Investigating the Regulation of the Innate Immune Responses of PRV-Becker and PRV-Bartha Infections in Neurons In Vitro

Abstract

Pseudorabies virus (PRV) is a swine alphaherpesvirus that is closely related to human herpes simplex virus type 1 (HSV-1) and varicella-zoster virus (VZV). The virus also infects a large number of mammals, including sheep, dogs, and rodents. In these non-natural hosts, infection with a virulent wild-type PRV strain (PRV- Becker), causes a neuropathic itch also known as “mad itch” which is followed by an uncontrolled systemic inflammation, leading to sudden death. Using a mouse footpad inoculation model, it was demonstrated that PRV-Becker infection induces the increased production of two proinflammatory cytokines (IL-6 and G-CSF) in peripheral nervous system (PNS) and central nervous system (CNS) tissues, very early after infection. This suggests that PRV infection activates the nervous system and initiates an early neuroinflammatory response that later escalates into a systemic inflammation. However, the molecular mechanisms used by PRV to regulate the innate immune responses specifically upon infection of neuronal cells remain unclear. This study aimed to establish an in vitro system that could mimic PRV infection in vivo and help to dissect the mechanisms that initiate this neuroinflammatory response. Using murine neuroblastomas (neuro-2A cells), we showed that all confluent neuro-2A cells are infected with PRV by 8 hours post inoculation (hpi). We found that the virulent PRV-Becker strain and the attenuated vaccine strain, PRV-Bartha, replicate to the same extent in confluent neuro-2A cells up to 10^5 plaque forming units (PFU) at 48 hpi. Compared to non-infected neuro-2A cells, PRV-Becker- and PRV-Bartha- infected cells show significant decreased IL-6 levels at 48 hpi. Moreover, PRV-Becker- and PRV-Bartha-infected neuro-2A cells do not produce significant amounts of G-CSF and type 1 interferon (IFN). Overall, we demonstrated that PRV infection of neuro-2A cells does not recapitulate the inflammatory cytokine production found after PRV infection of mice.