A. Golke

Equine herpesvirus type 1 (EHV-1)-induced rearrangements of actin filaments in productively infected primary murine neurons

Equine herpesvirus type 1 (EHV-1) causes respiratory disease, abortion and neurological disorders in horses. In the present study, we investigated reorganization of the cytoskeleton in neurons infected with two EHV-1 strains: Jan-E (wild-type strain) and Rac-H (attenuated strain). The studies were performed on primary murine neurons, which are an excellent model for studying neurotropism and neurovirulence of EHV-1. We have demonstrated for the first time that EHV-1 infection causes rearrangements in the actin network of neurons that are dependent on the virus strain and its adaptation to cell culture in vitro. Immunofluorescent labeling and confocal microscopy revealed the formation of long, thin projections in neurons infected with the Jan-E strain, which was probably associated with enhanced intracellular spread of the virus. The EHV-1 Rac-H strain caused disruption of the microfilaments system and general depolymerization of actin, but treatment of neurons with cytochalasin D or latrunculin A resulted in limitation of viral replication. It can therefore be assumed that actin filaments are required only at the early stages of infection. Our results allow us to suggest that the actin cytoskeleton participates in EHV-1 infection of primary murine neurons but is not essential, and that other components of the cytoskeleton and/or cellular mechanisms may be also involved during EHV-1 infection.

Influence of long-term equine herpesvirus type 1 (EHV-1) infection on primary murine neurons—the possible effects of the multiple passages of EHV-1 on its neurovirulence

Equine herpesvirus 1 (EHV-1), like other members of the Alphaherpesvirinae subfamily, is a neurotropic virus causing latent infections in the nervous system of the natural host. In the present study, we have investigated EHV-1 replication (wild-type Jan-E strain and Rac-H laboratory strain) during long-term infection and during the passages of the virus in cultured neurons. The studies were performed on primary murine neurons, which are an excellent in vitro model for studying neurotropism and neurovirulence of EHV-1. Using real-time cell growth analysis, we have demonstrated for the first time that primary murine neurons are able to survive long-term EHV-1 infection. Positive results of real-time PCR test indicated a high level of virus DNA in cultured neurons, and during long-term infection, these neurons were still able to transmit the virus to the other cells. We also compared the neurovirulence of Rac-H and Jan-E EHV-1 strains after multiple passages of these strains in neuron cell culture. The results showed that multiple passages of EHV-1 in neurons lead to the inhibition of viral replication as early as in the third passage. Interestingly, the inhibition of the EHV-1 replication occurred exclusively in neurons, because the equine dermal (ED) cells co-cultivated with neuroculture medium from the third passage showed the presence of large amount of viral DNA. In conclusion, our results showed that certain balance between EHV-1 and neurons has been established during in vitro infection allowing neurons to survive long-term infection.

The generation of CD8+ T-cell population specific for vaccinia virus epitope involved in the antiviral protection against ectromelia virus challenge.

Eradication of smallpox has led to cessation of vaccination programs. This has rendered the human population increasingly susceptible not only to variola virus infection but also to infections with other representatives of Poxviridae family that cause zoonotic variola-like diseases. Thus, new approaches for designing improved vaccine against smallpox are required. Discovering that orthopoxviruses, e.g. variola virus, vaccinia virus, ectromelia virus, share common immunodominant antigen, may result in the development of such a vaccine. In our study, the generation of antigen-specific CD8(+) T cells in mice during the acute and memory phase of the immune response was induced using the vaccinia virus immunodominant TSYKFESV epitope and CpG oligodeoxynucleotides as adjuvants. The role of the generated TSYKFESV-specific CD8(+) T cells was evaluated in mice during ectromelia virus infection using systemic and mucosal model. Moreover, the involvement of dendritic cells subsets in the adaptive immune response stimulation was assessed. Our results indicate that the TSYKFESV epitope/TLR9 agonist approach, delivered systemically or mucosally, generated strong CD8(+) T-cell response when measured 10 days after immunization. Furthermore, the TSYKFESV-specific cell population remained functionally active 2 months post-immunization, and gave cross-protection in virally challenged mice, even though the numbers of detectable antigen-specific T cells decreased.

Herpesviruses survival strategies - latency and apoptosis

Apoptosis is a process of programmed cell death in response to various stimuli, including virus infection. Herpesviruses have evolved the ability to interfere with apoptosis by its inhibition or activation in host cells. They can interfere with the extrinsic and intrinsic pathways of apoptosis. A special feature of herpesviruses is establishing a latent infection, during which expression of virus genes is strongly restricted and production of infectious virus particles is not observed. HSV-1 establishes latency in neurons, CMV in bone marrow progenitor cells and monocytes, EBV and HHV-8 in B cells. Studies show that latent infections also depend on prevention of the death of the infected cells. Control of apoptosis machinery by viruses may be critical for their reproduction and provision of the adequate yield of progeny virions. The present article summarizes the current knowledge about the latent viral infection and mechanisms of apoptosis modulation by selected viruses from the Herpesviridae family.

Acyclovir and trichostatin A modulate EHV-1 replication in murine neurons in vitro

Equine herpesvirus type 1 (EHV-1) is one of the most important viral pathogens of horses worldwide (2). It may cause respiratory disease, sporadic or epizootic abortions, or, recently more often, neurological disease known as equine herpesvirus myeloencephalopathy (EHM), which may be life-threatening and results in significant economic losses to the equine industry (1, 13, 15, 18, 19). It has been suggested that a single-nucleotide polymorphism in the EHV-1 DNA polymerase gene, which leads to amino acid variation (N752/D752), may be associated with outbreaks of EHM (3, 11, 13). D752 strains of EHV-1, which are statistically more often isolated from cases of EHM, were called neuropathogenic strains. However, it is worth mentioning that all EHV-1 strains show neurotropism and are capable of establishing latency in peripheral neurons. Moreover, EHV-1 may also establish latency in leukocytes (10). The main role of latency is to maintain the viral genome for a long time inside host cells, at the same time avoiding the immune response. On the other hand, the virus may reactivate and start productive replication at any time, especially during stress, which leads to the dissemination of progeny virions (17). The current approach to the control of EHV-1 infections is based on biosecurity measures and vaccination, but it is not sufficient. Immunity after infection or vaccination is usually incomplete and short-lived, and once latency has been established, the virus cannot be eliminated from host cells. Although some progress has been made in understanding the adaptive immunity to EHV-1, innate immunity remains poorly characterized, despite the fact that it is critically important for inducAcyclovir and trichostatin A modulate EHV-1 replication in murine neurons in vitro1)