THE EFFECTS OF HSV-1 ON FAS LIGAND EXPRESSION IN THE EYE

Denise Umpiérrez¹, Patrick Stuart², Biology Department, Washington University, St. Louis, MO¹, Dept. of Ophthalmology; Washington University in St. Louis²

Background: Herpes simplex virus Type 1 (HSV-1) infects 90% of the population, especially in childhood and adolescence. Infections by this neurotropic virus are characterized by an initial acute infection, followed by the establishment of latency in the proximal ganglia. Once latency has been established the virus can reactivate during periods of physical or emotional stress, at the same site as the initial infection. This reactivation of the virus can be especially dangerous in the eye because it can lead to irreparable damage as manifested by scarring of the cornea or retina, impaired vision, and, in severe cases, corneal melt resulting in blindness. The eye is an immune priviledged site, which is chacterized by reduced inflammatory responses and impaired adaptive immune responses, both of which lessens the likelihood of irreparable damage to the eye as a result of infection. In the eye, Fas ligand (FasL), a membrane protein, plays a major role in immune priviledge. FasL induces apoptosis in potentially harmful infammatory cells that carry the Fas protein as they enter the eye.

Aim: To determine whether HSV-1 affects FasL expression and/or function in the eye.

Methods: A transgenic mouse (CD95LP-Luc)with the luciferase reporter gene attached to the FasL promoter sequence was used in these experiments. Initially, we removed various organs and tissues to determine baseline levels of FasL expression in these transgenic mice. These organs and tissues were then treated with the reporter lysis buffer followed by bead-bonking and sonication to lyse the cells. Then luciferase protein activity were measured. Second, HSV-1 (KOS) was injected into the anterior chamber of one eye and PBS injected into the contralateral eye. The eyes and the trigeminal ganglia were harvested at 24 and 48 hours post inoculation. Third, to observe a different mode of infection, mice had one footpad infected with HSV-1 and the other left as a control. For both the anterior chamber and footpad injections, the same methods were used to lyse the cells and measure luciferase activity.

Results/Conclusion: In the baseline screening assay, we noted that the highest levels of luciferase are in the brain, testes and ovaries; other tissues, when not infected, show much lower FasL activity. After inoculation, luciferase levels were significantly higher in the eyes and the feet injected with HSV-1 than in the controls. From these and previous supporting studies conducted by M. Leibold, we conclude that HSV-1 infections in the eye result in increased in FasL expression. This we believe strengthens the immune privilege status of the eye by better preventing harmful inflammatory cells from entering the eye. Further research will be directed toward determining which herpes gene is responsible for the up-regulation of FasL.