Pseudorabies virus (PRV), also known as Suid herpesvirus 1 (SuHV1), belongs to the Herpesviridae family and is the causative agent of pseudorabies (PR) or Aujeszky’s disease (AD). Pigs are the natural host of PRV infection and the only animals that can survive PRV infection. PRV causes a highly contagious disease that severely threatens the pig industry, leading to reproductive failure, respiratory and neurological symptoms, and high mortality rates [
1]. Infection of other animals with PRV results in acute, fatal disease with intense pruritus. Currently, attenuated live vaccines are the primary means of preventing and controlling pseudorabies [
2].
The PRV genome can accommodate large foreign genes without compromising replicative ability, making it an ideal vector for expressing heterologous antigens. [
3]. PRV vectors can be used to construct multivalent or broad-spectrum attenuated live vaccines to concurrently prevent PRV and infections by other important animal pathogens [
4]. The PRV genome encodes 16 envelope glycoproteins that function in viral entry, egress and cell-to-cell spread. The gE glycoprotein is the major virulence protein enabling PRV to invade the host nervous system [
5]. Deletion of the gE gene significantly decreases virulence and prevents invasion of the trigeminal and olfactory nerve terminals [
6]. The gI-gE complex, together with gC, mediates viral release and impacts replication and virulence. Ablation of gI and gE functions dramatically affects PRV gene expression during infection. The gE glycoprotein can recruit the microtubule motor protein KIF1A to mediate retrograde axonal transport of PRV particles in neurons [
6,
7]. gG is an immunomodulatory envelope protein that induces host cell secretion of interleukin-8 (IL-8) to attract neutrophil and monocyte migration and increase PRV infectivity [
8]. gH is an envelope protein with fusion activity that can form a heterodimer with gL and, together with gB and gD, mediate PRV fusion with host cells [
9]. gI is an envelope protein that facilitates cell-to-cell spread and retrograde neuronal spread, forming a heterodimer with gE and interacting with the gM/gN complex to impact intercellular PRV diffusion [
10]. gK is an envelope protein that regulates viral budding and virulence, forming a heterodimer with UL20 and interacting with gB and gH/gL to impact intracellular transport and egress of PRV [
11,
12]. gK can also affect PRV infection and virulence in the eyes, nose and throat [
12].gL is an envelope protein with fusion activity that forms a heterodimer with gH and, together with gB and gD, mediates PRV fusion with host cells [
9]. gM is an envelope protein that regulates viral budding and cell-to-cell spread, forming a heterodimer with gN and interacting with the gE/gI complex to impact intracellular transport and budding of PRV [
13]. gN is an envelope protein that regulates viral budding and cell-to-cell spread, forming a heterodimer with gM and interacting with the gE/gI complex to impact intracellular transport and egress of PRV [
13,
14]. The TK gene encodes a nonstructural protein with enzymatic activity to phosphorylate deoxynucleosides, participating in PRV DNA replication and transcription. TK impacts PRV latent infection and virulence [
15]. TK-deleted or mutant PRV cannot establish latent infection in ganglia and exhibits attenuated virulence in mice and pigs [
16]. TK utilizes host cell nucleotide metabolic pathways to provide necessary deoxyribonucleoside triphosphates (dNTPs) for PRV but can also convert certain antivirals like acyclovir (ACV) into active metabolites to inhibit PRV replication. Numerous PRV proteins are being continually explored for biological functions [
17,
18]. Therefore,The glycoproteins gE and gI, along with the thymidine kinase (TK) gene, are major virulence determinants of PRV. gE enables neuroinvasion while TK impacts latent infection and virulence. Deletion of gE/gI/TK genes leads to dramatic attenuation of PRV.
In this study, we analyzed the transcriptomic changes in PK15 cells infected with the previously isolated virulent C strain, the attenuated SD2017gE/gI/TK strain with deletions of the major virulence determinants gE, gI and TK generated through homologous recombination using RNA-sequencing with Illumina platform. The goal was to elucidate the effects of key PRV virulence gene deletions on host cells, gain further insights into PRV pathogenesis, and establish a basis for novel attenuated live vaccine development.