Multiple genetic and environmental factors have been associated with an increased risk for rheumatoid arthritis (RA). Of these, the strongest associations have been seen with female sex, a family history of RA, the genetic factor the ‘shared epitope’ and with exposure to tobacco smoke. There is also renewed interest in mucosal inflammation and microbial factors as contributors to the development of RA. However, the identification of a ‘preclinical’ period of RA that can be defined as local or systemic autoimmunity as measured by autoantibodies and other biomarkers prior to the development of clinically-apparent synovitis suggests that the risk factors for RA are acting long prior to first clinical evidence of IA. As such, a major challenge to the field will be to investigate the full spectrum of the development of RA, from initiation and propagation of autoimmunity during preclinical RA and transition to clinically-apparent synovitis and classifiable RA, in order to determine which genetic and environmental factors are important at each stage of disease development. Understanding the exact role and timing of action of risk factors for RA is especially important given the advent of prevention trials in RA, and the hope that a full understanding of genetic and environmental factors in RA could lead to effective preventive interventions.

Objectives Studies suggest that rheumatoid arthritis (RA)-related autoimmunity is initiated at a mucosal site. However, the factors associated with the mucosal generation of this autoimmunity are unknown, especially in individuals who are at-risk for future RA. Therefore, we tested anti-cyclic citrullinated peptide (anti-CCP) antibodies in the sputum of RA-free first-degree relatives (FDRs) of RA patients and patients with classifiable RA. Methods We evaluated induced sputum and serum from 67 FDRs and 20 RA subjects for anti-CCP-IgA and anti-CCP-IgG, with cut-off levels for positivity determined in a control population. Sputum was also evaluated for cell counts, neutrophil extracellular traps (NETs) using sandwich ELISAs for protein/nucleic acid complexes, and total citrulline. Results Sputum anti-CCP-IgA and/or anti-CCP-IgG was positive in 17/67 (25%) FDRs and 14/20 (70%) RA subjects, including a portion of FDRs who were serum anti-CCP negative. In FDRs, elevations of sputum anti-CCP-IgA and anti-CCP-IgG were associated with elevated sputum cell counts and levels of NET complexes. Anti-CCP-IgA was associated with ever-smoking and elevated sputum citrulline levels. Conclusions Anti-CCP is elevated in the sputum of FDRs, including seronegative FDRs, suggesting the lung may be one site of anti-CCP generation in this population. The association of anti-CCP with elevated cell counts and NET levels in FDRs supports a hypothesis that local airway inflammation and NET formation may drive anti-CCP production in the lung and may promote the early stages of RA development. Longitudinal studies are needed to follow the evolution of these processes relative to the development of systemic autoimmunity and articular RA.

Objective To evaluate patterns of elevations of isotypes of rheumatoid factor (RF) and anti–citrullinated protein antibodies (ACPAs) pre–rheumatoid arthritis (RA) diagnosis and post–RA diagnosis. Methods Using the Department of Defense Serum Repository we identified 214 RA cases and 210 matched controls. Up to 3 pre–RA diagnosis and 1 post–RA diagnosis serum samples per subject were tested for RF and for IgA, IgG, and IgM ACPAs. The timing and trajectories of elevations of autoantibodies were evaluated. Results Autoantibody levels were elevated in cases versus controls a mean of 17.9 years before RA diagnosis for IgG ACPA, 14.2 years for IgA‐RF, 7.2 years for IgM‐RF, 6.2 years for IgA ACPA, and 5.0 years for both IgM ACPA and IgG‐RF (P < 0.01 for all comparisons). There were similar relationships for positive or negative autoantibody status, with cases first showing positivity for IgG ACPA 1.9 years pre‐RA and for IgA‐RF 1.7 years pre‐RA, followed by the other isotypes. Only IgA ACPA positivity was significantly increased in post–RA diagnosis samples (19% 0–2 years pre‐RA versus 39% >2 years post–RA diagnosis; P = 0.04). All autoantibody levels demonstrated an early initial elevation, a period of stability, then an increase immediately before RA diagnosis. A pre‐RA endotype of early elevation of autoantibodies was associated with increased use of biologic therapy, and a higher prevalence of sicca symptoms and lung disease post–RA diagnosis. Conclusion Differences in patterns of elevations of autoantibody isotypes have implications for understanding the pathophysiology of RA development. These include understanding what factors drive initial autoantibody elevations compared to what factors (including mucosal) drive later increases in autoantibody levels and a transition to clinically apparent RA, and how pre‐RA endotypes may influence post–RA diagnosis phenotypes.

