Enterovirus 68 3C protease cleaves TRIF to attenuate antiviral responses mediated by Toll-like receptor 3

Innate Immunity Evasion by Enteroviruses: Insights into Virus-Host Interaction

Enterovirus genus includes multiple important human pathogens, such as poliovirus, coxsackievirus, enterovirus (EV) A71, EV-D68 and rhinovirus. Infection with EVs can cause numerous clinical conditions including poliomyelitis, meningitis and encephalitis, hand-foot-and-mouth disease, acute flaccid paralysis, diarrhea, myocarditis and respiratory illness. EVs, which are positive-sense single-stranded RNA viruses, trigger activation of the host antiviral innate immune responses through pathogen recognition receptors such as retinoic acid-inducible gene (RIG-I)-likeand Toll-like receptors. In turn, EVs have developed sophisticated strategies to evade host antiviral responses. In this review, we discuss the interplay between the host innate immune responses and EV infection, with a primary focus on host immune detection and protection against EV infection and viral strategies to evade these antiviral immune responses.

MicroRNA and Pathogenesis of Enterovirus Infection

There are no currently available specific antiviral therapies for non-polio Enterovirus infections. Although several vaccines have entered clinical trials, the efficacy requires further evaluation, particularly for cross-strain protective activity. Curing patients with viral infections is a public health problem due to antigen alterations and drug resistance caused by the high genomic mutation rate. To conquer these limits in the development of anti-Enterovirus treatments, a comprehensive understanding of the interactions between Enterovirus and host cells is urgently needed. MicroRNA (miRNA) constitutes the biggest family of gene regulators in mammalian cells and regulates almost a half of all human genes. The roles of miRNAs in Enterovirus pathogenesis have recently begun to be noted. In this review, we shed light on recent advances in the understanding of Enterovirus infection-modulated miRNAs. The impacts of altered host miRNAs on cellular processes, including immune escape, apoptosis, signal transduction, shutdown of host protein synthesis and viral replication, are discussed. Finally, miRNA-based medication provides a promising strategy for the development of antiviral therapy.

Enterovirus D68 and Panton-Valentine Leukocidin-Positive Staphylococcus aureus Respiratory Coinfection with Fatal Outcome

A previously healthy 10-year-old girl with a 2-day history of upper respiratory illness and fever rapidly developed respiratory failure and sepsis with leukopenia, and expired despite attempts at resuscitation. Postmortem examination revealed bilateral necrotizing pneumonia and evidence of disseminated intravascular coagulation. Nasopharyngeal swabs and lung tissue submitted to the Centers for Disease Control and Prevention (CDC) were positive for Enterovirus D68 (EV-D68). Blood and lung cultures were positive for methicillin-resistant Staphylococcus aureus (MRSA). The isolates were submitted to the CDC and were found to be positive for the toxin Panton-Valentine leukocidin. We describe a fatality related to invasive toxin-mediated MRSA associated with EV-D68 coinfection, along with the clinical, laboratory, and autopsy findings, which provided important clues, prompting further investigation at the CDC to arrive at the correct diagnosis.

Recent advances on viral manipulation of NF-κB signaling pathway

NF-κB transcription factors regulate the expression of hundreds of genes primarily involved in immune responses. Signaling events leading to NF-κB activation constitute a major antiviral immune pathway. To replicate and persist within their hosts, viruses have evolved diverse strategies to evade and exploit cellular NF-κB immune signaling cascades for their benefit. We summarize recent studies concerning viral manipulation of the NF-κB signaling pathway downstream of pattern recognition receptors. Signal transduction mediated by pattern recognition receptors is a research frontier for both infectious disease and innate immunology.

Proteolysis of MDA5 and IPS-1 is not required for inhibition of the type I IFN response by poliovirus

BACKGROUND

The type I interferon (IFN) response is a critical component of the innate immune response to infection by RNA viruses and is initiated via recognition of viral nucleic acids by RIG-like receptors (RLR). Engagement of these receptors in the cytoplasm initiates a signal transduction pathway leading to activation of the transcription factors NF-κB, ATF-2 and IRF-3 that coordinately upregulate transcription of type I IFN genes, such as that encoding IFN-β. In this study the impact of poliovirus infection on the type I interferon response has been examined.

