Characterization of the collagen in the hexagonal lattice of Descemet's membrane: its relation to type VIII collagen

To investigate the nature of the hexagonal lattice structure in Descemet's membrane, monoclonal antibodies were raised against a homogenate of bovine Descemet's membranes. They were screened by immunofluorescence microscopy to obtain antibodies that label Descement's membrane. Some monoclonal antibodies labeled both Descemet's membrane and fine filaments within the stroma. In electron microscopy, with immunogold labeling on a critical point dried specimen, the antibodies labeled the hexagonal lattices and long-spacing structures produced by the bovine corneal endothelial cells in culture; 6A2 antibodies labeled the nodes of the lattice and 9H3 antibodies labeled the sides of the lattice. These antibodies also labeled the hexagonal lattice of Descemet's membrane in situ in ultrathin frozen sectioning. In immunofluorescence, these antibodies stained the sclera, choroid, and optic nerve sheath and its septum. They also labeled the dura mater of the spinal cord, and the perichondrium of the tracheal cartilage. In immunoblotting, the antibodies recognized 64-kD collagenous peptides both in tissue culture and in Descemet's membrane in vivo. They also recognized 50-kD pepsin-resistant fragments from Descemet's membranes that are related to type VIII collagen. However, they did not react either in immunoblotting or in immunoprecipitation with medium of subconfluent cultures from which type VIII collagen had been obtained. The results are discussed with reference to the nature of type VIII collagen, which is currently under dispute. This lattice collagen may be a member of a novel class of long-spacing fibrils.