BackgroundA possible association between mucosal immunization and inflammation, as well as the initiation and propagation of rheumatoid arthritis (RA), is attracting renewed interest. The aim of this study was to evaluate the possible occurrence and clinical correlations of circulating secretory immunoglobulin A (SIgA) antibodies against the second-generation cyclic citrullinated peptides (CCP) among patients with recent-onset RA followed prospectively over 3 years.MethodsBaseline serum samples from 636 patients with recent-onset RA were analyzed for SIgA anti-CCP antibodies by using an enzyme-linked immunosorbent assay with a secondary antibody directed against secretory component. SIgA anti-CCP status at baseline was analyzed in relation to smoking, HLA-DRB1/shared epitope (SE), and the disease course over 3 years. Significant findings were evaluated in regression analysis that included age, sex, smoking, and SE.ResultsSeventeen percent of the patients tested positive for circulating SIgA anti-CCP, and the occurrence was confirmed by detection of secretory component in an affinity-purified IgA anti-CCP fraction. SIgA anti-CCP positivity at baseline was associated with slightly higher baseline erythrocyte sedimentation rate (ESR) (mean 38 vs. 31 mm/first hour, p = 0.004) and C-reactive protein (CRP) (mean 30 vs. 23 mg/L, p = 0.047). During follow-up, SIgA anti-CCP-positive patients had a higher mean AUC regarding ESR (adjusted p = 0.003), although there were no significant differences regarding CRP, tender and swollen joint counts, or radiological joint damage (median Larsen progression 1.0 vs. 1.0, p = 0.22). SIgA anti-CCP was associated significantly with smoking (79 % ever smokers among SIgA anti-CCP-positive patients vs. 59 % in SIgA anti-CCP-negative patients, adjusted OR 2.19, 95 % CI 1.01–4.37, p = 0.027) but not with carriage of the SE (80 % vs. 73 %, p = 0.62).ConclusionsCirculating SIgA anti-CCP, which is present in a subgroup of patients with early RA, is not related to SE, but it is environmentally linked to cigarette smoking. This finding strengthens the hypothesis that immunization against citrullinated peptides and/or proteins may occur at mucosal surfaces of the airways. Analysis of SIgA antibodies in serum may be a convenient and more versatile means to investigate the “mucosal connection” in RA compared with analyses in mucosal fluid samples.

Rheumatoid arthritis (RA) is a chronic autoimmune inflammatory disease in which autoantibodies, such as anti-citrullinated protein antibodies (ACPA), can be detected in the serum of patients. Autoantibodies may appear in the circulation years before clinical signs of joint inflammation occur, indicating that early immunological pathogenetic steps take place outside of the joints. Although many of these mechanisms are currently unknown, the initial events leading up to ACPA production are thought to occur at mucosal surfaces. In this thesis, mucosa-associated secretory ACPA are investigated in the circulation and in local mucosal secretions to: (i) improve the understanding of the mucosal connection in RA; and (ii) investigate whether these antibodies can improve diagnostics and prognostics in early RA.We identified circulating secretory component containing (SC) ACPA in a subpopulation of patients (both early and established RA) and atrisk patients, with a prevalence of 16%-21%. In addition, SC ACPA was detected in bronchoalveolar lavage fluid (BALF) and IgA ACPA in saliva, indicating local production in the lungs and in the oral cavity. In at-risk patients who were positive for IgG ACPA, we found that the levels of circulating SC ACPA at inclusion predicted arthritis development. Circulating SC ACPA was associated with higher disease activity, including increased levels of inflammatory markers, in patients with early RA. Levels of circulating SC ACPA were associated with high-resolution computed tomography (HRCT) findings (parenchymal lung abnormalities and bronchiectasis) and smoking, but not with risk genes (shared epitope). We confirmed the presence of salivary ACPA and identified a novel association with increased disease activity and functional disability.In summary, SC ACPA is present in the sera of patients with RA who manifest different phases of the disease, and we found associations with arthritis onset, smoking, systemic inflammation, and lung abnormalities. SC ACPA is also detectable in mucosal secretions from the lungs and the oral cavity. These findings suggest that mucosal ACPA production may be an important factor in RA development and progression, and that serum SC ACPA should be further evaluated as a prognostic marker for disease onset among at-risk individuals.

Background Chronic mucosal irritation, by for instance smoking or periodontitis-associated microbes, has been suggested to be a key etiological trigger in anti-citrullinated protein antibody (ACPA) positive arthritis. Although circulating IgA-ACPAs, which are mainly monomeric, may associate with a worse disease course, the importance of dimeric secretory IgA- (sIgA-) ACPA at mucosal surfaces remains poorly defined. Levels of sIgA-ACPA in serum could possibly reflect ongoing immune responses to citrullinated proteins at mucosal surfaces, allowing for more convenient analyses than using mucosal fluids. Objectives To investigate whether sIgA-ACPA occurs in serum from patients with rheumatoid arthritis (RA), and to determine its relationship to disease severity, smoking, dental health, and levels of salivary IgA-ACPA. Methods Patients with established RA (n=113) were recruited at the rheumatology clinic of Falun Hospital, Sweden. Sampling of serum, saliva and clinical measures were collected at the same occasion. Disease activity was assessed by the 28-joint disease activity score (DAS28), functional ability by the Health Assessment Questionnaire (HAQ), and radiographic joint damage by chart reviews. Dental health and smoking habits were assessed by a questionnaire. ACPAs were detected by enzyme-linked immunoassays (ELISAs) using anti-CCP (aCCP) kits (EuroDiagnostica, Malmö, Sweden) with exchange of detection antibodies to polyclonal goat anti-secretory component for sIgA-aCCP, and polyclonal rabbit anti-human α-chain for IgA-aCCP. 46 blood donors served as controls. The cutoff for positive serum sIgA-aCCP test was set to 50 arbitrary units (AU)/mL, corresponding to >99th percentile of the controls. In saliva, IgA-aCCP was considered positive when the optical density ratio to the corresponding arginine peptide was > 1.5. Results The proportion of patients testing positive for aCCP in serum was 76% for IgG, 43% for IgA, and 26% for sIgA. All patients with a positive IgA-aCCP or sIgA-aCCP test also had IgG-aCCP. At the time of sampling, patients positive for sIgA-aCCP had higher mean DAS28 levels than sIgA-aCCP negative patients (3.7 vs 2.6, respectively, P=0.001), and higher mean HAQ (0.99 vs 0.67, P=0.042). IgA-aCCP in serum showed similar differences, but DAS28 remained higher among sIgA-aCCP positives also when analyzing IgA-aCCP positive patients alone (P=0.01). Regarding IgG-aCCP, no differences were found. Patients testing positive for IgA-aCCP in saliva had higher mean DAS28 (3.7 vs 2.8, P=0.049), while none of the IgA class aCCP tests associated with the presence of joint erosions. All aCCP tests were more often positive among ever smokers, but did not differ according to dental health. Conclusions Circulating sIgA-ACPA occur in RA, and associates with a more aggressive disease at the time of sampling. IgA-aCCP levels in serum and saliva also associate with a higher DAS28 score. As no such difference was seen regarding IgG-aCCP, these findings may suggest that ongoing immune responses to citrullinated...