Coxsackieviruses B1, B3, and B5 use decay accelerating factor as a receptor for cell attachment

Antiviral Defence Mechanisms during Early Mammalian Development

The type-I interferon (IFN) response constitutes the major innate immune pathway against viruses in mammals. Despite its critical importance for antiviral defence, this pathway is inactive during early embryonic development. There seems to be an incompatibility between the IFN response and pluripotency, the ability of embryonic cells to develop into any cell type of an adult organism. Instead, pluripotent cells employ alternative ways to defend against viruses that are typically associated with safeguard mechanisms against transposable elements. The absence of an inducible IFN response in pluripotent cells and the constitutive activation of the alternative antiviral pathways have led to the hypothesis that embryonic cells are highly resistant to viruses. However, some findings challenge this interpretation. We have performed a meta-analysis that suggests that the susceptibility of pluripotent cells to viruses is directly correlated with the presence of receptors or co-receptors for viral adhesion and entry. These results challenge the current view of pluripotent cells as intrinsically resistant to infections and raise the fundamental question of why these cells have sacrificed the major antiviral defence pathway if this renders them susceptible to viruses.

Observed Kinetics of Enterovirus Inactivation by Free Chlorine Are Host Cell-Dependent

Virucidal efficacies of disinfectants are typically assessed by infectivity assay utilizing a single type of host cell. Enteroviruses infect multiple host cells via various entry routes, and each entry route may be impaired differently by a given disinfectant. Yet, it is unknown how the choice of host cells affects the observed inactivation kinetics. Here, we evaluated the inactivation kinetics of echovirus 11 (E11) by free chlorine, ultraviolet (UV) irradiation, and heat, using three different host cells (BGMK, RD, and A549). Inactivation rates were independent of the host cell for treatment of E11 by UV or heat. Conversely, E11 inactivation by free chlorine occurred 2-fold faster when enumerated on BGMK cells compared with RD and A549 cells. Host cell-dependent inactivation kinetics by free chlorine were also observed for echovirus 7, 9, and 13, and coxsackievirus A9. E11 inactivation by free chlorine was partly caused by a loss in host cell attachment, which was most pronounced for BGMK cells. BGMK cells lack the attachment receptor CD55 and a key subunit of the uncoating receptor β2M, which may contribute to the differential inactivation kinetics for this cell type. Consequently, inactivation kinetics of enteroviruses should be assessed using host cells with different receptor profiles.

The Role of Viral Infections in the Onset of Autoimmune Diseases

Autoimmune diseases (AIDs) are the consequence of a breach in immune tolerance, leading to the inability to sufficiently differentiate between self and non-self. Immune reactions that are targeted towards self-antigens can ultimately lead to the destruction of the host's cells and the development of autoimmune diseases. Although autoimmune disorders are comparatively rare, the worldwide incidence and prevalence is increasing, and they have major adverse implications for mortality and morbidity. Genetic and environmental factors are thought to be the major factors contributing to the development of autoimmunity. Viral infections are one of the environmental triggers that can lead to autoimmunity. Current research suggests that several mechanisms, such as molecular mimicry, epitope spreading, and bystander activation, can cause viral-induced autoimmunity. Here we describe the latest insights into the pathomechanisms of viral-induced autoimmune diseases and discuss recent findings on COVID-19 infections and the development of AIDs.

Multiple subtypes of coxsackievirus group B can cause congenital heart disease

BACKGROUND

Different serotypes of coxsackievirus B (CVB), which is the most common cause of viral myocarditis, target cardiomyocytes through Coxsackie and Adenovirus Receptor and Decay-Accelerating Factor. Both receptors are expressed in the fetal heart. We hypothesized that infection with different serotypes of CVB during early pregnancy plays a role in pathogenesis of congenital heart defect (CHD).

METHODS

In this study, we use a murine model to infect with CVB1, CVB4, and combination of CVB3 + CVB4 during a critical period in gestation. We examined offspring of pregnant mice for fetal death and heart defects following viral infection.

