Lysosomal Acidity and Cathepsin L Activate Eosinophils via ARG1-Mediated Arginine Metabolism in Allergic Airway Inflammation

Eosinophils are the predominant immune cells implicated in the pathogenesis of asthma, highlighting the need for strategies to mitigate their effects. While previous studies have indicated a potential relationship between lysosomes and eosinophils, the precise role of lysosomes in eosinophil activation during asthma remains insufficiently understood. In this study, we demonstrated that lysosomal acidity and cathepsin L (CTSL) activity in eosinophils were elevated in asthmatic patients and mouse models. Genetic deletion or pharmacological inhibition of CTSL in eosinophils significantly attenuated allergic airway inflammation in vivo and suppressed eosinophil activation in vitro. CTSL in eosinophils promoted type 2 immune responses by upregulating arginase 1 (ARG1) expression and interacting with it, thereby enhancing ARG1 activity and altering arginine metabolism during eosinophil activation. This metabolic shift led to increased production of ornithine, which exacerbated inflammatory processes. Furthermore, lysosomal acidity and CTSL activity correlated with disease severity in asthmatic patients. Our findings reveal that lysosomal acidity and CTSL facilitate eosinophil activation through arginine metabolism, thereby promoting allergic airway inflammation.