Identification of citrullinated eukaryotic translation initiation factor 4G1 as novel autoantigen in rheumatoid arthritis

Peptidylarginine deiminase (PAD): A promising target for chronic diseases treatment

In 1958, the presence of citrulline in the structure of the proteins was discovered for the first time. Several years later they found that Arginine converted to citrulline during a post-translational modification process by PAD enzyme. Each PAD is expressed in a certain tissue developing a series of diseases such as inflammation and cancers. Among these, PAD2 and PAD4 play a role in the development of rheumatoid arthritis (RA) by producing citrullinated autoantigens and increasing the production of inflammatory cytokines. PAD4 is also associated with the formation of NET structures and thrombosis. In the crystallographic structure, PAD has several calcium binding sites, and the active site of the enzyme consists of different amino acids. Various PAD inhibitors have been developed divided into pan-PAD and selective PAD inhibitors. F-amidine, Cl-amidine, and BB-Cl-amidine are some of pan-PAD inhibitors. AFM-30a and JBI589 are selective for PAD2 and PAD4, respectively. There is a need to evaluate the effectiveness of existing inhibitors more accurately in the coming years, as well as design and production of novel inhibitors targeting highly specific isoforms.

Functional Analysis of Autoantibody Signatures in Rheumatoid Arthritis

For the identification of antigenic protein biomarkers for rheumatoid arthritis (RA), we conducted IgG profiling on high density protein microarrays. Plasma IgG of 96 human samples (healthy controls, osteoarthritis, seropositive and seronegative RA, n = 24 each) and time-series plasma of a pristane-induced arthritis (PIA) rat model (n = 24 total) were probed on AIT’s 16k protein microarray. To investigate the analogy of underlying disease pathways, differential reactivity analysis was conducted. A total of n = 602 differentially reactive antigens (DIRAGs) at a significance cutoff of p < 0.05 were identified between seropositive and seronegative RA for the human samples. Correlation with the clinical disease activity index revealed an inverse correlation of antibodies against self-proteins found in pathways relevant for antigen presentation and immune regulation. The PIA model showed n = 1291 significant DIRAGs within acute disease. Significant DIRAGs for (I) seropositive, (II) seronegative and (III) PIA were subjected to the Reactome pathway browser which also revealed pathways relevant for antigen presentation and immune regulation; of these, seven overlapping pathways had high significance. We therefore conclude that the PIA model reflects the biological similarities of the disease pathogenesis. Our data show that protein array analysis can elucidate biological differences and pathways relevant in disease as well be a useful additional layer of omics information.

Identification of key genes in osteoarthritis using bioinformatics, principal component analysis and meta-analysis

The present study aimed to identify key genes involved in osteoarthritis (OA). Based on a bioinformatics analysis of five gene expression profiling datasets (GSE55457, GSE55235, GSE82107, GSE12021 and GSE1919), differentially expressed genes (DEGs) in OA were identified. Subsequently, a protein-protein interaction (PPI) network was constructed and its topological structure was analyzed. In addition, key genes in OA were identified following a principal component analysis (PCA) based on the DEGs in the PPI network. Finally, the functions and pathways enriched by these key genes were also analyzed. The PPI network consisted of 241 nodes and 576 interactives, including a total of 171 upregulated DEGs [e.g., aspartylglucosaminidase (AGA), CD58 and CD86] and a total of 70 downregulated DEGs (e.g., acetyl-CoA carboxylase β and dihydropyrimidine dehydrogenase). The PPI network complied with an attribute of scale-free small-world network. After PCA, 47 key genes were identified, including β-1,4-galactosyltransferase-1 (B4GALT1), AGA, CD58, CD86, ezrin, and eukaryotic translation initiation factor 4 γ 1 (EIF4G1). Subsequently, the 47 key genes were identified to be enriched in 13 Gene Ontology (GO) terms and 2 Kyoto Encyclopedia of Genes and Genomes pathways, with the GO terms involving B4GALT1 including positive regulation of developmental processes, protein amino acid terminal glycosylation and protein amino acid terminal N-glycosylation. In addition, B4GALT1 and EIF4G1 were confirmed to be downregulated in OA samples compared with healthy controls, but only EIF4G1 was determined to be significantly downregulated in OA samples, as determined via a meta-analysis of the 5 abovementioned datasets. In conclusion, B4GALT1 and EIF4G1 were indicated to have significant roles in OA, and B4GALT1 may be involved in positive regulation of developmental processes, protein amino acid terminal glycosylation and protein amino acid terminal N-glycosylation. The present study may enhance the current understanding of the molecular mechanisms of OA and provide novel therapeutic targets.

