Rheumatoid arthritis associated autoantibodies in patients with synovitis of recent onset

Refining the complex rheumatoid arthritis phenotype based on specificity of the HLA-DRB1 shared epitope for antibodies to citrullinated proteins

OBJECTIVE

The main genetic risk factor for rheumatoid arthritis (RA), the HLA region, has been known for 25 years. Previous research has demonstrated, within the RA population, an association between HLA-DRB1 alleles carrying the shared epitope (SE) and antibodies directed against cyclic citrullinated peptides (anti-CCP antibodies). We undertook this study to make the first comparison of SE allele frequencies in the healthy population with those in RA patients who do or do not harbor anti-CCP antibodies.

METHODS

HLA-DRB1 typing was performed in 408 RA patients from the Leiden Early Arthritis Clinic (the Leiden EAC; a Dutch population-based inception cohort in which disease course was followed up over time), in 423 healthy Dutch controls, and in 720 affected members of 341 US multiplex (sibpair) families of Caucasian origin from the North American RA Consortium (NARAC) with well-established disease and fulfilling the American College of Rheumatology classification criteria for RA. The presence of anti-CCP antibodies was determined by enzyme-linked immunosorbent assay.

RESULTS

For the Leiden EAC, the odds ratio (OR) describing the association of 2 copies of the SE allele with anti-CCP positivity (using no copies of the SE allele in the healthy control group as the referent) was 11.79 (P < 0.0001), while the OR for 1 SE allele was 4.37 (P < 0.0001). No association with the SE was observed in the Dutch anti-CCP-negative RA patients. For the NARAC families, linkage and association analysis revealed the SE to be associated only with anti-CCP-positive disease and not with anti-CCP-negative disease. Stratified analyses indicated that anti-CCP antibodies primarily mediated association of the SE with joint damage or disease persistence.

CONCLUSION

HLA-DRB1 alleles encoding the SE are specific for disease characterized by antibodies to citrullinated peptides, indicating that these alleles do not associate with RA as such, but rather with a particular phenotype.

The Examination of Rheumatoid Factor and Other Serum Markers in Rheumatoid Arthritis

Rheumatoid factor (IgM-RF) has been widely used to diagnose rheumatoid arthritis (RA) in clinical practice. We investigated the RA diagnostic performances of anti-cyclic citrullinated peptide antibody (anti-CCP), matrix metalloproteinase-3 (MMP-3), anti-agalactosyl IgG antibody (CA*RF), and anti-calpastatin antibody (ACA) in comparison with IgM-RF. Among 68 RA patients, IgM-RF was positive in 31 (45.6%) and negative in 37 (54.4%). In the IgM-RF-positive group, positivity in anti-CCP, CA*RF, and ACA was 97%, 100%, and 97%, respectively, although that in MMP-3 (74%) was inferior to the others. On the other hand, in the IgM-RF-negative group, positivity in anti-CCP, MMP-3, and ACA was 73%, 81%, and 86%, respectively, although that in CA*RF was only 59%. We conclude that the combination of IgM-RF and anti-CCP/ACA will provide an accurate diagnosis of RA in clinical practice.

Early Undifferentiated Arthritis

Patients who cannot be classified as having a well-defined arthropathy typically are labeled as having undifferentiated arthritis. Some patients develop sufficient features to permit classification, whereas others remain undifferentiated, but with persistent joint inflammation, functional disability, and development of radiographic damage. Identifying the subset of patients destined to develop rheumatoid arthritis, spondyloarthropathy, or a more severe and persistent form of undifferentiated arthritis and choosing appropriate treatment strategies remain challenges for clinicians. Numerous investigative strategies are available with which to characterize undifferentiated arthritis and assess prognosis. This article discusses the characteristics of undifferentiated arthritis at presentation and the investigative strategies that can be used to predict prognosis and outcome early in the disease course. Therapeutic strategies also are explored.

Clinical significance of anti-CCP antibodies in rheumatoid arthritis

A number of novel autoantibodies have been recently described in rheumatoid arthritis (RA), and their clinical significance and possible pathogenic roles have been discussed. In particular, new autoantibodies to citrullinated proteins such as filaggrin and its circular form (cyclic citrullinated peptide: CCP) are especially noteworthy because of their high sensitivity and high specificity. There are many studies that anti-CCP antibodies may serve as a powerful serologic marker for early diagnosis of RA and prognostic prediction of joint destruction. Anti-citrullinated protein antibodies are locally produced in RA joints, and citrullinated proteins (most are fibrins) are localized in RA synovial tissue. This finding strongly suggests a possibility that local citrullination of intraarticular proteins might be the initial event leading to autoantibody production in RA. Genetic factors such as a gene polymorphism of the citrullinating enzyme, PADI, might be associated with the breakage of self-tolerance and induction of autoimmunity against citrullinated proteins.

Conventional X-Ray in Early Arthritis

This article reviews radiographic data from six cohorts of patients with early inflammatory arthritis. Of the patients, 8% to 15% had erosive disease at the first encounter with the rheumatologist. Classic scoring methods were applied to quantify damage, but baseline damage was low in early inflammatory arthritis. Yearly progression in damage score was assessed only in patients with high suspicion of rheumatoid arthritis at baseline or who had a final diagnosis of rheumatoid arthritis at follow-up and varied between 0.5% and 1.7% of the maximal damage of the scoring method per year. The large number of patients with zero values for erosions and lower progression rates will influence sample sizes in clinical trials in early inflammatory arthritis when including radiographic change as an outcome.

Antigen microarray profiling of autoantibodies in rheumatoid arthritis

OBJECTIVE

Because rheumatoid arthritis (RA) is a heterogeneous autoimmune disease in terms of disease manifestations, clinical outcomes, and therapeutic responses, we developed and applied a novel antigen microarray technology to identify distinct serum antibody profiles in patients with RA.

METHODS

Synovial proteome microarrays, containing 225 peptides and proteins that represent candidate and control antigens, were developed. These arrays were used to profile autoantibodies in randomly selected sera from 2 different cohorts of patients: the Stanford Arthritis Center inception cohort, comprising 18 patients with established RA and 38 controls, and the Arthritis, Rheumatism, and Aging Medical Information System cohort, comprising 58 patients with a clinical diagnosis of RA of <6 months duration. Data were analyzed using the significance analysis of microarrays algorithm, the prediction analysis of microarrays algorithm, and Cluster software.

RESULTS

Antigen microarrays demonstrated that autoreactive B cell responses targeting citrullinated epitopes were present in a subset of patients with early RA with features predictive of the development of severe RA. In contrast, autoimmune targeting of the native epitopes contained on synovial arrays, including several human cartilage gp39 peptides and type II collagen, were associated with features predictive of less severe RA.

CONCLUSION

Proteomic analysis of autoantibody reactivities provides diagnostic information and allows stratification of patients with early RA into clinically relevant disease subsets.

Identification of citrullinated alpha-enolase as a candidate autoantigen in rheumatoid arthritis

Antibodies against citrullinated proteins are highly specific for rheumatoid arthritis (RA), but little is understood about their citrullinated target antigens. We have detected a candidate citrullinated protein by immunoblotting lysates of monocytic and granulocytic HL-60 cells treated with peptidylarginine deiminase. In an initial screen of serum samples from four patients with RA and one control, a protein of molecular mass 47 kDa from monocytic HL-60s reacted with sera from the patients, but not with the serum from the control. Only the citrullinated form of the protein was recognised. The antigen was identified by tandem mass spectrometry as alpha-enolase, and the positions of nine citrulline residues in the sequence were determined. Serum samples from 52 patients with RA and 40 healthy controls were tested for presence of antibodies against citrullinated and non-citrullinated alpha-enolase by immunoblotting of the purified antigens. Twenty-four sera from patients with RA (46%) reacted with citrullinated alpha-enolase, of which seven (13%) also recognised the non-citrullinated protein. Six samples from the controls (15%) reacted with both forms. Alpha-enolase was detected in the RA joint, where it co-localised with citrullinated proteins. The presence of antibody together with expression of antigen within the joint implicates citrullinated alpha-enolase as a candidate autoantigen that could drive the chronic inflammatory response in RA.

