Opposite roles of CCR2 and CX3CR1 macrophages in alkali-induced corneal neovascularization.

PURPOSE: The purpose of this study was to investigate the role of infiltrating macrophages in the development of experimental corneal neovascularization.
METHODS: Corneal neovascularization was induced by alkali injury in mice deficient in a macrophage-tropic chemokine receptor, CCR2 or CX3CR1, or in mice treated with clodronate-liposomes (Cl2MDP-lip), which can selectively deplete monocytes/macrophages. Corneal neovascularization 2 weeks after alkali injury was assessed by immunostaining with anti-CD31 antibody. Intracorneal expression of proangiogenic and antiangiogenic factors was determined by reverse transcription-polymerase chain reaction.
RESULTS: CCR2-deficient mice exhibited reduced alkali-induced corneal neovascularization with reduced macrophage infiltration, whereas CX3CR1-deficient mice developed a more severe form of alkali-induced corneal neovascularization with reduced macrophage infiltration. Selective macrophage depletion by Cl2MDP-lip treatment failed to affect alkali-induced corneal neovascularization as evidenced by immunohistochemical analysis using anti-CD31 antibody, whereas intracorneal macrophage infiltration was markedly reduced. Alkali injury enhanced the expression of proangiogenic molecules, including matrix metalloproteinase-2, matrix metalloproteinase-9, and tumor necrosis factor alpha, and antiangiogenic factors, including a disintegrin and metalloprotease with thrombospondin (ADAMTS)-1, thrombospondin-1, and thrombospondin-2. Cl2MDP-lip-treated mice exhibited a reduction in the messenger RNA expression of these molecules.
CONCLUSION: Because CCR2- and CX3CR1-expressing macrophages exhibit opposite activities in angiogenesis, depletion of macrophages as a whole may not have apparent effects on alkali-induced corneal neovascularization.