Rheumatoid Factors

Comparison of the analytical and clinical performances of four anti-cyclic citrullinated peptide antibody assays for diagnosing rheumatoid arthritis

INTRODUCTION/OBJECTIVES

Anti-cyclic citrullinated peptide antibody (anti-CCP) is one of the most important serologic markers for diagnosing rheumatoid arthritis (RA). This study aimed to compare the analytical and clinical performances of the second- and third-generation anti-CCP assays.

METHODS

Four automated anti-CCP assays were evaluated: Chorus anti-CCP (Diesse Diagnostica), Elecsys anti-CCP (Roche Diagnostics), Atellica® IM anti-CCP IgG (Siemens Healthineers), and Quanta Flash® CCP3 (Inova Diagnostics Inc.). Analytical performance included the precision, linearity, correlation, and concordance rate. For evaluating the clinical performance, 240 patient samples (120 positive and 120 negative samples, determined by the Chorus anti-CCP assay) were used, including those with a diagnosis of RA (n = 132) and non-RA (n = 108). Using receiver operating characteristic (ROC) curve analysis, the sensitivity and specificity were evaluated.

RESULTS

All four assays that were evaluated showed good precision and linearity, and their correlation and concordance rates were in acceptable ranges. The area under the curve (AUC) values ranged from 0.888 to 0.914, showing a good diagnostic performance. The sensitivity and specificity of all assays were similar (88.0-97.2%).

CONCLUSIONS

All four anti-CCP assays showed good analytical and diagnostic performances for diagnosing RA. After adjusting the cutoff values, these assays are expected to show enhanced sensitivity and specificity. Key Points • Previous studies have described the diagnostic performance of a few immunologic markers in RA diagnosis, but nothing has been proven to be sufficiently good in clinical practice. • All four automated anti-CCP assays showed good analytical and diagnostic performances for diagnosing RA in clinical practice. • After adjusting the cutoff values, these assays are expected to show enhanced sensitivity and specificity. • The present study provides reassuring evidence that any of the studied commercially available anti-CCP tests for detecting rheumatoid arthritis provide similar diagnostic information to institutions that adopt these specific testing systems.

Acute phase reactant serum amyloid A in inflammation and other diseases

Acute-phase reactant serum amyloid A (A-SAA) plays an important role in acute and chronic inflammation and is used in clinical laboratories as an indicator of inflammation. Although both A-SAA and C-reactive protein (CRP) are acute-phase proteins, the detection of A-SAA is more conclusive than the detection of CRP in patients with viral infections, severe acute pancreatitis, and rejection reactions to kidney transplants. A-SAA has greater clinical diagnostic value in patients who are immunosuppressed, patients with cystic fibrosis who are treated with corticoids, and preterm infants with late-onset sepsis. Nevertheless, for the assessment of the inflammation status and identification of viral infection in other pathologies, such as bacterial infections, the combinatorial use of A-SAA and other acute-phase proteins (APPs), such as CRP and procalcitonin (PCT), can provide more information and sensitivity than the use of any of these proteins alone, and the information generated is important in guiding antibiotic therapy. In addition, A-SAA-associated diseases and the diagnostic value of A-SAA are discussed. However, the relationship between different A-SAA isotypes and their human diseases are mostly derived from research laboratories with limited clinical samples. Thus, further clinical evaluations are necessary to confirm the clinical significance of each A-SAA isotype. Furthermore, the currently available A-SAA assays are based on polyclonal antibodies, which lack isotype specificity and are associated with many inflammatory diseases. Therefore, these assays are usually used in combination with other biomarkers in the clinic.

The Clinical Application of Anti-CCP in Rheumatoid Arthritis and Other Rheumatic Diseases

Rheumatoid arthritis (RA) is a common rheumatic disease in Caucasians and in other ethnic groups. Diagnosis is mainly based on clinical features. Before 1998, the only serological laboratory test that could contribute to the diagnosis was that for rheumatoid factor (RF). The disease activity markers for the evaluation of clinical symptoms or treatment outcome were the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). As a matter of fact, the diagnosis of early RA is quite impossible, as the clinical criteria are insufficient at the beginning stage of the disease. In 1998, Schelleken reported that a high percentage of RA patients had a specific antibody that could interact with a synthetic peptide which contained the amino acid citrulline. The high specificity (98%) for RA of this new serological marker, anti-cyclic citrullinated antibody (anti-CCP antibody), can be detected early in RA, before the typical clinical features appear. The presence or absence of this antibody can easily distinguish other rheumatic diseases from RA. Additionally, the titer of anti-CCP can be used to predict the prognosis and treatment outcome after DMARDs or biological therapy. Therefore, with improvement of sensitivity, the anti-CCP antibody will be widely used as a routine laboratory test in the clinical practice for RA.

