Soluble complement receptor one (sCR1) inhibits the development and progression of rat collagen-induced arthritis

The potential application of complement inhibitors-loaded nanosystem for autoimmune diseases via regulation immune balance

The complement is an important arm of the innate immune system, once activated, the complement system rapidly generates large quantities of protein fragments that are potent mediators of inflammation. Recent studies have shown that over-activated complement is the main proinflammatory system of autoimmune diseases (ADs). In addition, activated complements interact with autoantibodies, immune cells exacerbate inflammation, further worsening ADs. With the increasing threat of ADs to human health, complement-based immunotherapy has attracted wide attention. Nevertheless, efficient and targeted delivery of complement inhibitors remains a significant challenge owing to their inherent poor targeting, degradability, and low bioavailability. Nanosystems offer innovative solutions to surmount these obstacles and amplify the potency of complement inhibitors. This prime aim to present the current knowledge of complement in ADs, analyse the function of complement in the pathogenesis and treatment of ADs, we underscore the current situation of nanosystems assisting complement inhibitors in the treatment of ADs. Considering technological, physiological, and clinical validation challenges, we critically appraise the challenges for successfully translating the findings of preclinical studies of these nanosystem assisted-complement inhibitors into the clinic, and future perspectives were also summarised. (The graphical abstract is by BioRender.).

A Dual-Targeted Metal-Organic Framework Based Nanoplatform for the Treatment of Rheumatoid Arthritis by Restoring the Macrophage Niche

Inflammatory infiltration and bone destruction are important pathological features of rheumatoid arthritis (RA), which originate from the disturbed niche of macrophages. Here, we identified a niche-disrupting process in RA: due to overactivation of complement, the barrier function of VSIg4⁺ lining macrophages is disrupted and mediates inflammatory infiltration within the joint, thereby activating excessive osteoclastogenesis and bone resorption. However, complement antagonists have poor biological applications due to superphysiologic dose requirements and inadequate effects on bone resorption. Therefore, we developed a dual-targeted therapeutic nanoplatform based on the MOF framework to achieve bone-targeted delivery of the complement inhibitor CRIg-CD59 and pH-responsive sustained release. The surface-mineralized zoledronic acid (ZA) of ZIF8@CRIg-CD59@HA@ZA targets the skeletal acidic microenvironment in RA, and the sustained release of CRIg-CD59 can recognize and prevent the complement membrane attack complex (MAC) from forming on the surface of healthy cells. Importantly, ZA can inhibit osteoclast-mediated bone resorption, and CRIg-CD59 can promote the repair of the VSIg4⁺ lining macrophage barrier to achieve sequential niche remodeling. This combination therapy is expected to treat RA by reversing the core pathological process, circumventing the pitfalls of traditional therapy.

The role of C5a-C5aR1 axis in bone pathophysiology: A mini-review

Bone remodeling is a physiological, dynamic process that mainly depends on the functions of 2 cell types: osteoblasts and osteoclasts. Emerging evidence suggests that complement system is crucially involved in the regulation of functions of these cells, especially during inflammatory states. In this context, complement component 5a (C5a), a powerful pro-inflammatory anaphylatoxin that binds the receptor C5aR1, is known to regulate osteoclast formation and osteoblast inflammatory responses, and has thus been proposed as potential therapeutic target for the treatment of inflammatory bone diseases. In this review, we will analyze the role of C5a-C5aR1 axis in bone physiology and pathophysiology, describing its involvement in the pathogenesis of some of the most frequent inflammatory bone diseases such as rheumatoid arthritis, and also in osteoporosis and bone cancer and metastasis. Moreover, we will examine C5aR1-based pharmacological approaches that are available and have been tested so far for the treatment of these conditions. Given the growing interest of the scientific community on osteoimmunology, and the scarcity of data regarding the role of C5a-C5aR1 axis in bone pathophysiology, we will highlight the importance of this axis in mediating the interactions between skeletal and immune systems and its potential use as a therapeutic target.

Sialylation-dependent pharmacokinetics and differential complement pathway inhibition are hallmarks of CR1 activity in vivo

Human Complement Receptor 1 (HuCR1) is a potent membrane-bound regulator of complement both in vitro and in vivo, acting via interaction with its ligands C3b and C4b. Soluble versions of HuCR1 have been described such as TP10, the recombinant full-length extracellular domain, and more recently CSL040, a truncated version lacking the C-terminal long homologous repeat domain D (LHR-D). However, the role of N-linked glycosylation in determining its pharmacokinetic (PK) and pharmacodynamic (PD) properties is only partly understood. We demonstrated a relationship between the asialo-N-glycan levels of CSL040 and its PK/PD properties in rats and non-human primates (NHPs), using recombinant CSL040 preparations with varying asialo-N-glycan levels. The clearance mechanism likely involves the asialoglycoprotein receptor (ASGR), as clearance of CSL040 with a high proportion of asialo-N-glycans was attenuated in vivo by co-administration of rats with asialofetuin, which saturates the ASGR. Biodistribution studies also showed CSL040 localisation to the liver following systemic administration. Our studies uncovered differential PD effects by CSL040 on complement pathways, with extended inhibition in both rats and NHPs of the alternative pathway compared to the classical and lectin pathways that were not correlated with its PK profile. Further studies showed that this effect was dose dependent and observed with both CSL040 and the full-length extracellular domain of HuCR1. Taken together, our data suggests that sialylation optimization is an important consideration for developing HuCR1-based therapeutic candidates such as CSL040 with improved PK properties and shows that CSL040 has superior PK/PD responses compared to full-length soluble HuCR1.

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.