Association of anti-cyclic citrullinated peptide antibodies, anti-citrullin antibodies, and IgM and IgA rheumatoid factors with serological parameters of disease activity in rheumatoid arthritis

We evaluated the association of anti-cyclic citrullinated peptide (CCP) antibody titers with serological markers of disease activity. We also compared three different anti-CCP antibody ELISAs with an anti-citrullin ELISA and the IgM and the IgA rheumatoid factor (RF) in their performance of discriminating between rheumatoid arthritis (RA) and other rheumatic diseases. Sera from 333 consecutive patients of the Rheumaeinheit der Medizinischen Poliklinik Munchen, an outpatient clinic for rheumatic diseases, were collected and tested. Anti-CCP antibodies were assayed with three different commercially available ELISAs. Antifilaggrin antibodies were tested with a commercially available ELISA using in vitro deiminated recombinant rat filaggrin. IgA-RF was analyzed with an ELISA, whereas IgM-RF was measured by latex-enhanced turbidimetry. Rheumatoid arthritis (RA) was diagnosed in 87 patients according to the revised classification criteria of the American College of Rheumatology (ACR), probable RA was diagnosed in 23 patients in an early phase not (yet) fulfilling the ACR criteria, and 223 patients had other rheumatic diseases. Differences in sensitivity and specificity were calculated using McNemar's test. A measure of agreement (kappa statistic) was used to examine whether the tests tended to identify the same patients as positive or negative. Correlations between CCP titers and other tests were analyzed by Spearman nonparametric rank correlation. No significant differences in sensitivity and specificity were found between the tested CCP assays (80.0-80.9% and 97.3-98.1%, respectively). All three CCP tests were slightly but not significantly more sensitive and specific than the anti-citrullin assay (77% and 92%, respectively), comparably sensitive but significantly more specific compared with the IgM-RF (86% and 82%, respectively), and significantly more sensitive but comparably specific compared with the IgA-RF (63% and 94.4%, respectively) in detecting the patients with RA. There was no significant correlation between anti-CCP, anti-citrullin, or IgM-RF or IgA-RF antibody titers and C-reactive protein, erythrocyte sedimentation rate, or white blood cell count. A weak but significant linear correlation was found between anti-CCP titers and IgM-RF titers (r = 0.2, P = 0.03). We could not find a significant difference between the three tested anti-CCP assays and the anti-citrullin test in terms of sensitivity and specificity. Compared with the IgM-RF, all the anti-CCP assays were superior in specificity and comparable in sensitivity. Compared with the IgA-RF, they were more sensitive and comparably specific in the discrimination of patients with RA from other rheumatic diseases. No correlation of any tested autoantibody titer with serological parameters of inflammation was found.

Association of mannose-binding lectin gene (MBL2) polymorphisms with rheumatoid arthritis in an Indian cohort of case-control samples

Single nucleotide polymorphisms in the mannose-binding lectin (MBL2) gene, as well as the serum MBL2 level, have been associated with various autoimmune diseases. We investigated whether such polymorphisms and/or the serum MBL2 level were associated with rheumatoid arthritis (RA) in an Indian population. The frequency of the B variant (codon 54) of the MBL2 gene was quite frequent in the healthy Indian population and was significantly (P=6.35x10(-6)) lower in RA patients. We replicated this association (P=1.78x10(-5)) in an independent cohort of control individuals. Promoter polymorphism at -550 nt showed a significant overrepresentation (P=0.003) of the minor allele G in severe RA patients compared with the less severe group. Haplotype LYA frequency was significantly (P=0.03) high in the less severe group, while the frequency of the HYA haplotype was significantly (P=0.04) increased in the severe RA patients. No statistically significant difference in serum MBL2 was observed as a whole, but the individuals homozygous for the LYA haplotype had significantly lower (P=0.017) serum MBL2 levels compared with individuals homozygous for the HYA haplotype. Therefore, the B variant of the MBL2 gene may be associated with protection from RA in our study population, and the promoter polymorphism (-550 nt) seems to have some role in disease progression.

Radiological outcome in rheumatoid arthritis is predicted by presence of antibodies against cyclic citrullinated peptide before and at disease onset, and by IgA-RF at disease onset

OBJECTIVE

To evaluate the significance of antibodies against cyclic citrullinated peptide (anti-CCP) and rheumatoid factors (RFs), before the onset of rheumatoid arthritis and when presenting as early disease (baseline), for disease activity and progression.

METHODS

93 of a cohort of 138 patients with early rheumatoid arthritis (<12 months of symptoms) had donated blood before symptoms of rheumatoid arthritis (defined as pre-patients) and were identified from among blood donors within the Medical Biobank of northern Sweden. Disease activity (erythrocyte sedimentation rate (ESR), C reactive protein, joint score, global visual analogue scale) and radiological destruction in hands and feet (Larsen score) were assessed at baseline and after two years. Anti-CCP antibodies and RFs were analysed using enzyme immunoassays. HLA shared epitope (SE) alleles (DRB1*0401/0404) were identified.

RESULTS

Patients with anti-CCP antibodies before disease onset had significantly higher Larsen score at baseline and after two years. In multiple regression analyses baseline values of anti-CCP/IgA-RF/IgG-RF/IgM-RF, swollen joint count, and Larsen score significantly predicted radiological outcome at two years. In logistic regression analyses, baseline values of anti-CCP antibodies/IgA-RF, therapeutic response at six months, and swollen joint count/ESR significantly predicted radiological progression after two years. The baseline titre of anti-CCP antibodies was higher in patients with radiological progression and decreased significantly in those with response to therapy. SE allele carriage was associated with a positive test for anti-CCP antibodies in pre-patients and in early rheumatoid arthritis.

CONCLUSIONS

Presence of anti-CCP antibodies before disease onset is associated with more severe radiological damage. The titre of anti-CCP antibodies is related to disease severity.

Accumulation of plasma cells expressing CXCR3 in the synovial sublining regions of early rheumatoid arthritis in association with production of Mig/CXCL9 by synovial fibroblasts

Accumulation of plasma cells in the synovium is one of the diagnostic hallmarks in the histopathological manifestations of rheumatoid arthritis (RA). This seems to be prominent even prior to significant B cell infiltration and/or formation of lymphoid follicles in the synovium. To clarify the mechanism of early plasma cell accumulation, we examined in situ expression of chemokines and their receptors using synovial targeting biopsy specimens, which were obtained under arthroscopy from early RA patients. By immunohistochemical staining, plasma cells were found to express a chemokine receptor CXCR3, while synovial fibroblasts in the synovial sublining regions expressed its ligand, Mig/CXCL9. By reverse transcription-polymerase chain reaction (RT-PCR), using targeted lesions of synovial tissues obtained by laser capture microdissection, expression levels of Mig/CXCL9 in the synovial sublining regions were remarkably high and were likely to be associated with interferon (IFN)-gamma expression. Furthermore, cultured synovial fibroblasts were confirmed to produce Mig/CXCL9 upon stimulation with IFN-gamma. Our results indicate that in the early stage of RA, plasma cells expressing CXCR3 may be recruited directly from the circulation into the synovial sublining regions by its ligand, Mig/CXCL9, produced by synovial fibroblasts.

