<immunology> 55-kD glycoproteins originally defined as differentiation antigens on T-lymphocytes, but also found on other cells including monocytes/macrophages. CD4 antigens are members of the immunoglobulin supergene family and are implicated as associative recognition elements in MHC (major histocompatibility complex) class II-restricted immune responses. On T-lymphocytes they define the helper/inducer subset. Cd4 antigens also serve as HIV receptors, binding directly to the envelope protein gp120 on HIV.

The protein structure on the surface of a human cell that allows HIV to attach, enter, and thus infect a cell. CD4 receptors are present on CD4 cells (helper T-cells), macrophages and dendritic cells, among others. Normally, CD4 acts as an accessory molecule, forming part of larger structures (such as the T-cell receptor) through which Tcells and other cells signal each other.

(12 Dec 1998)

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