Therapeutic Efficacy of a Trichinella Spiralis Paramyosin-Derived Peptide Modified With a Membrane-Targeting Signal in Mice With Antigen-Induced Arthritis

Helminth-derived molecules have the ability to modulate the host immune system. Our previous study identified a tetradecapeptide derived from Trichinella spiralis paramyosin (Ts-pmy) that could bind to human complement component C9 to inhibit its polymerization, making the peptide a candidate therapeutic agent for complement-related immune disorders. Here, the peptide underwent an N-terminal modification with a membrane-targeting signal (a unique myristoylated peptide) to improve its therapeutic efficacy. We found that the modified peptide had a binding affinity to human C9 that was similar to that of the original peptide, as confirmed by microscale thermophoresis assays. The binding of the modified peptide to human C9 resulted in the inhibition of C9-related complement activation, as reflected by the decreased Zn²⁺-induced C9 polymerization and the decreased C9-dependent lysis of rabbit erythrocytes. In addition, the original and modified peptides could both bind to recombinant mouse C9 and inhibit the C9-dependent lysis of rabbit erythrocytes in normal mouse serum (NMS), which meant that the peptides could cross the species barrier to inhibit complement activity in mice. Further in vitro and in vivo analyses confirmed that the peptide modification increased the retention time of the peptide. Furthermore, intraarticular injection of the modified peptide markedly ameliorated knee swelling and joint damage in mice with antigen-induced arthritis (AIA), as assessed histologically. These results suggested that the Ts-pmy-derived peptide modified with a membrane-targeting signal was a reasonable candidate therapeutic agent for membrane attack complex (MAC)-related diseases [such as rheumatoid arthritis (RA)] and the study presented a new modification method to improve the potential therapeutic effects of the peptide.

A novel soluble complement receptor 1 fragment with enhanced therapeutic potential

Human complement receptor 1 (HuCR1) is a pivotal regulator of complement activity, acting on all three complement pathways as a membrane-bound receptor of C3b/C4b, C3/C5 convertase decay accelerator, and cofactor for factor I-mediated cleavage of C3b and C4b. In this study, we sought to identify a minimal soluble fragment of HuCR1, which retains the complement regulatory activity of the wildtype protein. To this end, we generated recombinant, soluble, and truncated versions of HuCR1 and compared their ability to inhibit complement activation in vitro using multiple assays. A soluble form of HuCR1, truncated at amino acid 1392 and designated CSL040, was found to be a more potent inhibitor than all other truncation variants tested. CSL040 retained its affinity to both C3b and C4b as well as its cleavage and decay acceleration activity and was found to be stable under a range of buffer conditions. Pharmacokinetic studies in mice demonstrated that the level of sialylation is a major determinant of CSL040 clearance in vivo. CSL040 also showed an improved pharmacokinetic profile compared with the full extracellular domain of HuCR1. The in vivo effects of CSL040 on acute complement-mediated kidney damage were tested in an attenuated passive antiglomerular basement membrane antibody-induced glomerulonephritis model. In this model, CSL040 at 20 and 60 mg/kg significantly attenuated kidney damage at 24 h, with significant reductions in cellular infiltrates and urine albumin, consistent with protection from kidney damage. CSL040 thus represents a potential therapeutic candidate for the treatment of complement-mediated disorders.

Knee synovial fluid complement C3-β chain levels correlate with clinical symptoms of knee osteoarthritis

AIM

Early research found innate immune factor complement C3 in the synovial fluid (SF) and activated in serum of osteoarthritis (OA) patients. Whether synovial C3 comes from circulation, or is produced locally, is still unknown. It is also unclear whether synovial and circulating C3 is responsible to OA symptoms. A native C3 molecule consists of two chains, C3-α and C3-β. Small fragments breaking down from C3-α chain in serum and SF were reported to be related to OA severity. Little is known if C3-β chain is involved in the pathogenesis.

METHOD

In this study, we evaluated these important areas by biochemical analyses of C3-α and C3-β chains in both the SF and plasma of OA patients.

RESULTS

Our results showed that C3-α and C3-β levels in SF did not correlate with those in plasma, suggesting that synovial C3 is independently and locally produced, rather than being "leaked" from circulation. Synovial C3-β but not C3-α levels correlated with pain, other OA symptoms, function in daily living, and sports/recreational activities. Plasma C3-β levels only marginally correlated with pain, and plasma C3-α levels did not correlate with any of these OA symptoms.

CONCLUSION

We present first-hand evidence that the clinical symptoms of OA are mainly associated with C3 in the local SF rather than systemic circulation, suggesting local factors in the etiopathogenesis. Future local targeted therapies for pain management may be more effective and safer.

Role of complement and potential of complement inhibitors in myasthenia gravis and neuromyelitis optica spectrum disorders: a brief review

The complement system is a powerful member of the innate immune system. It is highly adept at protecting against pathogens, but exists in a delicate balance between its protective functions and overactivity, which can result in autoimmune disease. A cascade of complement proteins that requires sequential activation, and numerous complement regulators, exists to regulate a proportionate response to pathogens. In spite of these mechanisms there is significant evidence for involvement of the complement system in driving the pathogenesis of variety of diseases including neuromyelitis optica spectrum disorders (NMOSD) and myasthenia gravis (MG). As an amplification cascade, there are an abundance of molecular targets that could be utilized for therapeutic intervention. Clinical trials assessing complement pathway inhibition in both these conditions have recently been completed and include the first randomized placebo-controlled trial in NMOSD showing positive results. This review aims to review and update the reader on the complement system and the evolution of complement-based therapeutics in these two disorders.

Complement in the Initiation and Evolution of Rheumatoid Arthritis

The complement system is a major component of the immune system and plays a central role in many protective immune processes, including circulating immune complex processing and clearance, recognition of foreign antigens, modulation of humoral and cellular immunity, removal of apoptotic and dead cells, and engagement of injury resolving and tissue regeneration processes. In stark contrast to these beneficial roles, however, inadequately controlled complement activation underlies the pathogenesis of human inflammatory and autoimmune diseases, including rheumatoid arthritis (RA) where the cartilage, bone, and synovium are targeted. Recent studies of this disease have demonstrated that the autoimmune response evolves over time in an asymptomatic preclinical phase that is associated with mucosal inflammation. Notably, experimental models of this disease have demonstrated that each of the three major complement activation pathways plays an important role in recognition of injured joint tissue, although the lectin and amplification pathways exhibit particularly impactful roles in the initiation and amplification of damage. Herein, we review the complement system and focus on its multi-factorial role in human patients with RA and experimental murine models. This understanding will be important to the successful integration of the emerging complement therapeutics pipeline into clinical care for patients with RA.

Inhibition of complement C3 might rescue vascular hyporeactivity in a conscious hemorrhagic shock rat model

BACKGROUND

Vascular hyporeactivity in severe hemorrhagic shock could induce refractory hypotension and is an important cause of death. The global acute inflammatory response induced in shock triggers the over-expression of reactive oxygen species, NO, ET1 and TNF-α, which play essential roles in the pathology of vascular hyporeactivity. This leads to a hypothesis that inhibition of the complement system, the mediator of the inflammatory cascade, might be a promising therapeutic exploration for vascular hyporeactivity.

