Comparative analysis of replication characteristics of BoHV-1 subtypes in bovine respiratory and genital mucosa explants: a phylogenetic enlightenment

1 Cellular protein TTC4 and its cofactor HSP90 are pro-viral for bovine herpesvirus 1

Bovine Herpesvirus Type 1 (BoHV-1) infection causes infectious bovine rhinotracheitis and genital disease in cattle, with significant economic and welfare impacts. However, the role of cellular host factors during viral replication remains poorly characterised. A previously performed genome-wide CRISPR knockout screen identified pro- and antiviral host factors acting during BoHV-1 replication. Herein we validate a pro-viral role for a candidate from this screen: the cellular protein tetracopeptide repeat protein 4 (TTC4). We show that TTC4 transcript production is upregulated during BoHV-1 infection. Depletion of TTC4 protein impairs BoHV-1 protein production but does not reduce production of infectious virions, whereas overexpression of exogenous TTC4 results in a significant increase in production of infectious BoHV-1 virions. TTC4 itself is poorly characterized (especially in the context of virus infection), but is a known co-chaperone of heat shock protein 90 (HSP90). HSP90 has a well-characterized pro-viral role during the replication of diverse herpesviruses, and we therefore hypothesized that HSP90 is also pro-viral for BoHV-1. Drug-mediated inhibition of HSP90 using geldanamycin at sub-cytotoxic concentrations inhibited both BoHV-1 protein production and viral genome replication, indicating a pro-viral role for HSP90 during BoHV-1 infection. Our data demonstrates pro-viral roles for both TTC4 and HSP90 during BoHV-1 replication; possibly, interactions between these two proteins are required for optimal BoHV-1 replication, or the two proteins may have independent pro-viral roles.

Primary replication and invasion of the bovine gammaherpesvirus BoHV-4 in the genital mucosae

Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus that is widespread in cattle. Ex vivo models with bovine genital tract mucosa explants were set up to study molecular/cellular BoHV-4-host interactions. Bovine posterior vagina, cervix and uterus body were collected from cows at two stages of the reproductive cycle for making mucosa explants. The BoHV-4 replication kinetics and characteristics within the three different mucosae of animals in the follicular and luteal phase were assessed by virus titration. The number of plaques, plaque latitude and number of infected cells were determined by immunofluorescence. BoHV-4 replicated in a productive way in all genital mucosal tissues. It infected single individual cells in both epithelium and lamina propria of the genital mucosae at 24 hours post-inoculation (hpi). Later, small BoHV-4 epithelial plaques were formed that did not spread through the basement membrane. 50% of the number of BoHV-4 infected cells were identified as cytokeratin⁺ and CD172a⁺ cells in the three parts of the genital tract at 24 hpi. Upon a direct injection of genital explants with BoHV-4, fibrocytes became infected, indicating that the unidentified 50% of the infected cells are most probably fibrocytes. In this study, in vivo-related in vitro genital tract models were successfully established and the early stage of the pathogenesis of a genital infection was clarified: BoHV-4 starts with a productive infection of epithelial cells in the reproductive tract, forming small foci followed by a non-productive infection of surveilling monocytic cells which help BoHV-4 to invade into deeper tissues.

Productive replication of nephropathogenic infectious bronchitis virus in peripheral blood monocytic cells, a strategy for viral dissemination and kidney infection in chickens

In the present study, the replication kinetics of nephropathogenic (B1648) and respiratory (Massachusetts-M41) IBV strains were compared in vitro in respiratory mucosa explants and blood monocytes (KUL01⁺ cells), and in vivo in chickens to understand why some IBV strains have a kidney tropism. B1648 was replicating somewhat better than M41 in the epithelium of the respiratory mucosa explants and used more KUL01⁺ cells to penetrate the deeper layers of the respiratory tract. B1648 was productively replicating in KUL01⁺ monocytic cells in contrast with M41. In B1648 inoculated animals, 10^2.7–6.8 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8, 10 and 12 days post inoculation (dpi), 10^2.4–4.5 viral RNA copies/mL in plasma at 2, 4, 6, 8, 10 and 12 dpi and 10^1.8–4.4 viral RNA copies/10⁶ mononuclear cells in blood at 2, 4, 6 and 8 dpi. In M41 inoculated animals, 10^2.6–7.0 viral RNA copies/100 mg were detected in tracheal secretions at 2, 4, 6, 8 and 10 dpi, but viral RNA was not demonstrated in plasma and mononuclear cells (except in one chicken at 6 dpi). Infectious virus was detected only in plasma and mononuclear cells of the B1648 group. At euthanasia (12 dpi), viral RNA and antigen positive cells were detected in lungs, liver, spleen and kidneys of only the B1648 group and in tracheas of both the B1648 and M41 group. In conclusion, only B1648 can easily disseminate to internal organs via a cell-free and -associated viremia with KUL01⁺ cells as important carrier cells.