Insights into the study and origin of the citrullinome in rheumatoid arthritis

The presence of autoantibodies and autoreactive T cells to citrullinated proteins and citrullinating enzymes in patients with rheumatoid arthritis (RA), together with the accumulation of citrullinated proteins in rheumatoid joints, provides substantial evidence that dysregulated citrullination is a hallmark feature of RA. However, understanding mechanisms that dysregulate citrullination in RA has important challenges. Citrullination is a normal process in immune and non-immune cells, which is likely activated by different conditions (eg, inflammation) with no pathogenic consequences. In a complex inflammatory environment such as the RA joint, unique strategies are therefore required to dissect specific mechanisms involved in the abnormal production of citrullinated proteins. Here, we will review current models of citrullination in RA and discuss critical components that, in our view, are relevant to understanding the accumulation of citrullinated proteins in the RA joint, collectively referred to as the RA citrullinome. In particular, we will focus on potential caveats in the study of citrullination in RA and will highlight methods to precisely detect citrullinated proteins in complex biological samples, which is a confirmatory approach to mechanistically link the RA citrullinome with unique pathogenic pathways in RA.

Tumor-associated and disease-associated autoantibody repertoires in healthy colostrum and maternal and newborn cord sera

In this work, we studied autoantibody repertoires and Ig isotypes in 71 mothers and their 104 healthy newborns (including twins and triplets delivered term or premature). Newborns receive maternal IgG Abs via the placenta before birth, but developing infants must produce their own IgM and IgA Abs. We used an Ag microarray analysis to detect binding to a selection of 295 self-Ags, compared with 27 standard foreign Ags. The magnitude of binding to specific self-Ags was found to be not less than that to the foreign Ags. As expected, each newborn shared with its mother a similar IgG repertoire-manifest as early as the 24th week of gestation. IgM and IgA autoantibody repertoires in cord sera were highly correlated among the newborns and differed from their mothers' repertoires; the latter differed in sera and milk. The autoantibodies bound to self-Ags known to be associated with tumors and to autoimmune diseases. Thus, autoantibody repertoires in healthy humans--the immunological homunculus--arise congenitally, differ in maternal milk and sera, and mark the potential of the immune system to attack tumors, beneficially, or healthy tissues, harmfully; regulation of the tissue site, the dynamics, and the response phenotype of homuncular autoimmunity very likely affects health.

Prohibitin as a novel autoantigen in rheumatoid arthritis

The aim of this study

The aim of this study was to verify whether prohibitin is a novel autoantigen in rheumatoid arthritis.

Material and methods

First, recombinant human prohibitin (rhPHB) protein was cloned, expressed, and purified. Then the anti-prohibitin autoantibodies were detected by western blotting by using rhPHB protein to incubate sera from patients with rheumatoid arthritis (RA). Next, immunoprecipitation was employed to further illustrate whether anti-prohibitin antibodies exist in RA patients. And finally, autoantibodies against the rhPHB protein were investigated using a homemade ELISA kit through the assessment of 258 real clinical samples.

Results

It was revealed that anti-prohibitin antibodies existed in the sera of patients with RA. Reactivity of serum IgG against rhPHB was detected in 26 of 86 RA patients (30.3%), 7 of 86 systemic lupus erythematosus (SLE) patients (8.1%), and 1 of 86 apparently healthy donors (HC) (1.2%).

