ReviewDiagnostic value of anti-mutated citrullinated vimentin in comparison to anti-cyclic citrullinated peptide and anti-viral citrullinated peptide 2 antibodies in rheumatoid arthritis: An Italian multicentric study and review of the literature
Introduction
In the last years, the diagnostic approach to rheumatoid arthritis (RA), the most common chronic inflammatory joint disease, underwent significant changes. The urgent need to recognize and treat the disease as soon as possible to prevent joint disability allowed the development of a new set of classification criteria for RA to replace the outdated 1987 American College of Rheumatology (ACR) ones [1], [2]. In particular, new criteria have been derived in order to increase sensitivity and specificity for RA diagnosis in an earlier phase and they have been shown to perform a good discriminative ability with respect to the older ones [3]. In the same time, studies pointed to the importance of developing more sensitive and specific early diagnostic and prognostic tests in order to set up the most appropriate treatment according to different disease outcome and course. Rheumatoid factor (RF) is a well established diagnostic and prognostic biomarker for RA and can be detected in 60–80% of patients with established disease [4]. However, it can be detected in other autoimmune disorders, such as Sjögren's syndrome (SS), and in various non autoimmune conditions, including infectious diseases, as well as in healthy subjects. Of importance, RF is not helpful in the diagnosis of RA in its initial phases, being detected in less than 50% of patients with early disease [4]. In this setting, the deeper knowledge of the pathogenic mechanisms underlying synovial rheumatoid damage allowed the identification of a variety of citrullinated proteins that may act as potential autoantigens.
The antibodies specific for citrullinated proteins, that are almost exclusively detectable in RA sera, recognize a variety of citrullinated antigens, including α-enolase, fibrinogen, type II collagen and filaggrin and are collectively identified as ACPA or anti-citrullinated peptide/protein antibodies. Interestingly, high concentrations of ACPA have been detected in RA inflamed synovial tissue as well as synovial fluid [5], thus suggesting their possible role in synovial inflammation.
The most frequently used ELISA assay for ACPA detection is based on cyclic citrullinated peptides (CCP). Anti-CCP antibodies (Abs) have been demonstrated to be as sensitive as RF, but highly specific for RA and more specific than RF in early disease [6]. On the basis of several data confirming their predictive and prognostic role, anti-CCP have been included as new serologic criterion in the 2010 RA classification criteria [1], [7].
Recent studies highlighted the good diagnostic performance of specific Abs targeting two other citrullinated antigens, the viral citrullinated peptide 2 (VCP2), a peptide corresponding to the sequence 338–358 of the Epstein–Barr virus encoded protein 2 (EBNA-2), and MCV, mutated/recombinant citrullinated vimentin. All three anti-VCP2 isotypes have been demonstrated to be a good and sensitive diagnostic tool, being detected almost exclusively in RA patients with respect to control subjects and patients with other autoimmune diseases [8]. Moreover, anti-VCP2 appears to display a high concordance with anti-CCP and results to be associated with a higher risk of erosive disease [8], [9]. Citrullinated vimentin, the antigenic target of anti-Sa antibodies representing a highly specific marker for RA, has been recently identified as a good candidate for RA diagnosis [10]. Vimentin is an intermediate filament widely expressed in the synovium. It is secreted and citrullinated by macrophages undergoing apoptosis, largely present in the RA synovial microenvironment due to impaired clearance [11]. Thus, citrullinated vimentin has been considered a potential autoantigen with possible diagnostic value and an ELISA detecting Abs directed against recombinant MCV (anti-MCV) has been recently developed. Anti-MCV Abs have been suggested to provide a significant adjunctive diagnostic value in early as well as long-standing RA [12]. Moreover, interesting results coming from recent studies suggest that anti-MCV, as already shown for anti-CCP Abs, may be associated with induction and progression of subclinical atherosclerotic damage in early RA patients as detected by ultrasound evaluation of carotid intima-media thickness [13], [14]. Finally, their potential prognostic role in the prediction of disease radiographic progression has been hypothesized in a 10-year prospective study on a large cohort of RA patients [15].
