The 89B3A5 antibody recognizes mouse CD309 also known as vascular endothelial growth factor receptor 2, VEGFR2, KDR, protein tyrosine kinase receptor flk-1, and fetal liver kinase-1. Flk-1 is a member of the tyrosine protein kinase family, sub-family CSF-1/PDGF, that contains a single pass transmembrane receptor with a protein kinase domain and seven immunoglobulin-like domains in the extracellular region. Flk-1 is expressed at high levels in adult heart, lung, kidney, brain, and skeletal muscle; other tissues express at lower levels. Flk-1 is a receptor for VEGF or VEGFC; ligand binding plays a key role in vascular development and vascular permeability. The 89B3A5 antibody has been shown to be useful for flow cytometry.