CD3 (immunology)

CD3d molecule, delta
Identifiers
Symbol	CD3D
Alt. symbols	T3D
Entrez	915
HUGO	1673
OMIM	186790
PDB	1XIW
RefSeq	NM_000732
UniProt	P04234
Other data
Locus	Chr. 11 q23

CD3e molecule, epsilon
Identifiers
Symbol	CD3E
Entrez	916
HUGO	1674
OMIM	186830
RefSeq	NM_000733
UniProt	P07766
Other data
Locus	Chr. 11 q23

CD3g molecule, gamma
Identifiers
Symbol	CD3G
Entrez	917
HUGO	1675
OMIM	186740
RefSeq	NM_000073
UniProt	P09693
Other data
Locus	Chr. 11 q23

In immunology, the CD3 (cluster of differentiation 3) T-cell co-receptor helps to activate the cytotoxic T-Cell. It consists of a protein complex and is composed of four distinct chains. In mammals, the complex contains a CD3γ chain, a CD3δ chain, and two CD3ε chains. These chains associate with a molecule known as 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.

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.

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.

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.

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 diseases.

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