Involvement of toll-like receptors 3 and 7/8 in the neuropathogenesis of bovine herpesvirus types 1 and 5

Varicellovirus bovinealpha (BoAHV) 1 and 5 activate distinct toll-like receptors signaling pathways in neural cells

Varicellovirus bovinealpha (BoAHV) types 5 and 1 are closely-related, neurotropic alphaherpesviruses. BoAHV-5 is the etiological agent of non-suppurative meningoencephalitis in calves, whereas BoAHV-1 is responsible for several syndromes in cattle, including respiratory and reproductive diseases. The innate immune response mediated by TLR3 and TLR7 is crucial in controlling infection and modulating pro-inflammatory cytokines, such as IFNs. In this study, it was evaluated whether TLR3 and TLR7 agonists affect BoAHV replication and whether TLR stimulation has an effect on the IFN-λ3 response in neural cells. TLR3 and TLR7 expression in neural cells was induced by the TLR agonists, Poly I:C and Imiquimod, respectively. The antiviral effect of the agonists varied with the virus strain. TLR7 was suppressed early after BoAHV-5 infection and it was upregulated during BoAHV-1 infection. Imiquimod pre-treatment of neural cells induced higher levels of TLR7 mRNA and reduced the replication of the natural BoAHV-5/1 recombinant. In this study, TLR3 expression was completely inhibited during infection with BoAHV-5 and there was a marked up-regulation of TLR3 mRNA during BoAHV-1 infection. Poly I:C treatment up-regulated TLR3 expression in infected cells but a detrimental effect on BoAHV-5 replication was not observed. Infection of neural cells with the recombinant virus A665 stimulated TLR3 expression late in the infectious cycle. Steady levels of BoAHV-1 replication were maintained in the presence of IFN-λ3 and this cytokine was unable to slow the replication of BoAHV-5. For BoAHV-5/1 A663 strain there was a consistent induction of IFN-λ3 throughout the infection period and maximum A663 titers at advanced stages of the replication cycle were in agreement with a decrease in expression levels. The study emphasizes the importance of strain-specific factors, the infection phase and the cell type involved in virus- and agonist-induced TLR and IFN-λ3 expression. Furthermore, these results evidenced that a deeper analysis on the role and activity of TLR agonists on BoAHV infection should be conducted to evaluate their potential as preventive or therapeutic molecules.

Biphasic modulation of the TLR7 signaling pathway in bovine alphaherpesvirus (BoAHV) infection of neural cells

The study investigates the role of TLR7 in the modulation of the immune response during infection of neuronal cells by bovine alphaherpesvirus (BoAHV) types 1 and 5. TLR7 is essential for detecting viral RNA and activating immune pathways. In BoAHV-1 infection, TLR7 is upregulated early and persistently. In contrast, BoAHV-5 initially suppresses TLR7 expression, with a delayed upregulation at the end of the infectious cycle, reflecting the ability of the virus to evade early immune detection. Furthermore, BoAHV-1 induces a strong activation of MyD88 and NF-κB, leading to rapid viral replication, while BoAHV-5 triggers a weaker immune response, resulting in slower viral replication during the initial hours of infection. Additionally, BoAHV-1 progressively activates IRF-7 whereas BoAHV-5 shows delayed IRF-7 activation. Nevertheless, BoAHV-5 induces a strong IFNα/β response. The antiviral effect of the TLR7 agonist, Imiquimod was evident at the late phase of BoAHV-5 infection and it was mediated by IFN-β. These findings suggest that targeting TLR7 signaling could be a potential therapeutic approach to modulate immune responses and control viral replication. However, the effectiveness of TLR7 agonists like Imiquimod may vary depending on the virus type and its immune evasion strategies, highlighting the need for further research to explore other molecules in the TLR7 pathway.

