Activation of B cells through the B cell receptor or T cells through the CD3 complex follows a similar signaling pathway although, in many cases, different members of the same kinase families are used. ZAP-70 and Syk are members of the same family and have similar sequences and structures. Crosslinking of the CD3 receptor complex leads to the activation of Lck and Fyn which are Src family tyrosine kinases1,2. These kinases phosphorylate ITAM regions on the receptor which act as docking sites for ZAP-70. Phosphorylation of ZAP-70 by Lck leads to its activation. ZAP-70 then goes on to phosphorylate a number of adaptor proteins and helps activate other kinases as well as phospholipase Cγ. B cells are activated by crosslinking of the Ig receptor3. This activates Lyn, another member of the Src family. Through a similar sequence of events, Syk is activated. Syk is found in various hematopoietic cells such as B cells, platelets, macrophages, and mast cells. ZAP-70 is found primarily in T cells and is not expressed in normal B cells.
Chronic lymphocytic leukemia, a tumor of mature B cell origin, is one of the most common leukemias. The B cells of these donors express an unmutated variable region of the Ig heavy chain gene. More recent work has shown that these donors also express ZAP-70 and that this may be a better marker indicating the aggressive form of the disease4,5. Furthermore, it has been shown that signaling through the Ig receptor is better in ZAP-70 containing CLL cells as opposed to cells that only have Syk6. Responsiveness to anti-Ig is also increased in B cells transfected with ZAP-70.
Adding to our portfolio of ZAP-70 antibody reagents for flow cytometry, western blot, and IHC, BD Biosciences has developed a BD Cytometric Bead Array (CBA) Flex Set assay that measures total ZAP-70 from SDS denatured cell lysates. The BD CBA Flex Set assay utilizes an antibody-conjugated