Anti-CCP: history and its usefulness

Antibodies directed to cyclic citrullinated peptides (anti-CCP) are highly specific for rheumatoid arthritis (RA) and can easily be detected in sera by using commercially available immunoassays. The second version of the anti-CCP test (anti-CCP2) demonstrated high specificity (89-98%) and good sensitivity (41-88%) for RA. Commercially available ELISA methods from three different companies are on the market. All three CCP2 assays show similar results as all CCP2 assays use the same antigen-coated plates. This study was an evaluation of a new automated method for the determination of anti-CCP2 in a routine laboratory setting. Five hundred and fourty three serum samples were tested for anti-CCP2 within normal routine diagnostic using a commercially available ELISA and retested with a prelaunch version of a new and fully-automated method (EliA™). The results were comparable. The new automated assay is easy to use and demonstrated a diagnostic sensitivity of 80% and specificity of 97%.

Synovial intracellular citrullinated proteins colocalizing with peptidyl arginine deiminase as pathophysiologically relevant antigenic determinants of rheumatoid arthritis-specific humoral autoimmunity

OBJECTIVE

To address the ongoing debate concerning the specificity of synovial citrullinated proteins for rheumatoid arthritis (RA) and to analyze their pathophysiologic relevance to the induction or perpetuation of the RA-specific anti-citrullinated protein antibodies (ACPAs).

METHODS

Synovium of 19 RA patients and 19 non-RA controls was immunostained for the presence of citrullinated proteins with a mouse monoclonal antibody (F95), for the citrullinating enzyme peptidyl arginine deiminase type 2 (PAD-2), and for the free citrulline-producing enzyme inducible nitric oxide synthase (iNOS). Extending the RA cohort to 61 patients, the findings of anticitrulline staining in synovium were related to serum and synovial fluid ACPA levels, as measured by enzyme-linked immunosorbent assay.

RESULTS

F95 staining indicated the presence of synovial intracellular citrullinated proteins in 53% of RA samples versus 5% of control samples, whereas extracellular staining was not RA specific. Immunoblotting and inhibition experiments confirmed that the antibody recognized citrullinated proteins but not free citrulline. Accordingly, iNOS was equally found in RA and control synovium and in intracellular citrullinated protein-positive and intracellular citrullinated protein-negative samples. In contrast, intracellular citrullinated proteins colocalized with PAD-2, which was found in 59% of RA samples versus 17% of control samples. Independent of local disease activity, the presence of the RA-specific synovial intracellular citrullinated proteins was associated with significantly higher systemic and local ACPA levels and with local ACPA production in the joint.

CONCLUSION

These data confirm the presence of RA-specific intracellular citrullinated proteins in synovium. The link with PAD-2 and local and systemic ACPA levels emphasizes their pathophysiologic relevance for RA-specific humoral autoimmunity.

Diagnostic value and clinical significance of anti-CCP in patients with advanced rheumatoid arthritis

OBJECTIVES

To investigate the prevalence of anticyclic citrullinated peptide (anti-CCP) in patients with advanced rheumatoid arthritis (RA) and to compare it with those in control subjects. Further, to study the relation between the anti-CCP and the disease activity parameters in these patients.

PATIENTS AND METHODS

Seventy-six RA patients who had a mean disease duration of 9.8 years were included. Eighty-three age-matched non-RA volunteers were enrolled as the control group. Disease duration, duration of morning stiffness, swollen and tender joint counts, hand deformity, patient's assessment of pain, anti-CCP, rheumatoid factor (RF) and acute phase proteins were evaluated. The functional disability was also assessed with the Modified Health Assessment Questionnaire (HAQ).

RESULTS

Thirty-seven sera (48.7%) in the patient group and one serum (1.2%) in the control group were positive for anti-CCP. RF was positive in 45% of the RA cases and in 5% of controls. Sensitivity and specificity of anti-CCP reactivity for RA were 49.0% and 99.0%, respectively. HAQ score and duration of morning stiffness were found to be significantly associated with anti-CCP positivity. Disease duration, swollen joint count and anti-CCP positivity were the most important variables predicting hand deformity.

CONCLUSION

The prevalence, sensitivity and specificity of anti-CCP in patients with advanced RA were found to be similar to those reported in patients with early disease. Anti-CCP was significantly associated with some parameters of both disease activity and severity. Anti-CCP might be a useful parameter in clinical evaluation of patients with advanced RA.

Anti-citrullinated collagen type I antibody is a target of autoimmunity in rheumatoid arthritis

Rheumatoid arthritis (RA) is one of the most common autoimmune diseases, but its autoimmune mechanisms are not clearly understood. Recently, anti-citrullinated peptide antibodies have been specifically observed in sera of RA patients. Furthermore, we identified RA-susceptible variant in a gene encoding citrullinating enzyme, peptidylarginine deiminase type 4 (PADI4). Therefore, we hypothesized that proteins which are modified in RA synovium by PADI4 act as autoantigens. Subsequently, we obtained human collagen type I (huCI) as one of the autoantigens using a RA synoviocyte cDNA library by immunoscreening. We also investigated that the levels of anti-citrullinated huCI were significantly higher in RA patient sera than in normal control sera with high specificity (99%) and positively correlated with the levels of anti-cyclic citrullinated peptide (anti-CCP) antibodies. We concluded that huCI is a novel substrate protein of PADIs and that citrullinated huCI is a candidate autoantigen of RA.

HLA-DRB1 and anti-cyclic citrullinated peptide antibody production in rheumatoid arthritis

Anti-cyclic citrullinated peptide antibodies (anti-CCP) are a new diagnostic marker for rheumatoid arthritis (RA), which shows a specificity of 97% and a sensitivity of 81% in the second generation assay. About 61% of RA patients express HLA-DRB1*0401. In a cohort of patients with RA we investigated whether the expression of anti-CCP correlates with the carriage of certain genes on the HLA-DRB1 locus. Our data reveal a highly significant association between anti-CCP and HLA-DR4, and a weaker but still significant association with HLA-DR1. HLA-DRB1*0401 is not a prerequisite for anti-CCP production, but if HLA-DRB1*0401 was present, 90% of our RA patients were anti-CCP positive.

Anti-CCP and antikeratin antibodies in rheumatoid arthritis, primary Sjögren's syndrome, and Wegener's granulomatosis

The objective of this study was to investigate the frequency of antibodies against cyclic citrullinated peptides (anti-CCP) and keratin (AKA) in patients with rheumatoid arthritis (RA) as well as in patients with primary Sjögren's syndrome (pSS) and Wegener's granulomatosis (WG), who may present with rheumatoid factor (RF)-positive arthritis. The study group consisted of 46 patients with RA (26 patients were negative for RF), 32 with pSS, 22 with WG, and 40 healthy controls. The RF, anti-CCP, and AKA were detected in serum using the latex agglutination test, enzyme-linked immunosorbent assay, and indirect immunofluorescence, respectively. The agreement between those tests was evaluated by kappa test. No positive result for AKA was detected in pSS and WG patients, and anti-CCP was found in only one patient with pSS. The results of kappa tests were low, varying between 0.25 (RF-anti-CCP) and 0.02 (RF-AKA). The sensitivity and specificity values were 43 and 44% for RF, 65 and 98% for anti-CCP, and 58 and 100% for AKA, respectively, in RA patients. In the RF-negative RA group, AKA was found to have a high frequency (55%) in comparison to anti-CCP (38%). Seropositivity was found to be 87% for any one of the three autoantibodies tested in RA patients. With a higher specificity, values for RA, anti-CCP, and AKA seem to be helpful for the differential diagnosis of patients with RF-positive arthritis, which may include patients with WG and pSS, and screening of all three antibodies may increase the diagnostic performance.

The clinical and genetic associations of anti-cyclic citrullinated peptide antibodies in psoriatic arthritis

OBJECTIVES

Antibodies recognizing a cyclic citrullinated peptide (anti-CCP) are highly specific for rheumatoid arthritis (RA) but their role in psoriatic arthritis (PsA) remains unclear. The aim of this study was therefore to investigate the prevalence of anti-CCP antibodies in PsA and assess their clinical and genetic associations.

