Foot-and-Mouth Disease Virus: Molecular Interplays with IFN Response and the Importance of the Model

Leaderless foot-and-mouth disease virus serotype O did not cause clinical disease and failed to establish a persistent infection in cattle

The foot-and-mouth disease virus (FMDV) Leader proteinase Lpro inhibits host mRNA translation and blocks the interferon response which promotes viral survival. Lpro is not required for viral replication in vitro but serotype A FMDV lacking Lpro has been shown to be attenuated in cattle and pigs. However, it is not known, whether leaderless viruses can cause persistent infection in vivo after simulated natural infection and whether the attenuated phenotype is the same in other serotypes. We have generated an FMDV O/FRA/1/2001 variant lacking most of the Lpro coding region (ΔLb). Cattle were inoculated intranasopharyngeally and observed for 35 days to determine if O FRA/1/2001 ΔLb is attenuated during the acute phase of infection and whether it can maintain a persistent infection in the upper respiratory tract. We found that although this leaderless virus can replicate in vitro in different cell lines, it is unable to establish an acute infection with vesicular lesions and viral shedding nor is it able to persistently infect bovine pharyngeal tissues.

Inhibition of EV71 replication by an interferon-stimulated gene product L3HYPDH

Enterovirus 71 (EV71) is the common causative agent of hand-foot-mouth disease (HFMD). Despite evidence in mice model suggested that the interferon (IFN) signaling pathways play a role in defending against this virus, knowledge on the IFN-mediated antiviral response is still limited. Here we identified an IFN-stimulated gene (ISG) called L3HYPDH, whose expression inhibits EV71 replication. Mapping assay indicated that amino acids 61-120 and 295-354 are critical for its optimal antiviral activity. Mechanismly, L3HYPDH specifically inhibits protein translation mediated by EV71 internal ribosome entry site (IRES). Our data thus uncovered a new mechanism utilized by the host cell to restrict EV71 replication.

Development of a primary cell model derived from porcine dorsal soft palate for foot-and-mouth disease virus research and diagnosis

Foot-and-mouth disease (FMD) is a highly contagious viral disease of cloven-hoofed animals that has a significant socio-economic impact. One concern associated with this disease is the ability of its etiological agent, the FMD virus (FMDV), to persist in its hosts through underlying mechanisms that remain to be elucidated. While persistence has been described in cattle and small ruminants, it is unlikely to occur in pigs. One of the factors limiting the progress in understanding FMDV persistence and, in particular, differential persistence is the lack of suitable in vitro models. A primary bovine cell model derived from the dorsal soft palate, which is the primary site of replication and persistence of FMDV in cattle, has been developed, and it seemed relevant to develop a similar porcine model. Cells from two sites of FMDV replication in pigs, namely, the dorsal soft palate and the oropharyngeal tonsils, were isolated and cultured. The epithelial character of the cells from the dorsal soft palate was then assessed by immunofluorescence. The FMDV-sensitivity of these cells was assessed after monolayer infection with FMDV O/FRA/1/2001 Clone 2.2. These cells were also grown in multilayers at the air-liquid interface to mimic a stratified epithelium susceptible to FMDV infection. Consistent with what has been shown in vivo in pigs, our study showed no evidence of persistence of FMDV in either the monolayer or multilayer model, with no infectious virus detected 28 days after infection. The development of such a model opens up new possibilities for the study and diagnosis of FMDV in porcine cells.

Host-Specific Interplay between Foot-and-Mouth Disease Virus 3D Polymerase and the Type-I Interferon Pathway

Foot-and-mouth disease (FMD) is a highly contagious viral disease affecting cloven-hoofed animals. One of the issues related to this disease is the persistence of its causative agent, foot-and-mouth disease virus (FMDV). While the mechanisms of FMDV persistence remain unclear, there are clues that it may be related to protein-protein interactions (PPI) between viral proteins and cellular proteins involved in the interferon (IFN) response. Since FMDV persistence has been described in cattle, sheep and goats but not in swine, we screened PPI involving FMDV proteins and sixteen major type-I IFN pathway proteins from these four species by nanoluciferase-2-hybrid complementation assay, in order to identify new PPI and determine their host specificity. As the results concerning the 3Dpol were the most interesting in view of the limited data concerning its role in immune escape, we decided to focus particularly on this protein. The identified PPI were confirmed by GST pull-down. We identified PPI between 3Dpol and seven IFN pathway proteins, namely, IKKα, IKKε, IRF3, IRF7, NEMO, MDA5 and MAVS. These PPI are conserved among the four studied species, with the exception of the one between 3Dpol and MAVS, which was only found with the swine protein. We also showed, using luciferase reporter assays, that 3Dpol could inhibit the induction phase of the IFN pathway. These results demonstrate, for the first time, a putative role for 3Dpol in FMDV innate immune escape.

Hand-Foot-and-Mouth Disease-Associated Enterovirus and the Development of Multivalent HFMD Vaccines

Hand-foot-and-mouth disease (HFMD) is an infectious disease of children caused by more than 20 types of enteroviruses, with most cases recovering spontaneously within approximately one week. Severe HFMD in individual children develops rapidly, leading to death, and is associated with other complications such as viral myocarditis and type I diabetes mellitus. The approval and marketing of three inactivated EV-A71 vaccines in China in 2016 have provided a powerful tool to curb the HFMD epidemic but are limited in cross-protecting against other HFMD-associated enteroviruses. This review focuses on the epidemiological analysis of HFMD-associated enteroviruses since the inactivated EV-A71 vaccine has been marketed, collates the progress in the development of multivalent enteroviruses vaccines in different technical routes reported in recent studies, and discusses issues that need to be investigated for safe and effective HFMD multivalent vaccines.