Replication characteristics of equine herpesvirus 1 and equine herpesvirus 3: comparative analysis using ex vivo tissue cultures

Replication kinetics and invasion characteristics of equine herpesvirus-1 and -3 (EHV-1/-3) in nasal and vaginal mucosae were compared using explants. The explants were cultured during 96 h with little change in viability. The tissues were inoculated with EHV-1 03P37 (neuropathogenic), 97P70 (abortigenic) and EHV-3 04P57, collected at 0, 24, 48 and 72 h post inoculation (pi) and stained for viral antigens. Both EHV-1 and EHV-3 replicated in a plaquewise manner. The plaques were already observed at 24 h pi, their size increased over time and did not directly cross the basement membrane (BM). However, EHV-1 infected the monocytic cells (MC) and hijacked these cells to invade the lamina propria. In contrast, EHV-3 replication was fully restricted to epithelial cells; the virus did not breach the BM via a direct cell-to-cell spread nor used infected MC. EHV-1-induced plaques were larger in nasal mucosa compared to vaginal mucosa. The opposite was found for EHV-3-induced plaques. Both EHV-1 strains replicated with comparable kinetics in nasal mucosa. However, the extent of replication of the abortigenic strain in vaginal mucosa was significantly higher than that of the neuropathogenic strain. Two-to-five-fold lower numbers of EHV-1-infected MC underneath the BM were found in vaginal mucosa than in nasal mucosa. Our study has shown that (i) EHV-1 has developed in evolution a predisposition for respiratory mucosa and EHV-3 for vaginal mucosa, (ii) abortigenic EHV-1 replicates better in vaginal mucosa than neuropathogenic EHV-1 and (iii) EHV-3 demonstrated a strict epithelial tropism whereas EHV-1 in addition hijacked MC to invade the lamina propria.

Three viruses of the bovine respiratory disease complex apply different strategies to initiate infection

Bovine respiratory disease complex (BRDC) is the major cause of serious respiratory tract infections in calves. The disease is multifactorial, with either stress or reduced immunity allowing several pathogens to emerge. We investigated the susceptibility of bovine airway epithelial cells (BAEC) to infection by the three major viruses associated with the BRDC: bovine respiratory syncytial virus (BRSV), bovine herpesvirus type 1 (BHV-1) and bovine parainfluenza virus type 3 (BPIV3). For this purpose, two culture systems for well-differentiated BAEC were used: the air-liquid interface (ALI) system, where filter-grown BAEC differentiate into a pseudostratified respiratory epithelium and precision-cut lung slices (PCLS) where BAEC are maintained in the original tissue organisation. Comparative infection studies demonstrated that entry and release of BPIV3 occurred specifically via the apical membrane with ciliated cells being the major target cells. By contrast, airway epithelial cells were largely resistant to infection by BHV-1. When the epithelial barrier was abolished by opening tight junctions or by injuring the cell monolayer, BHV-1 infected mainly basal cells. Respiratory epithelial cells were also refractory to infection by BRSV. However, this virus infected neither differentiated epithelial cells nor basal cells when the integrity of the epithelial barrier was destroyed. In contrast to cells of the airway epithelium, subepithelial cells were susceptible to infection by BRSV. Altogether, these results indicate that the three viruses of the same disease complex follow different strategies to interact with the airway epithelium. Possible entry mechanisms are discussed.

Mimicking herpes simplex virus 1 and herpes simplex virus 2 mucosal behavior in a well-characterized human genital organ culture

We developed and morphologically characterized a human genital mucosa explant model (endocervix and ectocervix/vagina) to mimic genital herpes infections caused by herpes simplex virus types 1 (HSV-1) and 2 (HSV-2). Subsequent analysis of HSV entry receptor expression throughout the menstrual cycle in genital tissues was performed, and the evolution of HSV-1/-2 mucosal spread over time was assessed. Nectin-1 and -2 were expressed in all tissues during the entire menstrual cycle. Herpesvirus entry mediator expression was limited mainly to some connective tissue cells. Both HSV-1 and HSV-2 exhibited a plaque-wise mucosal spread across the basement membrane and induced prominent epithelial syncytia.