METHODS

The type I IFN response was assessed by measuring IFN-β mRNA levels using qRT-PCR and normalizing to levels of β-actin mRNA. The status of host factors involved in activation of the type I IFN response was examined by immunoblot, immunofluorescence microcopy and qRT-PCR.

RESULTS

The results show that poliovirus infection results in induction of very low levels of IFN-β mRNA despite clear activation of NF-κB and ATF-2. In contrast, analysis of IRF-3 revealed no transcriptional induction of an IRF-3-responsive promoter or homodimerization of IRF-3 indicating it is not activated in poliovirus-infected cells. Exposure of poliovirus-infected cells to poly(I:C) results in lower levels of IFN-β mRNA synthesis and IRF-3 activation compared to mock-infected cells. Analysis of MDA-5 and IPS-1 revealed that these components of the RLR pathway were largely intact at times when the type I IFN response was suppressed.

CONCLUSIONS

Collectively, these results demonstrate that poliovirus infection actively suppresses the host type I interferon response by blocking activation of IRF-3 and suggests that this is not mediated by cleavage of MDA-5 or IPS-1.

Mechanisms of Beta Cell Dysfunction Associated With Viral Infection

Type 1 diabetes (T1D) results from genetic predisposition and environmental factors leading to the autoimmune destruction of pancreatic beta cells. Recently, a rapid increase in the incidence of childhood T1D has been observed worldwide; this is too fast to be explained by genetic factors alone, pointing to the spreading of environmental factors linked to the disease. Enteroviruses (EVs) are perhaps the most investigated environmental agents in relationship to the pathogenesis of T1D. While several studies point to the likelihood of such correlation, epidemiological evidence in its support is inconclusive or in some instances even against it. Hence, it is still unknown if and how EVs are involved in the development of T1D. Here we review recent findings concerning the biology of EV in beta cells and the potential implications of this knowledge for the understanding of beta cell dysfunction and autoimmune destruction in T1D.

Microbial strategies for antagonizing Toll-like-receptor signal transduction

Within a few years of the discovery of Toll-like receptors (TLRs) and their role in innate immunity, viral and bacterial proteins were recognized to antagonize TLR signal transduction. Since then, as TLR signaling networks were unraveled, microbial systems have been discovered that target nearly every component within these pathways. However, recent findings as well as some notable exceptions promote the idea that more of these systems have yet to be discovered. For example, we know very little about microbial systems for directly targeting non-cytoplasmic portions of TLR signaling pathways, that is, the ligand interacting portions of the receptor itself. In this review, we compare and contrast strategies by which bacteria and viruses antagonize TLR signaling networks to identify potential areas for future research.

Global reemergence of enterovirus D68 as an important pathogen for acute respiratory infections

We previously detected enterovirus D68 (EV-D68) in children with severe acute respiratory infections in the Philippines in 2008-2009. Since then, the detection frequency of EV-D68 has increased in different parts of the world, and EV-D68 is now recognized as a reemerging pathogen. However, the epidemiological profile and clinical significance of EV-D68 is yet to be defined, and the virological characteristics of EV-D68 are not fully understood. Recent studies have revealed that EV-D68 is detected among patients with acute respiratory infections of differing severities ranging from mild upper respiratory tract infections to severe pneumonia including fatal cases in pediatric and adult patients. In some study sites, the EV-D68 detection rate was higher among patients with lower respiratory tract infections than among those with upper respiratory tract infections, suggesting that EV-D68 infections are more likely to be associated with severe respiratory illnesses. EV-D68 strains circulating in recent years have been divided into three distinct genetic lineages with different antigenicity. However, the association between genetic differences and disease severity, as well as the occurrence of large-scale outbreaks, remains elusive. Previous studies have revealed that EV-D68 is acid sensitive and has an optimal growth temperature of 33 °C. EV-D68 binds to α2,6-linked sialic acids; hence, it is assumed that it has an affinity for the upper respiratory track where these glycans are present. However, the lack of suitable animal model constrains comprehensive understanding of the pathogenesis of EV-D68.