Elevated Fab glycosylation of anti-hinge antibodies.

OBJECTIVE: Rheumatoid arthritis (RA) is characterized by systemic inflammation and the presence of anti-citrullinated protein antibodies (ACPAs), which contain remarkably high levels of Fab glycosylation. Anti-hinge antibodies (AHAs) recognize immunoglobulin G (IgG) hinge neoepitopes exposed following cleavage by inflammation-associated proteases, and are also frequently observed in RA, and at higher levels compared to healthy controls (HCs). Here, we investigated AHA specificity and levels of Fab glycosylation as potential immunological markers for RA. METHOD: AHA serum levels, specificity, and Fab glycosylation were determined for the IgG1/4-hinge cleaved by matrix metalloproteinase-3, cathepsin G, pepsin, or IdeS, using enzyme-linked immunosorbent assay and lectin affinity chromatography, in patients with early active RA (n = 69) and HCs (n = 97). RESULTS: AHA reactivity was detected for all hinge neoepitopes in both RA patients and HCs. Reactivity against CatG-IgG1-F(ab´)2s and pepsin-IgG4-F(ab´)2s was more prevalent in RA. Moreover, all AHA responses showed increased Fab glycosylation levels in both RA patients and HCs. CONCLUSIONS: AHA responses are characterized by elevated levels of Fab glycosylation and highly specific neoepitope recognition, not just in RA patients but also in HCs. These results suggest that extensive Fab glycosylation may develop in response to an inflammatory proteolytic microenvironment, but is not restricted to RA.

Interval prolongation of etanercept in rheumatoid arthritis, ankylosing spondylitis, and psoriatic arthritis: a randomized controlled trial.

OBJECTIVE: The majority of patients with a rheumatic disease treated with etanercept may be overexposed. Data regarding etanercept tapering are scarce, particularly in psoriatic arthritis (PsA) and ankylosing spondylitis (AS). We compared extending the dose interval to continuation of the standard dose and studied the success rate of etanercept discontinuation. Etanercept concentrations were measured throughout the study. METHOD: 160 patients with rheumatoid arthritis (RA), PsA, or AS with sustained minimal disease activity (MDA) were enrolled in this 18-month, open-label, randomized controlled trial. The intervention group doubled the dosing interval at baseline and discontinued etanercept 6 months later. The control group continued the standard dose for 6 months and doubled the dosing-interval thereafter. The primary outcome was the proportion of patients maintaining MDA at 6 month follow-up. RESULTS: At 6 months, MDA status was maintained in 47 patients (63%) in the intervention group and 56 (74%) in the control group (p = 0.15), with comparable results in all rheumatic diseases. And median etanercept concentrations decreased from 1.50 µg/mL (interquartile range 1.06- 2.65) to 0.46 µg/mL (0.28-0.92). In total, 40% discontinued etanercept successfully with maintained MDA for at least 6 months. CONCLUSION: Etanercept tapering can be done without losing efficacy in RA, PsA, and AS patients in sustained MDA. A substantial proportion of patients could stop etanercept for at least 6 months. In many patients, low drug concentrations proved sufficient to control disease activity. However, the risk of minor and major flares is substantial, even in patients continuing standard dosing.

Serum drug concentrations to optimize switching from adalimumab to etanercept in rheumatoid arthritis.

