How are lymphoblasts characterized in contrast to myeloblasts?

Lymphoblasts are characterized by the expression of terminal deoxynucleotidyl transferase (TdT), which is a DNA polymerase enzyme crucial for synthesizing the ends of DNA strands, particularly during the process of V(D)J recombination in developing lymphocytes. The presence of TdT is a hallmark for lymphoblastic leukemia and is used in the classification of acute lymphoblastic leukemia (ALL).

In contrast, myeloblasts, which are the immature precursors of myeloid cells, do not express TdT. Instead, myeloblasts are identified by the presence of myeloperoxidase (MPO), an enzyme involved in the oxidative burst of neutrophils. MPO is a marker for myeloid differentiation and its detection is key in identifying acute myeloid leukemia (AML).

The distinction between these cell types is significant in clinical pathology and hematology, as it assists in the diagnosis and classification of various hematological malignancies. Thus, lymphoblasts are specifically characterized by the presence of TdT, aiding in the identification of lymphocytic lineage, while myeloblasts are recognized by the presence of MPO, indicating myeloid lineage.