CD3
From haematologyetc.co.uk
- 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.
- B cells will not express CD3, and aberrant expression in AML is rare (in contrast to other T cell marker such as CD2 or CD7).
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SUMMARY TABLES
Note The colour and % refer to the proportion of cases expressing the markerExpression key. Additional comments on strength, or site of expression (if relevant) are given below the table.
Expression in primitive cell types | |||||||
---|---|---|---|---|---|---|---|
AML | CMML | B ALL | BL | T ALL | ETP ALL | MPAL | Hgn |
<5% | <5% | <5% | <5% | 80-100% | 80-100% | 20-40% | <5% |
Notes: CD3 exprssion is considered a very strong indicator of T lineage or mixed phenotype in acute leukaemia; however the where CD3 expression is weak or found only by immunohistchemistry then care should be taken in interpretation (see notes on MPAL and ETP-ALL). Note also that CD3 expression in acute leukaemia may be cytoplasmic or surface depending on cell maturity
CD13 expression: mature B cell neoplasms | |||||||
---|---|---|---|---|---|---|---|
CLL | MCL | FL | MZL | HCL | DLBCL | LPL | PCL |
<5% | <5% | <5% | <5% | <5% | <5% | <5% | <5% |
Notes: CD3 expression is not seen in mature B lymphoid disorders
Expression in mature T cell neoplasms* | ||||||
---|---|---|---|---|---|---|
ATLL | CTCL / Sezary | T-PLL | T-LGL | NK-LGL | ||
80-100% | 80-100% | 80-100% | 80-100% | <5% |
Notes: The level of CD3 expression is increased (compared to normal T cells) in T-PLL and T-LGL, and are lower than normal T cells in Sézary syndrome and ATLL.