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