A1.1  Characterisation of lung inflammation and identification of shared citrullinated targets in the lungs and joints of early rheumatoid arthritis

Background and Objectives To investigate if changes in the lungs are present in rheumatoid arthritis (RA) patients early in the disease process and to address the contribution of these changes to the initiation of the disease. Materials and Methods 24 RA patients with patient-reported symptom duration less than one year and naive to DMARD treatment and 15 healthy individuals were subjected to bronchoscopy and mucosal bronchial biopsies were retrieved. Histological analysis for identification of inducible bronchia associated lymphoid tissues (iBALT) and lymphocyte infiltration, as well as immunohistochemistry (IHC) for PAD enzymes, CD3, HLA-DQ and HLA-DR were performed. Presence of citrullinated targets were detected by IHC using biotinylated ACPA isolated from synovial fluid of RA patients. Mass spectrometry was used for identification of citrullinated epitopes in 6 lung and 8 synovial biopsies from RA patients. An in-house ELISA was setup to measure reactivity against new identified citrullinated targets in the serum of RA patients in two distinct early RA cohorts (n = 393) and a cohort of non-RA patients (n = 236) as disease controls. Results Bronchial lymphocyte infiltration and iBALT formation was observed in 55% of the ACPA+ RA patients but only 17% of ACPA- patients and 7% of healthy volunteers. Higher expression of CD3, HLA-DQ, HLA-DR and citrullinated targets was observed in bronchial biopsies of ACPA+ as compare to ACPA- RA patients. BAL fluids were enriched in both IgG and IgA ACPA as compared to paired serum samples. Mass spectrometry identified 5 proteins in the synovium (in total 8 sites) and 4 in the lungs (in total 6 sites) containing citrullinated residues. Two vimentin derived citrullinated peptides were present in a majority of both synovial and lung biopsies with slightly higher citrullinated/unmodified peptides ratios in the smokers as compared to non-smokers.14.5% of the RA patients tested by ELISA showed antibody reactivity against the new identified citrullinated target compared to 3.4% in the disease controls. Conclusions Signs of inflammation and local ACPA enrichment are present early in bronchial tissues of ACPA+ RA patients. Shared citrullinated targets in the lung and joints as well as systemic reactivity against these targets are present in RA patients. Our findings support the notion that early inflammatory events in the lungs may represent a critical initiating factor in the development of ACPA+ RA.