Background/Purpose: Recent data from our group have demonstrated that RA-related autoantibodies (Abs), including anti-CCP and RF, are detectable in sputum from subjects with early Classified RA (1987 criteria; <1 year from diagnosis) as well as those at elevated risk for future RA (Willis and Demoruelle 2013, in press). In this cross-sectional study, 71% of 49 subjects at elevated risk for future RA (At-Risk) had ≥1 RA-related Ab in sputa. By comparing the ratio of RA-related Ab to total immunoglobulin (Ig) levels in sputa and sera, a subset of these At-Risk subjects appeared to generate RA-related Abs in the lung. These findings support a hypothesis that the lung is a site of initial generation of RA-related autoimmunity; however, the stability and evolution of lung RA-related Abs in subjects at elevated risk for future RA is unknown.

Methods: From the 49 At-Risk subjects previously tested in cross-section, we studied 11 that had follow-up sputum testing (median 19 months from initial testing). These At-Risk subjects were from the Studies of the Etiology of RA (SERA) cohort and at elevated risk for future RA based on family history of RA, or seropositivity for RA-related Abs in absence of synovitis identified through community healthy screenings. All subjects had no history of RA and were without synovitis at the time of sputum testing based on 68-joint examination. Induced sputum was collected using nebulized 5% saline and a protocol designed to minimize salivary contamination. Sputa samples were homogenized with mechanical disruption, and tested for RA-related Abs using ELISAs: CCP2 (IgG, Axis-Shield), CCP3.1 (IgA/IgG, INOVA), and RF isotypes (IgM/A/G, INOVA). Sputum positivity for each RA-related Ab was determined based on previously established cut-off levels (2 standard deviations above the mean level in 21 healthy controls).

Results: In these 11 At-Risk subjects, the median number of RA-related Abs positive in sputa at initial testing was 1.0 (range 0-4). At follow-up, 6/11 (55%) had a net change in the number of positive sputa RA-related Abs. These changes included both gain (N=3) and loss (N=3) of ≥1 RA-related Ab. RF-IgA was the most likely Ab to become positive: 3 of 9 (33%) subjects initially sputa RF-IgA negative were RF-IgA positive in sputa at follow-up. CCP3.1 also detects IgA, and 4/11 (36%) subjects had a change in sputum CCP3.1 status (2 gained positivity, 2 lost positivity). Changes were not associated with smoking status. Additionally, in 4 subjects with Classified RA who had 2 sputa samples collected (median 8 months apart), 1 subject lost positivity for a single RA-related Ab (CCP2), and all other sputa RA-related Abs remained stable on repeat testing.

Conclusion: Sputum RA-related Abs are elevated and fluctuate over time in subjects at elevated risk for future RA. These results may represent evolving immune responses in the lung, and in particular mucosal IgA responses, that may be associated with generation and regulation of RA-related autoimmunity during the development of RA. Going forward, extended longitudinal study of these and additional subjects will be performed to evaluate the relationship between evolution in lung RA-related Abs and the development of serum RA-related Abs and/or incident clinically classifiable RA.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/rheumatoid-arthritis-related-autoantibodies-in-the-lung-evolve-over-time-in-subjects-at-elevated-risk-for-future-rheumatoid-arthritis/