CD4 and neurodegenerative disease: The search string used was as follows: (“Microglia” OR “astrocytes” OR “T lymphocytes” OR “B lymphocytes” OR “NK cells” OR “CD4+ T cells” OR “CD8+ T cells” OR “Th17 cells” OR “Th1 cells” OR “Treg cells”) AND (“neurodegenerative diseases” OR “Parkinson’s disease” OR “Alzheimer’s disease” OR “amyotrophic lateral sclerosis” OR “multiple sclerosis” OR “neuroinflammation”).