Open main menu
The T cell receptor complex with TCR-α and TCR-β chains (top), ζ-chain accessory molecules (bottom) and CD3 (represented by CD3γ, CD3δ and two CD3ε).

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 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.

CD3d molecule, delta
Alt. symbolsT3D
NCBI gene915
Other data
LocusChr. 11 q23
CD3e molecule, epsilon
NCBI gene916
Other data
LocusChr. 11 q23
CD3g molecule, gamma
NCBI gene917
Other data
LocusChr. 11 q23



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.[1]

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.

As a drug targetEdit

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.

As a drug target in cancer researchEdit

New anticancer drug treatments are being developed based upon the CD3 (cluster of differentiation 3) T cell co-receptor, with molecules being designed for altering the co-stimulatory signal to help get the T-cell to recognize the cancer cell and become fully activated. Cancers that possess the B7-H3 immunoregulatory checkpoint receptor on the tumor cell have been one such target in clinical trials. This B7-H3 protein is expressed on cancer cell for several types of cancer. Often two molecules will be in the drugs, one molecule will become attached to the T-cell’s CD3 and the other part attaches to the cancer cell.


CD3 is initially expressed in the cytoplasm of pro-thymocytes, the stem cells from which T-cells arise in the thymus. The pro-thymocytes differentiate into common thymocytes, 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 cells.

This high specificity, combined with the presence of CD3 at all stages of T-cell development, makes it a useful immunohistochemical marker for T-cells in tissue sections. The antigen remains present in almost all T-cell lymphomas and leukaemias, and can therefore be used to distinguish them from superficially similar B-cell and myeloid neoplasms.[2]


  1. ^ Kuby J, Kindt TJ, Goldsby RA, Osborne BA (2007). Kuby Immunology. San Francisco: W.H. Freeman. ISBN 1-4292-0211-4.
  2. ^ Leong AS, Cooper K, Leong FJ (2003). Manual of Diagnostic Cytology (2nd ed.). Greenwich Medical Media, Ltd. pp. 63–64. ISBN 1-84110-100-1.

Further readingEdit

  • Shiv P, Abul KA, Andrew W (2011). Cellular and Molecular Immunology: with STUDENT CONSULT Online Access. Philadelphia: Saunders. ISBN 1-4377-1528-1.

External linksEdit