Background/Purpose Recent data suggest rheumatoid arthritis (RA) may originate from an autoimmune response in inflamed mucosa. RA is associated with gingival and airway inflammation and alterations in the microbiomal composition in the gut. Furthermore, anti-citrullinated (cit) protein antibodies (ACPA) of the IgA class, the main secreted mucosal antibody, precede arthritis by years in a proportion of RA patients. When aiming to prevent arthritis it is critical to understand the source and regulation of autoantibody production in preclinical RA.

Objective to determine whether ACPA are produced at mucosal sites in ACPA positive individuals at risk for RA and to compare the ACPA isotype and fine specificity in mucosal fluids to peripheral blood.

Methods Saliva, sputum, faeces and peripheral blood were collected from 15 individuals with anti-cyclic cit protein (anti-CCP2) antibody positive arthralgia who are part of a cohort that is being prospectively followed for the possible development of arthritis. Saliva and sputum were collected during an early morning visit. Sputum was induced by inhalation of sodium chloride aerosols 4.5%. Mucus plugs were selected from sputum for extraction of supernatants. Faeces was collected at the same visit using stool collection kits and extracted using 6% BSA phosphate buffered saline. ACPA of IgA and IgG class were measured in mucosal fluids and blood using two cit fibrinogen peptides, one enolase peptide and one vimentin peptide and their respective arginine peptides as control.

Results Thirteen of 15 individuals tested positive for the anti-CCP2 test and ACPA in their blood at the day of mucosal fluid collection. Two patients tested positive for anti-CCP2 but negative for ACPA. Two other patients had high reactivity against both cit peptides and arginin controls and were also considered ACPA negative. Anti-cit fibrinogen, enolase and vimentin antibodies were detected in respectively 11, 4 and 3 individuals. The saliva of 4 patients contained IgA ACPA with positive tests for anti-cit enolase and anti-cit fibrinogen. The saliva of another patient tested positive for IgG anti-cit enolase and anti-cit fibrinogen. Other saliva, sputum and faeces samples tested negative for ACPA. All 5 patients with ACPA in saliva tested positive for the same antibodies in blood. In addition, in 3 of 5 patients ACPA were detected in blood that were not detected in saliva, including anti-cit fibrinogen, anti-cit vimentin and anti-cit enolase antibodies.

Conclusion Collection of saliva allows for the detection of ACPA in the saliva of a proportion of anti-CCP positive individuals at risk for RA. In these patients, IgG ACPA in blood are directed against more peptides compared to IgA ACPA in saliva. Future analyses should focus on further defining the precise source and regulation of mucosal ACPA compared to systemic ACPA. 

Acknowledgements The Dutch Reumafonds.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-mucosal-anti-citrullinated-protein-antibody-response-in-pre-clinical-rheumatoid-arthritis/