Conclusions

Prohibitin was proved to be a novel autoantigen and the corresponding anti-prohibitin autoantibodies were present in the RA patients' blood circulation.

Citrullination of autoantigens implicates NETosis in the induction of autoimmunity

Tolerance blocks the expression of autoantibodies, whereas autoimmunity promotes it. How tolerance breaks and autoantibody production begins thus are crucial questions for understanding and treatment of autoimmune diseases. Evidence implicates cell death and autoantigen modifications in the initiation of autoimmune reactions. One form of neutrophil cell death called NETosis deserves attention because it requires the post-translational modification of histones and results in the extracellular release of chromatin. NETosis received its name from NET, the acronym given to Neutrophil Extracellular Trap. The extracellular chromatin incorporates histones in which arginines have been converted to citrullines by peptidylarginine deiminase IV (PAD4). The deiminated chromatin may function to capture or 'trap' bacterial pathogens, thus generating an extracellular complex of deiminated histones and bacterial cell adjuvants. The complex of bacterial antigens and deiminated chromatin may be internalised by host phagocytes during acute inflammatory conditions, as arise during bacterial infections or chronic autoinflammatory disorders. The uptake and processing of deiminated chromatin together with bacterial adjuvants by phagocytes may induce the presentation of modified histone epitopes and co-stimulation, thus yielding a powerful stimulus to break tolerance. Autoantibodies to deiminated histones are prevalent in Felty's syndrome patients and are present in systemic lupus erythematosus (SLE) and patients with rheumatoid arthritis (RA). These observations clearly implicate histone deimination as an epigenetic mark that can act as an autoantibody stimulant.

Peptidylarginine deiminase 2, 3 and 4 have distinct specificities against cellular substrates: novel insights into autoantigen selection in rheumatoid arthritis

OBJECTIVE

To define the relationship between autoantigen citrullination and different peptidylarginine deiminase (PAD) enzymes in rheumatoid arthritis (RA).

METHODS

Citrullinated autoantigens were identified by immunoblotting control and ionomycin-activated human primary neutrophil lysate with RA sera. Autoantigen identity and citrullination sites were defined by mass spectrometry. PAD isoenzyme expression in human neutrophils was determined by immunoblotting. PAD substrate specificity was addressed in HL-60 cell lysates co-incubated with human recombinant PAD2, PAD3 and PAD4.

RESULTS

Although prominent protein citrullination is observed in ionomycin-activated neutrophils, RA sera only recognised a limited number of these citrullinated molecules. Among these, the authors identified that β and γ-actins are citrullinated on at least 10 arginine residues, generating a novel 47 kDa species that is frequently recognised by RA autoantibodies. Interestingly, the authors showed that the PAD enzymes expressed in human neutrophils (ie, PAD2, PAD3 and PAD4) have unique substrate specificities, independent of their subcellular distribution. Thus, only PAD2 was able to citrullinate native β/γ-actin, while histone H3 was only citrullinated by PAD4.

CONCLUSION

These studies identified β and γ-actins as novel citrullinated autoantigens in RA, allowing enzyme specificity against intracellular substrates to be addressed. The studies provide evidence that PAD enzymes have the intrinsic capacity to select unique protein targets. The authors propose that unique PAD specificity may play a role in autoantigen selection in RA.