METHODS

One hundred and twenty-six patients with PsA, 40 patients with seropositive RA and 40 controls were tested for the presence of anti-CCP antibodies, rheumatoid factor (RF) and the HLA-DRB1 shared epitope. Clinical and radiological data were collected prospectively on all patients and compared between anti-CCP-positive and -negative patients.

RESULTS

Seven (5.6%) patients with PsA were positive for anti-CCP antibodies compared with 0% of controls and 97% of patients with seropositive RA. The presence of anti-CCP antibodies in PsA was significantly associated with the HLA-DRB1 shared epitope (P<0.005), erosive disease (P<0.05), number of swollen joints (P<0.02) and DMARD use (P<0.05).

CONCLUSIONS

Overall, the increased prevalence of anti-CCP antibodies in this PsA population failed to reach statistical significance. However, when present, they were a marker of disease severity and had RA-linked MHC class II associations. Further studies are needed in a larger population of patients with PsA and appropriate controls to confirm any true association that may be present.

Fibrin deimination in synovial tissue is not specific for rheumatoid arthritis but commonly occurs during synovitides

Autoantibodies to deiminated (citrullinated) proteins are the most specific serological markers of rheumatoid arthritis (RA). Deimination is critical in generating the peptidic epitopes they recognize. In the synovial tissue (ST), deiminated forms of the alpha- and beta-chains of fibrin are their major autoantigenic targets (anti-human fibrin(ogen) autoantibodies (AhFibA)). We investigated whether the presence of deiminated fibrin in the ST was specific for RA, because this could explain why AhFibA are RA specific. In 13 patients with RA and 19 patients with various other rheumatological disorders, knee ST biopsies were collected in macroscopically inflamed areas identified under arthroscopy. Synovitis was histopathologically confirmed in all of the biopsies. By immunoblotting, using antisera to fibrin, Abs to citrullyl residues, and AhFibA purified from RA sera, deiminated fibrin was evidenced in ST extracts from all of the patients. Moreover, variations in the degree of fibrin deimination were observed that were not related to the disease. Immunohistochemical analysis, using Abs to citrullyl residues and an antiserum to fibrin on adjacent serial sections of ST, confirmed the results because deiminated proteins colocalized with fibrin in RA as well as in control patients. Therefore, fibrin deimination in the ST is a general phenomenon associated to any synovitis, which does not necessarily induce a B autoimmune response with production of AhFibA.

Autoantibodies to citrullinated proteins in rheumatoid arthritis: clinical performance and biochemical aspects of an RA-specific marker

Rheumatoid arthritis (RA) is a common, systemic autoimmune disease of which the exact etiology is not known. In the past 10 years, substantial progress has been made in the identification of the antigens specifically recognized by the autoantibodies of RA patients. A central factor in this respect is citrullination, a form of post-translational modification that is strongly associated with autoimmunity in RA. Here, we summarize and discuss our current knowledge on (i) autoantibody systems in RA, (ii) the occurrence of peptidylarginine deiminases and (iii) citrullinated proteins in natural and diseased environments, and (iv) genetic factors involved in RA that may influence the generation and presentation of citrullinated proteins and the resulting antibody production against these modified proteins. Citrullination of proteins may play a key role in the initiation and/or the progression of RA. The onset of citrulline-specific autoimmunity in RA is probably mediated by both environmental and genetic factors, and future studies will learn whether therapeutic intervention at the level of citrullination may provide new possibilities to treat RA.

Anti-Sa antibodies and antibodies against cyclic citrullinated peptide are not equivalent as predictors of severe outcomes in patients with recent-onset polyarthritis

The prognostic value of two antibodies targeting citrullinated antigens, anti-Sa and anti-cyclic citrullinated peptide (CCP), present at inclusion, was evaluated prospectively in a cohort of 165 consecutive patients with recent-onset or early polyarthritis (EPA) followed for up to 30 months. Patients were treated according to current Good Clinical Practice standards. Predefined outcomes were severe arthritis and persistent arthritis. At inclusion, a median of 3 months after disease onset, 133 (81%) patients fulfilled at least four American College of Rheumatology criteria for rheumatoid arthritis and 30 (18%) had erosive changes on radiographs of hands and feet. Disease-modifying anti-rheumatic drugs were used in close to 80% of the patients at 30 months. Joint damage increased linearly over time, whereas disease activity declined markedly and remained low at each follow-up. Autoantibodies were identified in 76 (46%) patients: rheumatoid factor (RF) in 68 (41%), anti-CCP in 53 (33%), and anti-Sa in 46 (28%). All three antibodies were correlated, but anti-Sa antibodies best predicted severity at 18 and 30 months. RF and anti-CCP performed less well. For both outcomes, anti-Sa alone performed better than any combination of antibodies. The presence of any autoantibody identified about 50 to 60% of the patients with poor outcomes. In multivariate analysis, anti-Sa (odds ratio (OR) 8.83), the presence of erosions at inclusion (OR 3.47) and increasing age (OR 1.06/year) were significantly associated with severity, whereas RF and anti-CCP were not significant predictors. Persistent arthritis was present in up to 84% of patients; autoantibodies were specific but poorly sensitive predictors of this outcome. We conclude that assays for antibodies against citrullinated antigens differ in their ability to predict poorer outcomes in patients with EPA. In our EPA cohort treated in accordance with current standards, detection of anti-Sa but not of RF or anti-CCP antibodies, in combination with clinical and radiological variables present at the first encounter, allowed the identification of a subgroup of EPA patients suffering more rapid and more severe joint damage over 30 months.

Citrullinated proteins have increased immunogenicity and arthritogenicity and their presence in arthritic joints correlates with disease severity

Autoantibodies directed against citrulline-containing proteins have an impressive specificity of nearly 100% in patients with rheumatoid arthritis and have been suggested to be involved in the disease pathogenesis. The targeted epitopes are generated by a post-translational modification catalysed by the calcium-dependent enzyme peptidyl arginine deiminase (PAD), which converts positively charged arginine to polar but uncharged citrulline. The aim of this study was to explore the effects of citrullination on the immunogenicity of autoantigens as well as on potential arthritogenicity. Thus, immune responses to citrullinated rat serum albumin (Cit-RSA) and to unmodified rat serum albumin (RSA) were examined as well as arthritis development induced by immunisation with citrullinated rat collagen type II (Cit-CII) or unmodified CII. In addition, to correlate the presence of citrullinated proteins and the enzyme PAD4 with different stages of arthritis, synovial tissues obtained at different time points from rats with collagen-induced arthritis were examined immunohistochemically. Our results demonstrate that citrullination of the endogenous antigen RSA broke immunological tolerance, as was evident by the generation of antibodies directed against the modified protein and cross-reacting with the native protein. Furthermore we could demonstrate that Cit-CII induced arthritis with higher incidence and earlier onset than did the native counterpart. Finally, this study reveals that clinical signs of arthritis precede the presence of citrullinated proteins and the enzyme PAD4. As disease progressed into a more severe and chronic state, products of citrullination appeared specifically in the joints. Citrullinated proteins were detected mainly in extracellular deposits but could also be found in infiltrating cells and on the cartilage surface. PAD4 was detected in the cytoplasm of infiltrating mononuclear cells, from day 21 after immunisation and onwards. In conclusion, our data reveal the potency of citrullination to break tolerance against the self antigen RSA and to increase the arthritogenic properties of the cartilage antigen CII. We also show that citrullinated proteins and the enzyme PAD4 are not detectable in healthy joints, and that the appearance and amounts in arthritic joints of experimental animals are correlated with the severity of inflammation.

