- A glycoprotein predominantly found on the surface of helper T cells. In humans, it is a receptor for HIV, enabling the virus to gain entry into its host.
- A cell bearing the CD4 surface receptor.
[c(luster of) d(ifferentiation antigen) 4.]
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[c(luster of) d(ifferentiation antigen) 4.]
A glyocprotein on the surface of helper T cells that serves as a receptor for HIV.
| Schematic representation of CD4 receptor. | |
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CD4 molecule
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| Identifiers | |
| Symbol | CD4 |
| Entrez | 920 |
| HUGO | 1678 |
| OMIM | 186940 |
| RefSeq | NM_000616 |
| UniProt | P01730 |
| Other data | |
| Locus | Chr. 12 pter-p12 |
CD4 (cluster of differentiation 4) is a glycoprotein expressed on the surface of
On T cells, CD4 is the co-receptor for the T cell receptor (TCR). It amplifies the signal generated by the TCR by recruiting the tyrosine kinase lck that is essential for activating many molecules involved in the signaling cascade of an activated T cell.
Like many cell surface receptors/markers, CD4 is a member of the immunoglobulin superfamily.
It has four immunoglobulin domains (D1 to D4) that are exposed on the extracellular surface of the cell:
CD4 uses its D1 domain to interact with the β2-domain of MHC class II molecules. 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).
The short cytoplasmic/intracellular tail (C) of CD4 contains a special sequence of amino acids that allow it to interact with the lck molecule described above.
CD4 is also a primary receptor used by HIV-1 to gain entry into host T cells.
The HIV-1 virus attaches to CD4 with a particular protein in its viral envelope known as gp120. The binding to CD4 creates a shift in the conformation of the viral gp120 protein allowing HIV-1 to bind to two other cell surface receptors on the host cell (the chemokine receptors CCR5 and CXCR4). Following another change in shape of a different viral protein (gp41), HIV inserts a fusion peptide into the host T cell that allows the outer membrane of the virus to fuse with the T-cell membrane.
HIV infection leads to a progressive reduction in the number of T cells possessing CD4 receptors and, therefore, the CD4 count is used as an indicator to help physicians decide when to begin treatment in HIV-infected patients.
| The T cell receptor complex | |
|---|---|
| The antigen receptor | TCR | TCRα | TCRβ | TCRγ | TCRδ |
| Accessory molecules | CD3 | CD3γ | CD3δ | CD3ε | ζ-chain (also called CD3ζ and TCRζ) |
| Co-receptors | CD8 (with two glycoprotein chains CD8α and CD8β) | CD4 |
| Ligands | |
| Transmembrane receptors: immune receptors | |
|---|---|
| Cytokine receptor | Type I: interleukin (IL-2, IL-3) - CSF (Erythropoietin, GM-CSF, G-CSF) - Glycoprotein
130/Oncostatin M - Leukemia inhibitory factor - common subunits (Common gamma chain, CSF2RB) Type II: interleukin
(IL22RA2) - interferon (IFNAR, IFNGR) |
| Pattern recognition/Toll-like | TLR 1 - TLR 2 - TLR 3 - TLR 4 - TLR 5 - TLR 6 - TLR 7 - TLR 8 - TLR 9 - TLR 10 |
| Fc receptor | ε (FcεRI, FcεRII) - γ (FcγRI, FcγRII, FcγRIII) - α/μ (FcαRI, Fcα/μR) - Neonatal |
| Lymphocyte homing receptor | CD44 - L-selectin - VLA-4 - LFA-1 |
| other | Antigen receptor (B-cell, T cell) - Complement - Formyl peptide - Immunophilins - Integrin - Killer-cell immunoglobulin-like - Scavenger |
| Proteins: clusters of differentiation (see also list of human clusters of differentiation) | |
|---|---|
| 1-50 | CD1 (CD1a-c, CD1d) - CD2 - CD3 - CD4 - CD5 - CD8 - CD9 - CD10 - CD11 (CD11a, CD11b, CD11c) - CD13 - CD14 - CD15 - CD16 - CD18 - CD19 - CD20 - CD21 - CD22 - CD23 - CD24 - CD25 - CD26 - CD27 - CD28 - CD29 - CD30 - CD31 - CD32 - CD33 - CD34 - CD35 - CD36 - CD37 -CD38 - CD40 - CD43 - CD44 - CD45 - CD46 - CD49 (CD49a, CD49b, CD49c, CD49d) |
| 51-100 | CD52 - CD53 - CD54 - CD55 - CD56 - CD58 - CD59 - CD61 - CD62 (CD62E, CD62L, CD62P) - CD63 - CD64 - CD66e - CD68 - CD70 - CD71 - CD72 - CD79 - CD80 - CD81 - CD82 - CD86 - CD88 - CD89 - CD90 - CD94 - CD95 - CD98 |
| 101-350 | CD103 - CD106 - CD114 - CD116 - CD117 - CD118 - CD120 - CD122 - CD130 - CD131 - CD132 - CD133 - CD134 - CD135 - CD137 - CD138 - CD141 - CD142 - CD143 - CD146 - CD147 - CD151 - CD152 - CD153 - CD154 - CD155 - CD162 - CD164 - CD169 - CD184 - CD206 - CD209 - CD257 - CD278 - CD281 - CD282 - CD283 - CD304 |
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![]() | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more | |
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