Fig. 4. Tie-2 staining is increased when tumour cells are present. (A) HUVECs were cultured on Transwell inserts as for net-like formation and stained with CD31 or with Tie-2. Staining is comparable in cells in monoculture and in co-culture for CD-31, but Tie-2 staining is visible only in HUVECs cultured with U87 in the well. (B) Control brain tissue is compared with tissue from U87 xenografts. CD31 staining is not significantly different in control and tumour sections, with only endothelial cells in vessel lumina staining positive. For Tie-2, staining is visible in vessels in control tissue. In U87 xenografts, more structures are Tie-2 positive, possibly caused by an increased number of microvessels.