Localization of collagen XVIII and endostatin in the human eye

Purpose: To investigate the localization of endostatin, a potent anglogenesis inhibitor, and its progenitor collagen XVIII in the human eye. Methods: Twelve normal human eyes were investigated. Immunohistochemistry of the anterior and posterior eye segment was performed using a polyclonal enclostatin and collagen XVIII antibody and a monoclonal collagen XVIII antibody. Specificity of the antibodies was confirmed by Western blot analysis. Results: The antibody against collagen XVIII stained Bowman's membrane, the lens capsule, the trabecular meshwork, and all epithelial and endothelial basal membranes in the anterior and posterior eye segment. In contrast the antibody against enclostatin showed a more distinct staining pattern. Intense intracellular staining for endostatin was present in the lens epithelium and in the non pigmented epithelium of the ciliary body. Extracellular presence of eridostatin could be detected in the lens capsule and all border membranes lining the aqueous humor including the anterior surface of the iris. The choroid was unstained. In the retina, staining was restricted to the inner limiting membrane and to en dothelial cells of larger vessels. Conclusions: Our results show that there is a ring of specifically enclostatin expressing structures forming a barrier around the anterior chamber and the vitreous. This might physiologically prevent vessels from sprouting into these avascular compartments.