Fibrinogen depletion enables neovascularization of the Anxa2^−/− retina. (A) ELISA of fibrinogen levels in plasma from P17 Anxa2^−/− mice treated with (0.19 ± 0.04 mg/mL; n = 7) or without (1.17 ± 0.09 mg/mL; n = 8) ancrod (***P < .001). (B) Representative cross-sections (magnification ×40) of retinas from P17 oxygen-treated Anxa2^−/− mice treated thereafter with or without ancrod and stained with DAPI (blue), isolectin B4 (green), and anti-fibrinogen (red). Close-up views of the peripheral retina are also shown (magnification ×200). S indicates sclera; V, vitreous body. Scale bars 500 and 100 μm, for magnification ×40 and ×200, respectively. (C) Representative immunoblot of fibrin in retinal tissue from P17 oxygen-treated Anxa2^−/− mice treated thereafter with or without ancrod. (D) Representative images showing total retinal area and regions of AV and VO from P17 oxygen-treated Anxa2^−/− mice treated thereafter with or without ancrod. Pixel number corresponding to each compartment is indicated below each image. Scale bars, 200 μm (magnification ×50). (E) Ratios of areas of VO to total retina (27.2% ± 1.7% vs 30.1% ± 1.3%) and NV to total retina (4.3% ± 0.09% vs 9.7% ± 0.2%) in P17 oxygen-treated Anxa2^−/− mice treated thereafter with or without ancrod (n = 5; NS indicates no significant difference, *** P < .001). (F) Enumeration of neovascular nuclei in retinal sections from P17 oxygen-treated Anxa2^−/− mice treated thereafter with (131.8 ± 5.3 nuclei per section) or without ancrod (79.4 ± 2.2 nuclei per section; n = 5; ***P < .001). The data are representative of 5 (B) or 3 (C) independent experiments.