Role of Early Glycation Amadori Products of Lysine-Rich Proteins in the Production of Autoantibodies in Diabetes Type 2 Patients

In diabetes, protein glycation mostly occurs at intrachain lysine residues resulting in the formation of early stage Amadori products which are finally converted to advance glycation end products (AGEs). Several studies have reported autoantibodies against AGEs in diabetes but not much data are found in respect of Amadori products. In this study, poly-l-lysine (PLL) was glycated with 50 mM glucose and the resultant Amadori products were estimated by fructosamine or nitroblue tetrazolium assay. We report high content of Amadori products in PLL upon glycation. Glycated PLL showed marked hyperchromicity in the UV spectrum, ellipticity changes in CD spectroscopy, and variations in ε-methylene protons shift in NMR. It was better recognized by autoantibodies in type 2 diabetics compared to the native PLL. Induced antibodies against glycated PLL were successfully used to probe early glycation in the IgG isolated from diabetes type 2 patients. Role of Amadori products of glycated proteins in the induction of autoantibodies in type 2 diabetes as well as in associated secondary complications has been discussed.     

Prevalence of autoantibodies against 3-DG-glycated H2A protein in type 2 diabetes

Advanced glycation end-products (AGEs) have been found to be critically involved in initiation or progression of diabetes secondary complications (nephropathy, retinopathy, neuropathy, and angiopathy). Various hyper-glycating carbonyl compounds such as 3-deoxyglucosone (3-DG) are produced in pathophysiological conditions that form AGEs in high quantity both in vivo and in vitro. In the first stage of this study, we glycated histone H2A protein by 3-DG, and the results showed the formation of various intermediates and AGEs as well as structural changes in the protein. In the second stage, we studied the immunogenicity of native and 3-DG-glycated H2A protein in female rabbits. The modified H2A was highly immunogenic, eliciting high titer immunogen-specific antibodies, while the unmodified form was almost nonimmunogenic. Antibodies against standard carboxymethyllysine (CML) and pentosidine were detected in the immunized female rabbits, which demonstrates the immunogenic nature of AGEs (CML and pentosidine) as well. The results show both structural perturbation and AGEs have the capacity of triggering the immune system due to the generation of neoepitopes that render the molecule immunogenic. This study shows the presence of autoantibodies against 3-DG-modified H2A, CML, and pentosidine in the sera of type 2 diabetes patients having secondary complications. Autoantibodies against damaged H2A and AGEs may be significant in the assessment of initiation/progression of secondary complications in type 2 diabetes mellitus patients or may be used as a marker for early detection of secondary complications in diabetes.     

Preferential recognition of epitopes on peroxynitrite-modified alpha-2-macroglobulin by circulating autoantibodies in rheumatoid arthritis patients

Abstract

Autoimmune responses against post-translationally modified antigens are a hallmark of several autoimmune diseases. In this work, we have studied the changes in alpha-2-macroglobulin (α₂M) upon modification by peroxynitrite. Furthermore, we have evaluated the immunogenicity of modified α₂M in experimental rabbits and rheumatoid arthritis (RA) patients. Peroxynitrite-modified α₂M showed disturbed microenvironment and altered aromatic residues under UV and fluorescence studies. Aggregation, reduction in β-sheet content, production of nitrotyrosine and shift in amide I and II bands were observed in the modified α₂M by polyacrylamide gel electrophoresis besides CD and FTIR spectroscopic analysis. The exposure of hydrophobic clusters and changes in contact positions were observed in ANS and ThT binding assays. Immunological studies using ELISA showed peroxynitrite-modified α₂M as highly immunogenic producing high titre of specific antibodies in immunized rabbits. Cross-reactivity studies revealed the polyspecificity of the elicited antibodies. Direct binding ELISA and competitive inhibition studies confirmed the presence of circulating antibodies in the sera of RA patients having high specificity towards the peroxynitrite-modified α₂M as compared to the native α₂M. Sera from healthy (normal) human subjects showed lower binding with the native and modified protein. This study confirms that peroxynitrite induces structural modifications in α₂M and makes it immunogenic. The presence of neo-antigenic determinants on modified α₂M with enhanced binding for circulating autoantibodies in RA patients could offer new possibilities for diagnosis and etiopathology of the disease.

