Leukocyte-mediated Injury to Corneal Endothelial Cells. A Model of Tissue Injury

Although leukocyte-mediated cell injury has long been suggested as a major mechanism of general tissue injury in acute and chronic inflammation, only limited data have been developed to directly implicate leukocytes in ocular tissue injury. In an effort to unravel the role and mechanisms of leukocyte-mediated injury to the cornea, an isolated corneal cup model was developed. For this model, peripheral bovine leukocytes were added to isolated bovine corneal cultures (corneal cup) in vitro, after which endothelial cell damage and death were evaluated morphologically. In general, corneal endothelial cell swelling was observed within 5-10 minutes after leukocyte exposure, followed by detachment of the corneal endothelium at a 30-75-minute interval. Grossly, the detached endothelium appeared as a floating sheet. Using trypan blue dye exclusion, cells in the sheet were found to be nonviable. When examined ultrastructurally, the sheet was found to consist of leukocytes and endothelial cell debris. Light-microscopic examination of the corneal cup at 5-10 minutes after leukocyte action demonstrated extensive endothelial cell damage, as indicated by cell membrane thickening, cytoplasmic vacuolization, and changes in nuclear shape. These changes in the endothelial cells were confirmed by electron microscopy. Vacuolization and swelling of the endothelium appeared as the first changes, induced by leukocyte interactions with the endothelial cell layer. In general, the endothelial cell nucleus became convoluted, mitochondria swelled, and the endoplasmic reticulum became dilated. These changes become more pronounced as the endothelial cells become detached from the underlying Descemet's membrane. Leukocyte interaction with corneal epithelium, on the other hand, did not result in cell detachment, but only cell damage. These studies demonstrate the ability of leukocytes to denude Descemet's membrane of endothelial cells and destroy corneal endothelial cells in vitro. They also suggest that the corneal cup model system will enhance both morphologic and biochemical evaluation of the mechanisms and consequences of leukocyte-mediated injury to the cornea, and thereby provide new insights into the mechanisms of endocular inflammation and tissue injury in vivo.