IgA rheumatoid factor in mucosal fluids and serum of patients with rheumatoid arthritis: immunological aspects and clinical significance

Exhaled Nitric Oxide Reflects the Immune Reactions of the Airways in Early Rheumatoid Arthritis

Patients with rheumatoid arthritis (RA) have altered levels of exhaled nitric oxide (NO) compared with healthy controls. Here, we investigated whether the clinical features of and immunological factors in RA pathogenesis could be linked to the NO lung dynamics in early disease. A total of 44 patients with early RA and anti-citrullinated peptide antibodies (ACPAs), specified as cyclic citrullinated peptide 2 (CCP2), were included. Their exhaled NO levels were measured, and the alveolar concentration, the airway compartment diffusing capacity and the airway wall concentration of NO were estimated using the Högman-Meriläinen algorithm. The disease activity was measured using the Disease Activity Score for 28 joints. Serum samples were analysed for anti-CCP2, rheumatoid factor, free secretory component, secretory component containing ACPAs, antibodies against Porphyromonas gingivalis (Rgp) and total levels of IgA, IgA1 and IgA2. Significant negative correlations were found between the airway wall concentration of NO and the number of swollen joints (Rho -0.48, p = 0.004), between the airway wall concentration of NO and IgA rheumatoid factor (Rho -0.41, p = 0.017), between the alveolar concentration and free secretory component (Rho -0.35, p = 0.023) and between the alveolar concentration and C-reactive protein (Rho -0.36, p = 0.016), but none were found for anti-CCP2, IgM rheumatoid factor or the anti-Rgp levels. In conclusion, altered NO levels, particularly its production in the airway walls, may have a role in the pathogenesis of ACPA-positive RA.

IgA immunoglobulin isotype of rheumatoid factor in primary Sjögren's syndrome

Primary Sjögren’s syndrome (pSS) is an autoimmune disease with autoantibodies overproduction, including rheumatoid factors (RF). RF-IgA, IgG immunoglobulin classes are suggested as potential biomarkers of pSS. We studied 76 patients with pSS (ACR/Eular 2017); laboratory tests included ESR, C-reactive protein, concentrations of gamma globulins, RF, Anti-SS-A/Ro, and anti-SS-B/La. Eye dryness and keratoconjunctivitis sicca were confirmed with Schirmer’s test, the ocular staining score (OSS) using lissamine green, fluorescein staining and biopsy of minor salivary gland with the histopathological evaluation. Differences between groups were analyzed with U Mann–Whitney test. Correlations between quantitative variables were assessed with the Spearman correlation coefficient.. The best diagnostic values of immunoglobulin concentration for discriminating pSS patients and healthy individuals are for RF-IgA. With cut-off of 21.5 EU/mL, the sensitivity is 72% and specificity is 100%. Very high specificity (100%) is also obtained for RF-IgM concentration of 74.1 EU/mL. Sensitivity is, however, smaller than that for RF-IgA and amounted to 61%. The RF-IgG is the poorest indicator of pSS with 51% of sensitivity and 95% of specificity. To summarize RF-IgA strongly associate with anti-SS-A and anti-SS-B autoantibodies. Both RF-IgA and RF-IgM may be used as diagnostic tools for pSS. Conclusions: among the three studied rheumatoid factor subtypes, RF-IgA showed the best diagnostic accuracy for pSS. RF-IgA correlated with anti-SS-A/Ro and anti-SS-B antibodies even more closely than RF-IgM. The assessment of the RF-IgA serum concentration may be helpful in the process of establishing pSS diagnosis.

Rheumatoid arthritis and the mucosal origins hypothesis: protection turns to destruction

Individuals at high risk of developing seropositive rheumatoid arthritis (RA) can be identified for translational research and disease prevention studies through the presence of highly informative and predictive patterns of RA-related autoantibodies, especially anti-citrullinated protein antibodies (ACPAs), in the serum. In serologically positive individuals without arthritis, designated ACPA positive at risk, the presence of mucosal inflammatory processes associated with the presence of local ACPA production has been demonstrated. In other at-risk populations, local RA-related autoantibody production is present even in the absence of serum autoantibodies. Additionally, a proportion of at-risk individuals exhibit local mucosal ACPA production in the lung, as well as radiographic small-airway disease, sputum hypercellularity and increased neutrophil extracellular trap formation. Other mucosal sites in at-risk individuals also exhibit autoantibody production, inflammation and/or evidence of dysbiosis. As the proportion of individuals who exhibit such localized inflammation-associated ACPA production is substantially higher than the likelihood of an individual developing future RA, this finding raises the hypothesis that mucosal ACPAs have biologically relevant protective roles. Identifying the mechanisms that drive both the generation and loss of externally focused mucosal ACPA production and promote systemic autoantibody expression and ultimately arthritis development should provide insights into new therapeutic approaches to prevent RA.

