In leukemic lymphoblasts, which type is most characteristically associated with the CALLA antigen?

The presence of the CALLA (Common Acute Lymphoblastic Leukemia Antigen) antigen is particularly associated with common acute lymphoblastic leukemia (ALL). This antigen serves as a crucial marker for identifying a specific subtype of ALL that typically includes both B-cell and T-cell characteristics, known as common ALL.

Common ALL generally arises from precursor B-lymphoblasts and is characterized by the presence of lineage-specific markers along with the CALLA antigen. This antigen is associated with the early stages of B-cell differentiation and serves as a significant diagnostic tool in distinguishing this form of leukemia from other types.

B-cell ALL primarily presents with B-cell lineage markers, while T-cell ALL exhibits markers pertinent to T-cell development. Null-cell ALL indicates an absence of surface markers typically seen in B or T cells, which do not express the CALLA antigen. Hence, the defining characteristic of common ALL, which is the expression of the CALLA antigen, is what makes it the correct choice in this context, providing important insight into the hematological classification and diagnosis of leukemia.