CD3

Summary

CD3 is a reliable marker of T cell lineage. Loss of expression is rare in T cell malignancies, and aberrant expression by other lineages is very infrequent.

Surface CD3 is acquired during thymic maturation, but is preceded by expression in cytoplams, smaking cytoplasmic CD3 is very useful in the diagnosis of acute T cell leukaemia.

On more mature neoplasms CD3 will be detected on the cell surface.

Normal expression and function

CD3 is not a single molecule, rather it is a multi-molecular complex (two epsilon (ε) chains, a gamma (γ) chain, a delta (δ) chain and a zeta (ζ) chain) that play a pivitol role in assembling and activating the T cell receptor. It is first expressed in the cytoplasm becoming expressed on as they mature. As an essential TCR component it is expressed almost exclusively by mature T cells.

Diagnostic role

• In T cell Acute Lymphocytic Leukaemia CD3 expression is mainly cytoplasmic (cyCD3). Surface (sCD3) is variably expressed in more mature forms of T-ALL.

• In mature T cell neoplasms sCD3 is found on T-prolymphocytic leukaemia, Sézary syndrome, Adult T cell leukaemia/lymphoma (ATLL), Angioimmunoblastic T cell lymphoma (AITL), T-Large granular lymphocytic leukaemia (T-LGL) and Hepatosplenic T-cell lymphoma.

• Natural Killer cell lymphoproliferative disorders do not express a conventional TCR so CD3 is not expressed.

Other relevant information:

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