Discovery of peptidylarginine deiminase-4 substrates by protein array: antagonistic citrullination and methylation of human ribosomal protein S2

Peptidylarginine deiminase (PAD) catalyzes the posttranslational citrullination of selected proteins in a calcium dependent manner. The PAD4 isoform has been implicated in multiple sclerosis, rheumatoid arthritis, some types of cancer, and plays a role in gene regulation. However, the substrate selectivity of PAD4 is not well defined, nor is the impact of citrullination on many other pathways. Here, a high-density protein array is used as a primary screen to identify 40 previously unreported PAD4 substrates, 10 of which are selected and verified in a cell lysate-based secondary assay. One of the most prominent hits, human 40S ribosomal protein S2 (RPS2), is characterized in detail. PAD4 citrullinates the Arg-Gly repeat region of RPS2, which is also an established site for Arg methylation by protein arginine methyltransferase 3 (PRMT3). As in other systems, crosstalk is observed; citrullination and methylation modifications are found to be antagonistic to each other, suggesting a conserved posttranslational regulatory strategy. Both PAD4 and PRMT3 are found to co-sediment with the free 40S ribosomal subunit fraction from cell extracts. These findings are consistent with participation of citrullination in the regulation of RPS2 and ribosome assembly. This application of protein arrays to reveal new PAD4 substrates suggests a role for citrullination in a number of different cellular pathways.

A proteomic investigation of B lymphocytes in an autistic family: a pilot study of exposure to natural rubber latex (NRL) may lead to autism

Autism is a multi-factorial neurodevelopmental disorder. We have investigated the molecular mechanism involved in a Chinese family with autism by a proteomic approach. Antibody chips containing 500 spots of human protein antibodies were used to screen for differentially expressed proteins in the peripheral B lymphocytes between autistic and non-autistic siblings in this family. Four proteins relevant to immuno-pathway, including IKKα that was up-regulated and Tyk2, EIF4G1 and PRKCI that were down-regulated, were identified differentially expressed in autistic versus non-autistic siblings. Western blot analysis and reverse transcription quantitative polymerase chain reaction validated the differential expression of these four proteins. Based on the function of these differentially expressed proteins, relevant studies on immunoglobulin E (IgE) level, nuclear factor kappa B signaling activation and cell cycle were conducted in both autistic and non-autistic children of this family. Considering the fact that the family members were in close contact with natural rubber latex (NRL) and that IgE-mediated cross-reactions could be triggered by Hevea brasiliensis (Hev-b) proteins in NRL, we hypothesize that immune reactions triggered by close contact with NRL might influence the functions of B lymphocytes by altering expression of certain proteins identified in our experiments thus contributing to the occurrence of autism.

Autoimmunity to specific citrullinated proteins gives the first clues to the etiology of rheumatoid arthritis

Rheumatoid arthritis (RA) is now clearly a true autoimmune disease with accumulating evidence of pathogenic disease-specific autoimmunity to citrullinated proteins. Citrullination, also termed deimination, is a modification of arginine side chains catalyzed by peptidylarginine deiminase (PAD) enzymes. This post-translational modification has the potential to alter the structure, antigenicity, and function of proteins. In RA, antibodies to cyclic citrullinated peptides are now well established for clinical diagnosis, though we argue that the identification of specific citrullinated antigens, as whole proteins, is necessary for exploring pathogenic mechanisms. Four citrullinated antigens, fibrinogen, vimentin, collagen type II, and alpha-enolase, are now well established, with others awaiting further characterization. All four proteins are expressed in the joint, and there is evidence that antibodies to citrullinated fibrinogen and collagen type II mediate inflammation by the formation of immune complexes, both in humans and animal models. Antibodies to citrullinated proteins are associated with HLA 'shared epitope' alleles, and autoimmunity to at least one antigenic sequence, the CEP-1 peptide from citrullinated alpha-enolase (KIHAcitEIFDScitGNPTVE), shows a specific association with HLA-DRB1*0401, *0404, 620W PTPN22, and smoking. Periodontitis, in which Porphyromonas gingivalis is a major pathogenic bacterium, has been linked to RA in epidemiological studies and also shares similar gene/environment associations. This is also the only bacterium identified that expresses endogenous citrullinated proteins and its own bacterial PAD enzyme, though the precise molecular mechanisms of bacterial citrullination have yet to be explored. Thus, both smoking and Porphyromonas gingivalis are attractive etiological agents for further investigation into the gene/environment/autoimmunity triad of RA.