Increased Kappa/Lambda Hybrid Antibody in Serum Is a Novel Biomarker Related to Disease Activity and Inflammation in Rheumatoid Arthritis

The κ/λ hybrid antibodies in normal human serum were reported recently, but their clinical relevance has not yet been explored. Rheumatoid arthritis (RA) is one of the major joint diseases, and the early diagnosis and treatment of RA remain a challenge. Here, we developed a double-sandwich enzyme-linked immunosorbent assay system to quantify relative serum κ/λ hybrid antibody levels in RA patients, osteoarthritis (OA) patients, and healthy controls (HC) in order to assess their potential use as a serological biomarker of early disease and clinical activity and to preliminarily investigate their immunomodulatory roles in RA. Surprisingly, we found that κ/λ hybrid antibody was markedly increased in both early and established RA. Serum κ/λ hybrid antibody levels were significantly correlated with clinical indexes and inflammatory markers in RA. Further analysis showed a positive correlation between κ/λ hybrid antibody levels and the 28-joint disease activity score (DAS28). In conclusion, serum κ/λ hybrid antibodies in RA were identified for the first time. High levels of κ/λ hybrid antibody may be a useful tool in distinguishing early RA from OA and HC. We suggest κ/λ hybrid antibody as a marker for disease activity. The increased κ/λ hybrid antibodies were associated with inflammatory conditions in RA.

Tryptase is a candidate autoantigen in rheumatoid arthritis

Autoimmune processes have been implicated in the development of rheumatoid arthritis (RA); however, specific autoantigens that play a role in the aetiology of RA have been lacking. In this study, we found that sera from RA patients were particularly immunoreactive against the protein tryptase. Compared with osteoarthritis (OA) patients and healthy controls, RA patients had relatively higher levels of tryptase and concomitant anti-tryptase antibodies in their synovial tissues and sera. Similarly, synovial fluid from RA patients, but not from OA patients, contained antibodies that recognized tryptase in vitro. In addition, serum tryptase levels in both early and late RA patients significantly correlated with clinical indices usually used to diagnose RA, such as rheumatoid factor, Disease Activity Score using 28 joint counts and autoantibodies against cyclic citrullinated peptide. Our results identify tryptase as a candidate autoantigen involved in the pathogenesis of RA and monitoring its levels may have diagnostic and prognostic value.

Efficacy and Safety of Rituximab in Biologic-Naive Patients with Rheumatoid Arthritis vs Anti-Tnf Therapy Failure

OBJECTIVES

Our aim was to compare an AntiCD20 therapy (rituximab) for rheumatoid arthritis in two patient populations (Group 1), anti-TNFα naïve patients and inadequate responders to Anti-TNFα therapy (Group 2).

METHODS

We analyzed the efficacy of the drug Rituximab (RTX) in RA patients who failed methotrexate (MTX) or had a relative or absolute contraindication to receive anti-TNFα therapy.

RESULTS

25 patients were identified according to the above criteria and followed up for a mean period of 6 months. Thirteen patients were biologic naïve and twelve patients had already failed anti-TNFα therapy. Group 1 used 2> DMARDs (32% vs 20%, p<0.005), group 2 had more years of disease progression (5±1.89 v s4.10±3.92, p<0.001). The remission as measured by the DAS28 reached faster in group 1 (1.25±0.12 vs 2.15±1.64, p<0,001). Severe infections especially by herpes viruses were more frequent in group 2.

CONCLUSIONS

Comparing clinical improvement in both groups the decrease of acute phase reactants and the clinical remission measured by DAS28 was reached in both groups, however it was reached more belatedly in group 2 (at 6 months), this is due to the fact that they have more years of the disease evolution and a higher HAQ.

