VEGF antagonist inhibits bone formation elicited by MDSCs expressing BMP4. (a) Radiography shows decreased bone formation in the BMP4+sFlt1 (B4+sFlt) site compared with the BMP4 (B4) site 4 weeks PI. (b) Quantitative analysis shows a significant difference in relative bone area between the BMP4+sFlt and BMP4 groups (*P < 0.05). (c–h) Alcian Blue staining shows reduced cartilage formation at 7 days and delayed cartilage resorption at 10 and 14 days in the BMP4+sFlt group compared with the BMP4 group. Magnification: ×200.