Interferon Gamma Prolongs Survival of Varicella-Zoster Virus-Infected Human Neurons In Vitro

Abstract

Infection of human neurons in vitro with varicella-zoster virus (VZV) at a low multiplicity of infection does not result in a cytopathic effect (CPE) within 14 days postinfection (dpi), despite production of infectious virus. We showed that by 28 dpi a CPE ultimately developed in infected neurons and that interferon gamma inhibited not only the CPE but also VZV DNA accumulation, transcription, and virus production, thereby prolonging the life of VZV-infected neurons.

FIG 1

Inhibition of VZV spread in human neurons by IFN-γ. VZV-infected neurons were untreated (top) or treated with IFN-γ (bottom) for 14 dpi, fixed, and immunostained for an immediate early protein (VZV ORF63, green) and a late protein (VZV ORF68, red); 4′,6-diamidino-2-phenylindole staining is blue.

FIG 2

Prevention of VZV-induced CPE in human neurons by IFN-γ. At 28 dpi, CPE developed in VZV-infected neurons (top panel), characterized by rounding of cell bodies (dashed arrows) with retraction and fragmentation of neurites resembling a string of beads (solid arrows). VZV-infected neurons cultured in the presence of IFN-γ remained healthy at 28 dpi (bottom panel), exhibiting large cell bodies (dashed arrows) and extensive neurite outgrowth that forms a mesh throughout the culture (solid arrows).

FIG 3

Inhibition of VZV DNA accumulation and viral transcription in VZV-infected human neurons by IFN-γ. VZV-infected human neurons were either untreated (black bars) or treated with IFN-γ (gray bars) for 28 days, when the abundances of viral DNA (left) and transcripts (right) corresponding to VZV ORF62, ORF63, ORF29, and ORF68 were determined. Data are mean cycle threshold (C_T) values ± standard deviations from 2 independent cultures.

FIG 4

Reduced production of infectious VZV in human neurons by IFN-γ. VZV-infected human neurons were either untreated (black bar) or IFN-γ treated (gray bar) for 28 days. At 28 dpi, when a CPE developed in untreated neurons, PFU were determined. Data are means ± standard deviations from 2 independent cultures.