The association of anti-CCP antibodies with disease activity in rheumatoid arthritis

Antibodies to citrullinated proteins have been described in patients with rheumatoid arthritis (RA) and these appear to be the most specific markers of the disease. Our objective was to determine the frequency of antibodies to cyclic citrullinated peptides (CCPs) in patients with RA and the association of anti-CCP antibodies with disease activity, radiological erosions and HLA DR genotype. Forty patients with RA and 38 patients with fibromyalgia were included in this study. Serum samples were collected from both patient groups with RA and fibromyalgia. Anti-CCP was measured by the corresponding enzyme-linked immunosorbent assay. Additionally, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), rheumatoid factor (RF), disease activity score (DAS), visual analog scala (VAS), HLA genotype and radiographic information were determined in patients with RA. The rate of sensitivity and specificity of anti-CCP reactivity for the diagnosis RA were measured (sensitivity 50%, specificity 100%). There is no significant difference between anti-CCP (+) and anti-CCP (-) RA patients for DAS28, VAS, ESR, CRP, disease duration, HLA genotype, and radiological assessment of hand. However, there was a significant difference between anti-CCP (+) and anti-CCP (-) RA patients for RF and the radiological assessment of left and right wrists (respectively, P < 0.05, P = 0.04, P = 0.01). There was no significant correlation between anti-CCP antibody and ESR, CRP, VAS, DAS 28 or radiological assessment. A small but significant correlation was found between RF and anti-CCP antibody (P = 0.02, r = 0.35).

Comparison of second- and third-generation anti-cyclic citrullinated peptide antibodies assays for detecting rheumatoid arthritis

BACKGROUND

The aims of the present study were to compare the diagnostic and clinical value of seven commercially available assays for second-generation anti-cyclic citrullinated peptide (CCP2) antibodies, anti-keratin antibodies (AKA) and rheumatoid factor (RF) determination in patients with rheumatoid arthritis (RA), and to check the potential advantages of a third-generation anti-CCP (CCP3) antibodies assay.

METHODS

Serum samples from 120 RA patients and from 170 controls were used to determine the sensitivity, the specificity, the positive (PPV) and negative predictive values (NPV) of CCP2 and CCP3 antibodies, AKA and RF assays. The respective performances of these tests were compared using a receiver-operating characteristics (ROC) curves methodology.

RESULTS

We found no significant differences in sensitivity and specificity between the tested anti-CCP assays. The CCP3 antibodies assay we evaluated was not significantly more sensitive than those of the second generation. Compared with RF technique, all anti-CCP assays showed better specificity, but lower sensitivity. In contrast, while of equivalent specificity, they proved to be more sensitive than AKA in the discrimination of RA from other rheumatic diseases.

CONCLUSIONS

Anti-CCP antibodies determination proved to be a powerful diagnostic tool, especially in RA patients with negative AKA or RF. The investigated CCP3 antibodies assay had no better diagnostic performances than the second-generation assays.

Multiplexed immunoassay for detection of rheumatoid factors by FIDISTM technology

Our objective was to (i) compare FIDIS Rheuma, a new multiplexed immunoassay designed for simultaneous detection of IgM class rheumatoid factors (RF) directed against Fc determinants of IgG from humans and animals, with agglutination and ELISA (conventional methods) and (ii) evaluate the clinical sensitivity and specificity of biological markers for rheumatoid arthritis (RA). To do this, FIDIS technology was employed using the Luminex system. It consists of distinct color-coded microsphere sets, a flow cytometer, and digital signal processing hardware and software. Agglutination and ELISA tests were performed with commercial kits. The study included 134 samples from RA patients and 105 from healthy blood donors. For human specificity, we compared FIDIS with latex agglutination and ELISA. Relative sensitivities were 98.9% and 88.5% and specificities were 90.2% and 94.6%, respectively. For animal specificity, we compared FIDIS with Waaler-Rose and ELISA. The results were 84.9% and 71.9% for the sensitivities and 97.5% and 98.4% for the specificities, respectively. Detection of IgG anti-CCP by ELISA and IgG antikeratin by immunofluorescence was also determined in order to compare their clinical sensitivity and specificity with IgM-RF, according to the method used. The results were: IgG anti-CCP 72.3%, 97.2%; IgG antikeratin 36.6%, 100%; latex agglutination 66.4%, 97.2%; Waaler-Rose 55.9%, 96.3%; FIDIS human 73.9%, 92.1%; FIDIS animal 49.2%, 97.2%; ELISA human 93.2%, 95.5%; and ELISA animal 74.6%, 91.3%. The results showed the efficiency of FIDIS with analytical performance equivalent to the conventional methods, but having the advantage of giving quantitative results (IU/mL).

