Expression of vascular endothelial growth factor and its receptors in inflamed and vascularized human corneas

To help further define the possible role of vascular endothelial growth factor (VEGF) in the pathogenesis of corneal neovascularization, the expression of VEGF and of its receptors Flt-1 and Flk-1 was investigated in various inflammatory corneal diseases.

Polyclonal antibodies to VEGF and its receptors were used for immunohistochemical staining of frozen sections of 38 human corneas with various degrees of neovascularization and inflammation. In addition, a panel of monoclonal antibodies was used to characterize the composition of the inflammatory infiltrates and to confirm the presence of neovascularization. Furthermore, VEGF concentrations were determined in vascularized corneas using a sensitive enzyme-linked immunosorbent assay.

VEGF was expressed by epithelial cells, by corneal endothelial cells, by vascular endothelial cells of limbal vessels and of newly formed vessels in the stroma, and weakly by keratocytes. Furthermore, VEGF expression was often markedly increased in inflamed corneas on epithelial cells and on vascular endothelial cells, particularly in the vicinity of macrophage infiltrates, and on fibroblasts in scar tissue. Correspondingly, VEGF concentrations were significantly higher in vascularized corneas compared with normal control corneas (P < 0.001). Expression of both VEGF receptors, Flt-1 and Flk-1, was increased on endothelial cells of newly formed vessels in the stroma of inflamed corneas compared with limbal vessels of normal control corneas. In addition, Flt-1 was also expressed by corneal endothelial cells and by macrophages, whereas Flk-1 expression was lacking.

These results demonstrate that VEGF, Flt-1, and Flk-1 are strongly expressed in inflamed and vascularized human corneas and, thus, may play an important role in corneal neovascularization.