Amplification of autoimmune disease by infection

Reports of infection with certain chronic persistent microbes (herpesviruses or Chlamydiae) in human autoimmune diseases are consistent with the hypothesis that these microbes are reactivated in the setting of immunodeficiency and often target the site of autoimmune inflammation. New experimental animal models demonstrate the principle. A herpesvirus or Chlamydia species can be used to infect mice with induced transient autoimmune diseases. This results in increased disease severity and even relapse. The evidence suggests that the organisms are specifically imported to the inflammatory sites and cause further tissue destruction, especially when the host is immunosuppressed. We review the evidence for the amplification of autoimmune inflammatory disease by microbial infection, which may be a general mechanism applicable to many human diseases. We suggest that patients with autoimmune disorders receiving immunosuppressing drugs should benefit from preventive antiviral therapy.

Predictive value of antibodies to cyclic citrullinated peptide in patients with very early inflammatory arthritis

OBJECTIVE

To study the prognostic value of antibodies to cyclic citrullinated peptide (anti-CCP) and rheumatoid factor (RF), alone and in combination, in patients with very early synovitis.

METHODS

A cross-sectional study was performed in patients with established inflammatory and noninflammatory disease to validate the assay in our unit and confirm previously reported sensitivities and specificities of anti-CCP antibodies. Subsequently, patients with synovitis of 3 months' duration were followed for 72 weeks and the ability of anti-CCP antibodies and RF to predict the development of rheumatoid arthritis (RA) and persistent inflammatory arthritis was assessed.

RESULTS

One hundred twenty-four patients were assessed in the initial cross-sectional study. Anti-CCP antibodies and RF were detected by ELISA in only 4% of patients with non-RA inflammatory disease and in no patient with noninflammatory disease. Ninety-six patients with very early synovitis were assessed longitudinally. In these patients with early arthritis, the combination of anti-CCP antibodies and RF had a specificity, positive predictive value (PPV), sensitivity, and negative predictive value (NPV) for a diagnosis of RA of 100%, 100%, 58%, and 88%, respectively. The specificity, PPV, sensitivity, and NPV of this antibody combination for the development of persistent disease-fulfilling classification criteria for RA were 97%, 86%, 63%, and 91%, respectively.

CONCLUSION

In patients with synovitis of 3 months' duration, a combination of anti-CCP antibodies and RF has a high specificity and PPV for the development of persistent RA. This autoantibody combination can be used to identify patients with disease destined to develop RA who may be appropriate for very early intervention.

Antibodies to citrullinated human fibrinogen (ACF) have diagnostic and prognostic value in early arthritis

BACKGROUND

The anti-cyclic citrullinated peptide (CCP) test has a high sensitivity and specificity for rheumatoid arthritis, although CCP is not the physiological target of the autoantibodies. Citrullinated fibrin is abundant in inflamed synovium

OBJECTIVE

To assess the diagnostic and prognostic value of antibodies against citrullinated fibrinogen (ACF), a soluble precursor of fibrin, in comparison with IgM-rheumatoid factor (IgM-RF) and the second generation anti-CCP test.

METHODS

In 379 patients with early arthritis (258 rheumatoid and 121 undifferentiated), the sensitivity, specificity, and positive predictive value of ACF, anti-CCP, and IgM-RF for diagnosing rheumatoid arthritis were calculated. Multivariate logistic regression analysis was used to assess the diagnostic and prognostic value (radiographic progression after two years) of the tests.

RESULTS

The sensitivities of the ACF, anti-CCP, and IgM-RF tests were 55.8%, 57.8%, and 44.6%, with specificities of 92.6%, 94.2%, and 96.7%, respectively. Approximately 30% of the IgM-RF negative patients were positive for ACF or anti-CCP or both. The ACF and anti-CCP test had a high agreement in early arthritis (kappa = 0.84). Of all baseline characteristics, the ACF test and the anti-CCP test were the best predictors for diagnosing rheumatoid arthritis at one year (odds ratio (OR) = 10.3 and 10.6, respectively) and for radiographic progression after two years (OR = 12.1 and 14.8).

CONCLUSIONS

ACF is as sensitive as anti-CCP and more sensitive than IgM-RF in diagnosing rheumatoid arthritis in early arthritis. The ACF test is also a good predictor of radiographic progression, with a performance similar to the anti-CCP test. The ACF test and the anti-CCP test are especially valuable in IgM-RF negative arthritis.

Antiferritin antibodies discovered by phage display expression cloning are associated with radiographic damage in rheumatoid arthritis

OBJECTIVE

Several autoantibodies have been described in individuals with rheumatoid arthritis (RA), leading to interest in the use of such antibodies as diagnostic or prognostic markers in RA as well as in their relevance to disease pathology. The objective of this study was to use a phage display expression cloning system to identify novel autoantibody targets in RA.

METHODS

We used immunoscreening of a phage-displayed complementary DNA (cDNA) library to isolate a cDNA clone encoding the ferritin heavy chain polypeptide. Antiferritin antibody levels in patients with early and established RA, healthy controls, and disease controls were measured by enzyme-linked immunosorbent assay. Antibody-positive and antibody-negative individuals were compared with respect to disease severity as measured by the modified Larsen score, demographic variables, rheumatoid factor status, and carriage of HLA-DRB1 shared epitope alleles.

RESULTS

Antiferritin antibodies were present in 60 (16%) of 366 patients with established RA, 23 (19%) of 118 patients with early RA, 2 (2.7%) of 73 healthy blood donors, 2 (2.1%) of 94 individuals with osteoarthritis, and 2 (2.1%) of 97 patients with systemic lupus erythematosus (P < 0.01, RA patients versus healthy and disease controls). Antiferritin antibodies were more common in men than in women (28.4% versus 12.2%; P < 0.001), and antiferritin levels were associated with the severity of joint damage (P = 0.01).

CONCLUSION

Antiferritin antibodies are observed in a subset of patients with RA, are present early in the disease course, and are associated with the severity of radiographic damage. Further studies are required to explore their potential as diagnostic and prognostic markers in RA.

Antibodies against cyclic citrullinated peptide are associated with HLA-DR4 in simplex and multiplex polyarticular-onset juvenile rheumatoid arthritis

OBJECTIVE

Anti-cyclic citrullinated peptide (anti-CCP) antibodies have been detected in patients with juvenile rheumatoid arthritis (JRA), particularly in those with polyarticular, rheumatoid factor (RF)-positive JRA. Our objectives were to determine whether anti-CCP antibodies are associated with HLA-DR4 in children with polyarticular JRA, whether anti-CCP antibodies are associated with clinical features of disease, and whether affected sibling pairs (ASPs) with JRA are concordant for this antibody.

METHODS

Stored serum samples obtained from 230 HLA-typed patients with JRA (77 with polyarticular-onset disease and 153 with pauciarticular- or systemic-onset disease), 100 JRA ASPs, and 688 healthy children were tested for anti-CCP antibodies and RF.

RESULTS

Thirteen percent of the patients with polyarticular-onset JRA and 2% of the other JRA patients exhibited anti-CCP antibodies, compared with only 0.6% of the controls. Fifty-seven percent of RF-positive patients with polyarticular-onset JRA had anti-CCP antibodies. HLA-DR4-positive patients with polyarticular-onset JRA were more likely to have anti-CCP antibodies than were those without HLA-DR4 alleles (odds ratio [OR] 5.20, 95% confidence interval [95% CI] 1.30-20.9). Anti-CCP antibodies were associated with polyarticular onset (OR 7.46, 95% CI 1.99-28.0), a polyarticular disease course (OR 9.78, 95% CI 1.25-76.7), and erosive disease (OR 14.3, 95% CI 3.01-67.9). Concordance rates for anti-CCP antibodies among ASPs were statistically significant.