Candidate autoantigens identified by mass spectrometry in early rheumatoid arthritis are chaperones and citrullinated glycolytic enzymes

Introduction

The aim of our study was to identify new early rheumatoid arthritis (RA) autoantibodies.

Methods

Sera obtained from 110 early untreated RA patients (<6 months) were analyzed by western blot using HL-60 cell extract, separated on one-dimensional and two-dimensional gel electrophoresis (1-DE, 2-DE). Sera from 50 healthy blood donors and 20 patients with non-RA rheumatisms were used as controls for 1-DE and 2-DE, respectively. The immunoreactive proteins were identified by MALDI-TOF mass spectrometric analysis and the presence of potential sites of citrullination in each of these proteins was evaluated. FT-ICR mass spectrometry was used to verify experimentally the effect of citrullination upon the mass profile observed by MALDI-TOF analysis.

Results

The 110 1-DE patterns allowed detection of 10 recurrent immunoreactive bands of 33, 39, 43, 46, 51, 54, 58, 62, 67 and 70 kDa, which were further characterized by 2-DE and proteomic analysis. Six proteins were already described RA antigens: heterogeneous nuclear ribonucleoprotein A2/B1, aldolase, α-enolase, calreticulin, 60 kDa heat shock protein (HSP60) and BiP. Phosphoglycerate kinase 1 (PGK1), stress-induced phosphoprotein 1 and the far upstream element-binding proteins (FUSE-BP) 1 and 2 were identified as new antigens. Post-translational protein modifications were analyzed and potentially deiminated peptides were found on aldolase, α-enolase, PGK1, calreticulin, HSP60 and the FUSE-BPs. We compared the reactivity of RA sera with citrullinated and noncitrullinated α-enolase and FUSE-BP linear peptides, and showed that antigenicity of the FUSE-BP peptide was highly dependent on citrullination. Interestingly, the anti-cyclic citrullinated peptide antibody (anti-CCP2) status in RA serum at inclusion was not correlated to the reactivity directed against FUSE-BP citrullinated peptide.

Conclusions

Two categories of antigens, enzymes of the glycolytic family and molecular chaperones are also targeted by the early untreated RA autoantibody response. For some of them, and notably the FUSE-BPs, citrullination is involved in the immunological tolerance breakdown observed earlier in RA patients. Autoantibodies recognizing a citrullinated peptide from FUSE-BP may enhance the sensibility for RA of the currently available anti-CCP2 test.

Autoantibodies binding to citrullinated telopeptide of type II collagen and to cyclic citrullinated peptides predict synergistically the development of seropositive rheumatoid arthritis

OBJECTIVES

To find out whether autoantibodies to citrullinated telopeptides of type I and II collagens and to cyclic citrullinated peptides (CCPs) predict the development of rheumatoid arthritis (RA).

METHODS

A case-control study (matched for sex, age and municipality) was nested within a Finnish cohort of 19072 adults who had neither arthritis nor a history of it at the baseline examination during 1973-7. 124 subjects developed RA by late 1989, and of these, 89 were positive for rheumatoid factor (RF). Preillness serum specimens were analysed for autoantibodies against arginine (A)- or citrulline (C)-containing synthetic telopeptides using a chemiluminescence method and for anti-CCPs Mark2 with an enzyme-linked immunosorbent assay method.

RESULTS

The mean levels of autoantibodies to citrulline-containing telopeptides and the C/A ratios of type I and II collagens and to CCP were higher in subjects who later developed RF-positive RA. In the highest tertiles of C/A (I), C/A (II) ratios and anti-CCPs levels, the relative risk of RF-positive RA was significantly increased. In the multifactorial model, only anti-CCPs retained its statistical significance. However, the interaction term of C/A (II) ratio and anti-CCPs proved to be statistically significant (p = 0.02). The subjects ranked into the highest tertiles of both C/A (II) ratio and anti-CCPs had an odds ratio of 20.06 (95% confidence interval, 4.37 to 92.06) of developing RF-positive RA compared with those in the lowest tertiles of these antibodies. None of the autoantibodies predicted RF-negative RA.

