cd4 molecule meaning
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 can infect a variety of CD4 + helper T-cells and macrophages that express the CD4 molecule on their surface.
- But, if there is a signal interruption, the cell stops downregulating CD8 and switches over to downregulating CD4 molecules, instead, eventually becoming a CD8 +, single positive cell.
- This is because its surface protein, gp120, specifically interacts with the CD4 molecule a chemokine receptor which is most commonly found on the surface of CD4 + T-Cells.
- HIV-1 entry to macrophages and T helper cells is mediated not only through interaction of the virion envelope glycoproteins ( gp120 ) with the CD4 molecule on the target cells but also with its chemokine coreceptors.
- T cells expressing CD4 molecules ( and not CD8 ) on their surface, therefore, are specific for antigens presented by MHC II and not by MHC class I ( they are " MHC class II-restricted " ).