Comprehensive Mutagenesis of Herpes Simplex Virus 1 Genome Identifies UL42 as an Inhibitor of Type I Interferon Induction

Role of Innate Interferon Responses at the Ocular Surface in Herpes Simplex Virus-1-Induced Herpetic Stromal Keratitis

Herpes simplex virus type 1 (HSV-1) is a highly successful pathogen that primarily infects epithelial cells of the orofacial mucosa. After initial lytic replication, HSV-1 enters sensory neurons and undergoes lifelong latency in the trigeminal ganglion (TG). Reactivation from latency occurs throughout the host’s life and is more common in people with a compromised immune system. HSV-1 causes various diseases depending on the site of lytic HSV-1 replication. These include herpes labialis, herpetic stromal keratitis (HSK), meningitis, and herpes simplex encephalitis (HSE). HSK is an immunopathological condition and is usually the consequence of HSV-1 reactivation, anterograde transport to the corneal surface, lytic replication in the epithelial cells, and activation of the host’s innate and adaptive immune responses in the cornea. HSV-1 is recognized by cell surface, endosomal, and cytoplasmic pattern recognition receptors (PRRs) and activates innate immune responses that include interferons (IFNs), chemokine and cytokine production, as well as the recruitment of inflammatory cells to the site of replication. In the cornea, HSV-1 replication promotes type I (IFN-α/β) and type III (IFN-λ) IFN production. This review summarizes our current understanding of HSV-1 recognition by PRRs and innate IFN-mediated antiviral immunity during HSV-1 infection of the cornea. We also discuss the immunopathogenesis of HSK, current HSK therapeutics and challenges, proposed experimental approaches, and benefits of promoting local IFN-λ responses.

The gamble between oncolytic virus therapy and IFN

Various studies are being conducted on oncolytic virotherapy which one of the mechanisms is mediating interferon (IFN) production by it exerts antitumor effects. The antiviral effect of IFN itself has a negative impact on the inhibition of oncolytic virus or tumor eradication. Therefore, it is very critical to understand the mechanism of IFN regulation by oncolytic viruses, and to define its mechanism is of great significance for improving the antitumor effect of oncolytic viruses. This review focuses on the regulatory mechanisms of IFNs by various oncolytic viruses and their combination therapies. In addition, the exerting and the producing pathways of IFNs are briefly summarized, and some current issues are put forward.

Host Zinc-finger CCHC-type containing protein 3 inhibits pseudorabies virus proliferation by regulating type I interferon signaling

Zinc finger CCHC-type containing protein 3 (ZCCHC3) acts as an antiviral factor that interacts with RIG-I and cGAS to modulate innate signaling against viral infections. Here, we investigated the role of porcine ZCCHC3 during pseudorabies virus (PRV) proliferation. We found that porcine ZCCHC3 plays an inhibitory role in the proliferation of PRV by regulating cellular innate immune responses. Further, overexpression of ZCCHC3 inhibited gB protein levels and viral titers, whereas knockdown of ZCCHC3 promoted viral growth. ZCCHC3 overexpression increased IFN-β expression to upregulate downstream gene expression, thus leading to the suppression of viral replication. However, PRV infection reduced the endogenous expression of ZCCHC3 in permissive cells. Importantly, PRV-encoded UL13 and UL24 proteins were identified to inhibit the expression of ZCCHC3, thus antagonizing its antiviral effect. Collectively, our data underscore the important role of ZCCHC3 against PRV infection and promote understandings of viral proteins in PRV pathogenesis.

Immunogenic cell stress and death

Dying mammalian cells emit numerous signals that interact with the host to dictate the immunological correlates of cellular stress and death. In the absence of reactive antigenic determinants (which is generally the case for healthy cells), such signals may drive inflammation but cannot engage adaptive immunity. Conversely, when cells exhibit sufficient antigenicity, as in the case of infected or malignant cells, their death can culminate with adaptive immune responses that are executed by cytotoxic T lymphocytes and elicit immunological memory. Suggesting a key role for immunogenic cell death (ICD) in immunosurveillance, both pathogens and cancer cells evolved strategies to prevent the recognition of cell death as immunogenic. Intriguingly, normal cells succumbing to conditions that promote the formation of post-translational neoantigens (for example, oxidative stress) can also drive at least some degree of antigen-specific immunity, pointing to a novel implication of ICD in the etiology of non-infectious, non-malignant disorders linked to autoreactivity.