Proteomic: New advances in the diagnosis of rheumatoid arthritis

BACKGROUND

Rheumatoid arthritis (RA) is a chronic autoimmune disease affecting the joints. A number of novel treatment modalities have been introduced over the past years, and rheumatologists are now attempting to institute optimal treatment in recent-onset arthritis. To facilitate diagnosis during the early stages of disease, when often not all clinical symptoms are manifest, a good serological marker is needed.

METHODS

Antibodies directed to citrullinated proteins provide this ability. The most sensitive assay for detecting these antibodies is the so-called anti-cyclic citrullinated peptide, second generation (CCP II) enzyme-linked immunosorbent assay (ELISA).

RESULTS

The diagnostic and prognostic potential of anti-CCP antibodies and the availability of a fully automated assay method lead us to conclude that the test is satisfactory for routine use as a serological marker of RA. In addition, we consider the potential of multiplex autoantibody assays, including miniaturized, high-throughput microarray technology, to improve diagnosis and prognostication in early onset arthritis patients.

Aspects of science in Scandinavian rheumatology--the making of a specialty

The five Scandinavian countries Denmark, Finland, Iceland, Norway, and Sweden have all contributed essential and unique knowledge to the science of rheumatology. The origins have varied between the countries. Bridges from basic science and international contacts have been essential for the quality and vitality of a small specialty in small countries. Inter-Scandinavian links as manifested in congresses and in the Journal are the visible superstructure of a far deeper and fertile common culture.

Does smoking stimulate rheumatoid factor production in non-rheumatic individuals?

Smoking has been associated with increased incidence of rheumatoid arthritis (RA), joint damage and positive rheumatoid factor (RF). Here we report an analysis of the association between smoking and IgM, IgG and IgA RF in a cohort of non-rheumatic individuals participating in a prospective longitudinal study of the incidence and significance of elevated RF. From the initial cohort of nearly 14,000 randomly selected individuals aged 52-80 years, 109 RF-positive and 187 RF-negative non-rheumatic participants were recruited. All participants were tested for RF at least twice at an interval ranging from 4 to 13 years. Of the RF-negative participants 21.9% were active smokers compared to 34.1% of IgM RF-positive (p=0.035), 20.8% of IgG RF-positive (N.S.) and 34.4% of IgA RF-positive participants (p=0.047). Smoking was most prevalent (44.8%) amongst participants with elevation of both IgM and IgA RF (p=0.008), and smokers were also significantly more likely to have a persistent elevation of RF than non-smokers (p=0.024). These findings indicate that smoking may influence the immune system, leading to increased production of IgM and IgA RF.

Diagnostic and prognostic characteristics of the enzyme linked immunosorbent rheumatoid factor assays in rheumatoid arthritis

OBJECTIVE

To determine the diagnostic and prognostic test qualities of the enzyme linked immunosorbent assays (ELISA) for rheumatoid factor isotypes in rheumatoid arthritis (RA), and to compare them with the latex fixation test.

METHODS

Rheumatoid factor tests were performed in 1988 consecutive new rheumatology outpatients within two months after their first visit to the outpatient clinic of the Department of Rheumatology of Leiden University hospital. The sensitivity, specificity, accuracy, and predictive values of the tests in discriminating RA from non-rheumatoid arthritis and erosive from non-erosive disease after two years of follow up were determined and presented as receiver operating characteristic curves and post-test probability curves.

RESULTS

The sensitivity of the ELISA for IgG, IgA, and IgM rheumatoid factor for RA versus all controls at optimal cut off titres was 72%, 44%, and 69%, respectively; the specificity was 52%, 84%, and 86%. For the latex fixation test the sensitivity was 66% and the specificity 91%. The post-test probability of RA, at a clinical prevalence rate of 12%, given a positive test result in the ELISAs for IgG, IgA, and IgM rheumatoid factor and the latex fixation test, was 17%, 27%, 40%, and 49%, respectively; with negative test results the probability was 7%, 8%, 5%, and 5%, respectively. The specificity of all tests in discriminating erosive from non-erosive RA at two years was low: 41%, 44%, 47%, and 58% for the ELISAs for IgG, IgA, and IgM rheumatoid factor and the latex fixation test, respectively.

CONCLUSION

The ELISAs for IgG and IgA rheumatoid factor are of no significance in diagnosing RA and in the prediction of erosive disease. The ELISA for IgM rheumatoid factor is a reasonable alternative for the latex fixation test when age and gender are taken in to consideration. The specificity of all rheumatoid factor tests in discriminating erosive from non-erosive RA is low.

