Signaling pathways triggered by the binding of PD-1 to its ligands, PD-L1 (B7-H1) and PD-L2 (B7-DC), are essential for regulating the balance between T-cell activation and tolerance, thereby contributing to the pathogenesis of various diseases such as autoimmunity, tumors, infectious diseases, and allergies (17, 106, 107). This evidence concerns the gene CD274 and allergic disease.