The monoclonal antibody 174/2 reacts with human plasmalemma vesicle associated protein (PLVAP), also known as PV1, PAL-E and FELS. PLVAP is a 60 kDa type II transmembrane glycoprotein which tends to form homodimers. PLVAP is widely expressed in the vasculature of normal tissues. The vascular staining pattern of PLVAP is quite unique among the endothelial cell antigens, since expression of other antigens (like ICAM-1, P-selectin, E-selectin or VCAM-1) is not limited to vascular endothelial cells. PLVAP expression in the vascular endothelial cells of the CNS is lost in association with formation of an intact blood-brain barrier. However, in the endothelium of human brain tumors expression of PLVAP is specifically up-regulated, making it a suitable antiangiogenic target for brain tumor therapy and cerebral edema. Furthermore, PLVAP is expressed in the vasculature of most other human tumors and as such useful as marker for tumor angiogenesis.