Immunochemical study of human immunoglobulin G Fc region

Fifteen murine monoclonal antibodies (mAb) were produced that reacted with conformational epitopes present on the Fc portion of all human IgG subclasses (PAN-Fc). Inhibition and sandwich ELISA were used to elucidate overlapping and distinct epitopes. The epitopes were aligned to form a continuous "chain" of overlapping determinants from the CH2-CH3 interface to the direction of hinge. The five more hinge-proximal epitopes demonstrated high lability both in competitive and sandwich assays, being completely or partially destroyed when any of these 15 other mAb bound the IgG first. Heat-inactivation of IgG caused full disruption of these epitopes. In contrast, epitopes situated at the opposite distal of the "chain" were more stable and mAb binding could only be affected by occupying an overlapping epitope. Under heat-inactivation these epitopes were affected, but not completely destroyed. Human IgG class anti-DNA autoantibodies were bound to insolubilized dsDNA and their reaction with PAN-Fc mAb was studied. mAb titration plots on IgG and dsDNA-IgG were compared. Five epitopes proved to be altered by antigen (dsDNA) binding. Two of these were the labile hinge-proximal epitopes and the other three were situated near the CH2-CH3 interface. Cross-reactivity of mAb with xenogeneic IgG was also studied. An "epitope map" of the crystallographic model of human IgG Fc portion drawn was based on these experimental data and printed matter, concerning the location of subclass-specific amino acids and homology regions of human and animal IgG.

Clinical implications of IgA rheumatoid factor subclasses

OBJECTIVES

To evaluate the diagnostic and pathogenetic significance of IgA rheumatoid factor (RF) subclasses in rheumatoid arthritis (RA).

METHODS

Rheumatoid factors of the IgA class and IgA1 and IgA2 subclasses were measured by enzyme linked immunosorbent assay in 58 patients with RA, 31 patients with other rheumatic diseases, 30 non-rheumatic individuals with increased concentrations of IgA RF, and in 100 randomly selected healthy controls.

RESULTS

Using a 95% cut off for the controls, 55% of the RA patients had increased total IgA RF, 64% IgA1 RF, and 60% IgA2 RF. RA patients with extraarticular manifestations more often had increased concentrations of IgA RF and both subclasses than patients without such manifestations (p < or = 0.01). Nearly all (31/32) RA patients with increased IgA RF had increases in both IgA RF subclasses, compared with 67% (20/30 of nonrheumatic symptom free individuals with increased IgA RF (p = 0.002).

CONCLUSION

Increased concentrations of the IgA2 RF subclass appears to be more specific for RA than increased IgA1 RF. Measurement of IgA RF subclasses may be clinically useful.

Specificity of IgM antiglobulins produced in rheumatoid arthritis and tropical infections

The measurement of rheumatoid factors is of limited value in West Africa due to the low rheumatoid factor seroprevalence among patients with rheumatoid arthritis and the increased seroprevalence among healthy individuals and those with infectious diseases in the region. Using ELISA methods, we have been able to increase the specificity of rheumatoid factor measurement although the sensitivity of this test remains low. Furthermore, among the infectious diseases studied, there was no preferential binding of rheumatoid factors to the Fab gamma portion of immunoglobulin over the Fc gamma portion.

Clinical significance of rheumatoid factor isotypes in seropositive arthritis

In this cross-sectional study a comparison was made of rheumatoid factor (RF) isotypes in 203 RF positive patients with arthritis. Of these, 129 had rheumatoid arthritis (RA) and 74 a milder disease that would formerly have been classified as probable RA. The majority (74%) of the RA patients had elevations of two or three RF isotypes compared with only 34% of the patients with the milder form of arthritis. A striking feature was that combined elevation of IgM RF and IgA RF was found in 67% of the RA patients compared to only 20% of the patients with milder arthritis who most frequently had an isolated elevation of IgM RF (41%). RA patients with an isolated elevation of IgA RF were younger and had a shorter disease history than RA patients with an isolated elevation in IgM RF or a combined elevation of IgA RF and IgM RF. The prevalence of raised IgM RF was, furthermore, found to increase with age and disease duration. We conclude that a raised level of IgA RF is an adverse phenomenon in patients with seropositive arthritis while patients with an isolated increase in IgM RF may be expected to experience a relatively mild disease course.