Communicated by Ramaswamy H. Sarma     

Preferential Recognition of Peroxynitrite Damaged Thymidine-Monophosphate by Anti-DNA Autoantibodies in Systemic Lupus Erythematosus

This study was undertaken to investigate the role of peroxynitrite (ONOO^?) modified thymine-5′-monophosphate (TMP) in the generation of anti-DNA autoantibodies in patients with systemic lupus erythematosus (SLE). TMP was exposed to ONOO^? in vitro and challenged in vivo. TMP and ONOO^?-modified-TMP were found to be nonimmunogenic in rabbits. TMP-linked-BSA and ONOO^?-modified-TMP-BSA induced high titer antibodies. Induced antibodies against ONOO^?-TMP-BSA show crossreactions with nucleic acids conformers. A high degree of specific binding by SLE autoantibodies with ONOO^?-TMP-BSA was observed. Our novel results provide an important insight into the immunological basis of anti-DNA autoantibodies generation in SLE.     

Rheumatoid arthritis–associated autoantibodies in non–rheumatoid arthritis patients with mucosal inflammation: a case–control study

IntroductionRheumatoid arthritis–associated autoantibodies (RA-AAB) can be present in serum years before clinical onset of rheumatoid arthritis (RA). It has been hypothesized that initiation of RA-AAB generation occurs at inflamed mucosal surfaces, such as in the oral cavity or lungs. The aim of this study was to assess systemic presence of RA-AAB in patients without RA who had oral or lung mucosal inflammation.MethodsThe presence of RA-AAB (immunoglobulin A [IgA] and IgG anti-cyclic citrullinated peptide 2 antibodies (anti-CCP2), IgM and IgA rheumatoid factor (RF), IgG anti-carbamylated protein antibodies and IgG and IgA anti-citrullinated peptide antibodies against fibrinogen, vimentin and enolase) were determined in sera of non-RA patients with periodontitis (PD, n = 114), bronchiectasis (BR, n = 80) or cystic fibrosis (CF, n = 41). Serum RA-AAB levels were compared with those of periodontally healthy controls (n = 36). Patients with established RA (n = 86) served as a reference group. Association of the diseases with RA-AAB seropositivity was assessed with a logistic regression model, adjusted for age, sex and smoking.ResultsLogistic regression analysis revealed that IgG anti-CCP seropositivity was associated with BR and RA, whereas the association with PD was borderline significant. IgA anti-CCP seropositivity was associated with CF and RA. IgM RF seropositivity was associated with RA, whereas the association with BR was borderline significant. IgA RF seropositivity was associated with CF and RA. Apart from an influence of smoking on IgA RF in patients with RA, there was no influence of age, sex or smoking on the association of RA-AAB seropositivity with the diseases. Anti-CarP levels were increased only in patients with RA. The same held for IgG reactivity against all investigated citrullinated peptides.ConclusionAlthough overall levels were low, RA-AAB seropositivity was associated with lung mucosal inflammation (BR and CF) and may be associated with oral mucosal inflammation (PD). To further determine whether mucosal inflammation functions as a site for induction of RA-AAB and precedes RA, longitudinal studies are necessary in which RA-AAB of specifically the IgA isotype should be assessed in inflamed mucosal tissues and/or in their inflammatory exudates.     

