CD4 - CD28 Antibody – Mouse

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]

Function: Accessory protein for MHC class-II antigen/T-cell receptor interaction. May regulate T-cell activation. Induces the aggregation of lipid rafts.

Subunit structure: 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. Ref.15 Ref.18 Ref.19 Ref.21 Ref.27

Subcellular location: Cell membrane; Single-pass type I membrane protein. Note: Localizes to lipid rafts. Removed from plasma membrane by HIV-1 Nef protein that increases clathrin-dependent endocytosis of this antigen to target it to lysosomal degradation. Cell surface expression is also down-modulated by HIV-1 Envelope polyprotein gp160 that interacts with, and sequesters CD4 in the endoplasmic reticulum. Ref.20

Post-translational modification: Palmitoylation and association with LCK contribute to the enrichment of CD4 in lipid rafts. Ref.16

Polymorphism: The OKT monoclonal antibodies are widely used for the analysis of human peripheral blood T-lymphocytes. OKT4 reacts with T-helper/inducer lymphocytes. The OKT4 epitope of the CD4 cell-surface protein is polymorphic in white, black, and Japanese populations. The variable phenotypic expression is due a CD4 polymorphism. OKT4 positive individuals carry Arg-265 and OKT4 negative individuals carry Trp-265 [

MIM:613949].

Miscellaneous: Primary receptor for HIV-1.

Sequence similarities: Contains 3 Ig-like C2-type (immunoglobulin-like) domains.Contains 1 Ig-like V-type (immunoglobulin-like) domain.