Placenta growth factor (PlGF) is a dimeric growth factor in the PDGF/VEGF family. Alternative splicing generates at least three human PlGF isoforms PlGF-1, PlGF-2, and PlGF-3. PlGF-2 is the only isoform that contains a heparin-binding region. It is expressed by villous trophoblasts, decidual cells, erythroblasts, keratinocytes, and some endothelial cells. PlGF competes with VEGF for binding and activating VEGF R1/Flt-1. This results in increased angiogenesis by making more VEGF available for activation of VEGF R2. PlGF-2 also exhibits heparin-dependent binding of Neuropilins-1 and -2 which serve as VEGF co-receptors. It can inhibit nerve growth cone collapse and induce monocyte production of inflammatory cytokines including VEGF.