Herpes simplex virus type-1 infection of corneal epithelial cells induces apoptosis of the underlying keratocytes.

The purpose of this study was to determine whether primary corneal infection with Herpes simplex virus (HSV)-1 induces keratocyte apoptosis in the rabbit. New Zealand white rabbit eyes were inoculated with HSV-1 strain 17 Syn+. Rabbits that developed slit lamp signs of epithelial infection were killed between 12 and 120 hr post infection. One cornea of each animal was fresh-frozen for TUNEL assay to detect DNA fragmentation in situ. The other cornea was fixed for transmission electron microscopy (TEM). Mechanical scrape wounded rabbit corneas were included as positive controls. DNA fragmentation consistent with apoptosis was detected in anterior keratocytes of corneas at 18, 24, and 48 hr after primary infection with HSV-1 and 2 hr after an epithelial scrape, but not in unwounded control corneas. Electron microscopic evidence of keratocyte apoptosis that included chromatin condensation, chromatin fragmentation, and cellular blebbing with formation of membrane bound cell fragments was detected in mechanical scrape wounded corneas and infected rabbit corneas at 12, 18, 24, 48, and 120 hr after infection, but not in unwounded control corneas. This study suggests that anterior stromal keratocyte apoptosis occurs following primary HSV-1 infection of the corneal epithelium. Previous studies have demonstrated that corneal epithelial scrape wounds induce apoptosis in the underlying keratocyte cells. We hypothesize that soluble mediators released by epithelial injury mediate anterior keratocyte apoptosis and that one of the physiologic functions of this epithelial-stromal apoptosis system is to limit viral extension.