Value of laboratory tests in early prediction of rheumatoid arthritis

Rheumatoid factor isotypes in rheumatoid arthritis diagnosis and prognosis: a systematic review and meta-analysis

OBJECTIVE

The first biomarker associated with the rheumatoid arthritis is rheumatoid factor (RF) and since the earliest reports a role has been proposed in the diagnosis and in the prediction of clinical features and outcome. The study of RF isotypes has further attempted to improve diagnostic accuracy and identify specific subgroups of patients. The main objective of this study is to provide an analysis of the literature on the role of RF isotypes in the diagnosis and prognosis of rheumatoid arthritis (RA).

METHODS

We performed a systematic literature review and meta-analysis on the role of RF isotypes in RA (only in English, from PubMed, search terms: "rheumatoid factor isotypes", "diagnosis", "prognosis" and "rheumatoid arthritis", last search 31 July 2022, two independent assessment of quality and biases, results included in tables and in the meta-analysis).

RESULTS

Thirty-six articles were examined (7517 patients). Testing all RF isotypes with latex test or nephelometry allows for the highest sensitivity (68.6%, 95% CI 66.2% to 71.0%); nonetheless, the determination of IgA isotype provides the highest specificity (91.4%, 95% CI 90.8% to 92.0%) and the highest positive likelihood ratio (7.7, 95% CI 5.7 to 10.4). When testing IgM isotype the highest diagnostic OR (21.7, 95% CI 16.1 to 29.3) is reached. When analysing anti-citrullinated protein antibodies, RF isotype determination increases diagnostic accuracy. On the other hand, these do not provide relevant prognostic information, as results are conflicting.

CONCLUSIONS

Testing RF allows the highest sensitivity, while IgA isotype the highest specificity and positive likelihood ratio for RA diagnosis. On the other hand, determination of RF isotypes dose not allow prognostic information, as data are limited and heterogeneous.

Utility of Opportunistic Infections, Joints' Involvement and Accuracy of Various Screening Tests to Diagnose Rheumatoid Arthritis Patients

Background and Objectives: Rheumatoid Arthritis (RA) is an auto-immune disease in which the body mistakenly considers some parts of its own system as pathogens and attacks them. Prevalence is approximately 0.75% in India. About 40% of the diseased become work disabled within 5 years from the onset of symptoms. The objective of this paper is to assess the sign/symptoms, joints' involvement, difficulties in daily activities and screening accuracy of serology tests of clinically suspected RA patients. Material and Methods: A cross-sectional cohort study design was conducted on two hundred ninety clinically suspected subjects who were referred by different OPDs of hospitals for screening. The profiles of study subjects were carried through a semi-structured, pre-tested schedule method. About 2 mL of blood samples were collected in a plain vial from each patient and tested for diagnostic tests RF, CRP and AntiCCP by using RF-Latex, CRP Latex and ELISA method, respectively, by the laboratory persons. Results: Joint pain shows to be a leading problem in RA as compared to other signs and symptoms. The majority of the study subjects suffer from knee problems (62%). Approximately equal numbers of RA-positive cases were screened by RF and AntiCCP tests. The CRP test screened about one-third of cases. CRP+ AntiCCP, RF+ AntiCCP and RF + CRP all have good sensitivity, and RF+ AntiCCP + CRP has a very high sensitivity for diagnosing RA. Conclusions: This study found that a substantiation of a major proportion of clinically suspected RA patients were suffering from knee pain. Predication of AntiCCP increased the possibility for the diagnosis of RA. However, RF was also moderately related to the diagnosis of RA, and the combination of both tests was more valuable.

Serum metabolomic and lipidomic profiling identifies diagnostic biomarkers for seropositive and seronegative rheumatoid arthritis patients

BACKGROUND

Diagnosing seronegative rheumatoid arthritis (RA) can be challenging due to complex diagnostic criteria. We sought to discover diagnostic biomarkers for seronegative RA cases by studying metabolomic and lipidomic changes in RA patient serum.

METHODS

We performed comprehensive metabolomic and lipidomic profiling in serum of 225 RA patients and 100 normal controls. These samples were divided into a discovery set (n = 243) and a validation set (n = 82). A machine-learning-based multivariate classification model was constructed using distinctive metabolites and lipids signals.

