Association of MHCII-positive leukocytes with the tumor vasculature. GI-101A tumor-bearing mice were i.v. injected with 5 × 106 pfu GLV-1h68 and tumors were harvested 42 days p.i., prepared immunohistologically and examined using confocal microscopy. (a, b) Association of MHCII-positive leukocytes cell cluster with the CD31-positive tumor vasculature (arrowhead) in GLV-1h68-infected tumors (a); isolated MHCII-positive cells in control tumors (b). (c) MHCII+/CD31+ cell invasion (arrowhead) of the endothelial intima and accumulation around tumor vessels. (d, e) The type IV collagen IV-containing basal membrane (red) of the tumor vasculature was thickened and loosley attached to endothelial cells (arrowhead) in GLV-1h68-infected tumors (d) compared to control tumors (e). MHCII-positive leukocytes were labelled with anti-MHCII antibody (red; a-c); tumor vasculature was marked with anti-CD31 antibody (blue), GFP fluorescence indicate viral-infected cells, and nuclei were stained with Hoechst (green in c; orange in d, e). All images are representative examples. Scale bars represent 300 μm (a, b), 75 μm (c-e).