RESULT

Fetuses from uninfected control dams showed normal heart development, while maternal CVB infection precipitates CHD: majorly ventricular septal defects (VSD) and non-compaction of ventricular myocardium (NC), with some infrequent cases of double outlet right ventricle, left ventricle wall rupture, right ventricle hypertrophy, and thickened/dysplastic semilunar valves. Infection of pregnant dams with CVB1 leads to 44% VSD and 41.2% NC cases, while with CVB4 leads to 31.7% VSD and 13.3% NC cases. Co-infection with CVB3 + CVB4 increases fetal pathology to 51.3% VSD and 41% NC cases. Infection can also result in fetal death, with higher incidences with CVB3 + CVB4 with 46.2% cases, compared to 33.3% by CVB1 and 21.7% by CVB4. Male fetuses were more susceptible to all phenotypes.

CONCLUSION

Our report shows that prenatal CVB infections can lead to pathogenesis of certain heart defects in mouse model, particularly exacerbated with co-infections. This data confirms a link between prenatal CVB infection and CHD development and highlights it is not unique to just one serotype of CVB.

ACE2 and COVID-19 Susceptibility and Severity

Sick, male, and older populations are more vulnerable to COVID-19. However, it remains unclear whether a common mechanism exists across different demographic characteristics. SARS-CoV-2 infection is initiated by the specific binding of the viral spike protein to angiotensin-converting enzyme 2 (ACE2). This study analyzed the demographics of pulmonary ACE2 expression, Mendelian randomization (MR) of ACE2 and COVID-19, and comparative tropism of SARS-CoV-2. The key features of SARS-CoV-2 tropism, including pulmonary ACE2 expression and ACE2-expressing cell types, showed distinct subphenotypes associated with the demographics of vulnerable COVID-19 populations, suggesting a hypothesis centered on “ACE2” to explain their interplay. Next, by integrating multiple COVID-19 cohorts of genome-wide association studies (GWASs) and cis-expression quantitative trait loci (cis-eQTLs) of ACE2, MR analysis demonstrated that ACE2 played a causal role in COVID-19 susceptibility and severity, suggesting ACE2 as a promising target for early COVID-19 treatment. Next, by analyzing the expression of host cell receptors using single-cell RNA sequencing (scRNA-seq) data of human lung tissues, comparative tropism analysis showed that SARS-CoV-2 and other respiratory viruses, but not non-respiratory viruses, had remarkably overlapping and enriched cellular tropism in alveolar type 2 (AT2) cells. This finding indicates the possibility of coinfection with SARS-CoV-2 and other respiratory viruses, perhaps implying sociovirology at the cellular level. Moreover, the binding of viral entry proteins to the compatible host cell receptors is under strong natural selection pressure. Therefore, comparative tropism might reveal the footprint of natural selection that shapes the virus population, which provides a novel perspective for understanding zoonotic spillover events.

Persistent coxsackievirus B1 infection triggers extensive changes in the transcriptome of human pancreatic ductal cells

Enteroviruses, particularly the group B coxsackieviruses (CVBs), have been associated with the development of type 1 diabetes. Several CVB serotypes establish chronic infections in human cells in vivo and in vitro. However, the mechanisms leading to enterovirus persistency and, possibly, beta cell autoimmunity are not fully understood. We established a carrier-state-type persistent infection model in human pancreatic cell line PANC-1 using two distinct CVB1 strains and profiled the infection-induced changes in cellular transcriptome. In the current study, we observed clear changes in the gene expression of factors associated with the pancreatic microenvironment, the secretory pathway, and lysosomal biogenesis during persistent CVB1 infections. Moreover, we found that the antiviral response pathways were activated differently by the two CVB1 strains. Overall, our study reveals extensive transcriptional responses in persistently CVB1-infected pancreatic cells with strong opposite but also common changes between the two strains.

