CCL2 and Parkinson disease: Proinflammatory cytokines are elevated in the blood of PD patients, including increased levels of IL-2 (32, 33)−6 (34–38)−8 (38), MCP-1 (monocyte chemoattractant protein-1) (38), MIP-1α (macrophage inflammatory protein-1 α) (38), RANTES (regulated upon activation, normal T-cell expressed and secreted) (38, 39), TNFα (35, 36, 40, 41), and IFNγ (38).