The latex test revisited. Rheumatoid factor testing in 8,287 rheumatic disease patients

Rheumatoid factor (RF) testing by latex fixation in 8,287 outpatients yielded a sensitivity of 81.6% and 78.0% at titers of 1:20 and 1:80, respectively, and a specificity against noninflammatory rheumatic disorders (NIRD) of 96.6% and 97.9% and against NIRD plus inflammatory disorders of 95.2% and 96.8%, respectively. The predictive value of a positive test result at the clinic prevalence rate for rheumatoid arthritis (RA) (16.4%) was approximately 80%, and was 70% at 10% prevalence and 10% at 1% prevalence. No associations of RF with age or sex were found in non-RA patients. RF titers increased minimally with age in RA patients and were higher in men than in women. This study suggests that latex testing is far more specific than has been believed and that the titer is not spuriously increased with age.

Natural anti-IgE auto-antibodies interfere with diagnostic IgE determination

A simple method is described which enables measurement of anti-IgE antibodies in free form as well as in immune complexes of IgE and anti-IgE. Anti-IgE antibodies were purified from serum of one selected blood donor with highly elevated levels of such autoantibodies. These purified anti-IgE auto-antibodies inhibited the measurement of myeloma IgE. Purification also revealed that 98% of the subject's serum IgE was masked by anti-IgE auto-antibodies. Our data suggest that IgE determinations in sera containing anti-IgE antibodies might be underestimated.

Molecular characterization of the gene sr of the saliva interacting protein from Streptococcus mutans OMZ175

The saliva interacting protein (74KSR) from Streptococcus mutans serotype f, which is immunologically related to antigen I/II from serotype c, also termed B, P1, PAc, is probably involved in the adherence process of Strep. mutans to the tooth surface. A solid-phase adherence assay showed that 38% of the binding of salivary glycoproteins to Strep. mutans OMZ175 was due to this protein. We have cloned and sequenced the 74KSR gene (sr), which produces a recombinant protein (rec195K) with a relative molecular mass of 195,000, as estimated by SDS-PAGE. The strong immunological relationship and functional identity of the 74KSR and rec195K indicate that the Mr 195K protein is probably a precursor form, post-translationally processed, of the 74KSR produced in Strep. mutans. The gene sr consists of 4667 bp and codes for a 171,177 Mr protein. Biochemical features of the protein (density in proline residues and hydrophobicity) may explain the difference observed between the SDS-PAGE estimated molecular mass of the immature protein and the one deduced from the nucleotide sequence. Intra-species hybridization experiments using three contiguous restriction fragments isolated from gene sr as probes showed that the sequence is highly similar in strains from serotypes c and e. We have also shown that a fraction of the heart specific antibodies induced in rabbits during immunization with the 74KSR or rec195K reacts predominantly with human IgG and suggest the hypothesis of antigen mimicry as an explanation for the production of anti-IgG autoantibodies. It will be of great importance to identify the cross-reactive epitopes within the molecule before considering its use in protective immunization against oral streptococci.

Rheumatic disorders in adults under 50. Guidelines for differential diagnosis

Rheumatic disorders are not uncommon in patients between 20 and 50 years of age, and the differential diagnosis may be difficult. However, after a careful history and thorough physical examination, the cause usually becomes apparent. Laboratory findings alone should not be relied on for diagnosis. Because the impact on younger adults may be devastating and the potential disability may be present for many years, these patients represent an important challenge for any practicing physician.

In vitro IgM rheumatoid-factor production induced by tetanus toxoid

In vitro stimulation of lymphocytes from healthy donors with well-defined polyclonal B cell activators may elicit the production of rheumatoid factor (RF) as well as other autoantibodies. Antigen stimulation may also result in polyclonal B cell activation, but it is not known if RF production is a feature of this response. Therefore, peripheral blood mononuclear cells from 36 healthy volunteers previously immunized to tetanus toxoid (TT) were stimulated in vitro for 9 days with a conventional antigen, TT, or pokeweed mitogen, a standard polyclonal B cell activator. Culture supernatants were analyzed for total IgG, total IgM, and IgM RF by ELISA. TT-induced IgM RF production was observed in 10/36 experiments compared to 18/36 experiments in which cells were cultured with pokeweed mitogen, with a similar magnitude of response to these respective stimulants. The in vitro IgM-RF response to TT did not require a recent in vivo TT booster immunization and was observed at an antigen does that elicits polyclonal B cell activation but not IgG specific anti-TT antibody. TT-induced IgM RF responder cultures demonstrated higher levels of total IgG and total IgM production than cultures not secreting IgM RF in response to TT. These results indicate that IgM RF production is a concomitant of the polyclonal B cell response elicited by a conventional antigen. Unlike other model systems, this antigen-induced RF response was not mediated by the action of IgG antibody containing immune complexes.