Reactive oxygen species favors Varicellovirus bovinealpha 5 (BoAHV-5) replication in neural cells

Varicellovirus bovinealpha (BoAHV) 1 and 5 are closely related neurotropic alphaherpesviruses with distinct neuropathogenic potential. BoAHV-5 causes meningoencephalitis in calves whereas encephalitis by BoAHV-1 infection is sporadic. the mechanisms underlying the differences in tropism and clinical outcomes of the infections are not yet completely understood. Here, we used neuroblastoma SH-SY5Y cells as non-differentiated in comparison with the SH-SY5Y neuronal-like cells obtained after exposing SH-SY5Y undifferentiated cells to trans-retinoic acid. We aimed to establish whether there was a relationship between the production of reactive oxygen species (ROS) and the kinetics of virus replication. We demonstrated that ROS production after BoAHV infection was higher in differentiated cells. Generation of ROS was also dependent on the infecting BoAHV strain. Higher ROS levels were produced during BoAHV-5 infection concomitantly with enhanced viral replication. We propose that increased ROS production mechanistically contributes to the tissue damage and neuroinflammation induced by BoAHV-5 infection. Future studies will determine specific targets of ROS that mediate the effects on viral replication.

Recombinant BoHV-5 glycoprotein (rgD5) elicits long-lasting protective immunity in cattle

BoHV-5 is a worldwide distributed pathogen usually associated with a lethal neurological disease in dairy and beef cattle resulting in important economic losses due to the cattle industry. Using recombinant gD5, we evaluated the long-duration humoral immunity of the recombinant vaccines in a cattle model. Here we report that two doses of intramuscular immunization, particularly with the rgD5ISA vaccine, induce long-lasting antibody responses. Recombinant gD5 antigen elicited tightly mRNA transcription of the Bcl6 and the chemokine receptor CXCR5 which mediate memory B cells and long-lived plasma cells in germinal centers. In addition, using an in-house indirect ELISA we observed higher and earlier responses of rgD5-specific IgG antibody and the upregulation of mRNA transcription of IL2, IL4, IL10, IL15, and IFN-γ in rgD5 vaccinated cattle, indicating a mixed immune response. We further show that rgD5 immunization protects against both BoHV -1 and -5. Our findings indicate that the rgD5-based vaccine represents an effective vaccine strategy to induce an efficient control of herpesviruses.

Modulation of granzymes mRNA expression in neural tissue of BoAHV-1 and BoAHV-5-infected cattle

Bovine alphaherpesviruses (BoAHV)-1 and 5 are neurotropic viruses of cattle which differ in their neuropathogenic potential. BoAHV-5 is responsible for non-suppurative meningoencephalitis in calves while BoAHV-1 can occasionally cause encephalitis. Granzymes (GZMs) are serine-proteases that participate in CD8⁺ T cells-mediated killing of virally-infected cells upon release through perforin (PFN)-formed pores in the cell membrane. Recently, six GZMs have been identified in cattle (A, B, K, H, M and O). However, their expression in bovine tissues has not been evaluated. In this study, the mRNA expression levels of PFN and GZMs A, B, K, H and M in the nervous system of calves experimentally-inoculated with BoAHV-1 or BoAHV-5 were analyzed at the three distinct stages of the infectious cycle of alphaherpesviruses: acute infection, latency and reactivation. This is the first report describing the expression of GZMs in bovine neural tissue and the first analysis of GZM expression in the context of bovine alphaherpesviruses neuropathogenesis. The findings revealed that PFN and GZM K are upregulated during BoAHV-1 or BoAHV-5 acute infection. In contrast to BoAHV-1, during BoAHV-5 latency a significant up-regulation of PFN, GZM K and GZM H was detected. PFN and GZM A, K and H expression was also up-regulated during BoAHV-5 reactivation. Therefore, a distinct pattern of PFN and GZM expression is evident along the infectious cycle of each alphaherpesvirus and this might contribute to the differences in BoAHV-1 and BoAHV-5 neuropathogenesis.

