Biologic Correlates of Radiologic Features of Systemic Sclerosis Interstitial Lung Disease

Abstract

Background and objectivesThe extent and pattern of radiological features (e.g., fibrosis, ground glass) can influence treatment approaches for systemic sclerosis-related interstitial lung disease (SSc-ILD). However, the pathobiology underlying these radiologic features is poorly understood and warrants further investigation.MethodsSixty-eight proteins were measured in bronchoalveolar lavage (BAL) fluid from 103 SSc-ILD participants in Scleroderma Lung Study I. Quantitative image analysis calculated the extent of fibrosis (QLF) and ground glass opacity (QGG) from concurrent high-resolution computerized tomography (HRCT) scans. The relationship between BAL proteins and quantitative HRCT scores was assessed by univariate and multivariate analyses.ResultsQLF scores correlated weakly with the extent of QGG, suggesting two distinct processes. In a univariate analysis, 25 proteins from several biologic pathways correlated with QLF scores, including pro-fibrotic factors, tissue remodeling proteins, proteins involved in monocyte/macrophage migration and activation, and proteins linked to inflammation and immune regulation. In contrast, QGG scores correlated with only 6 proteins of which four were unique and related to granulocyte activation, mobilization of bone marrow mesenchymal stem cells, and activation of T cells, B cells, macrophages and eosinophils. In the multivariate models, IL-4, CCL7, receptor activator of NF-κB, and tumor necrosis factor alpha were independently associated with QLF, whereas, IFN-γ was independently associated with QGG.InterpretationQLF and QGG represent distinct radiologic features of SSc-ILD, a conclusion reinforced by the presence of different biologic pathways present within BAL fluid that associate with each. The identified proteins and related biologic pathways may represent important therapeutic targets.