Synthesis of complement components by synovial membrane

Analysis of Complement Gene Expression, Clinical Associations, and Biodistribution of Complement Proteins in the Synovium of Early Rheumatoid Arthritis Patients Reveals Unique Pathophysiologic Features

Rheumatoid arthritis (RA) is an autoimmune disease characterized by synovial hyperplasia and inflammation. The finding of autoantibodies in seropositive RA suggests that complement system activation might play a pathophysiologic role due to the local presence of immune complexes in the joints. Our first objective was to explore the Pathobiology of Early Arthritis Cohort (PEAC) mRNA sequencing data for correlations between clinical disease severity as measured by DAS28-ESR (disease activity score in 28 joints for erythrocyte sedimentation rate) and complement system gene expression, both in the synovium and in blood. Our second objective was to determine the biodistribution using multiplex immunohistochemical staining of specific complement activation proteins and inhibitors from subjects in the Accelerating Medicines Partnership (AMP) RA/SLE study. In the PEAC study, there were significant positive correlations between specific complement gene mRNA expression levels in the synovium and DAS28-ESR for the following complement genes: C2, FCN1, FCN3, CFB, CFP, C3AR1, C5AR1, and CR1 Additionally, there were significant negative correlations between DAS28-ESR and Colec12, C5, C6, MASP-1, CFH, and MCP In the synovium there were also significant positive correlations between DAS28-ESR and FcγR1A, FcγR1B, FcγR2A, and FcγR3A Notably, CFHR4 synovial expression was positively correlated following treatment with the DAS28-ESR at 6 mo, suggesting a role in worse therapeutic responses. The inverse correlation of C5 RNA expression in the synovium may underlie the failure of significant benefit from C5/C5aR inhibitors in clinical trials performed in patients with RA. Multiplex immunohistochemical analyses of early RA synovium reveal significant evidence of regional alterations of activation and inhibitory factors that likely promote local complement activation.

Beyond Systemic Lupus Erythematosus and Anti-Phospholipid Syndrome: The Relevance of Complement From Pathogenesis to Pregnancy Outcome in Other Systemic Rheumatologic Diseases

Evidence about the relevance of the complement system, a highly conserved constituent of the innate immunity response that orchestrates the elimination of pathogens and the inflammatory processes, has been recently accumulated in many different rheumatologic conditions. In rheumatoid arthritis, complement, mainly the classical pathway, contributes to tissue damage especially in seropositive subjects, with complement activation occurring in the joint. Data about complement pathways in psoriatic arthritis are dated and poorly consistent; among patients with Sjögren syndrome, hypocomplementemia exerts a prognostic role, identifying patients at risk of extra-glandular manifestations. Hints about complement involvement in systemic sclerosis have been recently raised, following the evidence of complement deposition in affected skin and in renal samples from patients with scleroderma renal crisis. In vasculitides, complement plays a dual role: on one hand, stimulation of neutrophils with anti-neutrophil cytoplasmic antibodies (ANCA) results in the activation of the alternative pathway, on the other, C5a induces translocation of ANCA antigens, favouring the detrimental role of antibodies. Complement deposition in the kidneys identifies patients with more aggressive renal disease; patients with active disease display low serum levels of C3 and C4. Even though in dermatomyositis sC5b-9 deposits are invariably present in affected muscles, data on C3 and C4 fluctuation during disease course are scarce. C3 and C1q serum levels have been explored as potential markers of disease activity in Takayasu arteritis, whereas data in Behçet disease are limited to in vitro observations. Pregnancies in women with rheumatologic conditions are still burdened by a higher rate of pregnancy complications, thus the early identification of women at risk would be invaluable. A fine-tuning of complement activation is required from a physiological progression of pregnancy, from pre-implantation stages, through placentation to labour. Complement deregulation has been implicated in several pregnancy complications, such as recurrent abortion, eclampsia and premature birth; low complement levels have been shown to reliably identify women at risk of complications. Given its physiologic role in orchestrating pregnancy progression and its involvement as pathogenic effector in several rheumatologic conditions, complement system is an attractive candidate biomarker to stratify the obstetric risk among women with rheumatologic conditions.

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.

