Moreover, MDSC expansion goes at the same pace as the increased expression of immunosuppression-related genes, such as ARG1, IL-10, and COX-2 [39], and SLC18A2, L1CAM, S100A12, and CXCR4, which moderately correlates with MDSCs [38], suggesting that immune-related genes are involved in the pathogenesis of PD. The gene discussed is ARG1; the disease is Parkinson disease.