PRG2 encodes the proform of eosinophil major basic protein (proMBP), a highly expressed protein during human pregnancy with diverse biological functions 1. The protein functions as a cytotoxin and helminthotoxin while also inducing histamine release from basophils, playing key roles in antiparasitic defense and immune hypersensitivity reactions. The proform specifically acts as a proteinase inhibitor, forming disulfide-mediated complexes with pregnancy-associated plasma protein A (PAPPA) and angiotensinogen, thereby reducing their biological activity 1. In neuronal development, PRG2 localizes to axonal membranes where it inhibits PTEN phosphatase through direct protein-protein interaction, enabling PI(3,4,5)P3 accumulation necessary for axon branching and filopodia formation 2. PRG2 expression is dysregulated in various pathological conditions, including upregulation in placental disorders like placenta previa and percreta 3, overexpression in neuropsychiatric systemic lupus erythematosus correlating with disease activity 4, and presence in osteoarthritic synovial fluid as a mast cell marker 5. Clinically, PRG2 expression levels serve as predictive biomarkers, with lower expression associated with positive response to aspirin therapy in aspirin-exacerbated respiratory disease 6.