Replication characteristics of porcine reproductive and respiratory syndrome virus (PRRSV) European subtype 1 (Lelystad) and subtype 3 (Lena) strains in nasal mucosa and cells of the monocytic lineage: indications for the use of new receptors of PRRSV (Lena)

Recently, it has been demonstrated that subtype 3 strains of European type porcine reproductive and respiratory syndrome virus (PRRSV) are more virulent/pathogenic than subtype 1 strains. This points to differences in the pathogenesis. In the present study, a new polarized nasal mucosa explant system was used to study the invasion of the low virulent subtype 1 PRRSV strain Lelystad (LV) and the highly virulent subtype 3 PRRSV strain Lena at the portal of entry. Different cell types of the monocytic lineage (alveolar macrophages (PAM), cultured blood monocytes and monocyte-derived dendritic cells (moDC)) were enclosed to examine replication kinetics of both strains in their putative target cells. At 0, 12, 24, 48 and 72 hours post inoculation (hpi), virus production was analyzed and the infected cells were quantified and identified. Lena replicated much more efficiently than LV in the nasal mucosa explants and to a lesser extent in PAM. Differences in replication were not found in monocytes and moDC. Confocal microscopy demonstrated that for LV, almost all viral antigen positive cells were CD163⁺Sialoadhesin (Sn)⁺, which were mainly located in the lamina propria of the respiratory mucosa. In Lena-infected nasal mucosa, CD163⁺Sn⁺, CD163⁺Sn^- and to a lesser extent CD163^-Sn^- monocytic subtypes were involved in infection. CD163⁺Sn^- cells were mostly located within or in the proximity of the epithelium. Our results show that, whereas LV replicates in a restricted subpopulation of CD163⁺Sn⁺ monocytic cells in the upper respiratory tract, Lena hijacks a broader range of subpopulations to spread within the mucosa. Replication in CD163⁺Sn^- cells suggests that an alternative entry receptor may contribute to the wider tropism of Lena.

Immunity to Bovine Herpesvirus 1: I. Viral lifecycle and innate immunity

Bovine herpesvirus 1 (BHV-1) causes a variety of diseases and is globally distributed. It infects via mucosal epithelium, leading to rapid lytic replication and latent infection, primarily in sensory ganglia. Large amounts of virus can be excreted by the host on primary infection or upon recrudescence of latent infection, resulting in disease spread. The bovine immune response to BHV-1 is rapid, robust, balanced, and long-lasting. The innate immune system is the first to respond to the infection, with type I interferons (IFNs), inflammatory cytokines, killing of infected host cells, and priming of a balanced adaptive immune response. The virus possesses a variety of immune evasion strategies, including inhibition of type I IFN production, chemokine and complement binding, infection of macrophages and neutrophils, and latency. BHV-1 immune suppression contributes to the severity of its disease manifestations and to the bovine respiratory disease complex, the leading cause of cattle death loss in the USA.

Development and use of a polarized equine upper respiratory tract mucosal explant system to study the early phase of pathogenesis of a European strain of equine arteritis virus

The upper respiratory tract mucosa represents the first line of defense, which has to be overcome by pathogens before invading the host. Considering the economic and ethical aspects involved in using experimental animals for pathogenesis studies, respiratory mucosal explants, in which the tissue’s three-dimensional architecture is preserved, may be ideal alternatives. Different respiratory mucosal explant cultures have been developed. However, none of them could be inoculated with pathogens solely at the epithelium side. In the present study, equine nasal and nasopharyngeal explants were embedded in agarose (3%), leaving the epithelium side exposed to allow apical inoculation. Morphometric analysis did not show degenerative changes during 72 h of cultivation. The number of apoptotic cells in the mucosa slightly increased over time. After validation, the system was used for apical infection with a European strain (08P178) of equine arteritis virus (EAV) (10^7.6TCID₅₀/mL per explant). Impermeability of agarose to virus particles was demonstrated by the absence of labeled microspheres (40nm) and a lack of EAV-antigens in RK13 cells seeded underneath the agarose layer in which inoculated explants were embedded. At 72 hpi, 27% of the EAV-positive cells were CD172a⁺ and 19% were CD3⁺ in nasal explants and 45% of the EAV-positive cells were CD172a⁺ and 15% were CD3⁺ in nasopharyngeal explants. Only a small percentage of EAV-positive cells were IgM⁺. This study validates the usefulness of a polarized mucosal explant system and shows that CD172a⁺ myeloid cells and CD3⁺ T lymphocytes represent important EAV-target cells in the respiratory mucosa.

