Alkali-Induced Corneal Neovascularization Is Independent of CXCR2-Mediated Neutrophil Infiltration

Abstract

To study the role of infiltrating neutrophils in the development of experimental corneal neovascularization (CNV). CNV was induced by alkali injury in normal C57BL/6 mice, and the kinetics of neutrophil recruitment to the cornea and the CNV was detected by histologic analysis at multiple time points. Neutrophil recruitment to the corneas was inhibited by injection of anti-mouse granulocyte monoclonal antibodies (Ly-6G) or neutralizing anti-mouse CXCR2 antibodies. CNV was compared between the control and the specific antibody-treated mice 2 weeks after alkali injury, as quantified by CD31 immunostaining. Corneal vascular endothelial growth factor (VEGF) expression after injury was determined by reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemical staining. Many myeloperoxidase-positive neutrophils began to infiltrate the corneas 2 days after injury, but infiltration ceased by 14 days after injury. CNV became evident 7 days after injury, reached a maximal level at 14 days, and decreased thereafter. The mRNA expression of CXCR2 and its ligands, macrophage inflammatory protein 2 (CXCL2/MIP-2), and growth-related protein alpha (CXCL1/KC) increased markedly at 2 days after injury. Injection of either anti-mouse granulocyte monoclonal antibodies (Ly-6G) or neutralizing anti-mouse CXCR2 antibodies markedly, and to a similar extent, inhibited neutrophil recruitment to the cornea, indicating that neutrophil infiltration was mediated primarily by CXCR2. In contrast, these treatments failed to attenuate alkali-induced CNV. VEGF mRNA expression was enhanced 2 days after injury, and VEGF proteins were detected mainly in infiltrating mononuclear cells but not in neutrophils. CXCR2-mediated neutrophil infiltration contributes only marginally to the subsequent development of CNV.