Which type of cells can be identified using the TdT marker?

The TdT (terminal deoxynucleotidyl transferase) marker is specifically associated with immature lymphocytes, particularly in the context of lymphocyte development. This enzyme is present in the nucleus of precursor B and T lymphocytes during the early stages of differentiation. TdT is crucial for the process of V(D)J recombination, which facilitates the generation of diverse antigen receptors on lymphocytes.

In clinical practice, the presence of TdT is often used as a marker in the diagnosis of lymphoid malignancies, especially acute lymphoblastic leukemia (ALL). The detection of TdT helps to confirm the immature nature of the leukemic cells, distinguishing them from mature lymphocytes, which do not express this enzyme.

In contrast, stem cells, monocytes, and mature B cells do not typically express TdT. Stem cells can be identified with other surface markers, monocytes have distinct markers related to their lineage and function, and mature B cells possess surface immunoglobulins and other markers characteristic of their functional state, lacking TdT expression. This specificity makes the TdT marker a valuable tool for identifying immature lymphocytes within a sample.