Quantitation of rheumatoid factors (RF) of IgM, IgA and IgG isotypes by a simple and sensitive ELISA. Discrimination between false and true IgG-RF

An enzyme-linked immuno-sorbent assay (ELISA) for quantitation of rheumatoid factors (RF) of IgM, IgA and IgG isotypes has been established. A complex of human serum albumin (HSA) and rabbit IgG anti-HSA antibodies is used as antigen for RF. The binding of RF is detected by stepwise additions of biotinylated monoclonal antibodies specific for human IgM, IgG or IgA, alkaline phosphatase-conjugated streptavidin, and substrate. The assay is simple and applicable to routine testing of large numbers of sera. It discriminates between false and true IgG-RF by papain digestion of sera that turn out positive by the screening for IgG-RF. Of 241 randomly selected patients with rheumatoid arthritis (RA) as well as other rheumatoid and infectious diseases, 110 were Waaler-Rose-positive while 127 were IgM-RF-positive in ELISA. The correlation between the Waaler-Rose test and IgM-RF ELISA was highly significant (r = 0.82). By testing 65 of these sera (all IgM-RF positive), 25 (39%) were also true IgG-RF positive (42 (64%) in the screening). When 40 Waaler-Rose-positive RA patients were tested, 20 and 21 were also positive for IgG- and IgA-RF, respectively. Eight IgM-, one IgA- and no IgG-RF positive tests were recovered when 48 Waaler-Rose negative RA patients were studied.

Human rheumatoid factor reacting with rabbit IgG but not with human IgG

A patient, O.A., had in her serum an IgM rheumatoid factor (RF) of high titer which reacted equally well with monomeric and polymeric rabbit IgG, but showed no reaction with homologous or autologous monomeric and polymeric IgG, neither in hemagglutination nor in ELISA tests. In contrast to the usual specificity of RFs crossreacting with rabbit and human IgG, which require the presence of both the CH2 end CH3 domains, the O.A. RF showed reaction only against the CH3 domain. The existence of human RF not reacting with human IgG could challenge the notion that RF production is necessarily induced by autologous IgG and thus playing an important role in potentiating and regulating secondary immune responses. The O.A. RF might represent 1: an extreme case of heteroclitic antibody, 2: the internal image of a hypothetical Fc-receptor reacting with rabbit IgG but not with human IgG, 3: a result of polyclonal B cell activation, 4: an antigenic crossreaction with an unknown antigen with similarities to rabbit IgG but not to human IgG.

False-positive reaction for fibrin degradation products due to a monoclonal (IgM lambda) cryoglobulin with warm-reactive antibody activity for rabbit IgG

The serum of a patient with prolymphocytic leukemia and a hyperviscosity syndrome contained high levels of IgM, with a monoclonal peak on protein electrophoresis, and had a high titer for fibrin(ogen) degradation products, using a rabbit anti-fibrinogen reagent, without other evidence for disseminated intravascular coagulation. A monoclonal IgM lambda cryoglobulin was identified. It retained reactivity with the fibrin(ogen) degradation products reagent, but failed to react with human IgG by latex fixation. Binding activity for rabbit IgG (and absence of binding activity for human, goat, and bovine IgG) was also demonstrable by double diffusion in agarose, and by enzyme-linked immunoassay. By enzyme-linked immunoassay, binding of both F(ab)2 and Fab and, to a lesser extent, Fc fragments of rabbit IgG was found. Increased binding of heat-denatured rabbit IgG was observed, without inhibition by similarly denatured IgG of other species. The false-positive fibrin(ogen) degradation products reaction in the serum of this patient was due to a unique monoclonal IgM lambda cryoglobulin with warm-reactive antibody activity for an epitope displayed on native and denatured rabbit IgG, but absent on native or denatured human, goat, or bovine IgG, and present in both F(ab)2 and Fc regions of the IgG molecule.