METHODS

We use cobra venom factor (CVF) and the soluble form of CR1 (sCR1) which deplete or inhibit complement C3 respectively to examine its role in vascular hyporeactivity in a conscious hemorrhagic shock rat model.

RESULTS

We first confirmed the over-activation of C3 during shock and the down-regulation effects of CVF and sCR1 on C3. Then, both CVF and sCR1 could significantly mitigate the over-expression of serum NO, ET-1, TNF-α and reactive oxygen species. Finally, the vascular reactivity of superior mesenteric arteries (SMA) was examined in vitro, which confirmed the massive reduction of vascular reactivity in shock, which was significantly rescued by both CVF and sCR1.

CONCLUSIONS

Inhibition of C3 might improve the reactivity of SMA to norepinephrine during hemorrhagic shock possibly through the downregulation of NO, ET1, TNF-α and reactive oxygen radicals.

Function and regulation of self-reactive marginal zone B cells in autoimmune arthritis

Polyreactive innate-type B cells account for many B cells expressing self-reactivity in the periphery. Improper regulation of these B cells may be an important factor that underlies autoimmune disease. Here we have explored the influence of self-reactive innate B cells in the development of collagen-induced arthritis (CIA), a mouse model of rheumatoid arthritis. We show that splenic marginal zone (MZ), but not B-1 B cells exhibit spontaneous IgM reactivity to autologous collagen II in naı¨ve mice. Upon immunization with heterologous collagen II in complete Freund's adjuvant the collagen-reactive MZ B cells expanded rapidly, while the B-1 B cells showed a modest anti-collagen response. The MZ B cells were easily activated by toll-like receptor (TLR) 4 and 9-ligands in vitro, inducing proliferation and cytokine secretion, implying that dual engagement of the B-cell receptor and TLRs may promote the immune response to self-antigen. Furthermore, collagen-primed MZ B cells showed significant antigen-presenting capacity as reflected by cognate T-cell proliferation in vitro and induction of IgG anti-collagen antibodies in vivo. MZ B cells that were deficient in complement receptors 1 and 2 demonstrated increased proliferation and cytokine production, while Fcγ receptor IIb deficiency of the cells lead to increased cytokine production and antigen presentation. In conclusion, our data highlight self-reactive MZ B cells as initiators of the autoimmune response in CIA, where complement and Fc receptors are relevant in controlling the self-reactivity in the cells.

Suppression of Inflammation and Arthritis by Orally Administrated Cardiotoxin from Naja naja atra

Cardiotoxin (CTX) from Naja naja atra venom (NNAV) reportedly had analgesic effect in animal models but its role in inflammation and arthritis was unknown. In this study, we investigated the analgesic, anti-inflammatory, and antiarthritic actions of orally administered CTX-IV isolated from NNAV on rodent models of inflammation and adjuvant arthritis. CTX had significant anti-inflammatory effects in models of egg white induced nonspecific inflammation, filter paper induced rat granuloma formation, and capillary osmosis tests. CTX significantly reduced the swelling of paw induced by egg white, the inflammatory exudation, and the formation of granulomas. CTX reduced the swelling of paw, the AA clinical scores, and pathological alterations of joint. CTX significantly decreased the number of the CD4 T cells and inhibited the expression of relevant proinflammatory cytokines IL-17 and IL-6. CTX significantly inhibited the secretion of proinflammatory cytokine IL-6 and reduced the level of p-STAT3 in FLS. These results suggest that CTX inhibits inflammation and inflammatory pain and adjuvant-induced arthritis. CTX may be a novel therapeutic drug for treatment of arthritis.

Suppression of complement activation by recombinant Crry inhibits experimental autoimmune anterior uveitis (EAAU)

This study was initiated to explore the effect of recombinant rat Crry linked to the Fc portion of rat IgG2a (Crry-Ig) on the induction of experimental autoimmune anterior uveitis (EAAU) and on established disease. EAAU was induced in Lewis rats by immunization with bovine melanin-associated antigen (MAA). MAA sensitized animals received Crry-Ig, rat IgG2a (isotype control) or PBS separately before the onset of EAAU or after the onset of clinical disease. Administration of Crry-Ig suppressed the induction of EAAU while all animals injected with IgG2a or PBS developed the normal course of EAAU. Treatment with Crry-Ig resulted in the suppression of ocular complement activation as well as the functional activity of complement in the peripheral blood. At the peak of EAAU, levels of IFN-γ, IP-10, ICAM-1 and LECAM-1 were significantly reduced within the eyes of Crry-Ig treated Lewis rats. Importantly, administration of Crry-Ig even after the onset of EAAU resulted in a sharp decline in the disease activity and early resolution of EAAU. Collectively, the evidence presented here demonstrate that inhibition of complement by Crry-Ig results in low levels of inflammatory molecules-C3 activation products, MAC, cytokines, chemokines and adhesion molecules in the eye. Down-regulation of these molecules affects the infiltration and recruitment of inflammatory cells to the eye resulting in the inhibition of EAAU.

Collagen-induced arthritis

The mouse model collagen-induced arthritis (CIA) is a widely studied autoimmune model of rheumatoid arthritis. In this model, autoimmune arthritis is induced by immunization with type II collagen (CII) emulsified in complete Freund's adjuvant. This unit describes the steps necessary for the acquisition, handling, and preparation of CII, in addition to the selection of mouse strains, proper immunization technique, and methods for evaluation of the incidence and severity of arthritis. In this model, the first signs of arthritis appear approximately 21 to 28 days after immunization. The protocols in this unit should provide the investigator with all the necessary information required to reproducibly induce a high incidence of CIA in genetically susceptible strains of mice, and to critically evaluate the pathology of the disease.