RESULTS

Twenty-six metabolites and lipids were identified from the discovery cohort to construct a RA diagnosis model. The model was subsequently tested on a validation set and achieved accuracy of 90.2%, with sensitivity of 89.7% and specificity of 90.6%. Both seropositive and seronegative patients were identified using this model. A co-occurrence network using serum omics profiles was built and parsed into six modules, showing significant association between the inflammation and immune activity markers and aberrant metabolism of energy metabolism, lipids metabolism and amino acid metabolism. Acyl carnitines (20:3), aspartyl-phenylalanine, pipecolic acid, phosphatidylethanolamine PE (18:1) and lysophosphatidylethanolamine LPE (20:3) were positively correlated with the RA disease activity, while histidine and phosphatidic acid PA (28:0) were negatively correlated with the RA disease activity.

CONCLUSIONS

A panel of 26 serum markers were selected from omics profiles to build a machine-learning-based prediction model that could aid in diagnosing seronegative RA patients. Potential markers were also identified in stratifying RA cases based on disease activity.

Cohort profile: SCREEN-RA: design, methods and perspectives of a Swiss cohort study of first-degree relatives of patients with rheumatoid arthritis

PURPOSE

Rheumatoid arthritis (RA) is an insidious autoimmune disease, with an immunological onset years before diagnosis. Early interventions in preclinical stages could prevent or minimise the progression towards irreversible joint damage. The SCREEN-RA cohort (Evaluation of a SCREENing strategy for Rheumatoid Arthritis) aims to characterise the preclinical stages of the disease, to identify environmental risk factors, and to discover or validate novel biomarkers predictive for RA development.

PARTICIPANTS

SCREEN-RA includes an at-risk population for RA, namely first-degree relatives of patients with established RA.

FINDINGS TO DATE

The cohort started in 2009 is composed of mostly asymptomatic healthy individuals (total n=1458, 7262 person-years), with a mean age of 44 years at enrolment, 74% female and 91% Caucasian ethnicity. During the study period, 16 participants have developed RA. All participants provide baseline serum, DNA and RNA samples, and in a subset, stool samples and oral examination are performed for microbiota assessment. At enrolment, 10% of participants had asymptomatic autoimmunity associated with RA (n=147), 10% presented 'clinically suspect arthralgias' (n=143) and 3% reported arthralgias in conjunction with autoimmunity or high genetic risk (n=51). Studies with this cohort have uncovered risk factors for RA development, such as female hormonal factors, poor oral health or intestinal dysbiosis.

FUTURE PLANS

Future directions include immunological and 'multiomics' approaches to discover new biological markers of progression towards RA, as well as testing preventive interventions in 'high-risk' population.

Optical Biosensors for the Detection of Rheumatoid Arthritis (RA) Biomarkers: A Comprehensive Review

A comprehensive review of optical biosensors for the detection of biomarkers associated with rheumatoid arthritis (RA) is presented here, including microRNAs (miRNAs), C-reactive protein (CRP), rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA), interleukin-6 (IL-6) and histidine, which are biomarkers that enable RA detection and/or monitoring. An overview of the different optical biosensors (based on fluorescence, plasmon resonances, interferometry, surface-enhanced Raman spectroscopy (SERS) among other optical techniques) used to detect these biomarkers is given, describing their performance and main characteristics (limit of detection (LOD) and dynamic range), as well as the connection between the respective biomarker and rheumatoid arthritis. It has been observed that the relationship between the corresponding biomarker and rheumatoid arthritis tends to be obviated most of the time when explaining the mechanism of the optical biosensor, which forces the researcher to look for further information about the biomarker. This review work attempts to establish a clear association between optical sensors and rheumatoid arthritis biomarkers as well as to be an easy-to-use tool for the researchers working in this field.

Periodontal status correlates with anti-citrullinated protein antibodies in first-degree relatives of individuals with rheumatoid arthritis

AIM

To evaluate periodontal status in first-degree relatives of patients with rheumatoid arthritis (FDR-RA) and detect correlation with the presence of anti-citrullinated protein antibodies (ACPAs).

MATERIALS AND METHODS

Rheumatologic status and periodontal status were evaluated in a nested case-control study of FDR-RA with no diagnosis of RA at enrolment. The following parameters were assessed in 34 ACPA-positive (ACPA+) and 65 ACPA-negative (ACPA-) subjects: gingival index (GI), plaque index (PI), probing depth (PD), bleeding on probing (BOP) and clinical attachment level (CAL). We compared the two groups using conditional logistic regression.

