Lipopolysaccharide enhances human herpesvirus 1 replication and IL-6 release in epithelial cells

To investigate the effect of lipopolysaccharide (LPS) on human herpesvirus 1 (HHV-1) infection in epithelial cells. Two strains of HHV-1, HHV-1 F strain (HHV-1f) and HHV-1 strain-H129 with GFP knock-in (HHV-g4), were used to infect HCE-T and VERO cells at MOIs of 0.04 and 0.02, respectively. After 1 h, 0, 10, 50, and 100 μg/ml LPS was added to serum-free medium and the cells were cultured for up to 24 h. GFP fluorescence of HHV-g4 in cells was examined under a fluorescence microscope and imaged. HHV-1f titer was determined by quantitative real-time polymerase chain reaction (qPCR) in HCE-T cells and plaque assays in VERO cells. The expression of the viral ICP4 protein of HHV-1f was detected by Western blot assay. IL-6 and IL-10 levels in culture medium were determined by enzyme-linked immunosorbent assay (ELISA). Similar changes but at different degrees were found in HCE-T and VERO cells that were infected with HHV-1. GFP fluorescence of HHV-g4 and cell lesions increased in a dose-dependent manner. Virus titer was also enhanced by LPS stimulation in HCE-T and VERO cells. ICP4 expression was promoted at higher LPS concentrations (P = 0.04). In addition, viral infection resulted in increased expression of IL-6 in a dose-dependent manner at 12 and 24 h (P = 0.01), while IL-10 expression was unaffected by either HHV-1 infection or LPS stimulation. LPS promotes HHV-1 infection in epithelial cells, which suggests that gram-negative bacteria on ocular surfaces may aggravate HHV-1 infection.