Macrophage depletion inhibits experimental choroidal neovascularization

OBJECTiVE. To investigate the role of macrophages in the development of laser-induced choroidal neovascularization (CNV) by selective depletion with liposomal clodronate (Cl2MDP-LIP). METHODS. Laser photocoagulation was used to induce CNV in wild-type C57BL/6J mice. Animals were treated with intravenous (IV) and/or subconjunctival. (SC) Cl2MDP-LIP or PBS-LIP at the following time points: 2 days before, immediately after, 2 days before and immediately after, or 2 days after laser injury. CNV responses were compared on the basis of en masse volumetric measurements and fluorescein angiography after laser photocoagulation. Macrophages were identified by immunostaining for F4/80, and vascular endothelial growth factor (VEGF) expression was quantified by ELISA. RESULTS. Macrophages invaded the site of laser injury within 1 day of photocoagulation and peaked at 3 days. IV Cl2MDP-LIP significantly decreased the volume of CNV and angiographic leakage when administered 2 days before and/or immediately after laser injury, but not when administered 2 days after injury. SC Cl2MDP-LIP significantly decreased lesion volume when coadministered with IV PBS-LIP but not IV Cl2MDP-LIP. IV Cl2MDP-LIP was significantly more beneficial when administered 2 days before laser injury than immediately after, but combining SC Cl2MDP-LIP with W treatment eliminated this difference. Reduction in CNV volume correlated with VEGF protein levels and number of infiltrating macrophages. CONCLUSIONS. Generalized macrophage depletion reduced the size and leakage of laser-induced CNV and was associated with decreased macrophage infiltration and VEGF protein. These findings define the role of the macrophage as a critical component in initiating the laser-induced CNV response.