Microscopic lesions and modulation of gene expression in cervical medulla during BoAHV-1and BoAHV-5 infection: A mini-review

Bovine herpesvirus (BoAHV) types 1 and 5 are closely-related neurotropic alpha-herpesviruses. BoAHV-1 generally causes respiratory and genital disease but can occasionally cause encephalitis. BoAHV-5 is the causative agent of non suppurative meningoencephalitis in calves. During neuroinvasion, both viruses reach the central and peripheral nervous system. While brain alterations are well-described, the changes that occur in the medulla have not been fully detailed. In this work, we integrated and analyzed the virological findings, the microscopic lesions and the changes that occur in the expression of genes related to the innate immunity, cell cycle and apoptosis in the cervical medulla of calves experimentally-infected with BoAHV-1 and BoAHV-5. This will contribute to the understanding of the differential neuropathogenesis of these alpha-herpesviruses of cattle.

TLR activation, immune response and viral protection elicited in cattle by a commercial vaccine against Bovine Herpesvirus-1

The innate and acquired immune response induced by a commercial inactivated vaccine against Bovine Herpesvirus-1 (BoHV-1) and protection conferred against the virus were analyzed in cattle. Vaccination induced high levels of BoHV-1 antibodies at 30, 60, and 90 days post-vaccination (dpv). IgG1 and IgG2 isotypes were detected at 90 dpv, as well as virus-neutralizing antibodies. An increase of anti-BoHV-1 IgG1 in nasal swabs was detected 6 days post-challenge in vaccinated animals. After viral challenge, lower virus excretion and lower clinical score were observed in vaccinated as compared to unvaccinated animals, as well as BoHV-1-specific proliferation of lymphocytes and production of IFNγ, TNFα, and IL-4. Downregulation of the expression of endosome Toll-like receptors 8-9 was detected after booster vaccination. This is the first thorough study of the immunity generated by a commercial vaccine against BoHV-1 in cattle.

Brain-derived neurotrophic factor is down regulated after bovine alpha-herpesvirus 5 infection in both wild-type and TLR3/7/9 deficient mice

Neurotrophic factors have been implicated in the control of neuronal survival and plasticity in different brain diseases. Meningoencephalitis caused by bovine alpha-herpesvirus 5 (BoHV-5) infection is a frequent neurological disease of young cattle, being the involvement of apoptosis in the development of neuropathological changes frequently discussed in the literature. It's well known that Toll-like receptors (TLRs) can activate neuroinflammatory response and consequently lead to neuronal loss. However, there are no studies evaluating the expression of neurotrophic factors and their association with brain pathology and TLRs during the infection by BoHV-5. The current study aimed to analyze brain levels of neurotrophic factors along with neuropathological changes during acute infection by BoHV-5 in wild-type (WT) and TLR3/7/9 (TLR3/7/9-/-) deficiency mice. The infection was induced by intracranial inoculation of 1 × 104 TCID50 of BoHV-5. Infected animals presented similar degrees of clinical signs and neuropathological changes. Both infected groups had meningoencephalitis and neuronal damage in CA regions from hippocampus. BoHV-5 infection promoted the proliferation of Iba-1 positive cells throughout the neuropil, mainly located in the frontal cortex. Moreover, significant lower levels of brain-derived neurotrophic factor (BDNF) were detected in both BoHV-5 infected WT and TLR3/7/9 deficient mice, compared with non-infected animals. Our study showed that BDNF down regulation was associated with brain inflammation, reactive microgliosis and neuronal loss after bovine alpha-herpesvirus 5 infection in mice. Moreover, we demonstrated that combined TLR3/7/9 deficiency does not alter those parameters.

Bovine alphaherpesvirus type 5 replicates more efficiently than bovine alphaherpesvirus type 1 in undifferentiated human neural cells

