Interferon Gamma Inhibits Equine Herpesvirus 1 Replication in a Cell Line-Dependent Manner.

Seong K Kim,Akhalesh K Shakya,Dennis J O’Callaghan

doi:10.3390/pathogens10040484

Seong K Kim, Akhalesh K Shakya + Show 1 more

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https://doi.org/10.3390/pathogens10040484

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Abstract

The sole equine herpesvirus 1 (EHV-1) immediate-early protein (IEP) is essential for viral replication by transactivating viral immediate-early (IE), early (E), and late (L) genes. Here, we report that treatment of mouse MH-S, equine NBL6, and human MRC-5 cells with 20 ng/mL of IFN-γ reduced EHV-1 yield by 1122-, 631-, and 10,000-fold, respectively. However, IFN-γ reduced virus yield by only 2–4-fold in mouse MLE12, mouse L-M, and human MeWo cells compared to those of untreated cells. In luciferase assays with the promoter of the EHV-1 early regulatory EICP0 gene, IFN-γ abrogated trans-activation activity of the IEP by 96% in MH-S cells, but only by 21% in L-M cells. Similar results were obtained in assays with the early regulatory UL5 and IR4 promoter reporter plasmids. IFN-γ treatment reduced IEP protein expression by greater than 99% in MH-S cells, but only by 43% in L-M cells. The expression of IEP and UL5P suppressed by IFN-γ was restored by JAK inhibitor treatment, indicating that the inhibition of EHV-1 replication is mediated by JAK/STAT1 signaling. These results suggest that IFN-γ blocks EHV-1 replication by inhibiting the production of the IEP in a cell line-dependent manner. Affymetrix microarray analyses of IFN-γ-treated MH-S and L-M cells revealed that five antiviral ISGs (MX1, SAMHD1, IFIT2, NAMPT, TREX1, and DDX60) were upregulated 3.2–18.1-fold only in MH-S cells.

Highlights

Equine herpesvirus 1 (EHV-1) is a member of the Alphaherpesvirinae subfamily of the Herpesviridae and is a major equine pathogen that causes respiratory disease, abortion, and, in some cases, the neurological disease [1,2,3]
IFN-γ reduced the levels of viral immediate-early protein (IEP) by greater than 99% in MH-S and NBL6 cells (Figure 1B lane 4 and lane 13, respectively) as compared to those of non-treated cells (Figure 1B lanes 3 and 12, respectively)
The innate immune response is the first line of defense against viral pathogens, and in the horse, protective immunity to EHV-1 infection was characterized by a polarized IFN-γ dependent immunoregulatory cytokine response [22]

Summary

Introduction

Equine herpesvirus 1 (EHV-1) is a member of the Alphaherpesvirinae subfamily of the Herpesviridae and is a major equine pathogen that causes respiratory disease, abortion, and, in some cases, the neurological disease [1,2,3]. The most devastating outcome of EHV-1 infection is the induction of abortion in pregnant mares, which has a major economic impact on the horse industry. EHV-1 infection generates a short-lived humoral immunity in the horse but does not confer long-term protection, as disease often occurs following infection [4,5]. Interferon gammas (Type II IFN) plays a major role in controlling the host immune response against viral and intracellular bacterial pathogens [6,7] and is produced at high levels by T helper Type 1 (Th1) cells, CD8+ CTL, and NK cells in response to virus infection [8]. Phosphorylation leads to translocation of the signal transducer and activator of transcription 1 (STAT1) homodimers into the nucleus, where they bind to interferon gamma-activated sequence (GAS) sites on the promoters of downstream target genes. One of the major primary response genes is the transcription factor IRF1 that in turn activates a large number of secondary response genes, interferon-stimulated genes [14]

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