This infiltration of peripheral lymphocytes into the brain through the BBB occurs mainly because activated microglia and monocytes in the brains of patients with PD release proinflammatory cytokines and chemokines that act on the vascular endothelium to induce upregulation of cell adhesion molecules, including vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 (ICAM-1) [106] that disrupt the BBB and attract lymphocytes [97] expressing counterreceptors such as leukocyte function antigen-1 (LFA-1) to the neuronal injury site [106]. The gene discussed is ICAM1; the disease is Parkinson disease.