Relation between bone erosions and rheumatoid factor isotypes

Total rheumatoid factor (RF) activity and individual RF isotypes were measured in 62 patients with rheumatic diseases. Retrospective analysis of available x rays showed an association between IgA RF and the occurrence of periarticular bone erosions in hands. In contrast, IgG RF and IgM RF did not show any significant association with erosions. Furthermore, a close correlation was observed between the RF isotype levels in simultaneously drawn serum and synovial fluid samples. The possible significance of IgA RF in the pathogenesis of bone erosions is discussed.

IgA rheumatoid factor in Henoch-Schönlein purpura

Sera from 24 children with Henoch-Schönlein purpura (HSP) and 25 controls were tested for rheumatoid factor (RF) of various isotypes. None of the patients with HSP had RF of the IgG or IgM isotypes, whereas one of the controls had IgG RF and one had IgM RF. On the other hand, IgA RF was found in 13 (54%) of the HSP sera, but in only one of the controls (P less than 0.005). The IgA RF showed some cross-species reactivity, but it generally reacted better to human IgG than to rabbit IgG (P less than 0.01) or goat IgG (P less than 0.005). The mean serum IgA concentration was higher in IgA RF positive patients (245 +/- 92 mg/dl) than in IgA RF negative patients (171 +/- 69 mg/dl) (P less than 0.05). Moreover, there was a positive correlation between IgA RF concentration and the level of serum IgA above the mean concentration for age (P less than 0.05). When present, IgA RF concentration tended to be highest during the acute phase of the illness, but there was no correlation between IgA RF and the severity or duration of HSP. These results add to the growing list of immunologic abnormalities in HSP and suggest that IgA RF production may be linked to a basic disturbance of IgA production in HSP.

Prognostic factors and diagnostic criteria in early rheumatoid arthritis

The purpose of the present undertaking was to investigate prognosis of patients with non-specific or rheumatoid arthritis and to study the value of different diagnostic criteria for rheumatoid arthritis (RA) at the beginning of the disease. During the years 1973-75, a total of 442 patients with recent (less than or equal to 6 months) arthritis were studied at the Rheumatism Foundation Hospital, Heinola, Finland. In 1982 the outcome of the 200 patients with the diagnosis of RA or non-specific arthritis was established. Their ages at the time of the first hospitalization were 16-77 years, mean 41. There were 63 men and 137 women. The follow-up period was 6-9 years, mean 7.6. The outcome was measured by joint score, function score, the sum of ESR and CRP, X-ray index, outcome index, which was composed of the preceding ones, ESR, and CRP. The outcome was poor in half of the patients. Ninety-eight signs and symptoms registered at the first hospitalization were compared with the seven facets of outcome using Pearson's correlation coefficient r. The significances of the correlation coefficients were tested by Student's t-test. From 10 to 39 variables correlated highly significantly (p less than 0.001) with the measures of outcome; however, most of the variables had only moderate correlations. At best 14 variables showed 0.40 less than r less than 0.58 when correlated with the outcome index. In conclusion, at the onset of an arthritic disease symmetrical polyarthritis in peripheral joints, serum rheumatoid factor, X-ray changes, morning stiffness, high ESR, and old age correlated best with a destructive joint disease. Plasma proteins as indices of non-specific inflammation mattered less. The relationships between 22 entry variables and the seven facets of prognosis were further evaluated by means of stepwise multiple regression analysis. The results were essentially the same as reached above. One or two variables, most often the number of diseased peripheral joints and serum Waaler-Rose test, always explained the variance better than the number of ARA criteria alone. To study the value of the diagnostic criteria, diagnosis of the patients was made in the following three ways: RA with five or more erosive joints (N = 78), RF-positive and erosive RA (N = 93), RF-positive and nonerosive or RF-negative and erosive RA (N = 125). The patients outside each of the diagnostic groups formed the corresponding control groups.(ABSTRACT TRUNCATED AT 400 WORDS)

A study of IgM rheumatoid factors in a middle-aged population of Northern Norway

A random selection of 8807 blood samples was analysed for the presence of IgM rheumatoid factor (RF). The sera were obtained from an epidemiological survey of rheumatoid arthritis in a middle-aged population of Northern-Norway. The prevalence of IgM-RF was 1.36% for the total population, but a prevalence of IgM RF in healthy individuals between 0.48-0.49% was found with no significant difference between males and females. The majority of RF positive sera were low titred. Only 11.4% of the persons possessing serum IgM RF suffered from classical or definite rheumatoid arthritis. Eighty-one per cent of the IgM RF positive individuals converted to seronegativity in the course of 3.5 years.