Prohibitin Is Involved in Patients with IgG4 Related Disease

ObjectiveIgG4-related disease (IgG4-RD) is a chronic systemic disease involved in many organs and tissues. As only limited autoantigens have been found since the beginning of this century, the aim of this study was to reveal new candidate autoantigens of IgG4-RD.MethodsMultiple cell lines including HT-29, EA.hy926, HEK 293 and HepG2 were used to test the binding ability of circulating autoantibodies from IgG4-RD sera. The amino-acid sequence was then analyzed by matrix-assisted laser desorption/ionization time-of-flight tandem (MALDI-TOF/TOF) mass spectrometry. After the cloning and expression of recombinant putative autoantigen in a bacterial expression system, the corresponding immuno assay was set up and utilized to observe the prevalence of serum autoantibodies in a large set of confirmed clinical samples.ResultsOne positive autoantigen was identified as prohibitin. ELISA analysis showed that a majority of patients with IgG4-RD have antibodies against prohibitin. Anti-prohibitin antibodies were present in the sera of patients with definite autoimmune pancreatitis (25/34; 73.5%), Mikulicz’s disease (8/15; 53.3%), retroperitoneal fibrosis (6/11; 54.5%), other probable IgG4-RD (26/29; 89.7%) and Sjögren’s syndrome (4/30; 13.3%) but not in apparently healthy donors (1/70; 1.4%).ConclusionsAn association between prohibitin and patients with some IgG4-RD was observed, although the results were quite heterogeneous among different individuals within autoimmune pancreatitis, Mikulicz’s disease and retroperitoneal fibrosis.     

Determination of anti-AGE antibodies in human serum

The aim of this study was to develop an immunoenzyme method for the determination of anti-AGE antibodies in human serum. Human aortic elastin glycatedin vitro (AGE-elastin) was used as an antigen, expressing AGE-epitopes, common to all glycated proteins.Polyclonal serum from guinea-pig against AGE-Hemocyanin was obtained according to Nakayamaet al. [(1989)Biochem Biophys Res Commun 162: 740–45] and its specificity was tested via direct and competitive ELISA. Sera of 20 type 1 diabetic patients and 20 healthy subjects were tested using the method described. Seventeen patients had elevated levels of competing factors that may be anti-AGE antibodies, compared with the healthy group. The method could be used for investigation of different clinical groups of type 1 diabetic patients. Such a study would help in understanding the pathogenic role of autoantibodies against advanced glycation end products of proteins for the development of long-term diabetic complications.     

Physicochemical studies on glycation-induced structural changes in human IgG

Glycation of biomolecules leads to the formation of advanced glycation end products (AGEs). Glycation of immunoglobulin G (IgG) has been implicated in autoimmune diseases such as rheumatoid arthritis (RA). In this study, human IgG was glycated with physiological concentration of glucose. The changes induced in IgG were analyzed by UV, fluorescence, circular dichroism, and Fourier transform infrared (FTIR) spectroscopy; thermal denaturation studies, native, and Sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis. The ketoamine moieties and carbonyl content were also quantitated in glycated IgG. We report structural perturbations, increased carbonyl content, and ketoamine moieties in the glycated IgG. This may interfere with the normal function of IgG and may contribute to initiation of arthritic complications. AGEs damaged IgG may be used as a biomarker for early detection of RA and the associated secondary complications.     

Human anti-DNA autoantibodies and induced antibodies against ROS-modified-DNA show similar antigenic binding characteristics.

Alterations in DNA structure by hydroxyl radical modification was characterized by UV spectroscopy, Tm, nuclease S1 digestibility and base modification. In view of indicted role of oxygen free radicals in human diseases, an attempt has been made to precisely compare the antigen binding properties of induced antibodies against hydroxyl radical modified DNA with those of naturally occurring anti-DNA autoantibodies. Antibodies induced against ROS-DNA showed diverse antigen binding characteristics which were comparable with those derived from SLE patients. The immune IgG recognized native DNA, heat denatured DNA, and synthetic polynucleotides in B-/B-like conformations. IgG isolated from SLE sera showed preference for ROS-DNA in competition-inhibition assay. The antigenic diversity of induced antibodies and preference of circulating anti-DNA autoantibodies for ROS-DNA over that of native DNA demonstrates the possible role of modified DNA antigens in the pathogenesis of SLE.     

