The Role of Surfactant Protein A in Bleomycin-induced Acute Lung Injury

Rationale: Surfactant protein A (SP-A) is a collectin family member that has multiple immunomodulatory roles in lung host defense. SP-A levels are altered in the bronchoalveolar lavage (BAL) fluid and serum of patients with acute lung injury and acute respiratory distress syndrome, suggesting the importance of SP-A in the pathogenesis of acute lung injury. Objectives: Investigate the role of SP-A in the murine model of noninfectious lung injury induced by bleomycin treatment. Methods: Wild-type (WT) or SP-A deficient (SP-A(-/-)) mice were challenged with bleomycin, and various indices of lung injury were analyzed. Measurements and Main Results: On challenge with bleomycin, SP-A(-/-) mice had a decreased survival rate as compared with WT mice. SP-A(-/-) mice had a higher degree of neutrophil-dominant cell recruitment and the expression of the inflammatory cytokines in BAL fluid than did WT mice. In addition, SP-A(-/-) mice had increased lung edema as assessed by the increased levels of intravenously injected Evans blue dye leaking into the lungs. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling and active caspase-3 staining suggested the increased apoptosis in the lung sections from SP-A(-/-) mice challenged with bleomycin. SP-A also specifically reduced bleomycin-induced apoptosis in mouse lung epithelial 12 cells in vitro. Moreover, intratracheal administration of exogenous SP-A rescued the phenotype of SP-A(-/-) mice in vivo. Conclusions: These data suggest that SP-A plays important roles in modulating inflammation, apoptosis, and epithelial integrity in the lung in response to acute noninfectious challenges.