SPP1 and juvenile idiopathic arthritis: Increased concentrations of vascular endothelial growth factor (VEGF), a potent endothelial cell (EC) mitogen, its soluble receptors-1 and -2 (sVEGF-R1, sVEGF-R2), and osteopontin (OPN), a chemotactic factor that activates mononuclear cells, have been correlated to synovial angiogenesis assessed by Doppler ultrasonography of JIA patients [12].