Enhanced susceptibility to low-dose collagen-induced arthritis in CR1/2-deficient female mice--possible role of estrogen on CR1 expression

The influence of complement receptor 1 and 2 (CR1/2) was investigated on the susceptibility to low-dose collagen-induced arthritis (CIA) in wild-type (WT) and CR1/2-deficient DBA/1 mice. Significantly enhanced CIA was observed in female CR1/2-deficient mice compared with WT female mice, while male mutant and WT mice showed similar arthritis development. The enhanced CIA was accompanied with higher complement levels and a prolonged IgM anti-collagen type II response. When investigating whether estrogen contributed to the different arthritis susceptibility, we found that ovariectomy rendered WT females more sensitive to low-dose CIA and to the same extent as CR1/2-deficient females, while CR1/2-deficient mice were unaffected by ovariectomy. Notably, the ovariectomized WT mice displayed reduced CR1(+) B220(+) B-cell numbers and CR1 expression compared with sham-operated WT mice, suggesting a stimulatory effect of estrogen on CR1. In accordance, a significant correlation was observed between reduced CR1 expression in B cells and increased age in healthy female blood donors but not in male donors. Our findings demonstrate an important role of CR1/2 in suppressing CIA in female mice under low-antigen conditions. The data suggest that estrogen promote CR1 expression in B cells. These findings provide insight to the increased frequency of rheumatoid arthritis in postmenopausal women.

Drug delivery systems for the treatment of rheumatoid arthritis

Rheumatoid arthritis (RA) is a severe immune-mediated disease characterized by chronically progressive inflammation and destruction of joints and associated structures. Significant advances in our understanding of its pathophysiology and early diagnosis have led to improved therapy and better outcome. Nevertheless, a number of details in the pathogenesis of RA are still unknown and thus the disease cannot be cured at present. Therefore, current therapy aims at accomplishing complete and long-lasting remission. However, this goal is only achieved in a small proportion of patients, and partial remission and frequent relapses are a common problem. A significant number of patients still do not respond at all to available treatments. In addition, all antirheumatic and immune-modulating drugs developed so far carry a considerable risk of adverse effects, some of which can be severe or even life threatening. This is due, at least in part, to a lack of specificity of most drugs for the target tissue, and to a high volume of distribution for systemic application, which, together with rapid clearance of most drugs, requires frequent application of high dosages. Targeted drug delivery and prolongation of bioavailability would alleviate this issue significantly. This article, therefore, reviews a selection of studies that report promising strategies for joint specific delivery of antiarthritic drugs.

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.

CD59, a complement regulatory protein, controls choroidal neovascularization in a mouse model of wet-type age-related macular degeneration

We have shown that membrane attack complex (MAC) formation via the activation of the alternative pathway plays a central role in the laser-induced choroidal neovascularization (CNV). This study was undertaken to understand the role of a complement regulatory protein, CD59, which controls MAC assembly and function, in this model. CNV was induced by laser photocoagulation in C57BL/6 and Cd59a(-/-) mice using an argon laser. Animals from each group were sacrificed on day 1, 3, 5, and 7 postlaser. Retinal pigment epithelium-choroid-scleral tissue was examined to determine the incidence and size of CNV complex, and semiquantitative RT-PCR and Western blot analysis for CD59a was studied. Recombinant soluble mouse CD59a-IgG2a fusion (rsCD59a-Fc) protein was injected via i.p. or intravitreal routes 24 h before laser. Our results demonstrated that CD59a (both mRNA and protein) was down-regulated during laser-induced CNV. Cd59a(-/-) mice developed CNV complex early in the disease process. Increased MAC deposition was also observed in these Cd59a(-/-) mice. Administration of rsCD59a-Fc inhibited the development of CNV complex in the mouse model by blocking MAC formation and also inhibited expression of angiogenic growth factors. These data provide strong evidence that CD59a plays a crucial role in regulating complement activation and MAC formation essential for the release of growth factors that drive the development of laser-induced CNV in mice. Thus, our results suggest that the inhibition of complement by soluble CD59 may provide a novel therapeutic alternative to current treatment.

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.

Alternative Complement Pathway Activation Is Essential for Inflammation and Joint Destruction in the Passive Transfer Model of Collagen-Induced Arthritis

Activation of each complement initiation pathway (classical, alternative, and lectin) can lead to the generation of bioactive fragments with resulting inflammation in target organs. The objective of the current study was to determine the role of specific complement activation pathways in the pathogenesis of experimental anti-type II collagen mAb-passive transfer arthritis. C57BL/6 mice were used that were genetically deficient in either the alternative pathway protein factor B (Bf(-/-)) or in the classical pathway component C4 (C4(-/-)). Clinical disease activity was markedly decreased in Bf(-/-) compared with wild-type (WT) mice (0.5 +/- 0.22 (n = 6) in Bf(-/-) vs 8.83 +/- 0.41 (n = 6) in WT mice (p < 0.0001)). Disease activity scores were not different between C4(-/-) and WT mice. Analyses of joints showed that C3 deposition, inflammation, pannus, cartilage, and bone damage scores were all significantly less in Bf(-/-) as compared with WT mice. There were significant decreases in mRNA levels of C3, C4, CR2, CR3, C3aR, and C5aR in the knees of Bf(-/-) as compared with C4(-/-) and WT mice with arthritis; mRNA levels for complement regulatory proteins did not differ between the three strains. These results indicate that the alternative pathway is absolutely required for the induction of arthritis following injection of anti-collagen Abs. The mechanisms by which these target organ-specific mAbs bypass the requirements for engagement of the classical pathway remain to be defined but do not appear to involve a lack of alternative pathway regulatory proteins.

Strategies of therapeutic complement inhibition

The involvement of complement in the pathogenesis of a great number of partly life threatening diseases defines the importance to develop inhibitors which specifically interfere with its deleterious action. Endogenous soluble complement-inhibitors, antibodies or low molecular weight antagonists, either blocking key proteins of the cascade reaction or neutralizing the action of the complement-derived anaphylatoxins have successfully been tested in various animal models over the past years. Promising results consequently led to first clinical trials. This review is focused on different approaches for the development of inhibitors, on their site of action in the cascade, on possible indications for complement inhibition based on experimental animal data, and on potential side effects of such treatment.

Early cytokine profiles in the joint define pathogen clearance and severity of arthritis inChlamydia-induced arthritis in rats

OBJECTIVE

Although Chlamydia trachomatis-induced arthritis is among the most common rheumatic diseases having an identified infectious trigger, the pathogenesis of this arthritis is not well defined. We sought to investigate the host-microbe interactions that contribute to the severity of arthritis initiated by chlamydial infection.

