CX3CL1 and Parkinson disease: Protective effects of exogenous CX3CL1 administration has largely been shown in animal models of neuroinflammation [70], [71] but plasma levels of soluble CX3CL1 were also positively correlated with disease severity and progression in human PD patients, indicating that CX3CL1 also plays a role in chronic neurodegeneration [72].