The vascular endothelial growth factor receptor Flt-1 mediates biological activities: implications for a functional role of placenta growth factor in monocyte activation and chemo-taxis - Clauss, M; Weich, H; Breier, G; Knies, U; Röckl, W; Waltenberger, J; Risau, W (J.Biol. Chem, 1996)