METHODS

We established an experimental rat model of C. trachomatis-induced arthritis that recapitulates many pathologic features of the clinical disease. The severity of the arthritis was defined using an established histopathologic scoring system. Host clearance of the pathogen and local cytokine production were examined by enzyme-linked immunosorbent assays.

RESULTS

Lewis rats were susceptible to C. trachomatis-induced arthritis, whereas BN rats were relatively resistant to this disease. Significant differences in the histopathologic severity of arthritis were originally observed on day 21, and this prompted an examination of the acute phase of the arthritis. As early as day 5 after the onset of the arthritis, pathologic changes in Lewis rats were more severe than those in BN rats. An evaluation of the role of complement using cobra venom factor treatment excluded complement as being the key to differential sensitivity, because decomplementation did not eliminate the differences in arthritis severity between Lewis and BN rats. Host clearance, in contrast, was significantly different between the rat strains, with BN rats showing more prompt and effective clearance of the pathogen from both synovial tissues and spleen compared with Lewis rats. Local cytokine profiles demonstrated that host resistance was characterized by enhanced synovial expression of tumor necrosis factor alpha, interferon-gamma (IFNgamma), and interleukin-4.

CONCLUSION

These studies demonstrated that cytokines thought to be proinflammatory in nature can play an important role in host defense in infection-triggered arthritis and serve to highlight the dynamic cytokine relationships that constitute effective host-pathogen interactions.

Membrane complement regulatory proteins

A number of proteins anchored on the cell surface function to protect host tissues from bystander injury when complement is activated. In humans, they include decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46), complement receptor 1 (CR1, CD35) and CD59. Although disease conditions directly attributable to abnormal function of these proteins are relatively rare, it has become evident from recent studies using animal models that membrane complement regulatory proteins are important modulators of tissue injury in many autoimmune and inflammatory disease settings. Evidence is also emerging to support a role of these proteins in regulating cellular immunity. In this article, we highlight recent advances on the in vivo biology of membrane complement regulatory proteins and discuss their relevance in human disease pathogenesis and therapeutics.

Deletion of the gene encoding CD59a in mice increases disease severity in a murine model of rheumatoid arthritis

OBJECTIVE

To investigate the roles of CD59a in the protection of joint tissue in the context of murine antigen-induced arthritis (AIA).

METHODS

AIA was triggered in CD59a-deficient (CD59a(-/-)) mice and in CD59a-sufficient (CD59a(+/+)) controls; the course and severity of disease were compared between groups. The effects on arthritis of restoring CD59 to the joint in CD59a(-/-) mice by use of a membrane-targeted recombinant CD59 were also explored.

RESULTS

Disease, as assessed clinically by measurement of joint swelling on day 1 (P < 0.0001), day 2 (P < 0.01), and day 7 (P < 0.02) and histologically from indicators of joint damage on day 21 (P < 0.02), was significantly enhanced in CD59a(-/-) mice compared with CD59a(+/+) wild-type controls. Membrane attack complex (MAC) deposition in the arthritic joints of CD59a(-/-) mice was also increased compared with that in the joints of CD59a(+/+) controls. Restitution of CD59 activity in joints of CD59a(-/-) mice was attempted with soluble recombinant rat CD59 (sCD59) or with a novel membrane-targeted rat CD59 derivative (sCD59-APT542). Strong immunohistochemical staining of the synovial membrane and subsynovial tissue was apparent in sCD59-APT542-injected joints, but not in joints injected with untargeted sCD59. Intraarticular administration of sCD59-APT542 markedly ameliorated disease severity in CD59a(-/-) mice, knee swelling was significantly reduced over the time course of the disease, and joint damage, assessed histologically, was significantly milder on day 21 (P < 0.05).

CONCLUSION

These data firmly implicate the MAC of complement as a major effector of joint damage in the murine AIA model of rheumatoid arthritis (RA), and they provide a rationale for the inhibition of MAC assembly as a therapeutic strategy for RA.

Complement and immunity

Our body is in constant interaction with the environment. Some of the interactions involve the recognition and disposal of foreign substances that may harm the delicate balance between health and disease. The foreign elements, or antigens, include infectious organisms and lifeless macromolecules. The ability of the body to recognize what is dangerous and what is inconsequential, and to refrain from damaging what is perceived as self, are the main functions of the immune system. One important component of the innate immune response is the complement system. This article describes the different mechanisms of how complement is activated and the consequence of this activation, followed by a characterization of the complement's role in inflammation and autoimmunity, and the therapeutic considerations emanating from these studies.

An immunomodulatory GpG oligonucleotide for the treatment of autoimmunity via the innate and adaptive immune systems

Bacterial DNA and immunostimulatory CpG oligodeoxynucleotides (ODNs) activate the innate immune system to produce proinflammatory cytokines. Shown to be potent Th1-like adjuvants, stimulatory CpG motifs are currently used as effective therapeutic vaccines for various animal models of infectious diseases, tumors, allergies, and autoimmune diseases. In this study, we show that the application of an immunomodulatory GpG ODN, with a single base switch from CpG to GpG, can effectively inhibit the activation of Th1 T cells associated with autoimmune disease. Moreover, this immunomodulatory GpG ODN suppresses the severity of experimental autoimmune encephalomyelitis in mice, a prototypic Th1-mediated animal disease model for multiple sclerosis.

Generation of anti-complement "prodrugs": cleavable reagents for specific delivery of complement regulators to disease sites

Expression of biologically active molecules as fusion proteins with antibody Fc can substantially extend the plasma half-life of the active agent but may also influence function. We have previously generated a number of fusion proteins comprising a complement regulator coupled to Fc and shown that the hybrid molecule has a long plasma half-life and retains biological activity. However, several of the fusion proteins generated had substantially reduced biological activity when compared with the native regulator or regulator released from the Fc following papain cleavage. We have taken advantage of this finding to engineer a prodrug with low complement regulatory activity that is cleaved at sites of inflammation to release active regulator. Two model prodrugs, comprising, respectively, the four short consensus repeats of human decay accelerating factor (CD55) linked to IgG4 Fc and the three NH2-terminal short consensus repeats of human decay accelerating factor linked to IgG2 Fc have been developed. In each, specific cleavage sites for matrix metalloproteinases and/or aggrecanases have been incorporated between the complement regulator and the Fc. These prodrugs have markedly decreased complement inhibitory activity when compared with the parent regulator in vitro. Exposure of the prodrugs to the relevant enzymes, either purified, or in supernatants of cytokine-stimulated chondrocytes or in synovial fluid, efficiently cleaved the prodrug, releasing active regulator. Such agents, having negligible systemic effects but active at sites of inflammation, represent a paradigm for the next generation of anti-C therapeutics.

