The role of S100A8/A9 in the pathogenesis of acute exacerbations of pulmonary fibrosis

Acute exacerbation of idiopathic pulmonary fibrosis is a life-threatening condition characterized by neutrophilic inflammation. S100A8/A9, an alarmin released by activated neutrophils and monocytes/macrophages, plays a pivotal role in regulating inflammatory responses. However, its specific involvement in acute exacerbations of pulmonary fibrosis remains unclear. This study evaluated the role of S100A8/A9 in the pathogenesis of acute exacerbations of pulmonary fibrosis. S100A8/A9 levels were measured in bronchoalveolar lavage fluid and serum from patients with idiopathic interstitial pneumonia, with and without acute exacerbations. To model acute exacerbations of pulmonary fibrosis, mice were intratracheally administered bleomycin followed by lipopolysaccharide. Subsequently, inflammatory cell infiltration, cytokine levels, morphological changes, and fibrosis marker levels in lung tissue and airways were analyzed. S100A8/A9 levels were significantly higher in the bronchoalveolar lavage fluid and serum of patients with idiopathic interstitial pneumonia experiencing acute exacerbations relative to those without; these levels were correlated with patient prognosis. In an experimental mouse model, intratracheal administration of bleomycin followed by lipopolysaccharide resulted in a significant increase in airway S100A8/A9 levels compared with bleomycin alone and control mice. Anti-S100A8/A9 neutralizing antibody Ab45 mitigated airway inflammation and lung fibrosis in mice with acute exacerbations of pulmonary fibrosis, reducing S100A8/A9 levels and neutrophil extracellular traps. In vitro, recombinant S100A8/A9 or lipopolysaccharide and neutrophils activated and differentiated fibroblasts; these effects were inhibited by anti-S100A8/A9 neutralizing antibody Ab45 and the humanized form of Ab45 (HuAb45). These findings highlight S100A8/A9 as a potential prognostic biomarker and therapeutic target for acute exacerbations of pulmonary fibrosis.