Bovine herpesvirus (BoHV) types 1 and 5 are two closely related alpha-herpesviruses of cattle with neuroinvasive potential. BoHV-5 causes non-suppurative meningoencephalitis in calve whereas encephalitis caused by BoHV-1 has been occasionally reported. As an initial step to understand the biology of both BoHV types in neural cells, undifferentiated SH-SY5Y human neuroblastoma cells were infected with BoHV-1 strains Cooper and Los Angeles (LA), BoHV-5 strain 97/613 and A663, a BoHV-5/BoHV-1 natural recombinant. Cytopathic effect (CPE) in these cells was evident earlier for BoHV-5 strain 97/613 and CPE progression was slower for BoHV-1, particularly for Cooper strain. Virus antigen was detected as early as 8 h post-infection (hpi) for all strains, with the exception of BoHV-1 Cooper for which antigen expression was detectable by 24 hpi. All strains released detectable infectious virus in the extracellular medium by 8 hpi, confirming that undifferentiated SH-SY5Y cells are fully permissive to BoHV infection. Significantly different extracellular virus titers among the different strains were detected by 24 hpi, with BoHV-5 97/613 reaching the maximal virus production. The lowest extracellular titer was recorded for BoHV-1 Cooper at all the evaluated time-points. BoHV-1 Cooper, BoHV-1 LA and BoHV-5 97/613 had a steady increase in intracellular virus production. The evaluation of lysis plaques formation revealed that BoHV-5 A663 produced the largest plaques followed by BoHV-5 97/613. Both BoHV-1 strains produced smaller plaques when compared with BoHV-5. Despite a slower replicative cycle, strain A663 is more efficient in cell to cell dissemination. Thus, it is evident that BoHV-5 strains have growth advantages in undifferentiated neural cells compared with BoHV-1. This in vitro model might be useful to analyze the neuropathogenic potential of bovine alphaherpesviruses.

Cathelicidin bovine myeloid antimicrobial peptide (BMAP) 28 is involved in the inflammatory response against alpha-herpesviruses in the bovine nervous system

The role of the local innate immune response in the neuropathogenesis of bovine herpesvirus (BoHV) type 1 and 5 remains largely unknown. This study determined the gene transcriptional expression of relevant bovine cathelicidins, TNFα and IFNβ in the nervous system of experimentally-infected cattle during the different stages of BoHV-1 and BoHV-5 infectious cycle. We studied the modulation of bovine myeloid antimicrobial peptide (BMAP) 27 and 28 by alpha-herpesviruses during acute infection of the central nervous system (CNS). However, BMAP28 was the main cathelicidin modulated. BoHV-5 supressed BMAP28 expression mainly in frontal cortex and cervical medulla whereas BoHV-1 slightly induced the expression of cathelicidins in the olfactory and posterior cortex. The differences in the regulation of the innate response are likely related to distinct replication rates of both alpha-herpesviruses in the CNS. During latency and reactivation, BoHV-1 and -5 decreased BMAP28 and BMAP27 expression, accompanied by high levels of TNFα and IFNβ transcripts in the posterior brain region and medulla during BoHV reactivation. In terms of cytokines, a remarkably overexpression of IFNβ was induced by BoHV-5 (133.8-fold). In trigeminal ganglion (TG) both alpha-herpesviruses induced cathelidicins gene expression at all stages of the infection cycle, while only acute BoHV-5 infection increased TNFα (129-fold) mRNA levels. This study suggests that the pronounced downregulation of BMAP28 in BoHV-5-acutely-infected CNS is due to a decreased immune stimulation during viral infection, favouring its establishment in the CNS with a low replication rate until latency. Thus, cathelicidins, together with IFNβ and TNFα, are differentially regulated by BoHV-5 and BoHV-1 infections and this regulation is dependent on the stage of virus infection in the bovine nervous system.

Distinctive features of bovine alphaherpesvirus types 1 and 5 and the virus-host interactions that might influence clinical outcomes

Bovine herpesvirus types 1 (BoHV-1) and 5 (BoHV-5) are two closely related alphaherpesviruses. BoHV-1 causes several syndromes in cattle, including respiratory disease and sporadic cases of encephalitis, whereas BoHV-5 is responsible for meningoencephalitis in calves. Although both viruses are neurotropic, they differ in their neuropathogenic potential. This review summarizes the findings on the specific mechanisms and pathways known to modulate the pathogenesis of BoHV-1 and BoHV-5, particularly in relation to respiratory and neurological syndromes, which characterize BoHV-1 and BoHV-5 infections, respectively.