Immunogenicity and Protective Efficacy of a Vero Cell Culture-Derived Whole-Virus H7N9 Vaccine in Mice and Guinea Pigs

BackgroundA novel avian H7N9 virus with a high case fatality rate in humans emerged in China in 2013. We evaluated the immunogenicity and protective efficacy of a candidate Vero cell culture-derived whole-virus H7N9 vaccine in small animal models.MethodsAntibody responses induced in immunized DBA/2J mice and guinea pigs were evaluated by hemagglutination inhibition (HI), microneutralization (MN), and neuraminidase inhibition (NAi) assays. T-helper cell responses and IgG subclass responses in mice were analyzed by ELISPOT and ELISA, respectively. Vaccine efficacy against lethal challenge with wild-type H7N9 virus was evaluated in immunized mice. H7N9-specific antibody responses induced in mice and guinea pigs were compared to those induced by a licensed whole-virus pandemic H1N1 (H1N1pdm09) vaccine.ResultsThe whole-virus H7N9 vaccine induced dose-dependent H7N9-specific HI, MN and NAi antibodies in mice and guinea pigs. Evaluation of T-helper cell responses and IgG subclasses indicated the induction of a balanced Th1/Th2 response. Immunized mice were protected against lethal H7N9 challenge in a dose-dependent manner. H7N9 and H1N1pdm09 vaccines were similarly immunogenic.ConclusionsThe induction of H7N9-specific antibody and T cell responses and protection against lethal challenge suggest that the Vero cell culture-derived whole-virus vaccine would provide an effective intervention against the H7N9 virus.     

Antibodies against nitric oxide damaged poly L-tyrosine and 3-nitrotyrosine levels in systemic lupus erythematosus

Alterations in the amino acid structure or sequence can generate neo-epitopes from self-proteins causing autoaggressive immune attack. Reactive nitrogen species are an important factor that induces post-translational modification of proteins by cellular reduction and oxidation mechanism; cysteinyl-nitrosylation or tyrosine nitration leading to potentially pathogenic pathways. It was thought of interest to investigate the immunogenicity of nitrated poly L-tyrosine vis-á-vis its possible role in the induction of antibodies in systemic lupus erythematosus (SLE). Commercially available poly L-tyrosine was exposed to nitrating species and the damage was monitored by UV spectroscopy and alkaline gel electrophoresis. The results indicated the formation of 3-nitrotyrosine. Nitrated poly L-tyrosine induced higher titre antibodies as compared to the native form. Nitrated poly L-tyrosine was recognized by the autoantibodies present in the sera of patients suffering from SLE by enzyme immunoassays and band shift assay. The possible role of nitrated self-proteins has been discussed in the production of circulating anti-DNA antibodies in SLE.     

An Immunohistochemical Analysis to Validate the Rationale behind the Enhanced Immunogenicity of D-Ribosylated Low Density Lipo-Protein

Advanced glycation end products (AGEs) are thought to contribute to the abnormal lipoprotein profiles and increased risk of cardiovascular disease in patients with diabetes and renal failure. D-ribose is one of the naturally occurring pentose monosaccharide present in all living cells and is a key component of numerous biomolecules involved in many important metabolic pathways. Formation of D-ribose derived glycated low density lipoprotein (LDL) has been previously demonstrated but no studies have been performed to assess the immune complex deposition in the kidney of rabbits immunized with glycated LDL. In this study, LDL was glycated with D-ribose, and it was further used as an immunogen for immunizing NZW female rabbits. The results showed that female rabbits immunized with D-ribose modified LDL induced antibodies as detected by direct binding and competitive ELISA. The modified LDL was found to be highly immunogenic eliciting high titer immunogen-specific antibodies, while the native forms were moderately immunogenic. The induced antibodies from modified LDL exhibited wide range of heterogeneity in recognizing various proteins and amino acids conformers. Furthermore, our histopathological results illustrated the deposits of immune complex in glomerular basement membrane in rabbits immunized with D-ribose-LDL.     

