<p>Acute lung injury (ALI) remains a critical inflammatory condition with limited therapeutic interventions. This study explores the anti-inflammatory potential of calycosin (CAL), a bioactive flavonoid, in lipopolysaccharide (LPS)-induced MH-S alveolar macrophages cell line, with particular focus on macrophage polarization mechanisms. Through CCK-8 cytotoxicity assessment and subsequent experimental grouping (control, LPS, and LPS + CAL), we demonstrated CAL’s ability to significantly suppress LPS-triggered inflammatory mediators including IL-1β, TNF-α, and IL-6 at both transcriptional and protein levels. Flow cytometric analysis revealed CAL’s dual regulatory effect on macrophage polarization markers, downregulating M1-associated CD86 while enhancing M2-related CD206 expression. Transcriptomic profiling identified 5,944 differentially expressed genes in LPS-stimulated cells enriched in TNF signaling pathways, while CAL treatment specifically modulated 83 genes predominantly involved in TGF-β signaling. Mechanistic investigations identified Spon2 as a critical mediator, where CAL-induced Spon2 downregulation attenuated inflammation and promoted M2 polarization, effects corroborated through Spon2-shRNA knockdown and overexpression experiments. Notably, we newly demonstrate that Spon2 overexpression abolishes CAL-mediated suppression of TNF-α and activation of TGF-β/Smad2 signaling. These findings collectively establish CAL as a promising therapeutic candidate for ALI through its Spon2-mediated modulation of macrophage polarization dynamics.</p> Graphical abstract <p></p>