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Establishment of persistent CVB1 infection in PANC-1 cells using two CVB1 strains

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Extensive transcriptional responses in persistently CVB1-infected pancreatic cells

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Changes in pancreatic microenvironment, secretory pathway, and lysosomes

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Antiviral immune response was activated differently by the two CVB1 strains

Does enterovirus 71 urge for effective vaccine control strategies? Challenges and current opinion

Enterovirus 71 (EV71) is an infectious virus affecting all age groups of people around the world. It is one of the major aetiologic agents for HFMD (hand, foot and mouth disease) identified globally. It has led to many outbreaks and epidemics in Asian countries. Infection caused by this virus that can lead to serious psychological problems, heart diseases and respiratory issues in children younger than 10 years of age. Many studies are being carried out on the pathogenesis of the virus, but little is known. The host immune response and other molecular responses against the virus are also not clearly determined. This review deals with the interaction between the host and the EV71 virus. We discuss how the virus makes use of its proteins to affect the host's immunity and how the viral proteins help their replication. Additionally, we describe other useful resources that enable the virus to evade the host's immune responses. The knowledge of the viral structure and its interactions with host cells has led to the discovery of various drug targets for the treatment of the virus. Additionally, this review focusses on the antiviral drugs and vaccines developed by targeting various viral surface molecules during their infectious period. Furthermore, it is asserted that the improvement of prevailing vaccines will be the simplest method to manage EV71 infection swiftly. Therefore, we summarise numerous vaccines candidate for the EV71, such as the use of an inactivated complete virus, recombinant VP1 protein, artificial peptides, VLPs (viral-like particles) and live attenuated vaccines for combating the viral outbreaks promptly.

Simulating coxsackievirus B3 infection with an accessible computational model of its complete kinetics

We describe how to use a publicly available computational model for coxsackievirus B3 (CVB3) infection that we recast as a graphical user interface (GUI). The GUI-based implementation enables non-computationalists to incorporate systems-biology modeling into their research and teaching. The model simulates the full life cycle of CVB3, including the host antiviral response, and includes 44 alterable parameters. The model simplifies some viral life cycle processes to improve interpretability and utility when performing in silico experiments.

For complete details on the use and execution of this protocol, please refer to Lopacinski et al. (2021).

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Tool for simulating coxsackievirus B3 infections with a graphical user interface

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Extensive functionality for parameter changes, data display, and export

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Installations available for Windows, MacOS, or Linux

Enterovirus D: A Small but Versatile Species

Enteroviruses (EVs) from the D species are the causative agents of a diverse range of infectious diseases in spite of comprising only five known members. This small clade has a diverse host range and tissue tropism. It contains types infecting non-human primates and/or humans, and for the latter, they preferentially infect the eye, respiratory tract, gastrointestinal tract, and nervous system. Although several Enterovirus D members, in particular EV-D68, have been associated with neurological complications, including acute myelitis, there is currently no effective treatment or vaccine against any of them. This review highlights the peculiarities of this viral species, focusing on genome organization, functional elements, receptor usage, and pathogenesis.

Development of Group B Coxsackievirus as an Oncolytic Virus: Opportunities and Challenges

Oncolytic viruses have emerged as a promising strategy for cancer therapy due to their dual ability to selectively infect and lyse tumor cells and to induce systemic anti-tumor immunity. Among various candidate viruses, coxsackievirus group B (CVBs) have attracted increasing attention in recent years. CVBs are a group of small, non-enveloped, single-stranded, positive-sense RNA viruses, belonging to species human Enterovirus B in the genus Enterovirus of the family Picornaviridae. Preclinical studies have demonstrated potent anti-tumor activities for CVBs, particularly type 3, against multiple cancer types, including lung, breast, and colorectal cancer. Various approaches have been proposed or applied to enhance the safety and specificity of CVBs towards tumor cells and to further increase their anti-tumor efficacy. This review summarizes current knowledge and strategies for developing CVBs as oncolytic viruses for cancer virotherapy. The challenges arising from these studies and future prospects are also discussed in this review.

