Secretory anti-citrullinated protein antibodies in serum associate with lung involvement in early rheumatoid arthritis

Abstract

Objective: A 'mucosal connection' in RA presently attracts increasing attention. We recently described the occurrence of secretory antibodies to citrullinated protein (SC-ACPA) in sera from patients with recent-onset RA. The current study was performed to evaluate possible associations between serum levels of secretory ACPA and signs of lung involvement in patients with early, untreated RA.

Methods: One hundred and forty-two RA patients were included as part of the 'LUng Investigation in newly diagnosed RA' study. One hundred and six patients were examined with high-resolution CT (HRCT) and 20 patients underwent bronchoscopy, where bronchial biopsies and bronchoalveolar lavage fluid (BALF) samples were obtained. SC-ACPA in serum and BALF were detected by an enzyme-linked immunoassay. Antibody levels were related to smoking history, pulmonary function, HRCT, BALF cell counts and findings in bronchial biopsies.

Results: SC-ACPA occurred in 16% of the serum samples and in 35% of the BALF samples. SC-ACPA levels in serum correlated with SC-ACPA levels in BALF (σ = 0.50, P = 0.027) and were higher among patients with HRCT parenchymal lung abnormalities (P = 0.022) or bronchiectasis (P = 0.042). Also, ever smoking was more frequent among serum SC-ACPA-positive patients (91% vs 67%, P = 0.023), and the SC-ACPA levels correlated with the number of pack-years (σ=0.20, P = 0.020).

Conclusion: In early, untreated RA, serum levels of SC-ACPA reflect lung involvement in terms of local ACPA levels, smoking and lung abnormalities on HRCT. These findings strengthen the link between mucosal ACPA responses and the lungs in RA.

Keywords: anti-cyclic citrullinated peptide antibodies (ACPA); mucosal immunity; rheumatoid arthritis (RA); secretory antibodies.

Fig. 1

Smoking and different anti-citrullinated protein antibody isotypes in serum Smoking habits in relation to status (a) and levels (b) of different anti-citrullinated protein antibody (ACPA) isotypes in serum. *=P < 0.05.

Fig. 2

Secretory component-containing anti-citrullinated protein antibodies in relation to lung abnormalities on HRCT Levels of serum secretory component-containing anti-citrullinated protein antibodies (SC-ACPA) in relation to parenchymal (a) and airway (b) findings on HRCT, and levels of BALF SC-ACPA in relation to parenchymal (c) and airway (d) HRCT findings. *=P < 0.05. HRCT: high-resolution CT; BALF: bronchoalveolar lavage fluid.