The cluster of differentiation 4 (CD4) protein is a surface, type I membrane-embedded glycoprotein that is found on a wide range of cells: T-lymphocytes, B-cells, macrophages, granulocytes, and developmentally-dependent regions specific to the brain. It interacts with major histocompatibility complex (MHC) class II anti-genes, serves as the human immunodeficiency virus (HIV) receptor, and can initiate/augment early phase T-cell activation. In immune-mediated and central nervous system (CNS) infectious diseases, CD4 indirectly mediates neuronal damage.