CONCLUSION

Autoantibodies to citrullinated telopeptides of type I and II collagen and to CCPs exert a synergistic effect on the risk of seropositive RA.

Citrullination by peptidylarginine deiminase in rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex, multifactorial disease with genetic and immunological aspects. Because RA is an autoimmune condition, dysregulation of the immune system is implied. Many linkage and association studies have also indicated that multiple genetic factors are associated with RA. Although the contribution of each genetic factor is small, the combination of these factors affects RA development. Previous studies have suggested that genetic changes affect the internal immunological environment, which results in autoimmune diseases. More recent genetic studies indicate that the HLA-DRB gene is the predominant cause of RA and that other non-HLA genes are also involved. We reported that peptidylarginine deiminase (gene name abbreviated to PADI, protein name abbreviated to PAD) type 4 is the one of the non-HLA genetic factors involved in RA via citrullination. Antibodies against citrullinated proteins/peptides are highly specific to RA, but the physiological roles of PADI gene, PAD proteins as their products and citrullinated proteins/peptides are obscure. However, levels of anticitrullinated protein antibodies are apparently also increased and were involved in the pathogenesis of autoimmune arthritis in mice with collagen-induced arthritis (CIA). These data suggested that citrullinated protein and anticitrullinated protein antibodies play important roles in the development of RA. This review summarizes the relationship between RA and citrullination, as well as the role of PADI4 genetics.

Association of anti-cyclic citrullinated peptide antibody levels with PADI4 haplotypes in early rheumatoid arthritis and with shared epitope alleles in very late rheumatoid arthritis

OBJECTIVE

Anti-cyclic citrullinated peptide (anti-CCP) antibodies are rheumatoid arthritis (RA)-specific serologic markers. RA susceptibility has been associated with HLA-DRB1 shared epitope (SE) alleles and single-nucleotide polymorphism (SNP) haplotypes in the peptidyl arginine deiminase 4 gene (PADI4). This study was undertaken to determine whether anti-CCP levels are associated with PADI4 haplotypes and/or SE alleles in Korean patients with RA.

METHODS

Three nonsynonymous SNPs in PADI4 (padi4_89, padi4_90, and padi4_92) and SE alleles were genotyped, and serum anti-CCP levels were measured, in 311 patients with nonerosive or erosive RA. The relationships between anti-CCP levels and PADI4 haplotypes and/or SE alleles were analyzed statistically.

RESULTS

Anti-CCP levels were significantly higher in patients carrying the PADI4 RA risk haplotype than in patients who did not have the risk haplotype, among anti-CCP-positive patients with RA with a disease duration of <or=34 months (P = 0.041), but not among patients with a longer disease duration or among those who had erosive RA versus nonerosive RA. In contrast, the levels were significantly higher in SE carriers than in noncarriers among patients with RA with a disease duration of >or=141 months (P = 0.0037) and among those who had erosive RA (P = 0.000098), but not among patients who had a shorter disease duration or those who had nonerosive RA.

CONCLUSION

The PADI4 RA risk haplotype is associated with increased anti-CCP levels in RA patients with disease of short duration, and PADI4 may play a role in early RA. In contrast, SE alleles are associated with increased anti-CCP levels in RA patients with very longstanding disease and in patients with erosive RA, suggesting that SE alleles play a role in very late RA.