Prevention of collagen-induced arthritis in mice transgenic for the complement inhibitor complement receptor 1-related gene/protein y

The objective of these studies was to examine collagen-induced arthritis (CIA) in C57BL/6 mice transgenic for the rodent complement regulatory protein complement receptor 1-related gene/protein y (Crry) (Crry-Tg), a C3 convertase inhibitor. The scores for clinical disease activity and for histological damage in the joints were both significantly decreased in Crry-Tg mice in comparison to wild-type (WT) littermates. The production of both IgG1 and IgG2a anti-collagen Abs was reduced in the Crry-Tg mice, although spleen cell proliferation in response to collagen type II was not altered. The production of IFN-gamma, TNF-alpha, and IL-1beta by LPS-stimulated spleen cells was decreased, and IL-10 was increased, in cells from Crry-Tg mice in comparison to WT. The steady-state mRNA levels for IFN-gamma, TNF-alpha, and IL-1beta were all decreased in the joints of Crry-Tg mice in comparison to WT. The synovium from Crry-Tg mice without CIA contained the mRNA for the Crry transgene, by RT-PCR, and the synovium from transgenic mice with CIA exhibited little deposition of C3 protein by immunohistological analysis. These results suggest that suppression of CIA in Crry-Tg mice may be due to enhanced synthesis of Crry locally in the joint with decreased production of proinflammatory cytokines.

Release of endogenous anti-inflammatory complement regulators FHL-1 and factor H protects synovial fibroblasts during rheumatoid arthritis

Rheumatoid arthritis is a chronic inflammatory disease of unknown aetiology predominantly affecting cells and tissues of synovial joints. Here we show that the two important complement regulators FHL-1 and factor H play a protective anti-inflammatory role in rheumatoid arthritis. Expression analyses at the mRNA- and protein level show in vitro expression and secretion of both regulators by synovial fibroblasts derived from patients with rheumatoid arthritis. Similarly the two regulators are synthesized in vivo in diseased synovial tissue, and in particular synovial lining cells express high levels of FHL-1. The anti-inflammatory role of these regulators in rheumatoid arthritis is highlighted by their induction with IFN-gamma and dexamethasone, whilst the pro-inflammatory cytokine TNF-alpha had no effect. Transient transfection experiments with various FHL-1/factor H promoter-luciferase reporter constructs into cells of distinct origin show independent cell and tissue specific promoter regulated transcription of these two regulators. The inducible expression, specifically of FHL-1 has physiological consequences. By binding directly to surfaces the released proteins protect cells from inflammatory damage and complement-mediated cell lysis. This study shows a novel protective and anti-inflammatory role of the two important complement regulators FHL-1 and factor H in rheumatoid arthritis and suggests a disease controlling role of the two proteins.

Mechanisms of effects of complement inhibition in murine collagen-induced arthritis

OBJECTIVE

To determine the mechanisms of amelioration of collagen-induced arthritis (CIA) in DBA/1J mice by inhibition of complement activation.

METHODS

Mice received 2 intradermal injections of bovine type II collagen (CII), on days 0 and 21. From day 21 (immediately after the second injection of CII) through day 35, mice received intraperitoneal injections of either phosphate buffered saline (PBS), a monoclonal mouse antibody to murine C5 (anti-C5 antibody), or the C3 convertase inhibitor Crry-Ig.

RESULTS

On days 30 and 32, the clinical disease activity score was lower in mice treated with anti-C5 antibody than in those treated with Crry-Ig. Histopathologic evidence of joint damage was 75% lower in the mice treated with anti-C5 antibody than in those treated with either PBS or Crry-Ig. Spleen cells from mice receiving either form of complement inhibition exhibited decreased CII-stimulated proliferation, whereas increased proliferative responses were exhibited by lymph node cells from mice treated with Crry-Ig. Treatment with anti-C5 antibody decreased production of IgG1 anticollagen antibody, while production of IgG2a antibody was inhibited by both complement inhibitory treatments. CII-stimulated spleen cells from anti-C5-treated mice produced lower levels of tumor necrosis factor alpha (TNFalpha) and interleukin-10 (IL-10) compared with those from mice treated with Crry-Ig. Lower steady-state messenger RNA (mRNA) levels for TNFalpha, interferon-gamma (IFNgamma), IL-18, and IL-6 were observed in the joints of anti-C5-treated mice, and for IFNgamma and IL-6 in mice receiving Crry-Ig, all in comparison with PBS-treated mice. However, mRNA levels for IL-1beta and TNFalpha were lower in the joints after treatment with anti-C5 compared with Crry-Ig.

CONCLUSION

These results indicate that inhibition of complement in CIA leads to decreased production of IgG2a antibody and suppressed CII-induced spleen cell proliferation. The greater inhibitory effects on CIA of anti-C5 antibody in comparison with Crry-Ig may be attributable primarily to decreased levels of IL-1beta and TNFalpha mRNA in the joints.

Generation and characterization of transgenic mice expressing cobra venom factor

Cobra venom factor (CVF), the anticomplementary protein in cobra venom, activates the alternative complement pathway, eventually leading to complement consumption. Here, we describe the development of a transgenic mouse model for CVF. We generated a DNA construct containing the full-length cDNA for single-chain pre-pro-CVF. Expression of CVF was controlled by the alpha(1)-antitrypsin promoter to achieve liver-specific expression. Linearized DNA was microinjected into murine ovary cells (strain CD(2)F(1) (BALB/cxDBA/2J)) and the newborn mice were analyzed for stable integration of CVF DNA. After establishing the transgene, mice were propagated in a BALB/c background. The CVF mRNA was detected in the liver and, in some animals, in the kidney. CVF protein was detected in small amounts in the serum. Serum complement hemolytic activity in CVF-transgenic mice was virtually absent. The concentration of plasma C3 was significantly reduced. The CVF-transgenic animals show no unusual phenotype. They provide an animal model to study the effect of long-term complement depletion by continued activation, as well as the role of complement in host immune response and pathogenesis of disease.

