Immunohistochemical detection of microvessels, vascular basement membrane, and pericytes. A-D, representative immunohistochemical preparations stained with anti-CD31 antibody, anti-collagen IV antibody, or anti-α-smooth muscle actin (α-SMA) antibody to visualize endothelial cells, vascular basement membrane, and pericytes. The images refer to an untreated A-07-GFP tumor (A), an A-07-GFP tumor treated with 40 mg/kg/day sunitinib (B), an untreated R-18-GFP tumor (C), and an R-18-GFP tumor treated with 40 mg/kg/day sunitinib (D). E, microvascular density in untreated and sunitinib-treated A-07-GFP and R-18-GFP tumors. Points, means of 4 tumors; bars, SEM. F-G, microvascular density assessed by immunohistochemistry versus vessel density assessed by intravital microscopy in A-07-GFP (F) and R-18-GFP (G) tumors. Points, individual tumors; curves, curves fitted to the data by linear regression analysis.