Objective To examine serum autoantibodies to malondialdehyde–acetaldehyde (MAA) prior to rheumatoid arthritis (RA) diagnosis. Methods Concentrations of anti‐MAA antibody isotypes, anti–cyclic citrullinated peptide 2 (anti–CCP‐2), and IgM rheumatoid factor (IgM‐RF) were evaluated before and after RA diagnosis in samples from cases (n = 214) and controls (n = 210). The timing of elevations in autoantibody concentrations relative to RA diagnosis was explored using separate mixed models for each antibody and/or isotype. Associations between prediagnosis autoantibody concentrations in RA patients were examined using mixed effects linear regression models. Results Concentrations of IgG (log2 difference 0.34) and IgA (log2 difference 0.43) anti‐MAA antibodies in RA patients diverged from controls at 3.0 years and 2.3 years prior to diagnosis, respectively (P < 0.05 for both). There was no evidence of case–control divergence for IgM anti‐MAA antibody concentration. Anti–CCP‐2 and IgM‐RF concentrations diverged between RA patients and controls beginning at 17.6 years and 7.2 years prior to RA diagnosis, respectively. All 3 anti‐MAA antibody isotypes (IgA, IgM, and IgG) were significantly associated with anti–CCP‐2 antibody and RF concentrations prior to diagnosis (β = 0.22–0.27 for IgM‐RF; β = 0.44–0.93 for anti–CCP‐2) (P < 0.001). Conclusion IgG and IgA anti‐MAA autoantibodies are elevated prior to RA diagnosis but appear later in the preclinical course than anti–CCP‐2 or RF. These findings suggest that MAA formation and anti‐MAA immune responses could play a role in the transition from subclinical autoimmunity to clinically apparent arthritis.

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Objectives RA develops slowly over years. We tested for metabolic changes prior to RA onset using a large non-targeted metabolomics platform to identify novel pathways and advance understanding of RA development. Methods Two hundred and fifty-four incident RA cases with plasma samples drawn pre-RA onset in the Nurses’ Health Study (NHS) cohorts were matched 1:2 to 501 controls on age, race, menopause/post-menopausal hormone use and blood collection features. Relative abundances of 360 unique, known metabolites were measured. Conditional logistic regression analyses assessed associations between metabolites and incidence of RA, adjusted for age, smoking and BMI, accounting for multiple comparisons. Subgroup analyses investigated seropositive (sero+) RA and RA within 5 years of sample collection. Significant metabolites were then tested in a female military pre-RA case–control study (n = 290). Results In the NHS, metabolites associated with RA and sero+RA in multivariable models included 4-acetamidobutanoate (odds ratio (OR) = 0.80/s.d., 95% CI: 0.66, 0.95), N-acetylputrescine (OR = 0.82, 95% CI: 0.69, 0.96), C5 carnitine (OR = 0.84, 95% CI: 0.71, 0.99) and C5:1 carnitine (OR = 0.81, 95% CI: 0.68, 0.95). These were involved primarily in polyamine and leucine, isoleucine and valine metabolism. Several metabolites associated with sero+RA within 5 years of diagnosis were replicated in the independent military cohort: C5 carnitine (OR = 0.55, 95% CI: 0.33, 0.92), C5:1 carnitine (OR = 0.62, 95% CI: 0.39, 0.99) and C3 carnitine (OR = 0.57, 95% CI: 0.36, 0.91). Conclusion Several metabolites were inversely associated with incidence of RA among women. Three short-chain acylcarnitines replicated in a smaller dataset and may reflect inflammation in the 5-year period prior to sero+RA diagnosis.

Periodontal disease is more common in individuals with rheumatoid arthritis (RA) who have detectable anti-citrullinated protein antibodies (ACPAs), implicating oral mucosal inflammation in RA pathogenesis. Here, we performed paired analysis of human and bacterial transcriptomics in longitudinal blood samples from RA patients. We found that patients with RA and periodontal disease experienced repeated oral bacteremias associated with transcriptional signatures of ISG15 + HLADR hi and CD48 high S100A2 pos monocytes, recently identified in inflamed RA synovia and blood of those with RA flares. The oral bacteria observed transiently in blood were broadly citrullinated in the mouth, and their in situ citrullinated epitopes were targeted by extensively somatically hypermutated ACPAs encoded by RA blood plasmablasts. Together, these results suggest that (i) periodontal disease results in repeated breaches of the oral mucosa that release citrullinated oral bacteria into circulation, which (ii) activate inflammatory monocyte subsets that are observed in inflamed RA synovia and blood of RA patients with flares and (iii) activate ACPA B cells, thereby promoting affinity maturation and epitope spreading to citrullinated human antigens.

While the primary manifestation of rheumatoid arthritis (RA) is articular disease, extra-articular disease may also occur. In particular, pulmonary disease is a frequent extra-articular manifestation of seropositive RA and a leading cause of morbidity and mortality in this population. This review will highlight studies published in the last several years and will, in particular, discuss the relationship of antibodies to citrullinated protein/peptide antigens (ACPA) and lung disease in patients with RA. We will also review the data regarding the potential role of the lung and generation of RA-related autoantibodies in a period of disease development termed "preclinical RA." Finally, we will discuss the role of ACPA and other Abs in non-RA pulmonary diseases and discuss a research agenda for next steps in the understanding and management of the lung in RA.