Acute Infection with Venezuelan Equine Encephalitis Virus Replicon Particles Catalyzes a Systemic Antiviral State and Protects from Lethal Virus Challenge

Abstract

The host innate immune response provides a critical first line of defense against invading pathogens, inducing an antiviral state to impede the spread of infection. While numerous studies have documented antiviral responses within actively infected tissues, few have described the earliest innate response induced systemically by infection. Here, utilizing Venezuelan equine encephalitis virus (VEE) replicon particles (VRP) to limit infection to the initially infected cells in vivo, a rapid activation of the antiviral response was demonstrated not only within the murine draining lymph node, where replication was confined, but also within distal tissues. In the liver and brain, expression of interferon-stimulated genes was detected by 1 to 3 h following VRP footpad inoculation, reaching peak expression of >100-fold over that in mock-infected animals. Moreover, mice receiving a VRP footpad inoculation 6, 12, or 24 h prior to an otherwise lethal VEE footpad challenge were completely protected from death, including a drastic reduction in challenge virus titers. VRP pretreatment also provided protection from intranasal VEE challenge and extended the average survival time following intracranial challenge. Signaling through the interferon receptor was necessary for antiviral gene induction and protection from VEE challenge. However, VRP pretreatment failed to protect mice from a heterologous, lethal challenge with vesicular stomatitis virus, yet conferred protection following challenge with influenza virus. Collectively, these results document a rapid modulation of the host innate response within hours of infection, capable of rapidly alerting the entire animal to pathogen invasion and leading to protection from viral disease.

Venezuelan Equine Encephalitis Replicon Particles Can Induce Rapid Protection against Foot-and-Mouth Disease Virus

“…We demonstrated that treatment of the SK6 swine cell line with either VRP-poIFN-␣ or VRP-GFP rapidly inhibited subsequent FMDV replication and that the duration of inhibition lasted for at least 5 days. In agreement with Konopka et al (20), we found that VRP-induced protection requires a functional type I IFN system. Swine IB-RS-2 cells, which do not produce type I IFN, are not protected from FMDV infection by VRP-GFP treatment but are protected after VRP-poIFN-␣ treatment.…”

“…In IB-RS-2 cells pretreated with VRP-poIFN-␣, FMDV yield was reduced by approximately 2,000-fold at 24 h and 10,000-fold at 48 h. However, in VRP-GFP-pretreated IB-RS-2 cells, there was no reduction in FMDV yield compared to mockpretreated cells at either time. These results support the data of Konopka et al (20) indicating that a functional type I IFN system is required for the antiviral response induced by VRPs.…”

“…Empty VRPs have recently been shown to induce a rapid innate response in mice and protect against challenge with homologous VEE virus as well as the heterologous influenza virus but did not protect against VSV (20). We demonstrated that treatment of the SK6 swine cell line with either VRP-poIFN-␣ or VRP-GFP rapidly inhibited subsequent FMDV replication and that the duration of inhibition lasted for at least 5 days.…”

“…Serum samples of mice inoculated with VRP-GFP at different time points (3,6, and 24 h) were collected, and antiviral activity was tested in L929 cells as previously described (20). Briefly, serum samples were diluted 1:10 in medium and acidified to pH 2.0 for 24 h. Following neutralization to pH 7.4, the samples were titrated by 2-fold dilutions and added to confluent monolayers of L929 cells.…”

“…VRPs have been used as vaccine vectors for various foreign genes (16)(17)(18) including FMDV (unpublished data). Recently, Konopka et al (19,20) demonstrated that null VRPs, VRPs lacking any foreign gene, induce an early innate immune response in mice within 1 to 3 h postinfection (hpi), resulting in the upregulation of a number of ISGs and the production of type I IFN protein. Furthermore, null-VRP-inoculated mice are protected from lethal challenge with VEE as early as 6 h after VRP administration as well as 24 h later, and this pretreatment induced protection against heterologous challenge with influenza virus but not vesicular stomatitis virus (VSV) (20).…”