C5a receptor deficiency results in increased angiogenesis in ROP. WT, C3aR^−/−, or C5aR^−/− mice were subjected to the ROP model. (A) Retinal neovascularization was quantified on day p17 in WT and C3aR^−/− mice. Retinal neovascularization is presented as the number of epiretinal neovascular nuclei per section. Data are mean ± SEM (n = 12-13 pups per group) and are shown as percentage of control. Number of epiretinal nuclei in WT mice represents the 100% control. There was no significant difference between both groups. (B) Retinal neovascularization was quantified on day p17 in WT and C5aR^−/− mice. Data are mean ± SEM (n = 16-17 pups per group) and are shown as percentage of control. Number of epiretinal nuclei in WT mice represents the 100% control. *P < .005. (C) Paraffin-embedded axial sections (6 μm) of the retina were stained with PAS and hematoxylin, and neovascular tufts were observed anterior to the internal limiting membrane (arrows). C5aR^−/− mice displayed more neovascular tufts. Scale bars, 150 μm.