Cluster of differentiation 3 consists of five different polypeptide chains with molecular weights ranging from 16 to 28 kD. CD3 have four different invariant chains: CD3 gamma, CD3 delta, CD3 epsilon, and CD3 zeta. The CD3 antigen is expressed in early thymocytes and its appearance probably represents one of the earliest signs of commitment to the T cell lineage.
In immunology, Cluster of differentiation 3 as T-cell co-receptor helps to activate the cytotoxic T-Cell. CD3 consists of a protein complex and is composed of four distinct 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 complex functions to transduce intracellular signals during TCR antigen recognition. CD3 epsilon is one of at least three invariant proteins that associate with the variable antigen recognition chains of the T cell receptor and function in signal transduction.
Cluster of differentiation 3 has high specificity, 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.
Because cluster of differentiation 3 is required for T-cell activation, drugs (often monoclonal antibodies) that target it are being investigated as immunosuppressant therapies for type 1 diabetes and other autoimmune diseases.