RESULTS

In ACPA+ individuals, the mean, PD, BOP, CAL and number of sites per person with PD > 4 mm and BOP were significantly higher compared to the ACPA- group. All ACPA+ subjects had periodontitis: 44.1% presenting moderate and 47.1% severe periodontitis. ACPA- subjects had mainly mild (30.8%) and moderate (27%) periodontitis, differences being significantly different for both moderate periodontitis (p = 0.001) and severe periodontitis (p < 0.001). In multivariable analyses, ACPA status (p = 0.04) and age (p = 0.002) were significantly and independently associated with periodontal conditions.

CONCLUSION

High prevalence and severity of periodontitis in FDR-RA was associated with seropositivity to ACPAs. This further strengthens the hypothesis that periodontitis may be a risk factor in the development of RA.

Antibody modified gold nanoparticles for fast colorimetric screening of rheumatoid arthritis

Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic joint inflammation and one of the main causes of chronic disability worldwide with high prevalence in the ageing population. RA is characterized by autoantibody production, synovial inflammation and bone destruction, and the most accepted biomarker is rheumatoid factor (RF) autoantibodies. In this work, we developed a low-cost approach for the detection and quantification of the RF marker. This colorimetric immunosensor is based on gold nanoprobe crosslinking that results in extensive aggregation in the presence of the pentameric IgM RF. Aggregation of the nanoconjugates yields a color change from red to purple that can be easily observed by the naked eye. The interaction between nanoconjugates and the specific target was confirmed via dynamic light scattering (DLS), Raman spectroscopy and atomic force microscopy (AFM) imaging. This conceptual system shows a LOD of 4.15 UA mL^-1 IgM RF (clinical threshold is set for 20 IU mL^-1). The one-step biosensor strategy herein proposed is much faster than conventional detection techniques, without the need for secondary antibodies, additional complex washing or signal amplification protocols. To the best of our knowledge this is the first report on target induced aggregation of gold nanoprobes for quantitative colorimetric autoantibody detection.

Diagnostic accuracy of anti-keratin antibody for rheumatoid arthritis: a meta-analysis

OBJECTIVES

Anti-keratin antibody (AKA) is a serum antibody for patients with rheumatoid arthritis (RA), and it has a high specificity. Diagnostic role of AKA in RA was evaluated in this study.

METHODS

PubMed, EMBASE, and Web of Science were searched to acquire eligible studies. Articles published before 15 March 2018 were considered to be included. Quality Assessment of Diagnostic Accuracy Studies 2 was used to evaluate the risk of bias and application concern of the included articles. Pooled analysis of diagnostic indicators of AKA for RA was conducted by using a random effects model. Subgroup analysis was employed to explore the potential influencing factors. RevMan 5.3, Stata 11.0, and Meta-DiSc 1.4 software were used in this study.

RESULTS

A total of 15 studies (2350 positive and 2067 negative participants) were included. The pooled sensitivity was 0.46 (95% CI 0.44-0.48), pooled specificity was 0.94 (95% CI 0.93-0.95), and pooled diagnostic odds ratio was 15.86 (95% CI 9.48-26.52). In addition, the area under the curve was 0.7194.

CONCLUSIONS

The current evidence indicated that AKA has high diagnostic specificity in RA and may be useful for RA diagnostic application in clinic.

History and Diagnostic Value of Antibodies to Citrullinated Proteins in Rheumatoid Arthritis

Rheumatoid arthritis is a chronic inflammatory joint disease characterized by the presence of autoantibodies. The best known autoantibody is the rheumatoid factor. Another group of antibodies directed against citrullinated epitopes is proven to be more specific for rheumatoid arthritis. This review gives an overview of the history of the different anti-citrullinated protein antibody detection methods and their diagnostic and prognostic properties in RA.

Anti-cyclic citrullinated peptide antibodies in children with Juvenile Idiopathic Arthritis

AIM

The purpose of present study was to access the prevalence of anti-cyclic citrullinated peptide (anti-CCP) antibodies in children with Juvenile Idiopathic Arthritis (JIA), and to investigate the clinical significance and diagnostic value of the anti-CCP antibodies in correlation with age, sex & activity.

METHODS

This case-control study was performed on 50 patients with JIA in addition to 40 sex and age-matched children as a control group. The participants were recruited from rheumatology Outpatient Clinic of Cairo University Specialized Pediatric Hospital. Patients were subjected to full history taking, clinical examination, routine laboratory investigations and x-rays on involved joints. Both patients and controls underwent assay of anti-CCP antibodies by AxSYM Anti-CCP IgG Microparticle Enzyme Immunoassay (MEIA) which is a semi-quantitative determination of the IgG class of autoantibodies specific to cyclic citrullinated peptide (CCP) in patients' serum or plasma. Data were analyzed using Mann-Whitney U test, ANOVA, and independent-samples t-test by SPSS version 15.

