Background/Purpose: Multiple studies demonstrate that ACPAs are elevated in the serum years prior to the onset of seropositive RA during a preclinical period of autoimmunity. Importantly, the mechanisms and site of development ACPAs as well as their initial antigen targets in the preclinical period are unknown, although data suggest that initial production may occur at a mucosal site such as the lung. Therefore, we sought to explore ACPAs in the lung of subjects with RA and at-risk of future RA.

Methods: From the Studies of the Etiology of RA cohort, we included 17 established RA subjects, 45 subjects At-Risk of RA and 16 healthy Controls. RA subjects were all serum anti-CCP3.1 positive (IgG/IgA, Inova). At-Risk subjects were without RA, were at-risk of future RA based on familial (i.e. first-degree relative of RA patient) or serologic (i.e. serum anti-CCP3.1 positive identified in clinics or health fairs) risk, and included 19/45 (42%) who were serum anti-CCP3.1 positive. Paired serum and induced sputum were tested using a bead-based ACPA array for IgG reactivity to 29 individual citrullinated proteins/peptides and quantified by fluorescent intensity. A separate cohort of 22 healthy controls were used to set ACPA positive cut-off levels at a level that was positive in <5% of these controls. For analysis, At-Risk subjects were stratified as Serum ACPA(+) and Serum ACPA(-) based on our array results.

Results: Subject demographics are listed in the Table. Compared to Controls, positivity of ≥1 sputum ACPA was higher in RA (71%, p<0.01) and At-Risk subjects (40%, p=0.01). The median number of positive sputum ACPAs was higher in RA (p<0.01) and Serum ACPA(+) At-Risk subjects (p<0.01) compared to Controls. Several individual sputum ACPAs were more prevalent in RA and At-Risk subjects compared to Controls (Table footnotes 5-7). Of interest, antibodies to citrullinated fibrinogen, fibronectin and apolipoprotein E were more prevalent in Serum ACPA(-) and Serum ACPA(+) At-Risk subject compared to Controls. In RA, antibodies to citrullinated fibrinogen and fibronectin peptides were more prevalent than in Controls.

Conclusion: In this pilot study, we found ≥1 sputum ACPA in 71% of RA and 40% of At-Risk subjects. These data support our prior finding of elevated sputum anti-CCP-IgG in At-Risk and RA subjects by ELISA testing (Willis 2013). Furthermore, 25% of Serum ACPA(-) At-Risk subjects were sputum ACPA positive supporting these ACPAs may originate in the lung. In particular, citrullinated fibrinogen, fibronectin and apolipoprotein E may be early antigenic targets in the lung during preclinical phases of RA. Finally, the number of sputum ACPAs positive increased from Controls to Serum ACPA(+) At-Risk to RA subjects suggesting that epitope spreading likely occurs in the lung during phases of RA development. Additional longitudinal studies are needed to confirm and extend these findings as well as evaluate non-citrullinated protein reactivities in the lung.  

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/sputum-antibodies-to-individual-citrullinated-proteinpeptide-antigens-are-elevated-in-subjects-at-risk-of-future-ra-and-subjects-with-established-disease/