Integrin α5β1 supports endothelial cell survival during angiogenesis in vivo. (a) CAMs were stimulated with bFGF or saline and then treated for 24 hours with saline, anti-α5β1, and control Ab’s. CAMs were then injected with 50 μl FITC-annexin V, harvested 2 hours later, and analyzed directly by confocal microscopy. (b) Green pixels (annexin V positive) present per optical section were quantified. (c) CAMs treated as in a were cryosectioned and immunostained with anti–cleaved caspase-3 (anti-cl.csp3) (green) and anti-vWF (red). Cleaved caspase-3–positive blood vessels are yellow (arrows). (d) CAMs treated as in a were cryosectioned and immunostained with anti-vWF (red) and for DNA fragmentation (TUNEL staining, green). Arrows indicate blood vessels. Yellow structures are apoptotic blood vessels. (e) Soluble DNA isolated from CAMs treated as in a was electrophoresed on 1.6% agarose gels. Molecular-weight markers are 1-kb DNA ladders. Relative DNA cleavage was determined by densitometry. (f) Individual cells isolated from CAMs treated as in a were stained with FITC-annexin V.