Diagnostic Performance and Predictive Value of Rheumatoid Factor, Anti-citrullinated Peptide Antibodies, and the HLA Shared Epitope for Diagnosis of Rheumatoid Arthritis

Increased IL-33 in synovial fluid and paired serum is associated with disease activity and autoantibodies in rheumatoid arthritis

OBJECTIVES

IL-33, a newly found cytokine which is involved in joint inflammation, could be blocked by a decoy receptor-sST2. The expression and correlation of IL-33 and sST2 in rheumatoid arthritis (RA) are of great interest.

METHODS

Synovial fluid (SF) was obtained from 120 RA and 30 osteoarthritis (OA) patients, and paired sera were collected from 54 of these RA patients. The levels of IL-33 and sST2 were measured by ELISA.

RESULTS

SF IL-33 was significantly higher in RA than in OA, which was correlated with disease activity score 28, erythrocyte sedimentation rate, rheumatoid factor (RF)-IgM, RF-IgG, glucose phosphate isomerase (GPI), and immunoglobulin. Serum IL-33 was correlated positively with SF IL-33 in RA. Furthermore, it was correlated with RF-IgM and GPI. sST2 was partly detectable in RA (13 out of 54, 24.1%), while not in OA. Serum sST2 in RA had no significant correlation with serum IL-33 or SF IL-33. However, SFs from both RA and OA patients did not express sST2.

CONCLUSIONS

This study supported that IL-33 played an important role in the local pathogenesis of RA. Considering the tight correlation between IL-33 and clinical features, it may become a new target of local treatment.

On silico peptide microarrays for high-resolution mapping of antibody epitopes and diverse protein-protein interactions

We have developed a novel, silicon-based peptide array for broad biological applications, including potential for development as a real-time point-of-care platform. We employed photolithography on silicon wafers to synthesize microarrays (Intel arrays), containing every possible overlapping peptide within a linear protein sequence covering the N-terminal tail of human histone H2B. Arrays also included peptides with acetylated and methylated lysine residues reflecting post-translational modifications of H2B. We defined minimum binding epitopes for commercial antibodies recognizing modified and unmodified H2B peptides. We further demonstrated that this platform is suitable for highly sensitive methyltransferase and kinase substrate characterization. Intel arrays also revealed specific H2B epitopes recognized by autoantibodies in individuals with systemic lupus erythematosus (SLE) that have increased disease severity. By combining emerging nonfluorescence-based detection methods with an underlying integrated circuit, we are now poised to create a truly transformative proteomics platform with applications in bioscience, drug development, and clinical diagnostics.

Discovery of serum protein biomarkers in rheumatoid arthritis using MALDI-TOF-MS combined with magnetic beads

The aim of this study was to discover potential biomarkers for rheumatoid arthritis (RA) using Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry combined with magnetic beads. Proteomic fingerprint technology combining magnetic beads with MALDI-TOF-MS was used to profile and compare the proteomes in serum samples from 60 patients with RA, 35 patients with osteoarthritis and 36 healthy controls. The proteomic pattern associated with RA was identified by Biomarker Patterns Software. Model of biomarkers was constructed and evaluated through the Biomarker Patterns Software. A total of 33 discriminative peaks were identified to be related with RA, in which the 5 peaks with the mass-charge ratio (m/z) peaks at 15,715.5, 7,771.4, 8,959.4, 8,469.8 and 8,710.8 Da were used to construct a model for the diagnosis of RA by pattern recognition software. The blind testing data indicated a sensitivity of 86.7% and a specificity of 90.0% in RA diagnosis. These results demonstrated that potential protein biomarkers for RA could be discovered in serum by MALDI-TOF-MS combined with WCX magnetic beads. The diagnosis mode tree based on the five candidate biomarkers could provide a powerful and reliable diagnostic method for RA with high sensitivity and specificity.

Elevated serum interleukin 33 is associated with autoantibody production in patients with rheumatoid arthritis

OBJECTIVE

Interleukin 33 (IL-33) is a novel cytokine involved in joint inflammation in animal models. We analyzed the expression of IL-33 in the serum and synovial fluid of patients with rheumatoid arthritis (RA) and investigated its possible pathophysiological importance.