RESULTS

Anti-CCP positivity was identified amongst patients with JIA, particularly those JIA patients experiencing RF positive polyarticular disease onset. Above all, it is important that anti-CCP positivity and bone erosions, degree of joint damage, and ESR levels were significantly correlated.

CONCLUSION

Anti-CCP could be utilized as a valuable marker in the polyarticular form of JIA to direct early, and could be aggressive therapeutic intervention.

Association of susceptible genetic markers and autoantibodies in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disorder of unknown aetiology resulting in inflammation of the synovium, cartilage and bone. The disease has a heterogeneous character, consisting of clinical subsets of anti-citrullinated protein antibody (ACPA)-positive and APCA-negative disease. Although, the pathogenesis of RA is incompletely understood, genetic factors play a vital role in susceptibility to RA as the heritability of RA is between 50 and 60%, with the human leukocyte antigen (HLA) locus accounting for at least 30% of overall genetic risk. Non-HLA genes, i.e. tumour necrosis factor-α (TNF-α) within the MHC (major histocompatibility complex) have also been investigated for association with RA. Although, some contradictory results have originated from several studies on TNF-α gene, the data published so far indicate the possible existence of TNF-α gene promoter variants that act as markers for disease severity and response to treatment in RA. The correlation of HLA and non-HLA genes within MHC region is apparently interpreted. A considerable number of confirmed associations with RA and other autoimmune disease susceptibility loci including peptidylarginine deiminase type 4 (PADI4), protein tyrosine phosphatase non-receptor type 22 (PTPN22), signal transducer and activator of transcription (STAT4), cluster of differentiation 244 (CD244) and cytotoxic T lymphocyte-associated antigen 4 (CTLA4), located outside the MHC have been reported recently. In this review, we aim to give an update on recent progress in RA genetics, the importance of the combination of HLA-DRB1 alleles, non-HLA gene polymorphism, its detection and autoantibodies as susceptibility markers for early RA disease.

Prediction of future rheumatoid arthritis

Rheumatoid arthritis (RA) results from an interaction between genetic susceptibility and environmental factors. Several of these factors are known, such as family history of RA, high birth weight, smoking, silica exposure, alcohol nonuse, obesity, diabetes mellitus, rheumatoid factor, anti-citrullinated protein antibody, and genetic variants such as the shared epitope and protein tyrosine phosphatase nonreceptor type 22. The impact of these factors can be modeled in the 2 main groups at risk of RA: family members of patients with RA and seropositive persons with or without arthralgia. Current models have the potential to select individuals for preventive strategies.

Australian and New Zealand national evidence-based recommendations for the investigation and follow-up of undifferentiated peripheral inflammatory arthritis: an integration of systematic literature research and rheumatological expert opinion

AIM

To develop Australian and New Zealand (ANZ) recommendations for the investigation and follow-up of undifferentiated peripheral inflammatory arthritis (UPIA) using an evidence-based approach.

METHODS

Ten questions pertaining to the investigation and follow-up of patients with UPIA in daily rheumatological practice were defined by clinicians using a modified Delphi approach. A systematic literature search was conducted for each of the final questions. The results were presented to a workshop of 54 ANZ rheumatologists in May 2009. Discussions were held to develop consensus statements for each question, based on published evidence and clinical experience/expertise.

RESULTS

Ten recommendations were made on diagnostic value of clinical features in the patient's history and examination, predictors of poor prognosis and persistence, synovial fluid analysis, serology, imaging and human leukocyte antigen B27 testing. The lack of specific research to inform recommendations presented a challenge. Dynamic discussion groups outlined individual experience in areas without good quality clinical trial evidence. The median strength of support for the final set of recommendations was 7/10 (interquartile range 6-8), ranging from 6 to 9 for individual statements.

CONCLUSION

Ten ANZ recommendations for the investigation and follow-up of UPIA were formulated, based on available evidence and extensive clinical experience. The systematic literature review was of limited value while animated discussion of individual experience, with subsequent information exchange, highlighted the importance of merging clinical expertise with published literature to establish practical recommendations that can improve quality of care in rheumatology.

Multinational evidence-based recommendations on how to investigate and follow-up undifferentiated peripheral inflammatory arthritis: integrating systematic literature research and expert opinion of a broad international panel of rheumatologists in the 3E Initiative

Objective

To develop evidence-based recommendations on how to investigate and follow-up undifferentiated peripheral inflammatory arthritis (UPIA).

