Bruton's tyrosine kinase (Btk) is a nonreceptor tyrosine kinase whose function is critical for proper B cell development and signaling. The activity of Btk is regulated by Src mediated phosphorylation of the kinase domain at tyrosine 551 (Y551). This event induces Btk kinase activity and subsequent autophosphorylation at Y223. Phosphorylated Btk then associates with the cell membrane via the interaction of the PH domain with phosphatidylinositol 3, 4, 5-triphosphate.
The Tec family kinase Itk plays a critical role in signal transduction downstream of the T cell antigen receptor and has been implicated in the activation of phospholipase C-γ1 (PLCγ1), a key regulator of calcium mobilization and extracellular signal-regulated kinase (ERK) activation. Itk is regulated by an activating transphosphorylation event in which Y511 in the kinase domain is phosphorylated by Lck.
The 24a/BTK (Y551) monoclonal antibody recognizes the Y551-phosphorylated form of human Btk and the Y511 phosphorylated form of human Itk.