Eosinophil Granule Proteins in Chronic Rhinosinusitis: A Systematic Review of Biomarker Utility for Disease Characterization and Outcomes

Background/Objectives: Chronic rhinosinusitis (CRS) is a heterogeneous inflammatory condition increasingly understood through endotyping, with eosinophilic CRS (eCRS) representing a clinically distinct and often refractory phenotype. Eosinophils exert their pathogenic effects in part through the release of four highly cationic granule proteins—major basic protein (MBP), eosinophil cationic protein (ECP), eosinophil peroxidase (EPX), and eosinophil-derived neurotoxin (EDN)—each with distinct biological activities and measurable tissue and systemic expression profiles. Despite growing interest in precision medicine approaches to CRS management, the clinical utility of these granule proteins as biomarkers has not been systematically characterized. This systematic review evaluates the diagnostic and prognostic utility of eosinophil granule proteins as biomarkers in CRS.