Methods

697 rheumatologists from 17 countries participated in the 3E (Evidence, Expertise, Exchange) Initiative of 2008–9 consisting of three separate rounds of discussions and modified Delphi votes. In the first round 10 clinical questions were selected. A bibliographic team systematically searched Medline, Embase, the Cochrane Library and ACR/EULAR 2007–2008 meeting abstracts. Relevant articles were reviewed for quality assessment, data extraction and synthesis. In the second round each country elaborated a set of national recommendations. Finally, multinational recommendations were formulated and agreement among the participants and the potential impact on their clinical practice was assessed.

Results

A total of 39 756 references were identified, of which 250 were systematically reviewed. Ten multinational key recommendations about the investigation and follow-up of UPIA were formulated. One recommendation addressed differential diagnosis and investigations prior to establishing the operational diagnosis of UPIA, seven recommendations related to the diagnostic and prognostic value of clinical and laboratory assessments in established UPIA (history and physical examination, acute phase reactants, autoantibodies, radiographs, MRI and ultrasound, genetic markers and synovial biopsy), one recommendation highlighted predictors of persistence (chronicity) and the final recommendation addressed monitoring of clinical disease activity in UPIA.

Conclusions

Ten recommendations on how to investigate and follow-up UPIA in the clinical setting were developed. They are evidence-based and supported by a large panel of rheumatologists, thus enhancing their validity and practical use.

Prevalence of anti cyclic citrullinated peptide antibodies in Malaysian rheumatoid arthritis patients and its correlation with disease activity

AIM

The objectives of this study are to provide data regarding the prevalence of anti-cyclic citrullinated peptide (CCP) antibodies in Malaysian rheumatoid arthritis (RA) patients and to correlate the levels of anti-CCP antibody with the Disease Activity Score (DAS).

METHOD

We studied the prevalence of anti-CCP antibodies in 51 RA patients attending our clinic and 29 controls. We also looked for correlation between anti-CCP antibody levels with the DAS and parameters such as duration of disease, rheumatoid factor (RF) and disease-modifying anti rheumatic drug (DMARD) usage.

RESULTS

None of the controls demonstrated anti-CCP antibodies. Forty-one out of 51 patients (80.4%) were positive for anti-CCP antibodies. Sensitivity and specificity were 80.4% and 100% respectively in this study. Anti-CCP levels correlated significantly with rheumatoid factor, but no correlation was observed with the other parameters.

CONCLUSIONS

Anti-CCP antibody is prevalent in Malaysian RA patients at 80.4% and more sensitive than RF in our cohort of established RA patients. Even though the anti-CCP levels correlated with RF, it did not show correlation with DAS.

Meta-analysis: diagnostic value of serum anti-mutated citrullinated vimentin antibodies in patients with rheumatoid arthritis

Conventional tests are not always helpful in making a diagnosis of rheumatoid arthritis (RA). This study aimed to comprehensively and quantitatively summarize the evidence on the accuracy of anti-mutated citrullinated vimentin (MCV) assay in the diagnosis of RA. A comprehensive meta-review of data on the accuracy of MCV concentrations in the diagnosis of RA were carried out from 16 published studies. Furthermore, receiver operating characteristic curves were used to summarize the overall test performance. The summary estimates for MCV in the diagnosis of RA were: sensitivity 0.77 [95% confidence interval (CI) 0.75-0.78], specificity 0.89 (95% CI 0.87-0.90), positive likelihood ratio (LR+) 7.24 (95% CI 5.60-9.36), negative likelihood ratio (LR-) 0.28 (95% CI 0.23-0.34) and diagnostic odds ratio 29.66 (95% CI 21.09-41.71). The area under the summary receiver operating characteristic curves was 0.92. Data from meta-analysis suggest the accuracy of MCV assay in the diagnosis of RA is high, but ultimately clinician must consider the results of MCV tests combing with other conventional examinations and the clinical feature.

Anti-CCP2 is an adjunct to, not a surrogate for, rheumatoid factor in the diagnosis of rheumatoid arthritis: diagnostic utility of anti-CCP2 antibodies in Egyptian patients with rheumatoid arthritis

OBJECTIVES

To examine the diagnostic utility of the second generation of anti-cyclic citrullinated peptide (anti-CCP2) antibodies versus rheumatoid factor (RF) in rheumatoid arthritis (RA), and to study the association between anti-CCP2 and RA disease parameters.

