Molecular Features and Stages of Pulmonary Fibrosis Driven by Type 2 Inflammation

Systemic sclerosis (SSc) is a progressive, multi-organ disease with limited treatment options. While a recent proof-of-concept study using Romilkimab or SAR156597, a bi-specific IL-4/IL-13 antibody, suggests a direct role of these cytokines in the pathophysiology of SSc, their contributions to the balance between inflammation and fibrosis are unclear. Here, we determine the roles of type 2 inflammation in fibrogenesis using a Fos-related antigen 2 overexpressing transgenic mice (FRA2-Tg), which develop a spontaneous, age-dependent progressive lung fibrosis. We defined the molecular signatures of inflammation and fibrosis at three key stages in disease-progression, corresponding to pre-onset, inflammatory dominant, and fibrosis dominant biology, and revealed an early increase in cytokine-cytokine receptor interactions and antigen-processing and presentation pathways followed by enhanced Th2 and M2- macrophage driven type 2 responses. This type-2 inflammation progressed to extensive fibrotic pathology by 14-18 weeks of age with these gene signatures overlapping significantly with those seen in lungs of patients with SSc with interstitial lung disease (ILD). These changes were also evident in the histopathology which showed perivascular and peribronchiolar inflammation with prominent eosinophilia and accumulation of profibrotic M2-like macrophages followed by rapid progression to fibrosis with thickened alveolar walls with multifocal-fibrotic-bands and signs of interstitial-pneumonia. Critically, treatment with a bispecific antibody targeting IL-4 and IL-13 during the inflammatory phase abrogated the Th2 and M2-responses and led to near complete abrogation of lung fibrosis. These data recapitulate important features of fibrotic-progression in lungs of SSc-ILD patients and enhance our understanding of the progressive pathobiology of SSc. This study also further establishes FRA2-Tg mice as a valuable tool for testing future therapeutic agents in SSc-ILD.