Zeta-associated protein-70 (ZAP-70) is a member of the Syk family of tyrosine kinases, a group of proteins that attach to the zeta chain components of T-cell receptors to signal downstream events involved in the regulation of cell function, proliferation, and death. Research suggests that the ZAP-70 protein may also play an important role in natural killer (NK) cell activation and early B-cell development; however, it is not expressed in most normal mature B-cells. Expression of ZAP-70 has been reported in various lymphomas, including mantle cell lymphoma, small lymphocytic lymphoma and marginal zone lymphoma. During thymocyte development, ZAP-70 promotes survival and cell-cycle progression of developing thymocytes before positive selection (when cells are still CD4/CD8 double negative). Additionally, ZAP-70-dependent signaling pathway may also contribute to primary B-cells formation and activation through B-cell receptor (BCR).