A novel apoptotic interaction between HSV-1 and human corneal epithelial cells

Abstract

Purpose. Herpes simplex virus type 1 (HSV-1) infects the cornea possibly causing blindness. The specific mechanisms of herpetic keratitis are unclear. We aimed to investigate whether HSV-1 would up- or down-regulate the apoptotic pathway of human corneal epithelial (HCE) cells. Methods. HSV-1 infection of HCE and Vero cells was demonstrated (immunofluorescence) and apoptotic gene expression was quantified (ribonuclease protection assay). Caspase 8 protein activity (colorimetric assay) was quantified and compared to caspase 8 mRNA amounts from RPA experiments. The apoptotic index of HSV-1 infected HCE and Vero cells (apoptotic index = % of apoptotic cells in infected samples/mock treated samples) was obtained and compared to gene expression. Results. A down-regulation in apoptotic gene expression was observed in HSV-1 infected HCE cells in contrast to Vero cells (infected and mock treated). Caspase 8 protein levels mirrored caspase 8 mRNA levels in HSV-1 infected HCE cells. The apoptotic index also supports this down-regulation. HSV-1 infected human corneal epithelial cells and Vero cells at similar rates. Conclusions. HSV-1 down-regulates the apoptotic pathway of human corneal epithelial cells. This down-regulation of apoptotic gene expression seems to be cell specific. Also infectivity is excluded in playing a role in regulation of the apoptotic pathway because HSV-1 replicated at similar rates in HCE and Vero cells.