Extreme hypercomplementemia in the setting of mixed cryoglobulinemia

Elevated levels of complement components, C3 and C4, are often seen in inflammatory diseases. They are generally not thought to be responsible for organ injury but simply reflect stimulation of the immune system. Extremely high elevations of these components are rarely seen. Such values are usually reported in patients with hematopoietic malignancies. We report here a case of C3 elevation to 9.22 g/L (5 times the upper limit of normal) and C4 elevation to 2.48 g/L (6 times the upper limit of normal). To our knowledge, no prior elevations of this magnitude have been reported previously from our institution or in the published medical literature (+/- MEDLINE search, using keywords hypercomplementemia, C3, C4, and lymphoplasmacytic lymphoma). In this case, there appeared to be no adverse end-organ damage from the excessive complement components or their activation.

Z39Ig is co-expressed with activated macrophage genes

Z39Ig is a recently-identified gene with immunoglobulin-like domains whose function is unknown. We examined expression of Z39Ig in 1432 human cDNA libraries, and found it primarily in synovium of patients with rheumatoid arthritis, in placenta, and in lung. We analyzed its co-expression pattern using the Guilt-by-Association (GBA) algorithm, and found that it is most similar in expression to early genes in the classical complement system (C1qA, C1qB, C1qC, C1r, and C1 inhibitor), MHC class II genes (HLA-DR alpha, HLA-DR beta 1, and HLA-DP alpha 1), Fc receptors (Fc gamma RIIa and Fc epsilon R1), lysosomal protein (LAPTm5), tissue transglutaminase, and macrophage receptors (MARCO and CD163/M130). The sequence and expression data suggest that Z39Ig is a cell surface receptor, expressed in activated macrophages, and linked with the classical complement system, most likely in phagocytosis preceding antigen presentation. Knowledge of this gene may contribute to better understanding of the role of complement and activated macrophages in rheumatoid arthritis and systemic lupus.

Local production of complement proteins in rheumatoid arthritis synovium

OBJECTIVE

Complement has been repeatedly implicated in the pathogenesis of rheumatoid arthritis (RA) based on studies showing reduced levels of native complement components and increased levels of complement metabolites in plasma, synovial fluid (SF), and synovial tissue (ST) of RA patients. However, there is limited information on local production and activation of key factors of the complement cascade in RA synovium and their potential modulation by novel anticytokine therapies. This study was undertaken to characterize the expression of complement proteins and receptors in RA SF and ST.

METHODS

Using in situ hybridization, immunohistochemistry, and Western blot techniques, we assessed the presence of complement proteins C3, factor B (FB), and C5b-9, as well as the expression of complement receptors C3aR and C5aR in rheumatoid synovium. C3 and FB levels in SF were determined by enzyme-linked immunosorbent assay. Functional assessment was performed by examining the effects of soluble tumor necrosis factor receptor (sTNFR) p55 gene transfer in the SCID mouse model of RA.

RESULTS

Complement proteins and receptors could be localized in all RA synovial specimens, whereas in osteoarthritis (OA) synovium, only a few, single cells expressed complement proteins and receptors. No differences were noted in the concentration of C3 between RA and OA in SF; however, FB levels were markedly reduced in RA versus OA SF. In RA synovium, in contrast to OA synovium, local expression of complement factor and complement receptor messenger RNA was found throughout the various ST compartments, suggesting that activation of the complement cascade occurs in all parts of the rheumatoid synovium. Moreover, C5aR expression was up-regulated following overexpression of sTNFR p55 by adenovirus-based gene transfer.

CONCLUSION

In summary, local complement production and activation may play an important role in RA, and specific modulation and inhibition of local complement production could be an attractive therapeutic target for RA.

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.

Tissue distribution of the guinea-pig decay-accelerating factor

MCA44 is a monoclonal antibody (mAb) to guinea-pig decay-accelerating factor (DAF) and, using this mAb, tissue distribution of guinea-pig DAF was studied by immunofluorescence. Guinea-pig DAF was found to be expressed not only on the vascular endothelium but also on different types of cells, such as the tubular epithelium of the kidney, epidermal cells of the skin and synovial lining cells. As there was no significant reduction in staining intensity with MCA44 following treatment with phosphatidylinositol-specific phospholipase C, many guinea-pig DAF molecules expressed in these tissues may be of the transmembrane form.