METHODS

Fifty consecutive Egyptian patients with RA, 37 patients with other rheumatic diseases, and 10 healthy controls were recruited for testing for anti-CCP2 and immunoglobulin M (IgM) rheumatoid factor (RF). Assessment measures included the Disease Activity Score (DAS28) for disease activity, the Health Assessment Questionnaire - Disability Index (HAQ-DI) for disability and the Short Erosion Narrowing Score (SENS) for radiological damage.

RESULTS

The sensitivities of anti-CCP2 and IgM-RF in RA patients were 70% and 52%, with specificities of 91.5% and 89.4%, respectively. There was 73.2% agreement between anti-CCP2 and RF for all groups tested (kappa = 0.42, p<0.001) but agreement was only 66% for RA patients (kappa = 0.31, p<0.05). Anti-CCP2 had superior diagnostic properties [sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV)] than RF, but using both RF and anti-CCP2 enhanced the sensitivity to 78%, when either test was positive, and the specificity to 100%, with a PPV of 1, when both tests were positive. Anti-CCP2 titre was significantly correlated with disease severity [rheumatoid nodules, rheumatoid factor (RF), and radiological damage] and HAQ-DI (p<0.05) but not with parameters of disease activity.

CONCLUSION

Anti-CCP2 has superior diagnostic and prognostic properties in RA compared with RF. It should not replace RF as a serological test; however, since using both tests modestly increases sensitivity and markedly enhances specificity, so that diagnosis of RA is highly probable when both tests are positive.

The ESPOIR cohort: a ten-year follow-up of early arthritis in France: methodology and baseline characteristics of the 813 included patients

OBJECTIVES

The French Society of Rheumatology initiated a large national multicenter, longitudinal and prospective cohort, the so-called "ESPOIR cohort study" in order to set up databases to allow various investigations on diagnosis, prognostic markers, epidemiology, pathogenesis and medico-economic factors in the field of early arthritis and rheumatoid arthritis.

METHODS

Patients were recruited if they had undifferentiated arthritis or rheumatoid arthritis, of less than 6 months disease duration and if they were DMARD and steroids naïve. Patients have then to be followed every 6 months during the first 2 years then every year during at least 10 years. Clinical, biological, radiographic and medico-economic databases have been constituted to fit in the different objectives of the project and more than 20 scientific studies have already been accepted by the scientific committee.

RESULTS

813 patients were included (76.75% were female). The mean age was 48.07+/-12.55 years. The mean delay from the onset of symptoms to referral to the rheumatologist was 74.8+/-76.6 days. Baseline swollen and tender joint counts were 7.19+/-5.37 and 8.43+/-7.01; DAS28 score was 5.11+/-1.31. CRP was abnormal in 38.9% of the patients; 44.2%, 45.8% and 38.8% had respectively IgM rheumatoid factor (RF), IgA RF and anti-CCP antibodies. HLA DRB1*01 or 04 genes were found in 56.7% of them. Finally, 22% of these patients had erosions on hand or feet at baseline.

Autoantibodies to intracellular autoantigens and their B-cell epitopes: molecular probes to study the autoimmune response

A common laboratory finding in systemic autoimmune diseases is the presence of autoantibodies against intracellular autoantigens. Although their pathogenesis is not fully understood, autoantibodies are important tools for establishing diagnosis, classification, and prognosis of autoimmune diseases. Autoantibodies mainly target multicomponent complexes containing both protein antigens and (ribo)-nucleic acid(s), such as the spliceosome or Ro/La RNPs. In this review, we address the main characteristics and the clinical value of the main autoantibody types with respect to their disease association, and we describe the corresponding autoantigens, their biologic function, and their B-cell antigenic determinants (epitopes). The structural characteristics and clinical associations of these epitopes, and their utility as tools to investigate the autoimmune response, are discussed in detail. New insights into the pathogenetic role of epitopes in systemic autoimmunity are also examined. In this regard, using the defined structures of the B-cell antigenic epitopes, complementary epitopes can be designed according to the "molecular recognition" theory. These complementary epitopes can be used as probes to study pathogenetic and immunoregulatory aspects of the anti-idiotypic response. The origin of humoral autoimmunity and the spreading of the epitopes in systemic lupus erythematosus are also discussed. Finally, the ability of post-translational modifications to induce autoreactive immune attack via the generation of neo-epitopes is summarized.