Antiarthritic activity of an orally active C5a receptor antagonist against antigen-induced monarticular arthritis in the rat

OBJECTIVE

To determine if the new, orally active C5a receptor antagonist, the cyclic peptide AcF-[OPdChaWR], reduces the severity of pathology in a rat model of immune-mediated monarticular arthritis.

METHODS

Arthritis was induced in the right knee of previously sensitized rats by the intraarticular injection of methylated bovine serum albumin. Rats were examined for either 14 days or 28 days, or for 49 days following a second antigen challenge at 28 days. The C5a antagonist (1 or 3 mg/kg/day) and/or ibuprofen (30 mg/kg/day) were administered orally on a daily basis either before or after arthritis induction.

RESULTS

Rats receiving AcF-[OPdChaWR] had significant reductions in right knee swelling, gait disturbance, lavaged joint cell numbers, and right knee histopathology, as well as in serum levels of tumor necrosis factor alpha (TNFalpha) and intraarticular levels of interleukin-6 and TNFalpha on day 14. In the 14- and 28-day studies, ibuprofen resulted in a similar reduction in gait abnormalities and intraarticular inflammatory cells compared with the C5a antagonist, but was less effective in reducing knee swelling over the course of the study and had no effect on knee histopathology. Combination therapy with AcF-[OPdChaWR] and ibuprofen resulted in no greater efficacy than with the C5a antagonist alone. Rats injected twice with the antigen in the 49-day study displayed the most severe histopathology and this, as well as knee swelling and gait abnormalities, was significantly reduced by repeated treatment with the C5a antagonist.

CONCLUSION

An agent that inhibits the action of C5a in this model significantly reduced joint pathology, while ibuprofen was not effective. C5a antagonists could therefore have broader therapeutic benefits than nonsteroidal antiinflammatory drugs as antiarthritic agents for rheumatoid arthritis.

Coupling complement regulators to immunoglobulin domains generates effective anti-complement reagents with extended half-life in vivo

Complement activation and subsequent generation of inflammatory molecules and membrane attack complex contributes to the pathology of a number of inflammatory and degenerative diseases, including arthritis, glomerulonephritis and demyelination. Agents that specifically inhibit complement activation might prove beneficial in the treatment of these diseases. Soluble recombinant forms of the naturally occurring membrane complement regulatory proteins (CRP) have been exploited for this purpose. We have undertaken to design better therapeutics based on CRP. Here we describe the generation of soluble, recombinant CRP comprising rat decay accelerating factor (DAF) or rat CD59 expressed as Fc fusion proteins, antibody-like molecules comprising two CRP moieties in place of the antibody Fab arms (CRP-Ig). Reagents bearing DAF on each arm (DAF-Ig), CD59 on each arm (CD59-Ig) and a hybrid reagent containing both DAF and CD59 were generated. All three reagents inhibited C activation in vitro. Compared with soluble CRP lacking Fc domains, activity was reduced, but was fully restored by enzymatic release of the regulator from the Ig moiety, implicating steric constraints in reducing functional activity. In vivo studies showed that DAF-Ig, when compared to soluble DAF, had a much extended half-life in the circulation in rats and concomitantly caused a sustained reduction in plasma complement activity. When given intra-articularly to rats in a model of arthritis, DAF-Ig significantly reduced severity of disease. The data demonstrate the potential of CRP-Ig as reagents for sustained therapy of inflammatory disorders, including arthritis, but emphasize the need for careful design of fusion proteins to retain function.

Complement deficiency ameliorates collagen-induced arthritis in mice

Collagen-induced arthritis (CIA) is an experimental animal model of human rheumatoid arthritis being characterized by synovitis and progressive destruction of cartilage and bone. CIA is induced by injection of heterologous or homologous collagen type II in a susceptible murine strain. DBA/1J mice deficient of complement factors C3 (C3(-/-)) and factor B (FB(-/-)) were generated to elucidate the role of the complement system in CIA. When immunized with bovine collagen type II emulsified in CFA, control mice developed severe arthritis and high CII-specific IgG Ab titers. In contrast, the C3(-/-) and FB(-/-) were highly resistant to CIA and displayed decreased CII-specific IgG Ab response. A repeated bovine collagen type II exposure 3 wk after the initial immunization led to an increase in the Ab response in all mice and triggered arthritis also in the complement-deficient mice. Although the arthritic score of the C3(-/-) mice was low, the arthritis in FB(-/-) mice ranked intermediate with regard to C3(-/-) and control mice. We conclude that complement activation by both the classical and the alternative pathway plays a deleterious role in CIA.

Membrane complement regulators protect against the development of type II collagen-induced arthritis in rats

OBJECTIVE

To investigate changes in the distribution patterns of membrane complement regulators (MCRs) during the development of type II collagen-induced arthritis (CIA) and to examine the protective effects of these molecules against the augmentation of CIA in the knee joint.

METHODS

Immunohistochemistry was used to examine the distribution of the MCRs Crry, DAF, and CD59 in the synovium of knee joints before and 2, 4, and 10 weeks after induction of CIA by immunization with type II collagen. In addition, at 2 or 10 weeks after induction of CIA, rats were injected intraarticularly with anti-Crry and/or anti-CD59 as the F(ab')2 fraction of monoclonal antibodies (mAb). Knee joint swelling and histologic changes in the synovium were examined 2 weeks after mAb injection.

RESULTS

Synovial expression of Crry, DAF, and CD59 decreased in parallel with increased inflammation. When Crry and CD59 were functionally blocked at 2 weeks after the induction of CIA, swelling of the knee joints was markedly increased. Blocking of either regulator alone had no effect on swelling. Thickening of the synovial surface and proliferation of subsynovial tissue were all increased after blocking Crry and CD59, whereas blocking of either MCR alone had no effect. When both Crry and CD59 were blocked, deposits of membrane attack complex were found in the synovium.

CONCLUSION

Our findings indicate that in rats with CIA and severely inflamed synovium, local expression of MCR is reduced. The MCRs Crry and CD59 appear to suppress the development of CIA.