A number of recent studies, investigating the diagnostic performance of anti-MCV Abs with respect to RF and anti-CCP Abs both in early and long-standing RA, reported conflicting results. This may be partly due to study heterogeneity, choice of study population (healthy controls or patients with infectious or other chronic inflammatory diseases) or to disease phase (very early, early or long-standing RA). Overall, both in early and in established RA patients, anti-MCV Abs appear to perform as a slightly more sensitive diagnostic marker with respect to anti-CCP, with 12–15% of anti-CCP negative patients resulting positive for anti-MCV [12], [16], [17]. On the other hand, anti-CCP provides better diagnostic performance in terms of specificity, especially in studies enrolling patients with other inflammatory disease as controls [12], [18]. Moreover, in patients with early as well as established RA, anti-MCV Abs have been reported to be associated with a more active and severe disease and to perform better in classifying patients into broad and narrow responders and in predicting poor radiographic progression with respect to anti-CCP [15], [19], [20], [21]. However, a firm conclusion on the additional clinical and diagnostic utility of anti-MCV in RA with respect to other ACPA cannot be drawn and the limited sample size of population enrolled in the majority of the published studies surely hampers results and data interpretation. Therefore, aim of the present multicenter study was to evaluate the diagnostic performance in RA of the newly developed anti-MCV compared to that of anti-VCP2 and anti-CCP assays in a large cohort of RA patients.
Section snippets
Materials and methods
A total of 512 frozen stored sera from 285 patients with established RA diagnosed according to the 1987 ACR classification criteria [2], 136 patients with other chronic autoimmune/inflammatory or infectious diseases and 91 healthy subjects were evaluated. Patients and controls were randomly selected and collected from 10 Italian Centers belonging to the FIRMA group, an Italian association of experts in the field of autoimmune and chronic inflammatory rheumatic diseases. The disease control
Results
The ROC plot analysis identified a calculated AUC of 0.847 (95% CI, 0.808–0.887) for anti-CCP, 0.873 (95% CI, 0.844–0.903) for anti-VCP2 and 0.821 (95% CI, 0.785–0.858) for anti-MCV (Fig. 1). According to the obtained curves and considering a diagnostically acceptable 95% specificity, the optimal cutoff values resulted 5 (ratio) for anti-CCP, 21 U for anti-VCP2 and 55 U/mL for anti-MCV. Using the calculated cutoff values, sera from 167/285 RA patients (59%) resulted anti-MCV positive. In
Discussion
There is growing evidence that early diagnosis and prompt therapeutic intervention in the course of RA represent an important tool to obtain more efficient disease control, less long-term joint damage and subsequent functional disability and better disease outcome. Therefore, recent research focused on the development of specific laboratory tests to be employed in the early identification of RA with respect to other inflammatory joint disease patients and in the prediction of disease course. In
Take-home messages
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The present study on a large cohort of RA patients showed that, at the recommended cutoff value of 20 U/mL, anti-MCV can be detectable not only in 15% of healthy subjects, but also in a number of patients with chronic inflammatory and autoimmune disorders and infectious diseases, thereby reducing the Ab specificity to 65%.
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At cutoff value of 55 U/mL determined by ROC analysis, the anti-MCV assay showed a diagnostic sensitivity of 59% and a specificity of 92%.
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Results from the our study does not
Acknowledgments
Anti-MCV kits were kindly provided by Technogenetics s.r.l., Gruppo Bouty (Sesto San Giovanni, Milan, Italy) and anti-VCP2 by Astra Diagnostici srl (Milano, Italy) free of costs.
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2017, Immunology LettersCitation Excerpt :In circa 10% of anti-CCP2 negative and 30% of IgM RF seronegative RA patients, anti-MCV can be identified. Taken these findings together, the simultaneous assessment of anti-CCP and anti-MCV may improve the serological diagnostics of RA with a high specificity of approximately 98% [74,26]. Similarly to citrullination, carbamylation is a type of post-translational modifications of proteins, which provide a source of new epitopes that can be recognised as non-self antigens [75].
Analysis of four serum biomarkers in rheumatoid arthritis: association with extra articular manifestations in patients and arthralgia in relatives
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2016, Autoimmunity ReviewsProficiency testing for the detection of anti-citrullinated protein antibody in China
2015, Clinica Chimica ActaCitation Excerpt :With this classification system are positive serologic tests for rheumatoid factor (RF) and anti-citrullinated protein antibody (ACPA) [2]. Of these tests, those for ACPA have a higher sensitivity (88–98%) and a substantially higher specificity (70–80%) than those for RF and other autoantibodies, particularly in terms of early detection of RA [3–6]. In addition, RA can be categorized into 2 subsets based on the ACPA result: ACPA-positive RA which involves a more aggressive and destructive disease course and ACPA-negative RA [7].