CD4 and Parkinson disease: The search keywords utilized included microglia, astrocytes, T lymphocytes, B lymphocytes, NK cells, CD4+ T cells, CD8+ T cells, Th17 cells, Th1 cells, regulatory T (Treg) cells, neurodegenerative diseases, Parkinson’s disease, Alzheimer’s disease, amyotrophic lateral sclerosis, multiple sclerosis, and neuroinflammation.