Inhibition of MC recruitment to retinal vessels by postnatal treatment with anti–PDGFR-β Ab. (a–d) Distribution of systemically administered APB5 in the retina. APB5 (rat anti-mouse PDGFR-β mAb) was labeled with anti-rat Ab 3 hours after an intraperitoneal injection into a P4 neonate. Distribution of APB5 (b and d) coincided with the retinal vascular networks, as illustrated by type IV collagen (a and c). (e–h) Double immunofluorescent staining of PECAM and desmin at P5 (e and g), and PECAM and SMA at P8 (f and h). In contrast to the successive MC coverage in the control (g and h), APB5-treated mice failed to recruit MCs in the developing retina, with the exception of the continued presence of a few MCs (arrowheads) only at the roots of trunk vessels arising from the optic disc (e and f). Bars represent 20 μm. (i and j) Scanning electron microscopy depicting denuded endothelial tubes with complete absence of MC coverage in large vessels (i) and capillaries (j) in APB5-treated retina.