An in vitro model of leukocyte mediated injury to the corneal epithelium

To enhance efforts directed at unraveling the role and mechanisms of leukocytes in mediating injury to corneal epithelium, an isolated bovine corneal cup was developed and evaluated. Bovine peripheral leukocytes and lysates were added to the corneal epithelial surface of isolated cornea for various periods after which the degree of morphologic changes and cell damage were assessed using light and electron microscopy. Results of these studies indicate that leukocyte/epithelial cell interactions are characterized by five successive stages: (1) leukocyte adhesion to superficial layer of the epithelium, (2) leukocyte penetration beneath the superficial epithelium, (3) epithelial cell injury, (4) leukocyte phagocytosis of killed epithelial cells and (5) ulceration and total destruction of the full thickness of the epithelial layer. The above sequence appears to be both time and dose dependent; that is epithelial cells exposed to leukocytes for short periods (5-60 minutes) or to low dose levels (10(5) - 10(7) cells/ml) shows leukocyte adhesion and penetration beneath the superficial layer of the epithelium, (stage 1 and 2), while longer exposures (2-3 hours) or higher numbers of leukocytes (10(7) - 10(8) cells/ml), leads to deeper penetration of epithelium by leukocytes and epithelial injury (Stages 3,4,and 5). We also observed that direct contact of intact leukocytes with epithelial cells is apparently necessary to induce this type of injury. These findings demonstrate the ability of leukocytes to destroy corneal epithelial cells and the value of this new ocular model for studies of the basic immunology of ocular inflammation.