Restrictive IgG antibody response against mutated citrullinated vimentin predicts response to rituximab in patients with rheumatoid arthritis

IntroductionAntibodies against mutated citrullinated vimentin (AMCV) represent a useful diagnostic marker with correlation to disease activity in patients with rheumatoid arthritis (RA). Since seropositivity for citrullinated autoantibodies was predictive for response to B-cell depleting therapy (BCDT) with rituximab (RTX), we investigated whether differences in antibody fine reactivity and immunoglobulin (Ig) isotype kinetics among AMCV-positive patients could provide additional information about outcome.MethodsA total of 50 AMCV IgG-positive RA patients (RTX responders (RRs) n = 37 and non-responders (NRRs) n = 13) were analyzed for reactivity against MCV epitopes and co-existent AMCV isotypes IgM and IgA. Antibody titers were determined by enzyme-linked immunosorbent assay at baseline and 24 weeks after the first cycle of RTX, and compared to kinetics of rheumatoid factor (RF) and antibodies against cyclic citrullinated peptide (ACCP).ResultsRecognized MCV epitopes by AMCV IgG of RRs and NRRs showed similar baseline patterns, with reducing reactivity in RRs and unchanged or even expanding reactivity in NRRs upon RTX treatment. At baseline, RRs were more frequently negative for AMCV subtypes, especially for IgA (68 %), compared to NRRs (31 %). Being AMCV IgA-negative at baseline indicated a good treatment response to RTX (negative predictive value = 0.86). Co-existence of AMCV IgA and IgG with stable titers upon treatment were associated with poorer responses to RTX. Furthermore, reductions of AMCV IgA levels upon RTX correlated with the improvement of 28-joint Disease Activity Score (DAS28). In comparison, subtypes of RF and ACCP were not of additional value for prediction of RTX response.ConclusionsRestrictive IgG seropositivity against MCV with treatment-associated decline in fine reactivity and titers was predictive for response to RTX. Double-positivity for AMCV IgG and IgA was associated with failure to respond to BCDT, suggesting a pathogenetic and less sensitive IgA-producing B-cell subset in NRRs.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0717-z) contains supplementary material, which is available to authorized users.     

类风湿关节炎患者RF、ANA、CCP、Ig及炎症因子的水平测定及临床意义

目的:探讨类风湿关节炎(RA)患者血清类风湿性因子(RF)、抗核抗体(ANA)、抗环瓜氨酸肽(CCP)抗体、免疫球蛋白(Ig)、补体(C3、C4)以及炎症因子的水平及临床意义。方法:收集2016年9月至2017年4月我院收治的165例RA患者为RA组,其中RA活动期患者93例(RA活动组),RA缓解期患者72例(RA缓解组),并于同期随机选取30例健康体检者为对照组。采用免疫散射比浊法检测各组血清RF、IgM、IgG、IgA、C3、C4水平,采用酶联免疫吸附法(ELISA)检测各组血清CCP抗体,电化学发光法检测白介素-6(IL-6)、化学发光法检测白介素-8(IL-8)。免疫荧光法检测ANA。比较不同组别各检测指标水平,并分析RA患者RF、ANA、CCP抗体、Ig、C3、C4与炎症因子的相关性。结果:RA活动组、RA缓解组血清RF、ANA、CCP抗体、IgM、IgG、IgA、IL-6、IL-8水平高于对照组,且RA活动组血清RF、ANA、CCP抗体、IgM、IgG、IgA、IL-6、IL-8水平高于RA缓解组,差异均有统计学意义(P0.05)。RA活动组、RA缓解组血清C3、C4水平低于对照组,且RA活动组血清C3、C4水平低于RA缓解组,差异均有统计学意义(P0.05)。经Pearson积矩相关分析,RA活动期和缓解期患者血清RF、ANA、CCP抗体、IgM、IgG、IgA与炎症因子IL-6、IL-8呈正相关关系(P0.05),血清C3、C4与炎症因子IL-6、IL-8呈负相关关系(P0.05)。结论:RA患者体内RF、ANA、CCP抗体、Ig及IL-6、IL-8水平明显较高,C3,C4水平明显较低,活动期RA患者更为显著,联合检测可早期辅助诊断RA及判断病情进展,在临床上有重要的参考意义。     

Effects of glycated albumin on mesangial cells: evidence for a role in diabetic nephropathy

