EPO and airway hyperresponsiveness: Eosinophils in asthma contribute to the occurrence of airway hyperresponsiveness, tissue damage, and airway remodeling through their secreted factors, including TGF-β, and IL-13, leukotrienes, and eosinophil peroxidase (EPO), while also triggering mast cell degranulation via major basic protein and EPO [123].