Coxsackievirus B3-Its Potential as an Oncolytic Virus

Oncolytic virotherapy represents one of the most advanced strategies to treat otherwise untreatable types of cancer. Despite encouraging developments in recent years, the limited fraction of patients responding to therapy has demonstrated the need to search for new suitable viruses. Coxsackievirus B3 (CVB3) is a promising novel candidate with particularly valuable features. Its entry receptor, the coxsackievirus and adenovirus receptor (CAR), and heparan sulfate, which is used for cellular entry by some CVB3 variants, are highly expressed on various cancer types. Consequently, CVB3 has broad anti-tumor activity, as shown in various xenograft and syngeneic mouse tumor models. In addition to direct tumor cell killing the virus induces a strong immune response against the tumor, which contributes to a substantial increase in the efficiency of the treatment. The toxicity of oncolytic CVB3 in healthy tissues is variable and depends on the virus strain. It can be abrogated by genetic engineering the virus with target sites of microRNAs. In this review, we present an overview of the current status of the development of CVB3 as an oncolytic virus and outline which steps still need to be accomplished to develop CVB3 as a therapeutic agent for clinical use in cancer treatment.

Modeling the complete kinetics of coxsackievirus B3 reveals human determinants of host-cell feedback

Complete kinetic models are pervasive in chemistry but lacking in biological systems. We encoded the complete kinetics of infection for coxsackievirus B3 (CVB3), a compact and fast-acting RNA virus. The model consists of separable, detailed modules describing viral binding-delivery, translation-replication, and encapsidation. Specific module activities are dampened by the type I interferon response to viral double-stranded RNAs (dsRNAs), which is itself disrupted by viral proteinases. The experimentally validated kinetics uncovered that cleavability of the dsRNA transducer mitochondrial antiviral signaling protein (MAVS) becomes a stronger determinant of viral outcomes when cells receive supplemental interferon after infection. Cleavability is naturally altered in humans by a common MAVS polymorphism, which removes a proteinase-targeted site but paradoxically elevates CVB3 infectivity. These observations are reconciled with a simple nonlinear model of MAVS regulation. Modeling complete kinetics is an attainable goal for small, rapidly infecting viruses and perhaps viral pathogens more broadly. A record of this paper's transparent peer review process is included in the Supplemental information.

Natural Products as a Paradigm for the Treatment of Coxsackievirus - induced Myocarditis

Coxsackievirus B3 (CVB3), a member of the Picornaviridae family, is considered to be one of the most important infectious agents to cause virus-induced myocarditis. Despite improvements in studying viral pathology, structure and molecular biology, as well as diagnosis of this disease, there is still no virus-specific drug in clinical use. Structural and nonstructural proteins produced during the coxsackievirus life cycle have been identified as potential targets for blocking viral replication at the step of attachment, entry, uncoating, RNA and protein synthesis by synthetic or natural compounds. Moreover, WIN (for Winthrop) compounds and application of nucleic-acid based strategies were shown to target viral capsid, entry and viral proteases, but have not reached to the clinical trials as a successful antiviral agent. There is an urgent need for diverse molecular libraries for phenotype-selective and high-throughput screening.

Role of coxsackie-adenovirus receptor in cardiac development and pathogenesis of congenital heart disease

The coxsackie-adenovirus receptor (CAR) is a cell surface transmembrane protein originally recognized for its role as a binding site for coxsackie- and adeno-viruses. As such, it is believed to play an important role in pathogenesis of myocarditis. Other studies have suggested that CAR also plays an important role in embryonic development, which is not surprising given the strong expression of the receptor in heart, brain, liver, pancreas, kidney, small intestine, and various epithelia during development. A number of studies have looked at downregulation and upregulation of CAR and have confirmed the central role of CAR during critical periods of development. These studies all demonstrated embryonic lethality with variable phenotypes: electrophysiological abnormalities, cardiac structural deformations, and extracardiac abnormalities, such as lymphatic malformations. The purpose of this review is to summarize the existing literature about CAR and formulate some questions for future studies, with an emphasis on the role of CAR during embryonic heart development.

