CD4

CD4 (cluster of differentiation 4), is a glycoprotein encoded by the CD4 gene, and it is identified on the surface of immune cells, for example, monocytes, T helper cells, dendritic and macrophages cells. CD4 is similar to other cell surface receptors/markers, belongs to the immunoglobulin superfamily. This protein contains four immunoglobulin domains (D1 to D4) which are exposed on the extracellular surface of the cell, of which D1 and D3 like immunoglobulin variable (IgV) domains, and D2 and D4 like immunoglobulin constant (IgC) domains. Via its D1 domain, CD4 enables to interact with the β2-domain of MHC class II molecules. T cells exhibiting CD4 molecules (and not CD8) on their surface, hence, are specific for antigens presented by MHC II and not by MHC class I (they are MHC class II-restricted).
Mostly, CD4 is expressed in thymocytes (80–90%) and over 50% of the peripheral blood T-cells (helper/inducer subtype). Also, CD4 is a co-receptor of the T cell receptor (TCR) and aids TCR in communicating with antigen-presenting cells. Respectively, the TCR complex and CD4 each bind to distinct regions of the antigen-presenting MHCII molecule-α1/β1 and β2.
Gene ID: 920
UniProt ID: P01730