Nonenzymatically glycated proteins are preferentially transported across the glomerular filtration barrier, and the glomerular mesangium in diabetes is bathed with serum containing increased concentrations of glycated albumin. We investigated effects of glycated albumin on mesangial cells, which are involved in diabetic nephropathy. [³H]-thymidine incorporation was significantly inhibited when murine mesangial cells were grown in culture media containing human serum that had been nonenzymatically glycated by incubation for 4 days with 28 mM glucose. This inhibition was reversed when monoclonal antibodies that selectively react with Amadori products of glycated albumin were added to the culture media. Purified glycated albumin containing Amadori adducts of the glycation reaction induced significant inhibition of thymidine incorporation and stimulation of Type IV collagen secretion compared with cells cultured in the presence of purified nonglycated albumin. These changes were prevented when monoclonal antibodies specifically reactive with fructosyl-lysine epitopes in glycated albumin were added to the cultures. The antibodies had no effect on growth or collagen production in the presence of nonglycated albumin. The results provide the first evidence directly implicating Amadori adducts in glycated albumin in the pathogenesis of diabetic nephropathy, which is characterized by decreased cellularity in association with expansion of the mesangial matrix.     

Glycation end-products specific auto-antibodies in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease, which is highly inflammatory. Compared to a healthy control group, SLE patients exhibit a higher concentration of advanced glycation end products (AGEs) and a lower concentration of receptors for AGEs (RAGE) in serum, however, the exact aetiology is still unclear. In the present study, non-enzymatic glycation induced modification of human serum albumin (HSA) has been studied by biophysical techniques. Glycated HSA (G-HSA) was used as an antigen, and serum autoantibody levels were estimated in SLE and normal humans (NH) against it, using direct binding ELISA and competitive inhibition ELISA. Compared to N-HSA, remarkable structural modifications were observed in G-HSA. Modified HSA also showed increased pentosidine fluorescence (213.7 ± 13.4 AU). Glycation of HSA induced a conversion of α-helix and random coil to β-sheet and β-turns. Serum immuno assays results exhibited significantly (p < 0.001) higher binding of G-HSA with serum autoantibodies from SLE patients when compared with native HSA (N-HSA). Furthermore, competitive ELISA results showed significantly (p < 0.001) high percent inhibition of serum IgG from SLE patients with modified antigen. Chronic inflammation with excessive oxidative stress in SLE patients could be a possible reason for structural alterations in blood proteins, generating highly immunogenic unique new-epitopes. These in turn induce the generation of specific autoantibodies against G-HSA that may serve as a potential biomarker for SLE pathogenesis.     

Protein glycation inhibitory activities of Lawsonia inermis and its active principles

The protein glycation inhibitory activity of ethanolic extract of Lawsonia inermis (henna) plant tissues was evaluated in vitro using the model system of bovine serum albumin and glucose. Protein oxidation and glycation are posttranslational modifications that are implicated in the pathological development of many age-related disease processes. This study investigated the effects of Lawsonia inermis ethanolic extract and its components, on protein damage induced by a free radical generator in in vitro assay system. We found that alcoholic extract of Lawsonia inermis can effectively protect against protein damage and showed that its action is mainly due to Lawsone. In addition, the presence of gallic acid also plays an important role in the protective activity against protein oxidation and glycation. Two known compounds, namely, Lawsone and gallic acid previously isolated from this plant were subjected to glycation bioassay for the first time. It was found that the alcoholic extract, lawsone (1) and gallic acid (2) showed significant inhibition of Advanced Glycated End Products (AGEs) formation and exhibit 77.95%, 79.10% and 66.98% inhibition at a concentration of 1500 μg/mL, 1000 μg/mL and 1000 μM respectively. Lawsonia inermis, compounds 1 and 2 were found to be glycation inhibitors with IC₅₀ 82.06 ± 0.13 μg/mL, 67.42 ± 1.46 μM and 401.7 ± 6. 23 μM respectively. This is the first report on the glycation activity of these compounds and alcoholic extract of Lawsonia inermis.     

