IgA antibodies against oxidation-specific epitopes are generated by double negative B cells and are associated with impaired lung function in fibrotic interstitial lung diseases.
BackgroundFibrotic interstitial lung diseases (fILD) are characterized by progressive scarring of the lung and high mortality. Oxidation-specific epitopes (OSEs) form on oxidized lipids and proteins, are abundant in lungs of patients with fILD and perpetuate lung injury and fibrosis in animal models. OSE-targeting antibodies bind to OSEs and modulate their downstream effects. The objective of this study was to determine the association of OSE-targeting antibodies with lung function and other clinical outcomes, and to characterize OSE-specific B cell phenotypes in fILD. MethodsTo determine the association of OSE-targeting antibodies and clinical outcomes in fILD, we measured plasma levels of OSE-specific antibodies against the malondialdehyde modified LDL mimotope P1 and anti-ApoB100 immune complex (anti-ApoB100 IC) in patients with fILD and age-matched controls. We then performed B cell phenotyping of patients with idiopathic pulmonary fibrosis (IPF) and healthy controls utilizing mass cytometry time of flight (CyTOF). To investigate effects of pro-fibrotic mediators on anti-OSE IgA antibody production, we measured B cell responses to OSEs in vitro. ResultsCohort of 109 patients with fILD (Hypersensitivity Pneumonitis, Idiopathic Pulmonary Fibrosis, Nonspecific Interstitial Pneumonia, Connective Tissue Disease-Associated Interstitial Lung Disease) and 55 healthy donors, and a second cohort of 20 patients with IPF and 9 healthy donors were included in the study. OSE-specific antibody levels anti-P1 and anti-ApoB100 IC IgA and IgG were significantly elevated in participants with fILD compared to healthy donors (p<0.0001). Higher anti-OSE IgA was associated with worse baseline lung function, including forced vital capacity (FVC) (p<0.001) and diffusing capacity for carbon monoxide (DLCO) (p<0.01). IgA+CD27-CD21-CD11c+ double negative type 2 (DN2) B cells correlated with anti-OSE IgA levels (p<0.05) and were enriched in OSE-specific cells. DN2 B cell precursors, CXCR5-CD11c+ naive B cells and IgA+CD27-CD21-CD11c- DN3 B cells, were significantly expanded in IPF compared to healthy donors. Both DN2 and DN3 B cells correlated with plasmablast pools in IPF patients and showed high baseline levels of IL-21 receptor, which was reduced in more differentiated cells. TGF-{beta} combined with OSEs, but not OSEs alone, induced OSE-specific IgA production in vitro. ConclusionsCirculating anti-OSE IgA antibodies are elevated in patients with fibrotic ILDs regardless of underlying pathology and negatively correlate with lung function. These antibodies correlated with the DN2 B cell subset which was enriched in OSE-specific cells. Phenotypic analysis of B cell subsets showed expression of markers consistent with DN to plasmablast differentiation. Finally, TGF-{beta} promoted OSE-IgA production in vitro. These findings show a novel link between oxidative tissue damage, anti-OSE antibodies and DN2 B cells in fILD which may provide opportunities for new targeted therapies.