CD4 and Parkinson disease: Endothelial cell activation suggests a mechanism that favors the infiltration of immune cells, such as CD4+ and CD8+ lymphocytes, into the brain, whereas, in addition to these findings, the disruption of the blood–brain barrier at the level of the striatum and the midbrain further supports the position that endothelial activation in response to neuroinflammation contributes to the progression of PD [60].