METHODS

The concentration of IL-33 was measured by ELISA in the serum of 223 patients with RA and 159 controls. Anticyclic citrullinated peptide, rheumatoid factor (RF)-IgA, and RF-IgG were tested by ELISA. Antikeratin antibody and antiperinuclear factor were tested by indirect immunofluorescence assay. Erythrocyte sedimentation rate, C-reactive protein, and immunoglobulins were measured by standard laboratory techniques. The association of IL-33 level with clinical and serologic features of RA was analyzed. We tested the change of IL-33 level following tumor necrosis factor (TNF-α) blockade therapy in 40 patients with RA.

RESULTS

In contrast to almost no detectable IL-33 in osteoarthritis and healthy serum, IL-33 could be detected in 94 out of the 223 RA cases (42.2%). Serum IL-33 concentration was significantly higher in patients with RA than in control groups. The level of serum IL-33 decreased after anti-TNF treatment. The level of serum IL-33 was correlated with the production of IgM and RA-related autoantibodies including RF and anticitrullinated protein antibodies. However, no correlation was found between IL-33 concentration and acute-phase inflammation reactant or the score of the Disease Activity Index, suggesting a complex or indirect character of the link between IL-33 and the inflammation in RA.

CONCLUSION

The level of IL-33 is abnormally elevated in RA serum. The elevation of serum IL-33 was at least partly attributed to excessive TNF-α in RA. IL-33 might be involved in the regulation of autoantibody production in RA.

Correlation of anti-cyclic citrullinated antibody with hand joint erosion score in rheumatoid arthritis patients

BACKGROUND/AIMS

To examine the correlation between radiological joint damage and serological parameters in early rheumatoid arthritis (RA).

METHODS

This retrospective study reviewed the records of 216 patients diagnosed with RA and classified them according to disease duration: group 1, </= 24 months; group 2, > 24 months; and group 3, all patients combined. The extent of joint damage was assessed from plain radiographs using a modified version of the Larsen method and compared among groups.

RESULTS

The mean radiographic joint damage score was significantly higher in patients who had established RA (10.1 points) compared with those who had early RA. In group 1, the inflammatory parameters, erythrocyte sedimentation rate, and C-reactive protein were positively correlated with the joint damage score, but rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibody were not. A subgroup analysis revealed that the anti-CCP positive patients in groups 1 and 2 had greater joint damage scores than did the anti-CCP negative patients, but no difference in RF was observed between subgroups. Anti-CCP positivity was not significantly correlated with joint damage sores in group 3.

CONCLUSIONS

Anti-CCP positivity was significantly correlated with more severe joint damage at diagnosis. A correlation was observed between the radiological joint damage score and inflammatory parameters in early and established RA, indicating that anti-CCP can serve as a diagnostic tool and predict structural joint damage. These findings suggest anti-CCP positive patients should receive aggressive therapeutic intervention.

Contribution of PTPN22 1858T, TNFRII 196R and HLA-shared epitope alleles with rheumatoid factor and anti-citrullinated protein antibodies to very early rheumatoid arthritis diagnosis

OBJECTIVES

To evaluate the predictive value of TNFRII 196R, PTPN22 1858T and HLA-shared epitope (SE) alleles, RFs and anti-citrullinated protein antibodies (ACPAs) for RA diagnosis in a cohort of patients with very early arthritis.

METHODS

We followed up 284 patients who had swelling of at least two joints that had persisted for longer than 4 weeks but had been evolving for <6 months. At 2 yrs, patients were classified as having RA or non-RA rheumatic diseases according to the ACR criteria. Patients were genotyped with respect to TNFRII 196M/R and PTPN22 1858C/T polymorphisms and HLA-SE. The presence of IgA, IgG and IgM RF isotypes and ACPA was sought in sera collected at disease onset.