Differential expression of cyclins mRNA in neural tissues of BoHV-1- and BoHV-5- infected cattle

Bovine alphaherpesvirus types 1 (BoHV-1) and 5 (BoHV-5) are closely related alphaherpesviruses. BoHV-5 causes non-suppurative meningoencephalitis in calves. BoHV-1 is associated with several syndromes and, occasionally, can cause encephalitis. Although both viruses are neurotropic and they share similar biological properties, it is unknown why these alphaherpesviruses differ in their ability to cause neurological disease. Neural tissue samples were collected from BoHV-1- and BoHV-5-intranasally inoculated calves during acute infection, latency and reactivation and the levels of cyclins mRNA expression were analyzed by qRT-PCR. Striking differences in the levels of cyclins mRNA were particularly detected in trigeminal ganglion (TG). The expression levels of cyclins in TG during BoHV-5 latency suggest that these viruses utilize different strategies to persist in the host. It is apparent that a relationship between virus loads and cyclin mRNA levels can be established only during acute infection and other factors might be involved in the regulation of cell cycle components during BoHV latency and reactivation. Bovine alphaherpesviruses neuropathogenicity might be influenced by the differential control of cell cycle components by these herpesviruses. This is the first report on BoHV-5 modulation of cyclins expression in neural tissues from its natural host.

Immune responses in bovines to recombinant glycoprotein D of bovine herpesvirus type 5 as vaccine antigen

Bovine herpesvirus 5 (BoHV-5) is responsible for outbreaks of meningoencephalitis that cause important economic losses in young cattle. BoHV-5 glycoprotein D (gD5) is essential for attachment and penetration into permissive cells and targeting of host immune systems, inducing strong humoral and cellular immune responses. The aim of this study was to evaluate the vaccinal immune response of vaccines formulated with the recombinant BoHV-5 gD (rgD5) in bovines. For the experiment, 72 heifers were randomly allotted into 6 different groups with 12 animals each. Group 1: vaccine formulated using inactivated BoHV-5 (iBoHV-5) adjuvanted with ISA50V2; Group 2: iBoHV-5 associated with 100 µg of rgD5 adjuvanted with ISA50V2; Group 3: 100 µg of rgD5 adjuvanted with ISA50V2; Group 4: 100 µg of rgD5 adjuvanted with Al(OH)₃; Group 5: commercial vaccine; and Group 6: control group. Two doses were administered in a 26-day interval and the third after 357 days from primo vaccination. Cattle vaccinated with the vaccines formulated with iBoHV-5 plus rgD5 showed a significant (p < 0.01) five-fold increase in total immunoglobulin G (IgG) for BoHV-5, BoHV-1, and rgD5 as compared with the commercial and control groups. Also, a significant (p < 0.05) increase in IgG1 and IgG2a levels was induced in serum for rgD5. In addition, these same vaccines showed significant (p < 0.01) four-fold higher titers of BoHV-1 and -5 neutralizing antibodies. The results demonstrated that the rgD5 conserved important epitopes that were able to stimulate bovine humoral immunity response capable of viral neutralization of BoHV-1 and -5, suggesting it as a promising vaccine antigen to be used in vaccine for BoHV-1 and -5 endemic areas.

Bovine herpesvirus type 5 replication and induction of apoptosis in vitro and in the trigeminal ganglion of experimentally-infected cattle

Bovine herpesvirus (BoHV) types 1 and 5 are neuroinvasive. Cases of BoHV-1-induced encephalitis are not as frequent as those caused by BoHV-5. In this study, the capability of BoHV-5 to induce apoptosis in cell cultures and in the trigeminal ganglion during acute infection of experimentally-infected cattle was analyzed. Apoptotic changes in cell cultures agree with the ability of the viral strains to replicate in each cell line. Marked differences were observed between the in vitro induction of apoptosis by BoHV-1Cooper and BoHV-5 97/613 strains. Apoptotic neurons were clearly evident in the trigeminal ganglion of BoHV-1-infected calves. For BoHV-5 a fewer number of positive neurons was observed. There is an association between the magnitude of bovine herpesviruses replication and the induction of apoptosis in trigeminal ganglion. These findings suggest that the induction of apoptosis and the innate immune response orchestrate the final outcome of alpha herpesviruses infection of the bovine nervous system.