CONCLUSION

These data demonstrate increased anti-CCP antibody formation in HLA-DR4-positive patients with polyarticular-onset JRA. The overall prevalence of anti-CCP antibodies in JRA is low, but a substantial proportion of RF-positive patients with polyarticular-onset JRA have these antibodies. Anti-CCP antibodies in JRA are associated with polyarticular onset, a polyarticular course, and erosive disease.

Rheumatoid factor and anticitrullinated protein antibodies in rheumatoid arthritis: diagnostic value, associations with radiological progression rate, and extra-articular manifestations

BACKGROUND

Autoantibodies such as rheumatoid factor (RF) and anticitrullinated protein antibodies can be detected in rheumatoid arthritis (RA) sera.

OBJECTIVE

To determine the diagnostic values of RF, anticitrullinated protein antibodies, and the shared epitope (SE), and their associations with radiological progression rates and extra-articular manifestations.

METHODS

Population 1 consisted of sera from 315 patients, consecutively sent for detection of anticitrullinated protein antibodies, of which 264 were used to determine the sensitivity and specificity of RF and of antibodies against three synthetic citrullinated peptides: peptide A (pepA), peptide B (pepB), and CCP2. Population 2 consisted of sera from 180 longstanding RA patients and was used to determine associations of RA associated antibodies and the SE with radiological progression rates and extra-articular manifestations. Antibodies to pepA and pepB were detected by line immunoassay, and antibodies to CCP2 by ELISA. HLA Class II typing was performed by LiPA.

RESULTS

In population 1, we defined adapted cut offs corresponding to a specificity of >/=98.5%. This yielded the following sensitivities: RF 12.8%; anti-pepA antibodies 63.6%; anti-pepB antibodies 54.2%; and anti-CCP2 antibodies 73.7%. In population 2, significant differences in radiological progression rates were found between positive and negative patients for different RA antibodies and the SE. RF, but not anticitrullinated protein antibodies or the SE, were more frequent in patients with extra-articular manifestations.

CONCLUSION

A valid comparison of RA associated antibodies shows superior sensitivity of the anticitrullinated protein antibodies compared with RF. The presence of RA associated antibodies and the SE are indicative for poorer radiological outcome, and presence of extra-articular manifestations is associated with RF but not with anticitrullinated protein antibodies.

The role and clinical implications of G6PI in experimental models of rheumatoid arthritis

The antigens that trigger the pathogenic immune response in rheumatoid arthritis (RA) remain unknown. Until recently it was assumed that either viral or microbial antigens, or joint-specific antigens were the target of arthritogenic T and B lymphocytes in RA. Consequently, murine models of arthritis are induced by immunization with either joint-specific antigens such as type II collagen or microbial products such as streptococcal cell wall. In the K/B×N T-cell receptor transgenic mouse model arthritis is caused by a systemic autoimmune response to the ubiquitously expressed glycolytic enzyme glucose-6-phosphate isomerase (G6PI). The autoreactive transgenic T cells recognize G6PI and provide help for the production of arthritogenic IgG antibodies against G6PI. More recently it was shown that G6PI immunization induces severe symmetrical peripheral polyarthritis in genetically unaltered DBA/I mice. In that model CD4⁺ T cells are necessary not only for the induction but also for the effector phase of arthritis. Here we review the pathomechanisms that lead from systemic autoreactivity to arthritis in these models, consider the relevance of anti-G6PI immune reactivity for RA, and discuss the insights into the pathogenesis of RA and possibly other autoimmune conditions that can be gained from these models.

Clinical and pathophysiological significance of the autoimmune response to citrullinated proteins in rheumatoid arthritis

Rheumatoid arthritis (RA) is the most frequent human autoimmune disease, affecting about 1% of the adult population worldwide. A better knowledge of the autoimmune mechanisms involved is essential. We identified the epithelial targets of various autoantibodies specifically associated to RA, as variants of (pro)filaggrin. We also showed that these targets correspond to deiminated ("citrullinated") proteins, of which arginyl residues have been posttranslationally transformed into citrullyl residues by a peptidylarginine deiminase (PAD). Moreover, we and others established that citrullyl residues are indispensable elements of the epitopes recognized by these autoantibodies but only in the context of specific aminoacid sequences. We also demonstrated that these autoantibodies to citrullinated proteins (ACPA) are secreted by plasma cells of the synovial tissue and that their major targets correspond to citrullinated forms of the alpha- and beta-chains of fibrin, abundant in the tissue. These results have allowed the development of new efficient immunochemical methods for the detection of ACPA. Some of them are already commercially available. These new methods have permitted the high diagnostic value of ACPA which are present very early in the course of the disease, and also their prognostic value, to be confirmed. ACPA detection should therefore prove to be also a very valuable tool to guide the choice of therapeutic strategies, from the earliest stages of the disease. The synthesis of ACPA in the rheumatoid synovial tissue and the existence therein of a specific antigenic target constitute a strong argument for the involvement of this specific immunological conflict in the pathophysiology of RA. Indeed, it could lead to activation of effector mechanisms with pro-inflammatory effects, thus to formation in the tissue of new fibrin deposits, secondarily citrullinated. We therefore, propose a new pathophysiological model accounting for the self-maintenance and chronicity of rheumatoid inflammation. Numerous questions about the pathophysiological significance of the autoimmune response to deiminated proteins in RA remain to be answered to confirm this model.

A family based study shows no association between rheumatoid arthritis and the PADI4 gene in a white French population

BACKGROUND

Autoantibodies to citrullinated proteins (ACPA) are considered a specific marker for rheumatoid arthritis. Peptidylarginine deiminase (PAD) is the enzyme that converts arginyl into citrullyl residues; different isoforms of the enzyme are expressed in mammals. It has been suggested that the PADI4 gene may contribute to genetic susceptibility to rheumatoid arthritis, but conflicting results have been obtained in different populations.

OBJECTIVE

To test the hypothesis that the PADI4 gene may confer susceptibility to rheumatoid arthritis in a white French population, using powerful and highly reliable family based association tests.

METHODS

DNA samples were analysed from 100 families where one member was affected by rheumatoid arthritis and both parents were available for sampling. Five single nucleotide polymorphisms, located within the PADI4 gene and in its close proximity, were genotyped by restriction fragment length polymorphism, and haplotypes were constructed. The analysis involved use of the transmission disequilibrium test and genotype relative risk. ACPA were detected by ELISA on cyclic citrullinated peptides and on human deiminated fibrinogen.

RESULTS

No single SNP or haplotype was associated with the disease, or was preferentially transmitted. No association was found when patients were partitioned according to ACPA positivity.

CONCLUSIONS

No PADI4 haplotype is associated with rheumatoid arthritis in a white French population. The role of genes encoding the other PAD isoforms, or modulating tissue expression or enzyme activity, remains to be elucidated.

Diagnostic and prognostic values of anti glucose-6-phosphate isomerase antibodies in community-recruited patients with very early arthritis

The objective of this study was to determine the diagnostic and prognostic values of antiglucose-6-phosphate isomerase (GPI) antibodies in patients with very early arthritis. Anti-GPI antibodies were measured by ELISA using purified GPI from rabbit muscle in: (i) 383 sera from healthy blood donors (n = 120), well-established rheumatoid arthritis (RA) (n = 99) and non-RA differentiated arthritis (NRADA) (n = 164) patients; (ii) 195 sera obtained from community-recruited patients with very early inflammatory arthritis (VErA cohort) that were studied for 1 year and classified as having RA (n = 116), NRADA (n = 41), and undifferentiated arthritis (UA) (n = 38) after the follow-up period. The criterion for severity was the progression of radiographic damage. Prevalence of anti-GPI antibodies was significantly higher in well-established RA patients (45.4%) compared to healthy subjects (2.5%). Anti-GPI antibodies were also present in sera from NRADA: systemic lupus erythematosus 53%, polymyositis 45.4%, adult-onset Still's disease 44%, systemic sclerosis 42.8%, spondylarthropathies 25% and primary Sjögren's syndrome 5.8%. No significant association was found between the presence of anti-GPI antibodies and the 3 diagnostic groups from the VErA cohort. No correlation was observed between anti-GPI and autoantibodies usually associated with RA. Anti-GPI antibodies were not predictive of radiological progression in patients with very early arthritis. Thus, anti-GPI antibodies are not useful for discriminating RA from non-RA rheumatic diseases and do not constitute a predictive factor of structural damage.

