BoAHV-1 and -5 differentially modulate TLR3 signaling and type I IFN in neural cells

Varicellovirus bovinealpha (BoAHV)-1 and -5 (formerly known as bovine alphaherpesviruses 1 and 5) are closely-related neurotropic viruses with distinct neuropathogenic potential. In this study, we investigated how BoAHV-1 and BoAHV-5 modulate toll-like receptor 3 (TLR3) signaling pathway and type I interferon (IFN) response in neural cells. Stimulation of neural cells with the TLR3 agonist polyinosinic:polycytidylic acid (poly I:C) induced transient upregulation of TRIF, IRF-3, NF-κB, and IFN-α, mainly at early time points. BoAHV-1 infection triggered a delayed but sustained upregulation of IRF-3 and IFN-β, coinciding with a progressive increase in TRIF expression, which was subsequently downregulated at later stages. In contrast, BoAHV-5 infection elicited a rapid and robust early innate immune response characterized by strong IRF-3, NF-κB, and IFN-α transcription. Furthermore, BoAHV-5 induced sustained high IFN-β levels throughout infection, suggesting engagement of alternative antiviral pathways, likely RIG-I/MDA-5 receptors. These findings highlight distinct immunomodulatory strategies employed by BoAHV-1 and BoAHV-5 in neural cells. While BoAHV-1 infection is characterized by a delayed antiviral response, BoAHV-5 mounts a strong but transient immune response. BoAHV-5 suppresses TLR3 signaling and likely activates alternative pathways, such as RIG-I/MDA5 signaling. Overall, this study provides additional insight on BoAHV manipulation of the innate immunity and its role in neuropathogenesis.