Objectives: Inadequate response to adalimumab can be caused by insufficient blockade of the target tumour necrosis factor (TNF) at low serum concentrations. In such cases, patients may respond to another TNF inhibitor. We investigated whether the serum adalimumab concentration is related to the efficacy of a second TNF inhibitor, etanercept, in rheumatoid arthritis (RA). Methods: Patients with RA starting etanercept treatment were prospectively observed in the Reade Rheumatology Registry. In patients previously on adalimumab, serum concentrations were determined before treatment discontinuation. According to this concentration, three subgroups were formed: < 0.5 µg/mL, 0.5-5.0 µg/mL, and ≥ 5.0 µg/mL. The European League Against Rheumatism (EULAR) good/moderate response rate after 52 weeks of etanercept was compared between the switcher subgroups and biologic-naive patients. Results: In total, 449 consecutive patients were included, of whom 69 switched from adalimumab (15%) and 380 were biologic naive (85%). EULAR good or moderate response was achieved by 74% of the biologic-naive patients and by 72%, 50%, and 52% of switchers with adalimumab concentration < 0.5 µg/mL, 0.5-5.0 µg/mL, and ≥ 5.0 µg/mL, respectively (p = 0.15). Patients with an adalimumab concentration ≥ 0.5 µg/mL were significantly less likely to achieve EULAR good/moderate response on etanercept compared to biologic-naive patients, whereas patients with a concentration < 0.5 µg/mL did not significantly differ from patients starting etanercept without prior biologic treatment. Conclusion: RA patients with an inadequate response to adalimumab, in the presence of sufficient drug concentrations, benefit less from switching to another TNF inhibitor, etanercept.

The antibody response against human and chimeric anti-TNF therapeutic antibodies primarily targets the TNF binding region.

BACKGROUND: In a subset of patients, anti tumour necrosis factor (TNF) therapeutic antibodies are immunogenic, resulting in the formation of antidrug antibodies (ADAs). Neutralising ADAs compete with TNF for its binding site and reduces the effective serum concentration, causing clinical non-response. It is however unknown to which extent ADAs are neutralising. OBJECTIVES: To study which proportion of antibodies to human(ised) anti-TNF (adalimumab, golimumab, certolizumab) as well as chimeric anti-TNF (infliximab) is neutralising. METHODS: Neutralising capacity of ADAs was assessed using a TNF competition assay in ADA-positive sera of patients treated with adalimumab (n=21), golimumab (n=4), certolizumab (n=9) or infliximab (n=34) sent in to our diagnostic department. RESULTS: In 34 sera with ADAs to adalimumab, golimumab or certolizumab, >97% of the antibodies were neutralising. In 34 sera with ADAs to infliximab >90% of the antibodies were neutralising. Further characterisation of the broader antibody response to infliximab revealed that non-neutralising antibodies to infliximab do not target murine domains, but may bind infliximab-unique domains not involved in TNF binding (located outside the paratope). CONCLUSIONS: Our study shows that ADAs to human(ised) as well as chimeric anti-TNF therapeutic antibodies are largely neutralising. This highly restricted ADA response suggests an immunodominant role for the paratope of anti-TNF therapeutics.

Lower etanercept levels are associated with high disease activity in ankylosing spondylitis patients at 24 weeks of follow-up.

BACKGROUND: Previous data have shown that etanercept levels are associated with clinical response in rheumatoid arthritis. However, for ankylosing spondylitis (AS), data regarding this topic are inconclusive. OBJECTIVES: To investigate the relationship between etanercept levels and clinical response in patients with AS. METHODS: Observational prospective cohort study of 162 patients with AS =treated with etanercept, monitored during 24 weeks of treatment. Etanercept trough levels were determined, retrospectively, using an ELISA. Disease activity was measured using AS Disease Activity Score (ASDAS), including C-reactive protein (CRP) and Bath AS Disease Activity index (BASDAI). Active disease was defined as ASDAS≥2.1. Since etanercept is a drug administered at home there might have been some variation in trough level sampling. RESULTS: At 24 weeks etanercept levels were significantly higher in patients with ASDAS<2.1, (3.8 mg/L; IQR 2.5-5.2) compared with patients with ASDAS≥2.1 (2.3 mg/L; IQR 1.2-3.4; p≤0.001). Generalised estimating equation analysis demonstrated a statistically significant association between etanercept levels and ASDAS, BASDAI, CRP and erythrocyte sedimentation rate (all p<0.001). When patients were categorised into quartiles according to etanercept levels, the lowest quartile (etanercept<1.80 mg/L) comprised 35% of all patients with ASDAS≥2.1 while the highest quartile comprised only 14%. CONCLUSIONS: Disease activity and inflammation are associated with etanercept levels in patients with AS at 24 weeks of treatment. Measuring etanercept levels might help in identifying overtreatment and undertreatment and optimise etanercept therapy in AS.