Association of gene polymorphisms of CD55 with susceptibility to and severity of hand, foot, and mouth disease caused by enterovirus 71 in the Han Chinese population

Hand, foot, and mouth disease (HFMD) caused by enterovirus 71 (EV71) can lead to high morbidity and mortality, and genetic background plays an important role during the disease process. We investigated the association between the single-nucleotide polymorphism (SNP) rs2564978 of the CD55 gene and susceptibility to and severity of HFMD using the SNPs can multiple SNP typing methods. Soluble CD55 (sCD55) expression was significantly lower in the EV71 HFMD group than in the control group and lower in severe cases than in mild cases (P < .001). Moreover, CD55 rs2564978 (C vs T OR = 1.300, 95% CI, 1.120-1.509) was associated with the risk of EV71 infection, and genotype TC was related to the severity of the infection (TC vs TT OR = 4.523, 95% CI, 2.033-10.066). Our results suggest that sCD55 expression and the CD55 polymorphism rs2564978 may influence the susceptibility to and severity of EV71 infection.

Genetic Adaptation of Coxsackievirus B1 during Persistent Infection in Pancreatic Cells

Coxsackie B (CVB) viruses have been associated with type 1 diabetes. We have recently observed that CVB1 was linked to the initiation of the autoimmune process leading to type 1 diabetes in Finnish children. Viral persistency in the pancreas is currently considered as one possible mechanism. In the current study persistent infection was established in pancreatic ductal and beta cell lines (PANC-1 and 1.1B4) using four different CVB1 strains, including the prototype strain and three clinical isolates. We sequenced 5′ untranslated region (UTR) and regions coding for structural and non-structural proteins and the second single open reading frame (ORF) protein of all persisting CVB1 strains using next generation sequencing to identify mutations that are common for all of these strains. One mutation, K257R in VP1, was found from all persisting CVB1 strains. The mutations were mainly accumulated in viral structural proteins, especially at BC, DE, EF loops and C-terminus of viral capsid protein 1 (VP1), the puff region of VP2, the knob region of VP3 and infection-enhancing epitope of VP4. This showed that the capsid region of the viruses sustains various changes during persistency some of which could be hallmark(s) of persistency.

In the Crosshairs: RNA Viruses OR Complement?

Complement, a part of the innate arm of the immune system, is integral to the frontline defense of the host against innumerable pathogens, which includes RNA viruses. Among the major groups of viruses, RNA viruses contribute significantly to the global mortality and morbidity index associated with viral infection. Despite multiple routes of entry adopted by these viruses, facing complement is inevitable. The initial interaction with complement and the nature of this interaction play an important role in determining host resistance versus susceptibility to the viral infection. Many RNA viruses are potent activators of complement, often resulting in virus neutralization. Yet, another facet of virus-induced activation is the exacerbation in pathogenesis contributing to the overall morbidity. The severity in disease and death associated with RNA virus infections shows a tip in the scale favoring viruses. Growing evidence suggest that like their DNA counterparts, RNA viruses have co-evolved to master ingenious strategies to remarkably restrict complement. Modulation of host genes involved in antiviral responses contributed prominently to the adoption of unique strategies to keep complement at bay, which included either down regulation of activation components (C3, C4) or up regulation of complement regulatory proteins. All this hints at a possible “hijacking” of the cross-talk mechanism of the host immune system. Enveloped RNA viruses have a selective advantage of not only modulating the host responses but also recruiting membrane-associated regulators of complement activation (RCAs). This review aims to highlight the significant progress in the understanding of RNA virus–complement interactions.