RESULTS

HLA-SE alleles alone, concomitant presence of TNFRII 196R and PTPN22 1858T alleles, IgA, IgG and IgM RF alone and ACPA were found to be significantly associated with RA diagnosis. Using logistic regression analysis, the concomitant presence of RF and ACPA at disease onset was the best association to predict RA diagnosis. In patients (n = 34) who did not fulfil the ACR criteria for RA at inclusion but who progressed to ACR positivity, the study of the genetic risk markers did not contribute to predict RA diagnosis at 2 yrs.

CONCLUSIONS

PTPN22 1858T, TNFRII 196R and HLA-SE alleles do not improve the predictive value of RF and ACPA for RA diagnosis in our cohort, and do not contribute to an earlier diagnosis in undifferentiated patients initially negative for RF and ACPA.

Anti-citrullinated protein/peptide antibodies (ACPA) in rheumatoid arthritis: specificity and relation with rheumatoid factor

Anti-citrullinated protein/peptide antibodies (ACPA) are highly specific and sensitive markers for rheumatoid arthritis (RA). For instance, for the anti-CCP2 assay, sensitivities ranging from 55% to 80% and specificities ranging from 90% to 98% have been reported. Despite their high specificity, recent reports have suggested that ACPA may be found in some patients with other rheumatic autoimmune diseases, including psoriatic arthritis, systemic lupus erythematosus and Sjögren's syndrome. Also, the differences between the classical rheumatoid factor (RF) and ACPA, as well as the complementarity between both tests have recently been demonstrated more clearly. Indeed, both antibody systems have a different association with specific RA features like extra-articular manifestations, a different association with the HLA shared epitope and, behave differently following anti-TNF therapy.

Prediction models for rheumatoid arthritis during diagnostic investigation: evaluation of combinations of rheumatoid factor, anti-citrullinated protein/peptide antibodies and the human leucocyte antigen-shared epitope

OBJECTIVES

To calculate the probabilities for rheumatoid arthritis in a consecutive cohort of patients during diagnostic investigation. Different logistic regression models evaluating the value of human leucocyte antigen (HLA)-shared epitope determination and testing for rheumatoid factor and anti-citrullinated protein/peptide antibodies (ACPA) were fitted.

METHODS

1003 consecutive patients were included in the study, presenting a new diagnostic problem for which rheumatoid arthritis was included in the differential diagnosis. All patients were tested for ACPA, rheumatoid factor and HLA-shared epitope.

RESULTS

After 1 year, diagnoses were established: 153 patients had definite rheumatoid arthritis and 629 patients had rheumatoid arthritis excluded. Rheumatoid factor, used as a continuous marker, is useful in evaluating the probability for rheumatoid arthritis. Combined rheumatoid factor and shared epitope testing may provide additional predictive information, but combined ACPA and rheumatoid factor testing is superior. The redundancy of shared epitope testing in a model that includes ACPA testing can be explained by the high association between ACPA and shared epitope both in patients with rheumatoid arthritis and in those with non-rheumatoid arthritis. The value of rheumatoid factor testing increased if patients presented with at least one swollen joint at baseline.

CONCLUSION

Valid probabilities for rheumatoid arthritis during routine diagnostic investigation were calculated, and showed that the potential additional value of shared epitope testing disappears when ACPA testing is available. Combined rheumatoid factor and ACPA testing is useful, especially when rheumatoid factor is considered as a continuous parameter reflecting an increasing probability for rheumatoid arthritis at higher rheumatoid factor titres. The value of (continuous) rheumatoid factor testing increases when the a priori chance is higher.