A genome-wide association study of rheumatoid arthritis without antibodies against citrullinated peptides.

INTRODUCTION: Rheumatoid arthritis (RA) patients can be classified based on presence or absence of anticitrullinated peptide antibodies (ACPA) in their serum. This heterogeneity among patients may reflect important biological differences underlying the disease process. To date, the majority of genetic studies have focused on the ACPA-positive group. Therefore, our goal was to analyse the genetic risk factors that contribute to ACPA-negative RA. METHODS: We performed a large-scale genome-wide association study (GWAS) in three Caucasian European cohorts comprising 1148 ACPA-negative RA patients and 6008 controls. All patients were screened using the Illumina Human Cyto-12 chip, and controls were genotyped using different genome-wide platforms. Population-independent analyses were carried out by means of logistic regression. Meta-analysis with previously published data was performed as follow-up for selected signals (reaching a total of 1922 ACPA-negative RA patients and 7087 controls). Imputation of classical HLA alleles, amino acid residues and single nucleotide polymorphisms was undertaken. RESULTS: The combined analysis of the studied cohorts resulted in identification of a peak of association in the HLA-region and several suggestive non-HLA associations. Meta-analysis with previous reports confirmed the association of the HLA region with this subset and an observed association in the CLYBL locus remained suggestive. The imputation and deep interrogation of the HLA region led to identification of a two amino acid model (HLA-B at position 9 and HLA-DRB1 at position 11) that accounted for the observed genome-wide associations in this region. CONCLUSIONS: Our study shed light on the influence of the HLA region in ACPA-negative RA and identified a suggestive risk locus for this condition.

Patients non-responding to etanercept obtain lower etanercept concentrations compared with responding patients.

OBJECTIVE: To investigate the relationship between serum etanercept levels and clinical response. METHODS: In 292 etanercept-treated patients with rheumatoid arthritis clinical and pharmacological data were determined at baseline and after 1, 4 and 6 months of etanercept treatment. Differences in etanercept levels between good, moderate and European League Against Rheumatism (EULAR) non-responders were assessed after 6 months of therapy. RESULTS: After 6 months of therapy etanercept levels were significantly higher in good responders (median (IQR) 3.78 (2.53-5.17)) compared with both moderate 3.10 (2.12-4.47) and EULAR non-responders 2.80 (1.27-3.93) (all p<0.05). There was a significant association between clinical response and serum etanercept levels (regression coefficient 0.54, 95% CI 0.21 to 0.86, p=0.001). When patients were categorised into quartiles according to the height of etanercept levels, the lowest quartile (etanercept level <2.1 mg/l) comprised 40% of all non-responders. The highest quartile (etanercept level >4.7 mg/l) comprised 35% of all good EULAR responders. Anti-etanercept antibodies were detected in none of the sera. CONCLUSION: The authors demonstrated that lower etanercept levels were associated with non-response. Therapeutic drug monitoring and the possibility of the adjusted dosing regimes in the selected groups of patients should be investigated further as a possible tool to optimise treatment with etanercept.

Venous and arterial thromboembolic events in adalimumab-treated patients with antiadalimumab antibodies: a case series and cohort study.