Influenza A Virus Nucleoprotein Activates the JNK Stress-Signaling Pathway for Viral Replication by Sequestering Host Filamin A Protein

Influenza A virus (IAV) poses a major threat to global public health and is known to employ various strategies to usurp the host machinery for survival. Due to its fast-evolving nature, IAVs tend to escape the effect of available drugs and vaccines thus, prompting the development of novel antiviral strategies. High-throughput mass spectrometric screen of host-IAV interacting partners revealed host Filamin A (FLNA), an actin-binding protein involved in regulating multiple signaling pathways, as an interaction partner of IAV nucleoprotein (NP). In this study, we found that the IAV NP interrupts host FLNA-TRAF2 interaction by interacting with FLNA thus, resulting in increased levels of free, displaced TRAF2 molecules available for TRAF2-ASK1 mediated JNK pathway activation, a pathway critical to maintaining efficient viral replication. In addition, siRNA-mediated FLNA silencing was found to promote IAV replication (87% increase) while FLNA-overexpression impaired IAV replication (65% decrease). IAV NP was observed to be a crucial viral factor required to attain FLNA mRNA and protein attenuation post-IAV infection for efficient viral replication. Our results reveal FLNA to be a host factor with antiviral potential hitherto unknown to be involved in the IAV replication cycle thus, opening new possibilities of FLNA-NP interaction as a candidate anti-influenza drug development target.

Structures of Echovirus 30 in complex with its receptors inform a rational prediction for enterovirus receptor usage

Receptor usage that determines cell tropism and drives viral classification closely correlates with the virus structure. Enterovirus B (EV-B) consists of several subgroups according to receptor usage, among which echovirus 30 (E30), a leading causative agent for human aseptic meningitis, utilizes FcRn as an uncoating receptor. However, receptors for many EVs remain unknown. Here we analyzed the atomic structures of E30 mature virion, empty- and A-particles, which reveals serotype-specific epitopes and striking conformational differences between the subgroups within EV-Bs. Of these, the VP1 BC loop markedly distinguishes E30 from other EV-Bs, indicative of a role as a structural marker for EV-B. By obtaining cryo-electron microscopy structures of E30 in complex with its receptor FcRn and CD55 and comparing its homologs, we deciphered the underlying molecular basis for receptor recognition. Together with experimentally derived viral receptor identifications, we developed a structure-based in silico algorithm to inform a rational prediction for EV receptor usage.

Echovirus 30 (E30) belongs to the Enterovirus-B group and causes aseptic meningitis in humans. Here, the authors present the cryo-EM structures of the E30 E-particle, A-particle and the mature virion, as well as structures of E30 in complex with its receptor FcRn and CD55, and furthermore they describe a structure-based algorithm that allows the prediction of EV receptor usage.

The Role of Non-coding RNAs in Viral Myocarditis

Viral myocarditis (VMC) is a disease characterized as myocardial parenchyma or interstitium inflammation caused by virus infection, especially Coxsackievirus B3 (CVB3) infection, which has no accurate non-invasive examination for diagnosis and specific drugs for treatment. The mechanism of CVB3-induced VMC may be related to direct myocardial damage of virus infection and extensive damage of abnormal immune response after infection. Non-coding RNA (ncRNA) refers to RNA that is not translated into protein and plays a vital role in many biological processes. There is expanding evidence to reveal that ncRNAs regulate the occurrence and development of VMC, which may provide new treatment or diagnosis targets. In this review, we mainly demonstrate an overview of the potential role of ncRNAs in the pathogenesis, diagnosis and treatment of CVB3-induced VMC.

