Pulmonary surfactant protein A (SP-A)

Pulmonary surfactant protein A (SP-A) is a hydrophilic, oligomeric glycoprotein of the collectin family that is secreted by type II alveolar epithelial cells into the alveolar space[1][2][3][4]. Its core functions include acting as a pattern recognition molecule within the innate immune system, binding to diverse microorganisms via carbohydrate-recognition domains and enhancing their clearance through opsonization and promotion of phagocytosis by alveolar macrophages[3][4]. SP-A also regulates surfactant homeostasis by interacting with surfactant phospholipids and alveolar epithelial cells, contributing to the structural stability and function of the pulmonary surfactant film, especially under conditions of lung stress[1][2][3]. In humans, the protein is encoded by two genes (SFTPA1 and SFTPA2), giving rise to slightly different variants (SP-A1 and SP-A2), which may differ in their immunological and biophysical roles[2]. SP-A is implicated in the pathophysiology of several lung diseases and can serve as a biomarker of lung injury or interstitial disease[8]. There are currently no direct pharmacological agents targeting SP-A, but it is a component of natural and synthetic surfactants administered to treat neonatal respiratory distress syndrome[3]. Caveats: - No specific small-molecule or biologic drugs have been identified that selectively target SP-A, though it is included in some surfactant replacement formulations[3]. - Its role is primarily innate immunity and surfactant regulation, and not directly as a signal-transducing receptor or metabolic enzyme. - The protein is most clinically relevant as a biomarker and structural/immune molecule, not a canonical “drug target” in the narrow sense[3][8].

Other names

Surfactant protein ASFTPACollectin-1SP-A1SP-A2

For therapeutics containing surfactant protein A (as part of exogenous surfactant): reduces alveolar surface tension, promotes pathogen clearance, enhances surfactant film organization[2][3][4]