cd4 antigens meaning

[Medicine]
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.

HIV belongs to the class of viruses called retroviruses, which carry genetic information in the form of RNA . HIV infects T cells that carry the CD4 antigen on their surface.