Early Entry Events in Echovirus 30 Infection

Echovirus 30 (E30), a member of the enterovirus B species, is a major cause of viral meningitis, targeting children and adults alike. While it is a frequently isolated enterovirus and the cause of several outbreaks all over the world, surprisingly little is known regarding its entry and replication strategy within cells. In this study, we used E30 strain Bastianni (E30B) generated from an infectious cDNA clone in order to study early entry events during infection in human RD cells. E30B required the newly discovered Fc echovirus receptor (FcRn) for successful infection, but not the coxsackievirus and adenovirus receptor (CAR) or decay-accelerating factor (DAF), although an interaction with DAF was observed. Double-stranded RNA replication intermediate was generated between 2 and 3 h postinfection (p.i.), and viral capsid production was initiated between 4 and 5 h p.i. The drugs affecting Rac1 (NSC 23766) and cholesterol (filipin III) compromised infection, whereas bafilomycin A1, dyngo, U-73122, wortmannin, and nocodazole did not, suggesting the virus follows an enterovirus-triggered macropinocytic pathway rather than the clathrin pathway. Colocalization with early endosomes and increased infection due to constitutively active Rab5 expression suggests some overlap and entry to classical early endosomes. Taken together, these results suggest that E30B induces an enterovirus entry pathway, leading to uncoating in early endosomes.IMPORTANCE Echovirus 30 (E30) is a prevalent enterovirus causing regular outbreaks in both children and adults in different parts of the world. It is therefore surprising that relatively little is known of its infectious entry pathway. We set out to generate a cDNA clone and gradient purified the virus in order to study the early entry events in human cells. We have recently studied other enterovirus B group viruses, like echovirus 1 (EV1) and coxsackievirus A9 (CVA9), and found many similarities between those viruses, allowing us to define a so-called "enterovirus entry pathway." Here, E30 is reminiscent of these viruses, for example, by not relying on acidification for infectious entry. However, despite not using the clathrin entry pathway, E30 accumulates in classical early endosomes.

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

Enteroviruses are single-stranded positive-sense RNA viruses that primarily cause self-limiting gastrointestinal or respiratory illness. In some cases, these viruses can invade the central nervous system, causing life-threatening neurological diseases including encephalitis, meningitis and acute flaccid paralysis (AFP). As we near the global eradication of poliovirus, formerly the major cause of AFP, the number of AFP cases have not diminished implying a non-poliovirus etiology. As the number of enteroviruses linked with neurological disease is expanding, of which many had previously little clinical significance, these viruses are becoming increasingly important to public health. Our current understanding of these non-polio enteroviruses is limited, especially with regards to their neurovirulence. Elucidating the molecular pathogenesis of these viruses is paramount for the development of effective therapeutic strategies. This review summarizes the clinical diseases associated with neurotropic enteroviruses and discusses recent advances in the understanding of viral invasion of the central nervous system, cell tropism and molecular pathogenesis as it correlates with host responses.

Prospective virome analyses in young children at increased genetic risk for type 1 diabetes

Viruses are implicated in autoimmune destruction of pancreatic islet β cells, which results in insulin deficiency and type 1 diabetes (T1D)1-4. Certain enteroviruses can infect β cells in vitro5, have been detected in the pancreatic islets of patients with T1D6 and have shown an association with T1D in meta-analyses4. However, establishing consistency in findings across studies has proven difficult. Obstacles to convincingly linking RNA viruses to islet autoimmunity may be attributed to rapid viral mutation rates, the cyclical periodicity of viruses7 and the selection of variants with altered pathogenicity and ability to spread in populations. β cells strongly express cell-surface coxsackie and adenovirus receptor (CXADR) genes, which can facilitate enterovirus infection8. Studies of human pancreata and cultured islets have shown significant variation in enteroviral virulence to β cells between serotypes and within the same serotype9,10. In this large-scale study of known eukaryotic DNA and RNA viruses in stools from children, we evaluated fecally shed viruses in relation to islet autoimmunity and T1D. This study showed that prolonged enterovirus B rather than independent, short-duration enterovirus B infections may be involved in the development of islet autoimmunity, but not T1D, in some young children. Furthermore, we found that fewer early-life human mastadenovirus C infections, as well as CXADR rs6517774, independently correlated with islet autoimmunity.