Quantitative microscopic analysis of inflammation in rheumatoid arthritis synovial membrane samples selected at arthroscopy compared with samples obtained blindly by needle biopsy

OBJECTIVE

To evaluate microscopic measures of inflammation in rheumatoid arthritis synovial tissue samples selected at arthroscopy compared with those obtained blindly by needle biopsy from the suprapatellar pouch (SPP) of the same joint.

METHODS

Samples were selected at knee arthroscopy from the SPP and the lateral and medial gutters. Immediately following arthroscopy, a biopsy needle was inserted through the same portal into the SPP by a second investigator, and 3 further samples were obtained blindly. Using standard immunohistologic methods, all samples were analyzed by a single investigator without knowledge of the original tissue location and biopsy technique. Following staining with anti-CD3 and anti-CD68 monoclonal antibodies, T lymphocyte and macrophage infiltration were measured by quantitative analysis.

RESULTS

Synovial tissues from 14 patients were analyzed. In comparing microscopic measures of inflammation using the 2 procedures, mean scores of lining cell depth and the percentage of CD68+ cells in the lining layer correlated positively (tau = 0.59, P = 0.003 and tau = 0.73, P = 0.0003, respectively). In the sublining layer, CD3+ cell counts also correlated significantly (tau = 0.71, P = 0.0004). Sublining CD68+ cell counts did not correlate. This was explained by the observation that CD68+ cell infiltration in areas adjacent to articular cartilage was significantly greater than in the SPP (P = 0.01), suggesting preferential trafficking to this site by macrophages, but not by T lymphocytes. Macroscopic appearance at arthroscopy did not predict microscopic features.

CONCLUSION

Most microscopic measures of inflammation in synovial tissue samples obtained blindly from the SPP were similar to those determined in samples selected at arthroscopy. However, measurements in samples from the SPP may underestimate the intensity of macrophage infiltration in areas more adjacent to cartilage. These observations have important implications for future study of macrophage function in synovial tissue.

Elevated factor J levels in synovial fluid from patients with inflammatory arthropathies

Factor J (FJ) is a complement inhibitor that is able to regulate in vitro both the classical and alternative human complement pathways. In the search of its biological significance, we have analyzed FJ levels in synovial fluid from patients with different arthropathies, in which IL-6 levels had been previously measured. The pathologies included in this study were: rheumatoid arthritis (RA) (n = 21), crystal deposition diseases (CDD) (n = 6), osteoarthritis (OA) (n = 23), spondyloarthritis (SpA) (n = 3) and other inflammatory arthropathies (OIA) (n = 4). We found a good correlation between IL-6 and FJ levels (r = 0.33, p = 0.0132) in the 57 processed samples. Synovial fluids had high levels of IL-6 (median: 3000 pg/ml). Besides, we found that FJ levels were elevated (241 +/- 429 micrograms/ml) when compared with NHS (5.32 +/- 2.82 micrograms/ml). Considering OA patients as control group for non-inflammatory situation, we found that FJ levels were significantly elevated in inflammatory patients only if RA patients were excluded. Furthermore, there were also significant differences with CDD patients. In addition, we have examined the presence of this inhibitor in synovial fluid by Western blot after running gels at acid pH and electrophoretical transference at the same pH. In these experiments, we evidenced the presence of a cationic protein immunoreactive with polyclonal and monoclonal anti-FJ antibodies. In conclusion, FJ levels are elevated in pathological synovial fluids. FJ could be an acute phase reactant as other molecules present in the synovial fluid, or could be shed from extracellular matrix as a consequence of the high enzymatic activity present in the articular fluid or as a response to the inflammatory stimulus.

The effects of functional suppression of a membrane-bound complement regulatory protein, CD59, in the synovial tissue in rats

OBJECTIVE

To investigate the roles of CD59 in the synovial tissue by functional suppression of CD59.

METHODS

Rats treated with cobra venom factor to deplete complement or untreated rats were injected intraarticularly with 0.3 mg of the F(ab')2 fraction of a monoclonal antibody, 6D1, that inhibits the function of rat CD59. The circumference of knee joints was measured, and histologic changes in the synovium were studied.

