Description
ZAP-70, a member of the Syk family of protein tyrosine kinases, is a critical mediator of T-cell receptor (TCR)-induced signal transduction. It is predominantly expressed in T lymphocytes and natural killer (NK) cells, with additional immunoreactivity observed in mast cells, basophils, and early-stage B-lineage cells (pro/pre-B cells), while mature B cells typically lack expression. Immunohistochemical detection of ZAP-70 is a valuable diagnostic tool in the subclassification of chronic lymphocytic leukemia (CLL). ZAP-70 expression is typically observed in CLL cases harboring unmutated immunoglobulin heavy-chain variable region (IgVH) genes and is generally absent in cases with mutated IgVH genes. Notably, ZAP-70 positivity correlates with a more aggressive disease course and poorer prognosis in CLL patients.