Associations with smoking and shared epitope differ between IgA- and IgG-class antibodies to cyclic citrullinated peptides in early rheumatoid arthritis

OBJECTIVE

Smoking and HLA-DRB1/shared epitope (SE) alleles are risk factors for rheumatoid arthritis (RA) characterized by seropositivity for antibodies targeting citrullinated proteins (ACPAs)/cyclic citrullinated peptides (anti-CCP). Previously, mainly IgG-class antibodies have been studied. IgA-class antibodies are to a great extent related to mucosal immunity. The aim of this study was to explore interrelations between cigarette smoking, presence of SE, and seropositivity for circulating IgA and/or IgG anti-CCP antibodies among patients with early RA, to determine whether ACPAs of the IgA subclass are regulated by different mechanisms than those of the IgG subclass.

METHODS

Two cohorts of patients with early RA, from the first Epidemiological Investigations of RA trial (n = 1,663) and the second Early Intervention in RA trial (n = 199), were grouped into 4 subsets based on anti-CCP subclass status (IgG-/IgA-, IgG-/IgA+, IgG+/IgA-, and IgG+/IgA+), and each subset was compared with regard to associations with smoking (current and former) and presence of SE. Interaction between smoking and SE was calculated using the attributable proportion (AP) due to interaction (assessing deviation from additivity of effects).

RESULTS

Smoking was overrepresented among IgA anti-CCP-positive RA patients, regardless of whether IgG anti-CCP were present, whereas in patients with IgG anti-CCP alone, no association with smoking was found. SE alleles were overrepresented among IgG anti-CCP-positive patients, regardless of IgA anti-CCP status, and was not seen in patients with IgA anti-CCP alone. An interaction between ever smoking and SE was found with regard to the risk of IgG+/IgA+ RA (AP 0.5, 95% confidence interval 0.4, 0.6). No significant interaction was observed with regard to the risk of IgG-/IgA+ RA or IgG+/IgA- RA.

CONCLUSION

In patients with RA, a history of ever smoking was associated with seropositivity for IgA anti-CCP antibodies, whereas presence of SE was associated with seropositivity for IgG anti-CCP antibodies. An interaction between ever smoking and the SE was limited to the RA subset characterized by seropositivity for both IgG and IgA anti-CCP. These findings provide novel evidence that anti-CCP-positive RA can be divided into at least 3 serologically distinct subsets associated with different risk factors, indicating different modes of pathogenesis in RA.

Sputum autoantibodies in patients with established rheumatoid arthritis and subjects at risk of future clinically apparent disease

OBJECTIVE

To evaluate the generation of rheumatoid arthritis (RA)-related autoantibodies in the lung.

METHODS

Simultaneous collection of serum and induced sputum was performed in 21 healthy controls, 49 at-risk subjects without inflammatory arthritis but at risk of RA due to family history or seropositivity for anti-citrullinated protein antibodies, and 14 subjects with early RA. Samples were tested for anti-cyclic citrullinated peptide 2 (anti-CCP2), anti-CCP3, anti-CCP3.1, rheumatoid factor isotypes IgM, IgG, and IgA, and total IgM, IgG, and IgA.

RESULTS

One or more autoantibodies were present in sputum of 39% of at-risk seronegative subjects, 65% of at-risk seropositive subjects, and 86% of subjects with early RA. In at-risk seronegative subjects, the rate of anti-CCP3.1 positivity and the median number of autoantibodies were elevated in sputum versus serum. In subjects with early RA, the rate of positivity for several individual autoantibodies and the median number of autoantibodies were higher in serum than in sputum. Results in at-risk seropositive subjects were intermediate between these groups. In at-risk subjects with autoantibody positivity in sputum, the ratios of autoantibody to total Ig were higher in sputum than in serum, suggesting that these autoantibodies are generated or sequestered in the lung.

CONCLUSION

RA-related autoantibodies are detectable in sputum in subjects at risk of RA and in subjects with early RA. In a subset of at-risk subjects, the presence of sputum autoantibodies in the absence of seropositivity, and the increased autoantibody-to-total Ig ratios in sputum, suggest that the lung may be a site of autoantibody generation in the early development of RA. These findings suggest an important role of the lung in the pathogenesis of RA.