Interestingly, increased soluble PD-L1 (sPD-L1) has been found in the serum albumin AR patients, and levels of PD-L1 showed significant inverse correlations with eosinophil counts and disease severity, suggesting that PD-1/PD-L1 is differentially regulated in different compartments of the human body [64], leading to a downregulation of the allergic reaction. This evidence concerns the gene PDCD1 and allergic disease.