View source for CD3 (immunology)

[[Image:TCRComplex.png|thumb|237px|right|The ''[[T cell receptor]] complex'' with TCR-α and TCR-β chains (top), ζ-chain accessory molecules (bottom) and ''CD3'' (represented by [[CD3G|CD3γ]], [[CD3D|CD3δ]] and two [[CD3E|CD3ε]]).]]
{{infobox protein
| Name = [[CD3D|CD3d molecule, delta]]
| caption = 
| image = 
| width = 180px
| HGNCid = 1673
| Symbol = [[CD3D]] 
| AltSymbols = T3D
| EntrezGene = 915
| OMIM = 186790
| RefSeq = NM_000732
| UniProt = P04234
| PDB =  1XIW 
| ECnumber = 
| Chromosome = 11
| Arm = q
| Band = 23
| LocusSupplementaryData = 
}}
{{infobox protein
| Name = [[CD3E|CD3e molecule, epsilon]]
| caption = 
| image = 
| width = 180px
| HGNCid = 1674
| Symbol = [[CD3E]] 
| AltSymbols =
| EntrezGene = 916
| OMIM = 186830
| RefSeq = NM_000733
| UniProt = P07766
| PDB =   
| ECnumber = 
| Chromosome = 11
| Arm = q
| Band = 23
| LocusSupplementaryData = 
}}
{{infobox protein
| Name = [[CD3G|CD3g molecule, gamma]]
| caption = 
| image = 
| width = 180px
| HGNCid = 1675
| Symbol = [[CD3G]] 
| AltSymbols = 
| EntrezGene = 917
| OMIM = 186740
| RefSeq = NM_000073
| UniProt = P09693
| PDB =  
| ECnumber = 
| Chromosome = 11
| Arm = q
| Band = 23
| LocusSupplementaryData = 
}}
In [[immunology]], the '''CD3''' ('''[[cluster of differentiation]] 3''') [[T cell]] [[co-receptor]] helps to activate both the cytotoxic T cell (CD8+ naive T cells) and also T helper cells (CD4+ naive T cells). It consists of a protein complex and is composed of four distinct chains. In mammals, the complex contains a [[CD3G|CD3γ]] chain, a [[CD3D|CD3δ]] chain, and two [[CD3E|CD3ε]] chains. These chains associate with the [[T-cell receptor]] (TCR) and the [[ζ-chain]] (zeta-chain) to generate an activation signal in [[T lymphocytes]]. The TCR, ζ-chain, and CD3 molecules together constitute the TCR complex.

==Structure==
The CD3γ, CD3δ, and CD3ε chains are highly related cell-surface proteins of the [[immunoglobulin superfamily]] containing a single [[extracellular]] immunoglobulin domain.

Containing aspartate residues, the transmembrane region of the CD3 chains is negatively charged, a characteristic that allows these chains to associate with the positively charged TCR chains.<ref name="isbn1-4292-0211-4">{{cite book | vauthors = Kuby J, Kindt TJ, Goldsby RA, Osborne BA | title = Kuby Immunology | edition = | language = | publisher = W.H. Freeman | location = San Francisco | year = 2007 | origyear = | pages = | quote = | isbn = 1-4292-0211-4 }}</ref>

The intracellular tails of the CD3 molecules contain a single conserved motif known as an ''[[immunoreceptor tyrosine-based activation motif]]'' or ITAM for short, which is essential for the signaling capacity of the TCR.

The intracellular tails of the ζ chain contain 3 ITAM motifs.

==Regulation==
[[Phosphorylation]] of the ITAM on CD3 renders the CD3 chain capable of binding an [[enzyme]] called [[ZAP70]] (zeta associated protein), a [[kinase]] that is important in the signaling cascade of the T cell.

==As a drug target==
Because CD3 is required for [[T cell activation]], drugs (often [[monoclonal antibodies]]) that target it are being investigated as [[immunosuppressant]] therapies (e.g., [[otelixizumab]]) for [[type 1 diabetes]] and other [[autoimmune disease]]s.

==Immunohistochemistry==
CD3 is initially expressed in the cytoplasm of pro-thymocytes, the [[stem cell]]s from which T-cells arise in the [[thymus]]. The pro-thymocytes differentiate into common [[thymocyte]]s, and then into medullary thymocytes, and it is at this latter stage that CD3 antigen begins to migrate to the cell membrane. The antigen is found bound to the membranes of all mature T-cells, and in virtually no other cell type, although it does appear to be present in small amounts in [[Purkinje cell]]s.

This high specificity, combined with the presence of CD3 at all stages of T-cell development, makes it a useful [[immunohistochemistry|immunohistochemical]] marker for T-cells in tissue sections. The antigen remains present in almost all T-cell [[lymphoma]]s and [[leukaemia]]s, and can therefore be used to distinguish them from superficially similar [[B-cell]] and [[myeloid cell|myeloid]] [[neoplasm]]s.<ref name=Leong>{{cite book | vauthors =Leong AS, Cooper K, Leong FJ |year=2003|title=Manual of Diagnostic Cytology|edition=2nd|publisher=Greenwich Medical Media, Ltd.|pages=63–64|isbn=1-84110-100-1}}</ref>

== References ==
{{Reflist}}

== Further reading ==
{{refbegin}}
* {{cite book | vauthors = Shiv P, Abul KA, Andrew W | title = Cellular and Molecular Immunology: with STUDENT CONSULT Online Access | edition = | language = | publisher = Saunders | location = Philadelphia | year = 2011 | pages = | isbn = 1-4377-1528-1 }}
{{refend}}

==External links==
*{{Commonscatinline}}
*{{MeshName|CD3+Antigens}}
*[http://www.ebioscience.com/ebioscience/whatsnew/mousecdchart.htm Mouse CD Antigen Chart]
*[http://www.ebioscience.com/resources/human-cd-chart.htm Human CD Antigen Chart]

{{T cell receptor}}
{{Clusters of differentiation}}
{{Clusters of differentiation by lineage}}

{{DEFAULTSORT:Cd3 (Immunology)}}
[[Category:Clusters of differentiation]]
[[Category:T cells]]
[[Category:Immunology]]