Validation of a multiplex chip-based assay for the detection of autoantibodies against citrullinated peptides

Introduction

Autoantibodies directed against citrullinated proteins/peptides (ACPAs) are highly specific and predictive for the development of rheumatoid arthritis (RA). Different subgroups of RA patients, which have different prognoses and may require different treatments, are characterized by different autoantibody profiles. The objective of this study was to develop a microarray for the detection of multiple RA-associated autoantibodies, initially focusing on responses against citrullinated epitopes on candidate autoantigens in RA.

Methods

The microarray is based on Phadia''s ImmunoCAP ISAC system, with which reactivity to more than 100 antigens can be analyzed simultaneously, by using minute serum volumes (< 10 μl). Twelve citrullinated peptides, and the corresponding native arginine-containing control peptides, were immobilized in an arrayed fashion onto a chemically modified glass slide, allowing a three-dimensional layer with high binding capacity. The assay was optimized concerning serum dilution and glass surface, whereas each individual antigen was optimized concerning coupling chemistry, antigen concentration, and selection of spotting buffer. The performance of each peptide in the ImmunoCAP ISAC system was compared with the performance in enzyme-linked immunosorbent assays (ELISAs). Serum from 927 RA patients and 461 healthy controls from a matched case-control study were applied onto reaction sites on glass slides, followed by fluorescent-labeled anti-human immunoglobulin G (IgG) antibody. Fluorescence intensities were detected with a laser scanner, and the results analyzed by using image-analysis software.

Results

Strong correlations between the ImmunoCAP ISAC system and ELISA results were found for individual citrullinated peptides (Spearman ρ typically between 0.75 and 0.90). Reactivity of RA sera with the peptides was seen mainly in the anticyclic citrullinated peptide 2 (CCP2)-positive subset, but some additional reactivity with single citrullinated peptides was seen in the anti-CCP2-negative subset. Adjusting for reactivity against arginine-containing control peptides did not uniformly change the diagnostic performance for antibodies against the individual citrullinated peptides.

Conclusions

The multiplexed array, for detection of autoantibodies against multiple citrullinated epitopes on candidate RA autoantigens, will be of benefit in studies of RA pathogenesis, diagnosis, and potentially as a guide to individualized treatment.     

Anti-factor Xa antibodies in patients with antiphospholipid syndrome and their effects upon coagulation assays

IntroductionThe aim of this study was to examine the prevalence and functional effects of antibodies directed against Factor (F)Xa and other serine proteases (SP) in patients with antiphospholipid syndrome (APS).MethodsSerum from patients with APS (n = 59), systemic lupus erythematosus (SLE; n = 106), other autoimmune rheumatic disease (ARD; n = 63) and 40 healthy controls (HC) were tested for IgG activity against thrombin (Thr), FXa, FVIIa, phosphatidylserine (PS)/FXa and antithrombin (AT)-III by enzyme-linked immunosorbent assay (ELISA). Anti-FXa positive IgG were purified to measure their avidity by chaotropic ELISA and functional effects upon clotting time (FXa-ACT) and FXa enzymatic activity (± AT-III).ResultsAnti-FXa IgG were found in patients with SLE (49.1%) and APS (33.9%) (P <0.05) but not in ARD controls and HC. In contrast, anti-Thr and anti-PS/FXa IgG were identified in other ARD and anti-FVIIa IgG were low in all groups. The avidity of APS-IgG to FXa was significantly higher than SLE-IgG (P <0.05). Greatest prolongation of FXa-ACT was observed with APS-IgG and greatest inhibitory effect upon FXa enzymatic activity was found with APS-IgG followed by SLE-IgG compared to HC-IgG. ATIII inhibition of FXa was significantly reduced by APS-IgG compared with HC and SLE (P <0.05) and did not correlate with binding to AT-III.ConclusionAPS anti-FXa IgG have higher avidity to FXa and greater effects upon the enzymatic and coagulant activity of FXa compared with SLE anti-FXa IgG. Further studies of anti-FXa antibodies in APS, SLE and other non-autoimmune thrombotic disease cohorts are now required to evaluate whether targeting FXa with selective inhibitors in patients bearing anti-FXa antibodies may be an effective treatment strategy.