Aberrant Expression of the Autoantigen Heterogeneous Nuclear Ribonucleoprotein-A2 (RA33) and Spontaneous Formation of Rheumatoid Arthritis-Associated Anti-RA33 Autoantibodies in TNF-α Transgenic Mice

Human TNF-alpha transgenic (hTNFtg) mice develop erosive arthritis closely resembling rheumatoid arthritis (RA). To investigate mechanisms leading to pathological autoimmune reactions in RA, we examined hTNFtg animals for the presence of RA-associated autoantibodies including Abs to citrullinated epitopes (anti-cyclic citrullinated peptide), heterogeneous nuclear ribonucleoprotein (hnRNP)-A2 (anti-RA33), and heat shock proteins (hsp) (anti-hsp). Although IgM anti-hsp Abs were detected in 40% of hTNFtg and control mice, IgG anti-hsp Abs were rarely seen, and anti-cyclic citrullinated peptide Abs were not seen at all. In contrast, >50% of hTNFtg mice showed IgG anti-RA33 autoantibodies, which became detectable shortly after the onset of arthritis. These Abs were predominantly directed to a short epitope, which was identical with an epitope previously described in MRL/lpr mice. Incidence of anti-RA33 was significantly decreased in mice treated with the osteoclast inhibitor osteoprotegerin and also in c-fos-deficient mice lacking osteoclasts. Pronounced expression of hnRNP-A2 and a smaller splice variant was seen in joints of hTNFtg mice, whereas expression was low in control animals. Although the closely related hnRNP-A1 was also overexpressed, autoantibodies to this protein were infrequently detected. Because expression of hnRNP-A2 in thymus, spleen, brain, and lung was similar in hTNFtg and control mice, aberrant expression appeared to be restricted to the inflamed joint. Finally, immunization of hTNFtg mice with recombinant hnRNP-A2 or a peptide harboring the major B cell epitope aggravated arthritis. These findings suggest that overproduction of TNF-alpha leads to aberrant expression of hnRNP-A2 in the rheumatoid joint and subsequently to autoimmune reactions, which may enhance the inflammatory and destructive process.

Effect of age on prevalence of anticitrullinated protein/peptide antibodies in polyarticular juvenile idiopathic arthritis

OBJECTIVES

Anticitrullinated protein/peptide antibodies (ACPA) have an excellent diagnostic performance for rheumatoid arthritis (RA). Despite similarities between RA and polyarticular juvenile idiopathic arthritis (JIA), the prevalence of ACPA in polyarticular JIA is low. We wanted to evaluate the influence of age, disease duration and total immunoglobulin G (IgG) concentration on ACPA positivity in this cohort.

METHODS

Patients with JIA were classified according to age and International League of Associations for Rheumatology classification. Sixty-one JIA patients aged less than 16 yr were included and classified as polyarticular JIA (poly JIA <16; n=23) or non-polyarticular JIA (n=38). In addition, a group of 21 polyarticular JIA patients, aged more than 16 yr (poly JIA >16) and a group of 51 RA patients were included. Antibodies to the synthetic citrullinated peptides pepA and pepB were detected by line immunoassay and antibodies to cyclic citrullinated peptides (CCP2) by enzyme-linked immunosorbent assay. Serum IgG was measured by fixed-time immunonephelometry.

RESULTS

No ACPA reactivity was observed in the non-polyarticular group. In poly JIA <16, only 1/23 had anti-CCP2 antibody, whereas in poly JIA >16 patients a significantly higher fraction was detected (6/21). All but one of the anti-CCP2 reactive patients were rheumatoid factor (RF) positive. Assessing anti-CCP2 antibody concentration as a continuous variable, significantly higher titres were found in poly JIA >16 compared with poly JIA <16. No correlation between anti-CCP2 concentration and total IgG was detected. Four patients demonstrated immunoreactivity against pepA and pepB; all of them were anti-CCP2 reactive, poly JIA >16 patients.

CONCLUSIONS

ACPA are present in low prevalence in polyarticular JIA and are particularly found in the RF-positive subset. With age, a significant increase in anti-CCP2 positivity is observed in polyarticular JIA patients.

Sensitive immunoassays for the autoantibodies reacting against citrullinated carboxy-terminal telopeptides of type I and type II collagens in patients with rheumatoid arthritis

We developed sensitive assay methods for autoantibodies recognizing the citrullinated synthetic peptides derived from type I and type II collagens in patients with rheumatoid arthritis (RA). These peptides were tested with the chemiluminescence method (Nichols Advantage