody-induced arthritis in mice

The alternative pathway (AP) of complement is required for the induction of collagen Ab-induced arthritis (CAIA) in mice. The objective of this study was to examine the effect of a recombinant AP inhibitor containing complement receptor 2 and factor H (CR2-fH) on CAIA in mice. CR2 binds to tissue-fixed activation fragments of C3, and the linked fH is a potent local inhibitor of the AP. CAIA was induced in C57BL/6 mice by i.p. injections of 4 mAb to type II collagen (CII) on day 0 and LPS on day 3. PBS or CR2-fH (250 or 500 microg) were injected i.p. 15 min after the mAb to CII on day 0 and 15 min after LPS on day 3; the mice were sacrificed on day 10. The disease activity score (DAS) was decreased significantly (p < 0.001) in both groups receiving CR2-fH compared with the PBS. Histology scores for inflammation, pannus, bone damage, and cartilage damage decreased in parallel with the DAS. C3 deposition in the synovium and cartilage was significantly reduced (p < 0.0001) in the mice treated with CR2-fH. In vitro studies with immune complexes containing type II collagen and mAb to CII showed that CR2-fH specifically inhibited the AP with minimal effect on the classical pathway (CP) and no effect on the lectin pathway (LP). The relative potency of CR2-fH in vitro was superior to mAbs to factor B and C5. Thus, CR2-fH specifically targets and inhibits the AP of complement in vitro and is effective in CAIA in vivo.

Lessons from animal models of arthritis over the past decade

This review summarizes the major developments in animal models of arthritis in the past decade. It focuses on novel transgenic models, addresses the involvement of cytokines and discusses novel findings in cartilage and bone erosion. It is clear that interest has been raised in the direct arthritogenic role of autoantibodies, apart from T cell involvement, and their interaction with cells through Fcgamma receptors. In addition, a role for IL-6 and IL-17 and Th17 cells seems apparent in most T cell-driven arthritis models, with environmental triggering through Toll-like receptors contributing to this process. Further insights into enzymes involved in cartilage proteoglycan loss in arthritis, as well as mediators regulating bone erosion and bone apposition, have been gained.