In chronic idiopathic urticaria autoantibodies against Fc epsilonRII/CD23 induce histamine release via eosinophil activation

BACKGROUND

Chronic idiopathic urticaria is a common skin disorder characterized by recurrent, transitory, itchy weals for more than 6 weeks. An autoimmune origin has been suggested based on the findings of auto-antibodies (Abs) directed against either the alpha subunit of the high-affinity IgE receptor or the IgE molecule in nearly half of the patients.

OBJECTIVE

To identify other autoantigen targets in patients with chronic idiopathic urticaria.

METHODS

We used pooled IgG derived from 133 patients with chronic idiopathic urticaria to screen a random peptide library to identify disease-relevant autoantigen peptides. Among the identified peptides, one was recognized by the vast majority of patients' sera. Abs against this peptide were affinity purified from the patients' sera and assayed for their ability to induce histamine release from basophils.

RESULTS

We identified a peptide that showed similarity with the low-affinity IgE receptor (Fc epsilonRII/CD23) expressed on lymphomonocytes and eosinophils. Anti-peptide IgG Abs purified from the patients' sera bound cell surface CD23 and were able to induce histamine release from basophils. This effect appeared to be mediated by the release of major basic protein from eosinophils upon engagement of CD23. The same effects were obtained with the sera from mice immunized with the CD23 peptide.

CONCLUSION

Our results indicate that patients with chronic idiopathic urticaria have Abs against CD23 and that eosinophils, which infiltrate the skin of these patients, play a crucial role in maintaining the disease through the release of major basic protein upon engagement of the low-affinity IgE receptor by such auto-Abs.

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.

Genetic and genomic studies of PADI4 in rheumatoid arthritis

OBJECTIVES

Strong genetic association of rheumatoid arthritis (RA) with PADI4 (peptidyl arginine deiminase) has previously been described in Japanese, although this was not confirmed in a subsequent study in the UK. We therefore undertook a further study of genetic association between PADI4 and RA in UK Caucasians and also studied expression of PADI4 in the peripheral blood of patients with RA.

METHODS

Seven single-nucleotide polymorphisms (SNP) were genotyped using polymerase chain reaction (PCR)-restriction fragment length polymorphism in 111 RA cases and controls. A marker significantly associated with RA (PADI4_100, rs#2240339) in this first data set (P = 0.03) was then tested for association in a larger group of 439 RA patients and 428 controls. PADI4 transcription was also assessed by real-time quantitative PCR using RNA extracted from peripheral blood mononuclear cells from 13 RA patients and 11 healthy controls.

RESULTS

A single SNP was weakly associated with RA (P = 0.03) in the initial case-control study, a single SNP (PADI4_100) and a two marker haplotype of that SNP and the neighbouring SNP (PADI4_104) were significantly associated with RA (P = 0.02 and P = 0.03 respectively). PADI4_100 was not associated with RA in a second sample set. PADI4 expression was four times greater in cases than controls (P = 0.004), but expression levels did not correlate with the levels of markers of inflammation.

CONCLUSION

PADI4 is significantly overexpressed in the blood of RA patients but genetic variation within PADI4 is not a major risk factor for RA in Caucasians.

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.

Evaluating inflammatory joint disease: how and when can autoantibodies help?