The functional haplotype of peptidylarginine deiminase IV (S55G, A82V and A112G) associated with susceptibility to rheumatoid arthritis dominates apoptosis of acute T leukemia Jurkat cells

Peptidylarginine deiminase IV (PADI4) posttranslationally converts peptidylarginine to citrulline. It plays an essential role in immune cell differentiation and apoptosis. A haplotype of single-nucleotide polymorphisms (SNPs) in PADI4 is functionally relevant as a rheumatoid arthritis (RA) gene. It could increase enzyme activity leading to raised levels of citrullinated protein and stimulating autoantibody. Previously, our study showed that inducible PADI4 causes haematopoietic cell death. Herein, we further investigate whether RA risk PADI4 haplotype (SNP PADI4; S55G, A82V and A112G) and the increase of its enzymatic activity induce apoptosis. In the tetracycline (Tet)-On Jurkat T cells, ionomycin (Ion) only treatment didn't induce apoptosis however it promoted inducible PADI4-decreased cell viability and -enhanced apoptosis. Through in vitro and in vivo PADI enzyme activity assay, we demonstrated that PADI4 enzyme activity of SNP PADI4 was higher than RA non-risk PADI4 haplotype (WT PADI4). The effect of SNP PADI4-induced apoptosis was superior to WT PADI4. In addition, both Ion and SNP PADI4 synergistically provoked apoptosis were compared with both Ion and WT PADI4. Concurrently, in the conditionally inducible SNP PADI4 cells of Ion treatment-induced apoptosis, not only the expression of Bcl-xL was down-regulated and Bax up-regulated, but also cytochrome c was released from mitochondria to cytoplasm in significant amounts. Western blotting data showed the increase in apoptosomal caspase activation during programmed cell death in the inducible SNP PADI4 cells subsequent to Ion treatment. These data demonstrated that both SNP PADI4 increasing their enzyme activity could enhance apoptosis through the mitochondrial pathway and further provide a conceivable explanation in the pathogenesis of RA following the upregulation of PADI4 activity in its SNPs.

Autoantibodies in rheumatoid arthritis: a review

Emerging insights into the importance of B cells in the pathogenesis of rheumatoid arthritis (RA) as highlighted by the efficacy of B cell depletion is one factor that has contributed to the upsurge of interest in the potential role of autoantibodies both as disease markers and with respect to a pathogenic role. Since the initial description of rheumatoid factor (RF), a large number of both disease-specific and non-specific autoantibodies have been described in patients with RA including antibodies to type II collagen (CII), immunoglobulin binding protein (BiP) and antibodies directed at citrullinated peptides (anti-CCP) and other citrullinated proteins such as vimentin (anti-Sa) . Despite some overlap the serological profile of RA does appear to be distinct from other diseases such as SLE . Although the precise mechanisms responsible for the formation of these antibodies have not been well defined their presence must reflect the interaction between T and B cells believed to be relevant to the pathogenesis of RA. The specificity of the association of such factors as anti-CCP and anti-BiP with RA may reflect unique pathogenic events leading to the processing and presentation of the "cryptic self" . Ease of measurement and stability make autoantibodies attractive diagnostic and prognostic markers particularly in early disease when it may be difficult to distinguish self-limiting synovitis from persistent disease . The purpose of this article is to provide an overview of the current state of knowledge of the spectrum of autoantibodies thus far characterised in individuals with rheumatoid arthritis, and discuss their diagnostic, prognostic and pathogenetic relevance.

Antibodies to citrullinated proteins in rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease of unknown etiology, characterized by chronic joint inflammation that often leads to joint destruction. Diagnosis of RA is currently based on the revised classification criteria of the American College of Rheumatology (ACR); however, it remains imprecise, especially early in the course of disease. Rheumatoid factor (RF) has been widely used in clinical practice as a useful serological marker for diagnosis of RA. Although RF is the only serological test in the criteria of the ACR, its specificity is limited since RF can be also detected in other rheumatic diseases. Because the current therapeutic strategies in RA employ increasingly aggressive regimens from early stage of the disease, more specific serological markers than RF are desirable. Recently, anti-cyclic citrullinated peptide (anti-CCP) antibodies have attracted attention as a useful marker for the diagnosis of RA with high specificity. In addition to the diagnostic properties, anti-CCP antibodies showed to be a good prognostic marker for joint destructions. In this review, we will explain about the clinical usefulness of anti-CCP antibodies for the daily practice of RA.