Susceptibility of neuron-like cells derived from bovine Wharton's jelly to bovine herpesvirus type 5 infections

Background

Bovine herpesvirus type 5 (BoHV-5), frequently lethal in cattle, is associated with significant agricultural economic losses due to neurological disease. Cattle and rabbits are frequently used as models to study the biology and pathogenesis of BoHV-5 infection. In particular, neural invasion and proliferation are two of the factors important in BoHV-5 infection. The present study investigated the potential of bovine Wharton’s jelly mesenchymal stromal cells (bWJ-MSCs) to differentiate into a neuronal phenotype and support robust BoHV-5 replication.

Results

Upon inducing differentiation within a defined neuronal specific medium, most bWJ-MSCs acquired the distinctive neuronal morphological features and stained positively for the neuronal/glial markers MAP2 (neuronal microtubule associated protein 2), N200 (neurofilament 200), NT3 (neutrophin 3), tau and GFAP (glial fibrillary acidic protein). Expression of nestin, N200, β-tubulin III (TuJI) and GFAP was further demonstrated by reverse transcriptase polymerase chain reaction (RT-PCR). Following BoHV-5 inoculation, there were low rates of cell detachment, good cell viability at 96 h post-infection (p.i.), and small vesicles developed along neuronal branches. Levels of BoHV-5 antigens and DNA were associated with the peak in viral titres at 72 h p.i. BoHV-5 glycoprotein C mRNA expression was significantly correlated with production of progeny virus at 72 h p.i. (p < 0.05).

Conclusion

The results demonstrated the ability of bWJ-MSCs to differentiate into a neuronal phenotype in vitro and support productive BoHV-5 replication. These findings constitute a remarkable contribution to the in vitro study of neurotropic viruses. This work may pave the way for bWJ-MSCs to be used as an alternative to animal models in the study of BoHV-5 biology.

Immobilization of pseudorabies virus in porcine tracheal respiratory mucus revealed by single particle tracking

Pseudorabies virus (PRV) initially replicates in the porcine upper respiratory tract. It easily invades the mucosae and submucosae for subsequent spread throughout the body via blood vessels and nervous system. In this context, PRV developed ingenious processes to overcome different barriers such as epithelial cells and the basement membrane. Another important but often overlooked barrier is the substantial mucus layer which coats the mucosae. However, little is known about how PRV particles interact with porcine respiratory mucus. We therefore measured the barrier properties of porcine tracheal respiratory mucus, and investigated the mobility of nanoparticles including PRV in this mucus. We developed an in vitro model utilizing single particle tracking microscopy. Firstly, the mucus pore size was evaluated with polyethylene glycol coupled (PEGylated) nanoparticles and atomic force microscope. Secondly, the mobility of PRV in porcine tracheal respiratory mucus was examined and compared with that of negative, positive and PEGylated nanoparticles. The pore size of porcine tracheal respiratory mucus ranged from 80 to 1500 nm, with an average diameter of 455±240 nm. PRV (zeta potential: −31.8±1.5 mV) experienced a severe obstruction in porcine tracheal respiratory mucus, diffusing 59-fold more slowly than in water. Similarly, the highly negatively (−49.8±0.6 mV) and positively (36.7±1.1 mV) charged nanoparticles were significantly trapped. In contrast, the nearly neutral, hydrophilic PEGylated nanoparticles (−9.6±0.8 mV) diffused rapidly, with the majority of particles moving 50-fold faster than PRV. The mobility of the particles measured was found to be related but not correlated to their surface charge. Furthermore, PEGylated PRV (-13.8±0.9 mV) was observed to diffuse 13-fold faster than native PRV. These findings clearly show that the mobility of PRV was significantly hindered in porcine tracheal respiratory mucus, and that the obstruction of PRV was due to complex mucoadhesive interactions including charge interactions rather than size exclusion.