Structural Requirements for the Complement Regulatory Activities of C4BP

C4b-binding protein (C4BP) is a regulator of the classical complement pathway C3 convertase (C4bC2a complex). It is a disulfide-linked polymer of seven alpha-chains and a unique beta-chain; the alpha- and beta-chains are composed of eight and three complement control protein (CCP) domains, respectively. To elucidate the importance of the polymeric nature of C4BP and the structural requirements for the interaction between C4b and the alpha-chain, 19 recombinant C4BP variants were created. Six truncated monomeric variants, nine polymeric variants in which individual CCPs were deleted, and finally, four variants in which double alanine residues were introduced between CCPs were functionally characterized. The smallest truncated C4BP variant still active in regulating fluid phase C4b comprised CCP1-3. The monomeric variants were less efficient than polymeric C4BP in degrading C4b on cell surfaces. All three N-terminal CCP domains contributed to the binding of C4b and were important for full functional activity; CCP2 and CCP3 were the most important. The spatial arrangements of the first CCPs were found to be important, as introduction of alanine residues between CCPs 1 and 2, CCPs 2 and 3, and CCPs 3 and 4 resulted in functional impairment. The results presented here elucidate the structural requirements of individual CCPs of C4BP, as well as their spatial arrangements within and between subunits for expression of full functional activity.

Cutting edge: C3, a key component of complement activation, is not required for the development of myelin oligodendrocyte glycoprotein peptide-induced experimental autoimmune encephalomyelitis in mice

Experimental autoimmune encephalomyelitis (EAE), an inflammatory demyelinating disease of the CNS, is regarded as an experimental model for multiple sclerosis. The complement has been implicated in the pathogenesis of multiple sclerosis. To clarify the role of C in mouse EAE, we immunized mice deficient in C3 (C3(-/-)) and their wild-type (C3(+/+)) littermates with myelin oligodendrocyte glycoprotein peptide 35-55. C3(-/-) mice were susceptible to EAE as much as the C3(+/+) mice were. No differences were found for the production of IL-2, IL-4, IL-12, TNF-alpha, and IFN-gamma between C3(+/+) and C3(-/-) mice. This finding shows that C3, a key component in C activation, is not essential in myelin oligodendrocyte glycoprotein peptide-induced EAE in mice.

Therapeutic efficacy of a novel membrane-targeted complement regulator in antigen-induced arthritis in the rat

OBJECTIVE

Complement system activation is strongly implicated as a factor in the pathogenesis of chronic synovitis in human rheumatoid arthritis. The objective of this study was to explore the therapeutic potential and local retention of a novel membrane-targeting complement regulatory protein, derived from human complement receptor 1, in the experimental setting of rat antigen-induced arthritis.

METHODS

Sensitized animals were treated at the time of arthritis induction with a single intraarticular (IA) dose of the membrane-targeting regulator APT070, a non-membrane-targeting control regulator (APT898), or vehicle control, and disease was assessed clinically and histologically. In addition, immunocytochemical analysis was performed on sections from normal rat knee joints at various time points after IA injection with APT070.

RESULTS

Animals treated with APT070 showed a dose-dependent therapeutic effect, with significantly milder clinical and histologic disease compared with both other treatment groups (P < 0.008 at the higher dose) and minimal evidence of erosive disease at study end in the active treatment group. Immunoperoxidase and immunofluorescence studies demonstrated local retention of APT070 on cell surface membranes within the normal joint up to 48 hours after IA injection.

CONCLUSION

These results show that IA complement inhibition represents an effective therapeutic strategy in experimental arthritis, by demonstrating that the exogenous delivery of a membrane-targeting complement regulator can result in prolonged synovial cell surface binding and significant clinical benefit in vivo. Complement inhibitory strategies of this type should be considered as novel therapies in human inflammatory arthritis.

Soluble complement receptor 1 (CD35) delivered by retrovirally infected syngeneic cells or by naked DNA injection prevents the progression of collagen-induced arthritis

OBJECTIVE

The complement system is important in the development of autoimmune inflammation, including rheumatoid arthritis (RA) and collagen-induced arthritis (CIA). Complement receptor 1 (CR1) is involved in regulation of complement activity. Studies on models of autoimmunity have demonstrated that soluble CR1 (sCR1) is a potent therapeutic agent. The present study was thus undertaken to investigate the feasibility of antiinflammatory gene therapy to prevent CIA by delivery of genes encoding truncated sCR1 (tsCR1) and dimeric tsCR1-Ig.

METHODS

Syngeneic fibroblasts or arthritogenic splenocytes, engineered to express tsCR1 using retrovirus-mediated gene transfer, were injected into DBA/1 recipients that had been immunized with bovine type II collagen (CII). In separate experiments, naked DNA containing tsCR1 and tsCR1-Ig genes was injected intramuscularly into the immunized animals. The clinical development of arthritis was monitored, anti-CII levels measured, and antigenic T cell response studied. Affinity-purified tsCR1-Ig was assayed for its inhibitory effect on the alternative complement pathway in mouse serum.

RESULTS

Treatment of CII-immunized mice with the tsCR1-expressing cells inhibited development of CIA, reduced anti-CII antibody levels, and inhibited T cell response to CII in vitro. Intramuscular injections of DNA encoding the CR1 genes prevented the progression of disease. Furthermore, compared with full-length sCR1, purified tsCR1-Ig was more active in inhibiting the murine alternative complement pathway.

CONCLUSION

Our findings demonstrated that tsCR1 and tsCR1-Ig, when delivered via gene therapy, had a beneficial effect on autoimmune inflammation. These results indicate that targeting the complement system in RA patients may be of clinical importance.

Complement activation and inhibition in experimental models of arthritis

Complement activation has been implicated as a pathological process in a number of inflammatory and autoimmune disorders including chronic rheumatoid arthritis (RA). Animal models of experimental arthritis have been widely used to investigate the pathogenesis of RA and also in the development of novel therapies. Many of these models are complement-dependent and both incidence and progression of disease can be influenced by complement inhibition. In certain situations, local inhibition is of greater therapeutic benefit than systemic decomplementation. An increasing awareness and availability of a wide range of naturally occurring complement regulatory proteins can now offer a more targeted approach to complement inhibition while the availability of novel engineering strategies has also improved the efficiency of this process. The success of complement inhibition in the experimental models described should offer a novel therapeutic approach to the treatment of human inflammatory arthritis.