CXCR4 and Parkinson disease: Emerging evidence suggests the crucial role of fractalkine in neuron-to-glia communication signalling in PD29, and SDF-1 is correlated with the apoptosis of PD-related neurons by activating chemokine receptor 4 (CXCR4)30.In contrast to our findings, previous studies have reported that peripheral RANTES is significantly elevated and suggested that CCL5 produced from the CNS penetrates into the serum through the BBB31.