Increased expression of proteins associated with non-microglia myeloid cells, such as CD163, has been observed in the brains of PD patients.227 An increase in the macrophages, specifically CD163+ macrophages was also detected in the area of neurodegeneration in rodent PD models.228 The CCL2-CCR2 axis has been implicated in the infiltration of monocytes into the inflamed brain.229 Studies in PD mouse models and patients have shown upregulation and activation of CCR2, suggesting a detrimental role of infiltrating monocytes in PD. Here, CCL2 is linked to Parkinson disease.