A Mouse Herpesvirus Induces Relapse of Experimental Autoimmune Arthritis by Infection of the Inflammatory Target Tissue

It is not known what is required for successive relapses in autoimmune diseases or evolution to a progressive chronic disease. Autoimmune arthritis caused by passive transfer of autoantibodies against glucose 6-phosphate isomerase is transient and therefore lends itself well to test for what might extend the disease. Herpesviruses have long been suspected of contributing to human autoimmune disease. We infected mice with a murine gamma-herpesvirus (MHV-68). In immunodeficient mice, transient arthritis was followed by a relapse. This was due to lytic viral infection of synovial tissues demonstrated by PCR, immunohistochemistry, and electron microscopy. Latent infection could be reactivated in the synovium of normal mice when treated with Cytoxan and this was associated with increased clinical arthritis. We conclude that herpesviruses may play an ancillary pathogenic role in autoimmune arthritis by infection of the inflammatory target tissue.

Anti-CCP antibody test predicts the disease course during 3 years in early rheumatoid arthritis (the Swedish TIRA project)

OBJECTIVES

To evaluate the diagnostic sensitivity of antibodies to cyclic citrullinated peptide (CCP) in recent onset rheumatoid arthritis (RA) at diagnosis and 3 years later, and to evaluate anti-CCP antibody as a predictor of the disease course during 3 years.

METHODS

242 patients with recent onset (< or =1 year) RA were followed up regularly during 3 years after inclusion in the Swedish multicentre study "TIRA" 1996-98. Anti-CCP antibodies were analysed by an enzyme immunoassay (EIA). Rheumatoid factors (RFs) were analysed by latex agglutination and two isotype-specific (IgM and IgA) EIAs. Disease activity was assessed by plasma CRP, ESR, 28 joint disease activity score, and the physician's global assessment of disease activity. Functional ability was evaluated by the Health Assessment Questionnaire.

RESULTS

Overall, the diagnostic sensitivity of anti-CCP antibodies was 64% and the proportion of positive tests increased with the number of fulfilled classification criteria according to the American College of Rheumatology. The anti-CCP antibody results correlated with RF, but were better than RF as predictor of a more aggressive disease course. After 3 years 5/97 patients had changed anti-CCP status: 2 from negative to positive and 3 from positive to negative. The mean level of anti-CCP antibodies declined by 131 U/ml during the 3 year follow up (95% CI 34 to 228 U/ml).

CONCLUSION

The anti-CCP antibody assay has a similar diagnostic sensitivity to that of RF in early RA, but is better as a predictor of the disease course over 3 years. Although the mean serum level declines, anti-CCP antibody positivity remains essentially unaltered 3 years after diagnosis and start of antirheumatic treatment.

Diagnostic and clinical value of anti-cyclic citrullinated peptide antibodies compared with rheumatoid factor isotypes in rheumatoid arthritis

OBJECTIVE

To assess the additional diagnostic and clinical value of the second test generation of anti-cyclic citrullinated peptide antibodies (CCP2) compared with rheumatoid factor isotypes (IgG-RF, IgA-RF, IgM-RF) in patients with rheumatoid arthritis.

METHODS

This was a prospective study on 715 patients: rheumatoid arthritis (n = 295), degenerative or other inflammatory joint disease (n = 163), connective tissue disease or vasculitis (n = 103), and healthy controls (n = 154). Sera from each subject were tested for CCP2 and RF isotypes by enzyme linked immunosorbent assay (ELISA). Agreement with clinical indices such as disease activity, joint destruction, disease duration, and other laboratory tests was assessed. Sensitivity and specificity of the tests were evaluated taking the clinical diagnosis as the gold standard.

RESULTS

Highest sensitivity was found for IgM-RF (66.4%) and CCP (64.4%). Highest specificity was achieved by CCP (97.1%) and IgG-RF (91.0%). In rheumatoid patients with high disease activity or severe joint damage, CCP was more often present (81.4% and 83.6%) than all RF isotypes. Of special diagnostic value was the detection of positive CCP in 34.5% of all patients with rheumatoid arthritis when all measured RF isotypes (IgG-RF, IgA-RF, and IgM-RF) were negative.

CONCLUSIONS

As a screening method for rheumatoid arthritis the IgM-RF and the CCP assays are superior to other RF isotypes. Positivity in the highly specific CCP ELISA supports the diagnosis of rheumatoid arthritis. CCP proved to be a powerful diagnostic tool, especially in ambiguous cases or RF negative patients with rheumatoid arthritis.

Influence of arginine deimination on antigenicity of fibrinogen

Autoreactivity is controlled at various steps by numerous mechanisms and is a key to understanding and treating autoimmune disease. Recently, an antibody against deiminated fibrinogen (DI-FBG) was detected in patients with rheumatoid arthritis (RA) with high specificity and sensitivity. DI-FBG converted enzymically by peptidyl arginine deiminase, was also detected in synovial membrane. In the present study, we investigated whether antibody to DI-FBG is produced in mice immunized with DI-FBG. Mice were immunized with DI-FBG in the presence or absence of adjuvant. Production of the specific antibody was only induced with adjuvant. The resulting antibody was specific for DI-FBG and did not react with intact/native fibrinogen. Furthermore, it recognized deiminated human fibrinogen and cyclic citrullinated peptide (CCP). These results suggested that mouse fibrinogen acquires antigenicity in mice through deimination and therefore, autoantibody such as that detected in RA patients specifically may be induced.

Association between HLA class II genes and autoantibodies to cyclic citrullinated peptides (CCPs) influences the severity of rheumatoid arthritis

OBJECTIVE

The functional role of HLA class II molecules in the pathogenesis of rheumatoid arthritis (RA) is unclear. HLA class II molecules are involved in the interaction between T and B lymphocytes required for long-lived B cell responses and generation of high-affinity IgG antibodies. We undertook this study to investigate the relationship between HLA class II gene polymorphisms and RA-specific IgG antibodies against cyclic citrullinated peptides (anti-CCP antibodies).

METHODS

High-resolution HLA-DR and DQ typing and anti-CCP-2 antibody testing were performed on 268 RA patients from the Early Arthritis Clinic cohort at the Department of Rheumatology of the Leiden University Medical Center. The presence of anti-CCP antibodies was analyzed in carriers of the different DR and DQ alleles. Disease progression was measured over a period of 4 years by scoring radiographs of the hands and feet using the Sharp/van der Heijde method.

RESULTS

Carriership of the individual alleles HLA-DRB1*0401, DRB1*1001, DQB1*0302, and DQB1*0501 was associated with the presence of anti-CCP antibodies. Carriers of DQ-DR genotypes containing proposed RA susceptibility alleles were significantly more often anti-CCP antibody positive. Carriership of one or two HLA-DRB1 shared epitope (SE) alleles was significantly associated with production of anti-CCP antibodies (odds ratio [OR] 3.3, 95% confidence interval [95% CI] 1.8-6.0 and OR 13.3, 95% CI 4.6-40.4, respectively). An increased rate of joint destruction was observed in SE+, anti-CCP+ patients (mean Sharp score 7.6 points per year) compared with that in SE-, anti-CCP+ patients (2.4 points per year) (P = 0.04), SE+, anti-CCP- patients (1.6 points per year) (P < 0.001), and SE-, anti-CCP- patients (1.6 points per year) (P < 0.001).

