Infectious Laryngotracheitis Virus Viral Chemokine-Binding Protein Glycoprotein G Alters Transcription of Key Inflammatory Mediators In Vitro and In Vivo

Abstract

Infectious laryngotracheitis virus (ILTV) is an alphaherpesvirus that infects chickens, causing upper respiratory tract disease and significant losses to poultry industries worldwide. Glycoprotein G (gG) is a broad-range viral chemokine-binding protein conserved among most alphaherpesviruses, including ILTV. A number of studies comparing the immunological parameters between infection with gG-expressing and gG-deficient ILTV strains have demonstrated that expression of gG is associated with increased virulence, modification of the amount and the composition of the inflammatory response, and modulation of the immune responses toward antibody production and away from cell-mediated immune responses. The aims of the current study were to examine the establishment of infection and inflammation by ILTV and determine how gG influences that response to infection. infection studies using tracheal organ tissue specimen cultures and blood-derived monocytes and infection studies in specific-pathogen-free chickens showed that leukocyte recruitment to the site of infection is an important component of the induced pathology and that this is influenced by the expression of ILTV gG and changes in the transcription of the chicken orthologues of mammalian CXC chemokine ligand 8 (CXCL8), chicken CXCLi1 and chicken CXCLi2, among other cytokines and chemokines. The results from this study demonstrate that ILTV gG interferes with chemokine and cytokine transcription at different steps of the inflammatory cascade, thus altering inflammation, virulence, and the balance of the immune response to infection. Infectious laryngotracheitis virus is an alphaherpesvirus that expresses gG, a conserved broad-range viral chemokine-binding protein known to interfere with host immune responses. However, little is known about how gG modifies virulence and influences the inflammatory signaling cascade associated with infection. Here, data from and infection studies are presented. These data show that gG has a direct impact on the transcription of cytokines and chemokine ligands (such as chicken CXCL8 orthologues, among others), which explains the altered balance of the inflammatory response that is associated with gG during ILTV infection of the upper respiratory tract of chickens. This is the first report to associate gG with the dysregulation of cytokine transcription at different stages of the inflammatory cascade triggered by ILTV infection of the natural host.

Cytokine gene transcription in the trachea, Harderian gland, and trigeminal ganglia of chickens inoculated with virulent infectious laryngotracheitis virus (ILTV) strain

“…However, upregulation of the IFN-α gene was observed from 3 dpi to 5 dpi, which coincided with the recruitment of effector cells to the trachea. These findings are consistent with those reported by Coppo et al (2018), where ILTV infection of the tracheal mucosa in vitro (trachea organ culture) did not result in upregulation of either IFN-α or IFN-β; nevertheless, in vivo infection resulted in the transcription upregulation of IFN-α (but not IFN-β). Additionally, it has been reported that herpes simplex virus type 1 (HSV-1) proteins, such as ICP0, vp16, US11, and US3, either interfere with or block the production of proteins necessary to complete the type I IFN signalling pathway.…”

“…the former conclusion, Coppo et al (2018) suggest that in an early study (Lee et al, 2010) the transcription upregulation of pro-inflammatory genes (chCXCLi1, chCXCli2, and IL6) observed in the primary chicken embryo lung cells after ILTV infection most likely originates from remaining leukocyte populations in the lung primary cell culture.…”

“…By 5 dpi, parallel to the most severe histopathological changes observed in the trachea (Figure 3(c)), the peak transcription of inflammatory cytokine IL-1β, chemokine ligand chCXCLi2, interferons α and γ, as well as interleukins IL-10 and IL-13 genes was detected (Figure 2). Recently, marked differences in gene transcription patterns after ILTV infection of tracheal tissues (in vivo), characterized by clustered increases in transcription, as compared to trachea organ cultures (ex vivo) which showed lesser changes, indicated that the enhanced transcription observed in the trachea is being induced in distinct cellular types recruited to the site of infection (Coppo et al, 2018). Based on and (e) 9 dpi epithelial cell hyperplasia with increased collagen bundles; (f) viral genome load per trachea at 1 dpi (median 4.34), 3 dpi (median 8.72), 5 dpi (median 4.95), 7 dpi (median 1.88), 9 dpi (median 2.44).…”

“…A second study found that early after challenge with a virulent ILTV strain transcription of the interferon γ (IFNγ) gene increased in the trachea of chickens immunized with a live attenuated vaccine but transcription of the IFNγ gene remained at a basal level in non-immunized but challenged chickens (Vagnozzi et al, 2016). More recently, Coppo et al (2018) showed that transcription of chCXCLi1, CXCLi2, and other cytokine genes was notably influenced by the expression of the broad range viral chemokine binding protein gG.…”

Virus survey in populations of two subspecies of bent-winged bats (Miniopterus orianae bassanii and oceanensis) in south-eastern Australia reveals a high prevalence of diverse herpesviruses

“…The assay for Torovirinae used an artificial oligonucleotide construct containing the primer binding regions for the respective primers. Successful extraction of RNA was confirmed in positive extraction controls using reverse transcription PCRs targeting conserved motifs in domain III of the paramyxovirus RNA-dependent RNA polymerase gene (applied to cell culture stocks of NDV) or targeting mRNA from the chicken housekeeping gene; glyceraldehyde-3-phosphate dehydrogenase (applied to cell culture stocks of ILTV) [41,42].…”