The diagnosis of inflammatory joint disease rests on a constellation of symptoms, signs, laboratory test results and, occasionally, histological findings. Classification criteria have been developed by national learned societies, international panels of experts or, more rarely, an expert working alone. These criteria are intended to provide a common language for therapeutic trials and international publications. Yet, they are often inappropriately used as diagnostic tools for the individual patient. Identification of an early seroimmunologic marker with high sensitivity and specificity for classifying patients with recent-onset joint disease is a daunting challenge. Test performance characteristics such as sensitivity, specificity, positive and negative predictive values, and the positive or negative likelihood ratio help to assess the diagnostic usefulness of a laboratory test in a specific situation. The difference between the pretest and posttest likelihoods of obtaining a positive or negative result measures the usefulness, or performance, of a laboratory test in a specific situation according to the prevalence of the disease. A higher positive likelihood ratio indicates a more useful test. In a patient with inflammatory joint disease, the diagnosis can be sought by assaying a limited number of autoantibodies according to a decision tree. Thus, IgM rheumatoid factors (latex test or ELISA) and antibodies to filaggrin or other citrullinated proteins (antikeratin antibodies by indirect immunofluorescent assay or anticyclic citrullinated peptides by ELISA) identify more than 70% of cases of early rheumatoid arthritis with greater than 98% specificity. If these markers are negative, testing for antinuclear antibodies by indirect immunofluorescent assay on HEp-2 cells identifies 99% of cases of lupus and progressive systemic sclerosis. Confirmation of the diagnosis can be obtained by characterizing the autoantibodies: thus, presence of antidouble-stranded DNA (dsDNA, by the Farr radioimmunoassay, indirect immunofluorescent assay on Crithidia luciliae, or ELISA (IgG)) or of antinucleosome antibodies (ELISA) indicates lupus, whereas anticentromere, antitopoisomerase I (Scl 70), and antinucleolar antibodies point to progressive systemic sclerosis. A positive test for antibodies to soluble nuclear antigens of the U1 RNP type suggests mixed connective tissue disease or lupus but may indicate scleroderma. Anti-Sm antibodies are found in fewer than 10% of lupus patients but are highly specific. Anti-SSA (Ro) and anti-SSB (La) suggest lupus or primary Sjögren's syndrome. When tests are negative for ANA, several antibodies to cytoplasmic organelles are valuable diagnostic tools, such as anti-J01 for polymyositis syndromes and antiribosome antibodies for lupus, although their sensitivity is modest (20-25%). Finally antineutrophil cytoplasmic antibodies (ANCAs) ensure the diagnosis of small-vessel vasculitides, which often involve the lungs and kidneys. Thus, in diffuse Wegener's granulomatosis, ANCAs exhibiting the classic cytoplasmic pattern and corresponding by ELISA to anti-PR3 are found. In microscopic polyangiitis the ANCAs are peripheral and correspond by ELISA to antimyeloperoxidase antibodies. Tests for other antibodies are less often needed to evaluate inflammatory joint disease.

Clinical utility of the anti-CCP assay in patients with rheumatic diseases

OBJECTIVES

To determine the frequency of antibodies to cyclic citrullinated peptides (CCP) in a group of patients with a diversity of rheumatic diseases.

METHODS

249 consecutive sera from an arthritis clinic sent for rheumatology testing were selected for testing with the anti-CCP2 assays and for the presence of rheumatoid factor (RF). Patient charts were reviewed for demographic information, clinical diagnosis, radiographic information, and other laboratory data.

RESULTS

The sensitivity and specificity of anti-CCP reactivity for the diagnosis of rheumatoid arthritis (RA) were 66.0% and 90.4%, respectively. This compared with the sensitivity and specificity of RF for RA at 71.6% and 80.3%. Furthermore, 10/29 (34%) RF- patients with RA demonstrated reactivity to CCP. The presence of either anti-CCP or RF increased testing sensitivity for diagnosis of RA to 81.4%; the presence of both RF and anti-CCP demonstrated a testing specificity similar to that of anti-CCP reactivity alone for the diagnosis of RA (91.1%).

CONCLUSIONS

The detection of anti-CCP is useful for the diagnosis of RA, in fact even more so than RF, because of its higher specificity.

Genotypes and phenotypes: should genetic markers and clinical predictors drive initial treatment decisions in rheumatic diseases?

Using patients' genetic and phenotypic profiles to identify the best available drug therapy for individual cases remains a clinical aspiration. Considerable recent research has developed this theme in rheumatoid arthritis (RA). Seven reports have evaluated how the high-risk epitope and other genes influence RA susceptibility and severity. There is strong evidence that the shared epitope influences susceptibility, but inconclusive evidence concerning whether it effects severity. The interleukin-1 gene cluster and IL-4/IL-4 genes influence erosive disease, but their effects are mainly in late RA. A further ten studies examined links with erosive disease. Fewer reports evaluated phenotypes: six studies examined outcome predictions using rheumatoid factor and antikeratin/anticyclic citrullinated peptide antibodies and two looked at conventional clinical measures. Anticyclic citrullinated peptide antibodies are useful in establishing the diagnosis of RA, but rheumatoid factor potentially provides the most useful prognostic information. The value of genotyping RA patients in defining their clinical course and determining the most suitable treatment remains unproven.

Clinical epidemiology: diagnostic and prognostic tests

Recent studies of diagnostic and prognostic tests have commonly examined serological tests and new imaging techniques. Antifilaggrin antibodies have been found to be highly specific for the diagnosis of rheumatoid arthritis (RA), but uncertainty remains about the sensitivity of this test, particularly in early RA. Magnetic resonance imaging and ultrasound continue to be explored as methods to detect synovitis and erosions in RA. Several recent studies have confirmed the association between the human leukocyte antigen DRB1 shared epitope and worse radiographic outcomes in patients with RA. Interlaboratory variation in detecting autoantibodies remains a concern, as does overuse of tests for antineutrophil cytoplasmic autoantibodies.