OBJECTIVE: We observed 3 patients who developed severe venous and arterial thromboembolic events during treatment with adalimumab, 2 of whom had rheumatoid arthritis (RA) and 1 of whom had psoriatic arthritis. Antiadalimumab antibodies were detected in all 3 patients. We undertook this study to determine whether the development of antiadalimumab antibodies was associated with thromboembolic events during adalimumab treatment. METHODS: A retrospective search (with blinding with regard to antiadalimumab antibody status) for thromboembolic events was performed in a prospective cohort of 272 consecutively included adalimumab-treated RA patients. Incidence rates were calculated and hazard ratios (HRs) were estimated using Cox regression. None of the index patients were part of the cohort. RESULTS: Antiadalimumab antibodies were detected in 76 of 272 patients (28%). Eight thromboembolic events were found, 4 of which had occurred in patients with antiadalimumab antibodies. The incidence rate was 26.9/1,000 person-years for patients with antiadalimumab antibodies and 8.4/1,000 person-years for patients without those antibodies (HR 3.8 [95% confidence interval 0.9-15.3], P = 0.064). After adjustment for duration of followup, age, body mass index, erythrocyte sedimentation rate, and prior thromboembolic events, the HR was 7.6 (95% confidence interval 1.3-45.1) (P = 0.025). CONCLUSION: These findings suggest that the occurrence of venous and arterial thromboembolic events during adalimumab treatment is higher in patients with antiadalimumab antibodies than in those without antiadalimumab antibodies. Patient numbers were relatively small; therefore, validation in other cohorts is mandatory.

Longitudinal humoral response after SARS-CoV-2 vaccination in ocrelizumab treated MS patients: To wait and repopulate?

OBJECTIVE: The objective of this study was to measure humoral responses after SARS-CoV-2 vaccination in MS patients treated with ocrelizumab (OCR) compared to MS patients without disease modifying therapies (DMTs) in relation to timing of vaccination and B-cell count. METHODS: OCR treated patients were divided into an early and a late group (cut-off time 12 weeks between infusion and first vaccination). Patients were vaccinated with mRNA-1273 (Moderna). B-cells were measured at baseline (time of first vaccination) and SARS-CoV-2 antibodies were measured at baseline, day 28, 42, 52 and 70. RESULTS: 87 patients were included (62 OCR patients, 29 patients without DMTs). At day 70, seroconversion occurred in 39.3% of OCR patients compared to 100% of MS patients without DMTs. In OCR patients, seroconversion varied between 26% (early group) to 50% (late group) and between 27% (low B-cells) to 56% (at least 1 detectable B-cell/µL). CONCLUSIONS: Low B-cell counts prior to vaccination and shorter time between OCR infusion and vaccination may negatively influence humoral response but does not preclude seroconversion. We advise OCR treated patients to get their first vaccination as soon as possible. In case of an additional booster vaccination, timing of vaccination based on B-cell count and time after last infusion may be considered.

Anti-infliximab antibodies are already detectable in most patients with rheumatoid arthritis halfway through an infusion cycle: an open-label pharmacokinetic cohort study.

BACKGROUND: This study in patients with rheumatoid arthritis (RA) treated with infliximab describes prospectively the course of (anti)infliximab levels within an infusion cycle to assess at what moment patients develop low/no infliximab trough levels and/or detectable anti-infliximab levels. METHODS: Infliximab treated RA patients were included in this descriptive open-label cohort study. During one infusion cycle (anti-)infliximab levels were assessed just before and one hour after infusion, and subsequently at 50%, 75% and at the end of the infusion cycle (pre-infusion). RESULTS: 27 patients were included. The median infliximab levels decreased from 77.0 mg/l (p25-p75: 65-89) one hour after the infusion to pre-infusion levels of 0.0 mg/l (p25-p75: 0.0-3.1). In 7 (26%) patients pre-infusion anti-infliximab antibodies were detected; these antibodies were already present halfway through the infusion cycle in 5 of the 7 individuals. Patients with detectable pre-infusion anti-infliximab antibodies have significantly more often low/no infliximab levels (< 1 mg/l) halfway trough the infusion cycle (in 5/7 patients) compared to patients without detectable pre-infusion anti-infliximab antibodies (0/20 patients, p < 0.001). CONCLUSIONS: Most anti-infliximab forming patients have detectable anti-infliximab antibodies halfway through an infusion cycle, which implies that these patients are exposed to nontherapeutical infliximab levels during more than half of their infusion cycle. As none of the patients without anti-infliximab antibodies had no/low-infliximab levels halfway through the infusion cycle, the presence of pre-infusion anti-infliximab antibodies seems a sensitive and specific predictor for no/low infliximab-levels.

