The 33 monoclonal antibody specifically recognizes Tunica interna endothelial cell kinase-2 (Tie2) which is also known as CD202b or Angiopoietin-1 receptor. Tie2 (CD202b) is a single-pass type I membrane protein that is encoded by TEK (TEK receptor tyrosine kinase) which belongs to the receptor tyrosine kinase (RTK) family. The extracellular region of Tie2 (CD202b) contains an N-terminal IgC2-like domain followed by three EGF-like domains, an additional IgC2-like domain and three fibronectin type III domains. The intracellular region contains a protein kinase domain. TIE receptors, designated Tie1 and Tie2 (Tek) have a tissue distribution which is limited primarily to cells of endothelial origin. Binding of angiopoietin 1 to Tie2 (CD202b) leads to downstream receptor-mediated signaling that is involved in angiopoiesis and survival of endothelial cells. Tie2 has been shown to be required for the normal development of vascular structures during embryogenesis. It has also been demonstrated to play a role in normal and pathological angiogenesis in adults. Mutations in the TEK gene cause multiple cutaneous and mucosal venous malformations (VMCM). Tie2 has a predicted molecular weight of 126 kD, but may be observable at ~130-165 kDa. This antibody has been reported to recognize human and mouse Tie2 but not Tie1.