CD4

PDB 1wip EBI

CD4 correceptor

CD4 receptor

CD4 and LAG-3 with opposing functions

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Reference ranges for blood tests - white blood cells

CD4 (cluster of differentiation 4) is a glycoprotein found on the surface of immune cells such as T helper cells, monocytes, macrophages, and dendritic cells. It is a co-receptor that assists the T cell receptor (TCR) in communicating with an antigen-presenting cell.

Structure

CD4 is a single-chain transmembrane glycoprotein with four extracellular immunoglobulin-like domains (D1 to D4) that are encoded by the CD4 gene located on chromosome 12 in humans. The D1 domain is responsible for binding to the major histocompatibility complex (MHC) class II molecules on antigen-presenting cells.

Function

CD4 plays a critical role in the immune system by aiding the activation of T helper cells. When the TCR on a T helper cell recognizes an antigen presented by an MHC class II molecule, CD4 binds to the MHC class II molecule, stabilizing the interaction and enhancing the signal transduction that leads to T cell activation. This process is essential for the adaptive immune response, including the activation of B cells to secrete antibodies and the activation of cytotoxic T cells to kill infected cells.

Clinical Significance

CD4 is a primary receptor for the human immunodeficiency virus (HIV). HIV binds to CD4 on the surface of T helper cells, allowing the virus to enter and infect the cell. The progressive loss of CD4+ T cells in HIV-infected individuals leads to acquired immunodeficiency syndrome (AIDS), characterized by a severely weakened immune system.

Measurement

The number of CD4+ T cells in the blood is a key indicator of immune function in individuals with HIV. CD4 counts are used to monitor the progression of HIV infection and to guide treatment decisions. A normal CD4 count ranges from 500 to 1,500 cells per cubic millimeter of blood. A count below 200 cells/mm³ is one of the criteria for diagnosing AIDS.

Related Pages

• T helper cell
• Major histocompatibility complex
• Antigen-presenting cell
• Human immunodeficiency virus
• Acquired immunodeficiency syndrome
• B cell
• Cytotoxic T cell