Spinning straw into gold: description of a disruptive rheumatology research platform inspired by the COVID-19 pandemic.

Clinical research projects often use traditional methods in which data collection and signing informed consent forms rely on patients' visits to the research institutes. However, during challenging times when the medical community is in dire need of information, such as the current COVID-19 pandemic, it becomes more urgent to use digital platforms that can rapidly collect data on large numbers of patients. In the current manuscript, we describe a novel digital rheumatology research platform, consisting of almost 5000 patients with autoimmune diseases and healthy controls, that was set up rapidly during the COVID-19 pandemic, but which is sustainable for the future. Using this platform, uniform patient data can be collected via questionnaires and stored in a single database readily available for analysis. In addition, the platform facilitates two-way communication between patients and researchers, so patients become true research partners. Furthermore, blood collection via a finger prick for routine and specific laboratory measurements has been implemented in this large cohort of patients, which may not only be applicable for research settings but also for clinical care. Finally, we discuss the challenges and potential future applications of our platform, including supplying tailored information to selected patient groups and facilitation of patient recruitment for clinical trials.

Circulating microparticles remain associated with complement activation despite intensive anti-inflammatory therapy in early rheumatoid arthritis.

OBJECTIVES: Rheumatoid arthritis (RA) is a chronic systemic inflammatory disease characterised by synovitis and joint destruction. The pathogenesis of RA is not clear, but is considered to be an immune-mediated inflammatory disorder, in which the complement system plays an important role. Although cell-derived microparticles (MPs) have been associated with inflammation and complement activation, it is unknown whether MPs are either cause or consequence. Therefore, we investigated whether circulating MPs differ between patients with very early as yet untreated arthritis and healthy controls, and whether intensive anti-inflammatory treatment of such patients affects circulating MPs. METHODS: Patients with RA (n=24) and controls (n=15) were included. Nine patients with RA were re-evaluated after 8 weeks of intensive treatment with a combination of drugs ('COmBination therapy in Rheumatoid Arthritis' (COBRA) scheme). Disease activity was measured by erythrocyte sedimentation rate (ESR), C reactive protein (CRP) and Disease Activity Score for 28 joints (DAS28). Flow cytometry was used to study MPs and exposure of complement activator molecules and complement components. RESULTS: At baseline, concentrations of MPs exposing C1q, CRP or serum amyloid-P (SAP)were all significantly elevated in patients with early RA compared to controls (p=0.003, p=0.002 and p=0.003, respectively). Upon treatment, DAS28 score, ESR and CRP levels significantly decreased (p=0.008, p=0.008 and p=0.012), but the concentrations of circulating MPs and MPs exposing complement components or activator molecules were unaffected. CONCLUSION: Circulating MPs exposing complement components or activator molecules are elevated in early RA. Since a strong anti-inflammatory therapy suppressed inflammation in patients with early RA but not levels of circulating MPs, it is unlikely that inflammation is the main underlying cause of MP release in these patients.

Clinical response, pharmacokinetics, development of human anti-chimaeric antibodies, and synovial tissue response to rituximab treatment in patients with rheumatoid arthritis.

OBJECTIVES: To analyse whether persistence of synovial B lineage cells and lack of clinical response to rituximab treatment in patients with rheumatoid arthritis (RA) are associated with low rituximab serum levels and anti-rituximab antibody (ARA) formation. METHODS: Fifty-eight patients with RA were treated with rituximab. The clinical response was determined 24 weeks after each treatment course using the Disease Activity Score evaluated in 28 joints (DAS28) and EULAR response criteria. Rituximab serum levels, ARAs and synovial B lineage cell numbers were determined before and after treatment. RESULTS: Four weeks after treatment rituximab serum levels were highly variable. Low rituximab levels were associated with ARA formation (in five patients (8.6%)) and high baseline erythrocyte sedimentation rate. Interestingly, serum rituximab levels were not related to persistence of synovial B lineage cells or clinical response. Furthermore, response to treatment and re-treatment was similar in ARA-positive and ARA-negative patients. CONCLUSION: There is clear variability in serum levels after rituximab treatment, but rituximab levels are not lower in patients with persistence of synovial B lineage cells or lack of clinical response. The current treatment schedule suffices to induce and maintain a clinical response, even when ARAs are formed.