RESULTS

Joint swelling, thickening of the synovial tissues, infiltration of inflammatory cells into the synovium, and deposition of membrane attack complex (MAC) on the synovial surface were observed after intraarticular injection of 6D1. The inflammatory reaction reached its peak at 24 hours after injection, and finally subsided to normal within 3 days. It was suggested that functional suppression of CD59 in the synovium induced MAC formation followed by synovitis. Serum complement depletion did not completely suppress this reaction. This indicates that complement existing in the joint space is important for the formation of MAC on the synovial surface and for induction of synovitis.

CONCLUSION

The membrane-bound complement regulatory protein, CD59, plays a key role in the protection of joints against MAC-mediated synovial injury and in maintaining the normal integrity of the joint.

Vitronectin modulates the expression of complement components of the terminal pathway synthesized by human umbilical vein endothelial cells in vitro

In this study we demonstrate that human endothelial cells (EC) synthesize mRNA for vitronectin by using techniques based on reverse transcriptase (RT) reaction and polymerase chain reaction (PCR). The identification of vitronectin mRNA, shown by sequence analysis of PCR-amplified RT product of RNA extracted from EC, clearly demonstrates that these cells synthesize mRNA for vitronection. We further investigated whether vitronectin in serum-free EC cultures regulates the net expression of the terminal complement pathway, measured as the terminal complement complex (TCC) bound to co-cultured agarose beads which activate the alternative pathway. Presence of polyclonal F(ab')2 anti-human vitronectin (VN) antibodies, regardless of concentration (10-80 micrograms/ml), significantly reduced the binding of monoclonal anti-C3c antibodies to co-cultured beads, whereas the binding of monoclonal anti-TCC antibodies was unaltered or significantly increased compared with controls. Despite some interexperimental variation in the results, addition of vitronectin (10-80 micrograms/ml) to the EC resulted in an inversely related pattern compared with experiments using anti-VN antibodies. The binding indices of anti-C3c are comparable to the controls. On the other hand, there is a steady concentration-dependent (10-80 micrograms of vitronectin added) reduction in binding of anti-TCC up to approximately 60%. The results indicate that vitronectin regulates the expression of synthezised and surface-bound TCC in serum-free EC cultures, comparable to previous findings in serum.

Serum clusterin and vitronectin in alcoholic cirrhosis

Clusterin and vitronectin are multifunctional regulatory proteins which both serve as complement lysis inhibitors. Previous data have strongly suggested that serum vitronectin is mainly produced in the liver, whereas the biosynthetic origin for serum clusterin has not been determined. In the present study we aimed to determine the role of the liver in producing these proteins and to evaluate the proteins as possible markers of liver failure. We therefore quantified clusterin and vitronectin in serum from patients suffering from alcoholic liver cirrhosis (n = 83), and in serum-free culture supernatants from the hepatoma cell line HepG2. The median clusterin concentration was 0.20 g/l in cirrhosis and 0.37 g/l in the controls, whereas corresponding vitronectin values were 0.19 and 0.26 g/l, respectively. The concentration of both proteins showed significant correlation (p < 0.0001) with disease severity and with established plasma markers of hepatic synthetic function, such as albumin and prothrombin complex. The clusterin level, but not the vitronectin level, correlated with survival (p = 0.005). The rates of synthesis of clusterin, vitronectin and C3 from HepG2 cells were 0.02, 0.21 and 1.9 micrograms/10(6) cells/24 h, respectively. From the present data we conclude that clusterin (as vitronectin and C3) is mainly produced in the liver and may be a useful marker in the evaluation of severity of liver disease and prognosis of patients with alcoholic cirrhosis.

Inherited deficiencies of complement in rheumatic diseases

Inherited complement deficiencies are rare but occur with increased frequency in systemic lupus erythematosus. This selective review summarizes the fundamentals of complement activation and biology and focuses on recent findings. system lupus erythematosus is highly associated with homozygous C1q deficiencies and with C4A null allotypes, and homozygous C2 and C3 deficiencies are less uniformly associated with autoimmune disease. This hierarchy of disease associations suggests the importance of an intact early classic activation pathway in preventing systemic lupus erythematosus. Assays of complement activation products may have greater sensitivity and specificity for systemic lupus erythematosus disease activity and lupus flares.