This gene encodes a membrane glycoprotein of T lymphocytes that interacts with major histocompatibility complex class II antigenes and is also a receptor for the human immunodeficiency virus. This gene is expressed not only in T lymphocytes, but also in B cells, macrophages, and granulocytes. It is also expressed in specific regions of the brain. The protein functions to initiate or augment the early phase of T-cell activation, and may function as an important mediator of indirect neuronal damage in infectious and immune-mediated diseases of the central nervous system. Multiple alternatively spliced transcript variants encoding different isoforms have been identified in this gene. [provided by RefSeq, Aug 2010]

CD4: Accessory protein for MHC class-II antigen/T-cell receptor interaction. May regulate T-cell activation. Induces the aggregation of lipid rafts. Associates with LCK. Binds to HIV-1 gp120 and to P4HB/PDI and upon HIV-1 binding to the cell membrane, is part of P4HB/PDI- CD4-CXCR4-gp120 complex. Interacts with HIV-1 Envelope polyprotein gp160 and protein Vpu. Interacts with Human Herpes virus 7 capsid proteins. Interacts with PTK2/FAK1; this interaction requires the presence of HIV-1 gp120.

Protein type: Membrane protein, integral; Cell surface

Chromosomal Location of Human Ortholog: 12p13.31

Cellular Component: T cell receptor complex; endoplasmic reticulum membrane; endoplasmic reticulum lumen; early endosome; plasma membrane; integral to membrane; lipid raft; external side of plasma membrane

Molecular Function: protein binding; protein homodimerization activity; enzyme binding; transmembrane receptor activity; zinc ion binding; extracellular matrix structural constituent; coreceptor activity; receptor activity; glycoprotein binding; protein kinase binding; MHC class II protein binding

Biological Process: maintenance of cellular protein localization; viral reproduction; positive regulation of interleukin-2 biosynthetic process; cytokine production; T cell selection; positive regulation of calcium-mediated signaling; defense response to Gram-negative bacterium; signal transduction; induction by virus of cell-cell fusion in host; enzyme linked receptor protein signaling pathway; T cell receptor signaling pathway; regulation of defense response to virus by virus; positive regulation of peptidyl-tyrosine phosphorylation; cell surface receptor linked signal transduction; positive regulation of protein kinase activity; T cell costimulation; protein palmitoleylation; innate immune response; entry into host cell; immune response; transmembrane receptor protein tyrosine kinase signaling pathway; regulation of T cell activation; T cell differentiation

Disease: Okt4 Epitope Deficiency