Anti-infliximab and anti-adalimumab antibodies in relation to response to adalimumab in infliximab switchers and anti-tumour necrosis factor naive patients: a cohort study.

OBJECTIVE: To investigate how antibodies against anti-tumour necrosis factor (anti-TNF) agents influence response after switching from infliximab to adalimumab in rheumatoid arthritis (RA). METHODS: This cohort study consisted of 235 patients with RA, all treated with adalimumab. At baseline 52 patients (22%) had been previously treated with infliximab ('switchers'), and 183 (78%) were anti-TNF naive. Disease activity (using the 28-joint count Disease Activity Score (DAS28)) and presence of antibodies against infliximab and adalimumab were assessed. Clinical response to adalimumab was compared between switchers and anti-TNF naive patients and their anti-infliximab and anti-adalimumab antibody status. RESULTS: After 28 weeks of adalimumab treatment the decrease in DAS28 (Delta DAS28) for the 235 patients was 1.6+/-1.5 (mean+/-SD). Anti-adalimumab antibodies were detected in 46 patients (20%). Delta DAS28 was 1.8+/-1.4 in patients without anti-adalimumab and 0.6+/-1.3 in patients with anti-adalimumab (p<0.0001). Thirty-three of the 52 switchers (63%) had anti-infliximab antibodies. Patients with anti-infliximab more often developed anti-adalimumab than anti-TNF naive patients (11 (33%) vs 32 (18%); p=0.039). Delta DAS28 was greater for anti-TNF naive patients (1.7+/-1.5) than for switchers without anti-infliximab antibodies (Delta DAS28=0.9+/-1.4) (p=0.009). Delta DAS28 for switchers with anti-infliximab was 1.2+/-1.3 and did not differ significantly from anti-TNF naive patients (p=0.262). CONCLUSION: Switchers with anti-infliximab antibodies more often develop antibodies against adalimumab than anti-TNF naive patients. Response to adalimumab was limited in switchers without anti-infliximab antibodies, which raises the question whether a second anti-TNF treatment should be offered to patients with RA for whom an initial treatment with an anti-TNF blocker fails, in the absence of anti-biological antibodies.

Arthritis development in patients with arthralgia is strongly associated with anti-citrullinated protein antibody status: a prospective cohort study.

BACKGROUND: Anti-citrullinated protein antibodies (ACPA) are associated with increased risk for rheumatoid arthritis. OBJECTIVE: To investigate the effect of the presence and levels of ACPA on arthritis development in patients with arthralgia. METHODS: Patients with arthralgia positive for ACPA or IgM rheumatoid factor (IgM-RF) were tested for the shared epitope (SE) and were prospectively followed up for at least 12 months. Absence of clinical arthritis at inclusion and arthritis development during follow-up were independently confirmed by two investigators. Cox regression hazard analyses were used to calculate hazard ratios (HRs) for arthritis development. RESULTS: 147 patients with arthralgia were included (50 ACPA positive, 52 IgM-RF positive and 45 positive for both antibodies). After a median follow-up of 28 months (interquartile range (IQR) 19-39), 29 patients developed arthritis in a median of 4 (IQR 3-6) joints and 26 (90%) of these were ACPA positive. The presence of ACPA (HR = 6.0; 95% confidence interval (95% CI) 1.8 to 19.8; p = 0.004), but not of IgM-RF (HR = 1.4, 95% CI 0.6 to 3.1) nor the SE (HR = 1.5, 95% CI 0.7 to 3.0), was associated with arthritis development. Within the group of ACPA-positive patients, the risk for arthritis was enhanced by the presence of IgM-RF (HR = 3.0; 95% CI 1.4 to 6.9; p = 0.01) and high ACPA levels (HR = 1.7; 95% CI 1.1 to 2.5; p = 0.008), but not the SE (HR = 1.0; 95% CI 0.5 to 2.1; p = 1.0). CONCLUSION: In patients with arthralgia the presence of ACPA (but not of IgM-RF or SE) predicts arthritis development. The risk in ACPA-positive patients may be further increased by the concomitant presence of IgM-RF or high levels of ACPA.