CONCLUSION

HLA class II RA susceptibility alleles are associated with production of anti-CCP antibodies. Moreover, more severe disease progression is found in RA patients with both anti-CCP antibodies and SE alleles.

SLC22A4 and RUNX1: identification of RA susceptible genes

Recently we reported that SLC22A4 and RUNX1 are associated with rheumatoid arthritis (RA). SLC22A4 is an organic cation transporter with unknown physiological function, and RUNX1 is a hematological transcriptional regulator that has been shown to be responsible for acute myelogenic leukemia. It is suggested that the association of RUNX1 with RA is due to its regulation of expression of SLC22A4. Because the physiological function of SLC22A4 is still unclear, further investigation is needed into how SLC22A4 affects RA susceptibility. Although the association of RUNX1 with RA was identified as a regulatory factor of SLC22A4, it is possible that RUNX1 is a key molecule in autoimmunity, as it has been reported to be associated with systemic lupus erythematosus and psoriasis, two other autoimmune diseases.

A combination of autoantibodies to cyclic citrullinated peptide (CCP) and HLA-DRB1 locus antigens is strongly associated with future onset of rheumatoid arthritis

Antibodies against cyclic citrullinated peptide (CCP) and rheumatoid factors (RFs) have been demonstrated to predate the onset of rheumatoid arthritis (RA) by years. A nested case–control study was performed within the Northern Sweden Health and Disease study cohort to analyse the presence of shared epitope (SE) genes, defined as HLA-DRB1*0404 or DRB1*0401, and of anti-CCP antibodies and RFs in individuals who subsequently developed RA. Patients with RA were identified from among blood donors whose samples had been collected years before the onset of symptoms. Controls matched for age, sex, and date of sampling were selected randomly from the same cohort. The SE genes were identified by polymerase chain reaction sequence-specific primers. Anti-CCP2 antibodies and RFs were determined using enzyme immunoassays. Fifty-nine individuals with RA were identified as blood donors, with a median antedating time of 2.0 years (interquartile range 0.9–3.9 years) before presenting with symptoms of RA. The sensitivity for SE as a diagnostic indicator for RA was 60% and the specificity was 64%. The corresponding figures for anti-CCP antibodies were 37% and 98%, and for RFs, 17–42% and 94%, respectively. In a logistic regression analysis, SE (odds ratio [OR] = 2.35), anti-CCP antibodies (OR = 15.9), and IgA-RF (OR = 6.8) significantly predicted RA. In a combination model analysis, anti-CCP antibodies combined with SE had the highest OR (66.8, 95% confidence interval 8.3–539.4) in predicting RA, compared with anti-CCP antibodies without SE (OR = 25.01, 95% confidence interval 2.8–222.2) or SE without anti-CCP antibodies (OR = 1.9, 95% confidence interval 0.9–4.2). This study showed that the presence of anti-CCP antibodies together with SE gene carriage is associated with a very high relative risk for future development of RA.

Evaluation of anti-citrullinated filaggrin antibodies as hallmarks for the diagnosis of rheumatic diseases

BACKGROUND

Anti-filaggrin antibodies (AFA) are among the most specific antibodies for rheumatoid arthritis, so procedures for their detection should be included in early biological diagnoses. AFA can be detected by indirect immunofluorescence (anti-keratin antibodies, AKA) or by new enzyme immunoassays (EIA). Their comparative performance needs to be established.

OBJECTIVE

To compare these technical procedures to optimise the serological diagnosis of rheumatoid arthritis.

METHODS

Results obtained using AKA and EIA were compared in 271 sera from 140 patients with rheumatoid arthritis at various stages, 98 patients with other autoimmune diseases, and 33 healthy subjects. EIA were successively undertaken with citrullinated linear filaggrin peptide (home made EIA) or cyclic citrullinated peptide (CCP2, commercial kits). Rheumatoid factor (RF) was assessed by EIA in all patients.

RESULTS

Anti-CCP2 kits showed the best sensitivity and specificity (65% and 96%, respectively). Among the 140 patients with rheumatoid arthritis, those with very recent disease (less than six months' duration, n = 21) were studied as a separate group. In this group, the sensitivity of anti-CCP2 kits decreased to approximately 50%. Nevertheless this assay remained the most accurate when compared with AKA or home made EIA using linear filaggrin peptides. The combination of anti-CCP2 and RF only slightly increased the sensitivity of the diagnosis of very early rheumatoid arthritis.

CONCLUSIONS

Kits using citrullinated cyclic peptides (CCP2) were more suitable than either AKA or EIA using linear filaggrin peptides for the diagnosis of early rheumatoid disease.

Citrullinated proteins: sparks that may ignite the fire in rheumatoid arthritis

Antibodies directed to citrullinated proteins (e.g. anti-CCP [cyclic citrullinated peptide] antibodies) are highly specific for rheumatoid arthritis (RA). These antibodies are produced at the site of inflammation in RA, and therefore citrullinated antigens are also expected to be present in the inflamed synovium. We discuss literature showing that the presence of citrullinated proteins in the synovium is not specific for RA. The RA-specific antibodies are therefore most likely the result of an abnormal immune response that specifically occurs in RA patients. It was recently shown that presence of anti-CCP antibodies precedes the onset of clinical symptoms of RA by years. It thus appears that it may take years for initial events that cause the generation of anti-CCP antibodies to develop into full-blown disease.

Rheumatoid arthritis in beta-thalassemic trait: clinical, serologic and immunogenetic profile

OBJECTIVES

To investigate the clinical, serologic, radiologic and immunogenetic characteristics of rheumatoid arthritis (RA) occurring in patients with beta-thalassemic trait as compared with RA in control patients from the same geographical area.

MATERIALS AND METHODS

Twenty-eight patients with beta-thalassemic trait fulfilling the American College of Rheumatology (ACR) criteria for RA were compared with a control group of twenty-eight RA patients matched for age, sex, disease duration and place of birth. Clinical and routine laboratory assessment, including anti-keratin antibodies and anti-citrullinated peptide antibodies, was carried out in the two groups. The patients were also evaluated for HLADRB1 alleles and radiologic damage.

RESULTS

No differences were found with regard to clinical indexes of disease activity, laboratory parameters, and joint erosions. The immunogenetic analysis did not show any significant difference, the percentage of patients with alleles encoding for the shared epitope being similar in the two groups (61% vs. 57%). As for the extra-articular features, we found a trend for a lower prevalence of sicca syndrome in the beta-thalassemic group (14% vs. 39%; P = 0.06). Rheumatoid nodules were not found in beta-thalassemic patients while they were present in two RA patients in the control group.

CONCLUSIONS

The chronic polyarthritis occurring in beta-thalassemic trait carriers can be regarded as a true RA similar to that found in Mediterranean countries, possibly characterized by a low prevalence of extra-articular features.

Anti-Sa antibodies: prognostic and pathogenetic significance to rheumatoid arthritis

Anti-Sa antibodies are detected in the serum of 20-47% of patients with rheumatoid arthritis. These antibodies have a high degree of specificity for the disease, and appear to identify a subset of early rheumatoid arthritis patients destined to have aggressive and destructive disease. It has recently been confirmed that anti-Sa antibodies are directed to citrullinated vimentin, thus placing them in the anti-citrulline family of autoantibodies. The Sa antigen has previously been shown to be present in synovium. This, along with the demonstration of citrullinated proteins in rheumatoid synovium, suggests that anti-Sa antibodies may play a pathogenetic role in the initiation and/or persistence of rheumatoid synovitis.