Evasion of I Interferon-Mediated Innate Immunity by Pseudorabies Virus

Type I interferon (IFN-I) mediated innate immunity serves as the first line of host defense against viral infection, ranging from IFN-I production upon viral detection, IFN-I triggered signaling pathway that induces antiviral gene transcription the antiviral effects of IFN-I induced gene products. During coevolution, herpesviruses have developed multiple countermeasures to inhibit the various steps involved to evade the IFN response. This mini-review focuses on the strategies used by the alphaherpesvirus Pseudorabies virus (PRV) to antagonize IFN-I mediated innate immunity, with a particular emphasis on the mechanisms inhibiting IFN-I induced gene transcription through the JAK-STAT pathway. The knowledge obtained from PRV enriches the current understanding of the alphaherpesviral immune evasion mechanisms and provides insight into the vaccine development for PRV control.

Pseudorabies Virus DNA Polymerase Processivity Factor UL42 Inhibits Type I IFN Response by Preventing ISGF3-ISRE Interaction

Alphaherpesviruses are large dsDNA viruses with an ability to establish persistent infection in hosts, which rely partly on their ability to evade host innate immune responses, notably the type I IFN response. However, the relevant molecular mechanisms are not well understood. In this study, we report the UL42 proteins of alphaherpesvirus pseudorabies virus (PRV) and HSV type 1 (HSV1) as a potent antagonist of the IFN-I-induced JAK-STAT signaling pathway. We found that ectopic expression of UL42 in porcine macrophage CRL and human HeLa cells significantly suppresses IFN-α-mediated activation of the IFN-stimulated response element (ISRE), leading to a decreased transcription and expression of IFN-stimulated genes (ISGs). Mechanistically, UL42 directly interacts with ISRE and interferes with ISG factor 3 (ISGF3) from binding to ISRE for efficient gene transcription, and four conserved DNA-binding sites of UL42 are required for this interaction. The substitution of these DNA-binding sites with alanines results in reduced ISRE-binding ability of UL42 and impairs for PRV to evade the IFN response. Knockdown of UL42 in PRV remarkably attenuates the antagonism of virus to IFN in porcine kidney PK15 cells. Our results indicate that the UL42 protein of alphaherpesviruses possesses the ability to suppress IFN-I signaling by preventing the association of ISGF3 and ISRE, thereby contributing to immune evasion. This finding reveals UL42 as a potential antiviral target.

Herpesvirus DNA polymerase processivity factors: Not just for DNA synthesis

Herpesviruses encode multiple proteins directly involved in DNA replication, including a DNA polymerase and a DNA polymerase processivity factor. As the name implies, these processivity factors are essential for efficient DNA synthesis, however they also make additional contributions to DNA replication, as well as having novel roles in transcription and modulation of host processes. Here we review the mechanisms by which DNA polymerase processivity factors from all three families of mammalian herpesviruses contribute to viral DNA replication as well as to additional aspects of viral infection.

Herpes Simplex Virus Type 1 Interactions with the Interferon System

The interferon (IFN) system is one of the first lines of defense activated against invading viral pathogens. Upon secretion, IFNs activate a signaling cascade resulting in the production of several interferon stimulated genes (ISGs), which work to limit viral replication and establish an overall anti-viral state. Herpes simplex virus type 1 is a ubiquitous human pathogen that has evolved to downregulate the IFN response and establish lifelong latent infection in sensory neurons of the host. This review will focus on the mechanisms by which the host innate immune system detects invading HSV-1 virions, the subsequent IFN response generated to limit viral infection, and the evasion strategies developed by HSV-1 to evade the immune system and establish latency in the host.