Are sputum autoantibodies more clinically relevant in idiopathic pulmonary fibrosis than serum autoantibodies?

Background: The adaptive immune system plays a role in the pathogenesis of idiopathic pulmonary fibrosis (IPF) has been reported previously. However, the association between airway and circulating autoantibodies (AAbs) levels is unclear. The aim of this study is to investigate the link between the AAb levels in airway and circulation in stable patients with IPF. Materials and Methods: From June 2016 to March 2017, 21 stable IPF patients and 22 healthy volunteers were recruited. We established Luminex interacting AAbs with bead-antigen complex to detect the immunoglobulin G antibodies levels of ten autoantigens which were matched serum (Se) and sputum (Sp) samples collected from recruited subjects, including Smith (Sm), Anti-ribosomal P antibody (P0), Sjögren syndrome type A antigen (SSA), La/Sjögren syndrome type B antigen (SSB), DNA topoisomerase (Scl-70), histidyl-tRNA synthetase (Jo-1), U1 small nuclear ribonucleoprotein (U1-SnRNP), thyroid peroxidase, Proteinase 3, and Myeloperoxidase. Spearman's rank correlation matrix was applied to explore the associations of Ab profiles between Se and Sp. Results: For IPF patients, Spearman's correlation matrix showed multiple intercorrelations among Sp-AAbs and Sp-AAbs (P < 0.05), while only the levels of AAb against Sm and anti-La in Se were correlated with those Sp-AAb counterparts (P < 0.05). For healthy individuals, only anti-La in Se was associated with those Sp-AAb counterparts (P < 0.05). For IPF patients, there was a positive correlation between carbon monoxide diffusing capacity (DLCO)% predicted and Sp-anti-P0 level (r = 0.464, P = 0.034). Forced vital capacity% predicted was positively correlated with Sp-anti-Scl-70 level (r = 0.466, P = 0.033). Conclusion: Comparing to Se-AAbs, Sp-AAbs are more associated with clinical parameters in the patients with IPF. In order to better understand the role of autoimmunity in the pathogenesis of IPF, detection of Sp-AAbs for local autoimmune responses may be a good choice.