The formation of autoantibodies and antibodies to TNF-α blocking agents in relation to clinical response in patients with ankylosing spondylitis.

OBJECTIVES: To investigate the influence of antibody formation to TNF-α blocking agents on the clinical response in AS patients treated with infliximab (IFX), etanercept (ETA), or adalimumab (ADA), and to investigate the development of ANA, ANCA, and anti-dsDNA antibodies in association with the formation of antibodies to TNF-α blocking agents. METHODS: Consecutive AS outpatients with active disease who started treatment with IFX (n=20), ETA (n=20), or ADA (n=20) were included in this longitudinal observational study. Clinical data were collected prospectively at baseline and after 3, 6, and 12 months of anti-TNF-α treatment. At the same time points, serum samples were collected. In these samples, antibodies to TNF-α blocking agents, serum TNF-α blocker levels, and ANA, ANCA, and anti-dsDNA antibodies were measured retrospectively. RESULTS: Anti-IFX, anti-ETA, and anti-ADA antibodies were induced in 20%, 0%, and 30% of patients, respectively. Although ANA, ANCA, and anti-dsDNA antibodies were detected during anti-TNF-α treatment, no significant association was found between the presence of these autoantibodies and the formation of antibodies to TNF-α blocking agents. Patients with anti-IFX or anti-ADA antibodies had significantly lower serum TNF-α blocker levels compared to patients without these antibodies. Furthermore, significant negative correlations were found between serum TNF-α blocker levels and assessments of disease activity. CONCLUSIONS: This study indicates that antibody formation to IFX or ADA is related to a decrease in efficacy and early discontinuation of anti-TNF-α treatment in AS patients. Furthermore, autoantibody formation does not seem to be associated with antibody formation to TNF-α blocking agents.

Preferential decrease in IgG4 anti-citrullinated protein antibodies during treatment with tumour necrosis factor blocking agents in patients with rheumatoid arthritis.

OBJECTIVE: To investigate the dynamics of IgG1 and IgG4 anti-citrullinated protein antibody (ACPA) subclasses during anti-tumour necrosis factor (TNF) treatment in patients with rheumatoid arthritis (RA). METHODS: IgG, IgG1 and IgG4 ACPA levels were determined by ELISA on anti-citrullinated fibrinogen (ACF) and IgG1 : IgG4 ACPA ratios were calculated. A pilot study was performed in 28 ACF-positive patients treated with infliximab for one year. Confirmation of the results was obtained using a cohort of 180 consecutive patients treated with adalimumab for 28 weeks. RESULTS: The median reduction in ACF levels was 31% for total IgG, 29% for IgG1, 40% for IgG4 and 22% for the IgG4 : IgG1 ACF ratio in the infliximab cohort. In adalimumab-treated patients, ACF levels declined 14% for total IgG and IgG1, and 36% for IgG4 ACF; the IgG4 : IgG1 ratio was reduced by 24% (all percentage values p<0.05). The decrease in antibody levels was correlated with the clinical response; European League Against Rheumatism good responders had the greatest decline in antibody levels and this effect was most pronounced for IgG4 (48% reduction). The IgG4 : IgG1 ACF ratio preferentially decreased in patients with adequate therapeutic adalimumab levels. CONCLUSION: ACPA subclass distribution is modulated by effective anti-inflammatory treatment. The preferential decline of IgG4 ACPA, reflected by the decreased IgG4 : IgG1 ratio, suggests a beneficial effect of anti-TNF treatment on chronic antigenic stimulation by citrullinated proteins. This effect may be directly anti-TNF mediated or the result of effective dampening of the inflammation in the rheumatoid joint.