Slow Infection due to Lowering the Amount of Intact versus Empty Particles Is a Characteristic Feature of Coxsackievirus B5 Dictated by the Structural Proteins

Enterovirus B species typically cause a rapid cytolytic infection leading to efficient release of progeny viruses. However, they are also capable of persistent infections in tissues, which are suggested to contribute to severe chronic states such as myocardial inflammation and type 1 diabetes. In order to understand the factors contributing to differential infection strategies, we constructed a chimera by combining the capsid proteins from fast-cytolysis-causing echovirus 1 (EV1) with nonstructural proteins from coxsackievirus B5 (CVB5), which shows persistent infection in RD cells. The results showed that the chimera behaved similarly to parental EV1, leading to efficient cytolysis in both permissive A549 and semipermissive RD cells. In contrast to EV1 and the chimera, CVB5 replicated slowly in permissive cells and showed persistent infection in semipermissive cells. However, there was no difference in the efficiency of uptake of CVB5 in A549 or RD cells in comparison to the chimera or EV1. CVB5 batches constantly contained significant amounts of empty capsids, also in comparison to CVB5's close relative CVB3. During successive passaging of batches containing only intact CVB5, increasing amounts of empty and decreasing amounts of infective capsids were produced. Our results demonstrate that the increase in the amount of empty particles and the lowering of the amount of infective particles are dictated by the CVB5 structural proteins, leading to slowing down of the infection between passages. Furthermore, the key factor for persistent infection is the small amount of infective particles produced, not the high number of empty particles that accumulate.IMPORTANCE Enteroviruses cause several severe diseases, with lytic infections that lead to rapid cell death but also persistent infections that are more silent and lead to chronic states of infection. Our study compared a cytolytic echovirus 1 infection to persistent coxsackievirus B5 infection by making a chimera with the structural proteins of echovirus 1 and the nonstructural proteins of coxsackievirus B5. Coxsackievirus B5 infection was found to lead to the production of a high number of empty viruses (empty capsids) that do not contain genetic material and are unable to continue the infection. Coinciding with the high number of empty capsids, the amount of infective virions decreased. This characteristic property was not observed in the constructed chimera virus, suggesting that structural proteins are in charge of these phenomena. These results shed light on the mechanisms that may cause persistent infections. Understanding events leading to efficient or inefficient infections is essential in understanding virus-caused pathologies.

Hantavirus entry: Perspectives and recent advances

Hantaviruses are important zoonotic pathogens of public health importance that are found on all continents except Antarctica and are associated with hemorrhagic fever with renal syndrome (HFRS) in the Old World and hantavirus pulmonary syndrome (HPS) in the New World. Despite the significant disease burden they cause, no FDA-approved specific therapeutics or vaccines exist against these lethal viruses. The lack of available interventions is largely due to an incomplete understanding of hantavirus pathogenesis and molecular mechanisms of virus replication, including cellular entry. Hantavirus Gn/Gc glycoproteins are the only viral proteins exposed on the surface of virions and are necessary and sufficient to orchestrate virus attachment and entry. In vitro studies have implicated integrins (β_1-3), DAF/CD55, and gC1qR as candidate receptors that mediate viral attachment for both Old World and New World hantaviruses. Recently, protocadherin-1 (PCDH1) was demonstrated as a requirement for cellular attachment and entry of New World hantaviruses in vitro and lethal HPS in vivo, making it the first clade-specific host factor to be identified. Attachment of hantavirus particles to cellular receptors induces their internalization by clathrin-mediated, dynamin-independent, or macropinocytosis-like mechanisms, followed by particle trafficking to an endosomal compartment where the fusion of viral and endosomal membranes can occur. Following membrane fusion, which requires cholesterol and acid pH, viral nucleocapsids escape into the cytoplasm and launch genome replication. In this review, we discuss the current mechanistic understanding of hantavirus entry, highlight gaps in our existing knowledge, and suggest areas for future inquiry.

Enterovirus infection and type 1 diabetes: unraveling the crime scene

Enteroviruses (EV) have been historically associated to type 1 diabetes. Definitive proof for their implication in disease development is lacking, but growing evidence suggests that they could be involved in beta cell destruction either directly by killing beta cells or indirectly by creating an exacerbated inflammatory response in the islets, capable of attracting autoreactive T cells to the 'scene of the crime'. Epidemiological and serological studies have been associated with the appearance of islet autoimmunity and EV RNA has been detected in prospective studies. In addition, the EV capsid protein has been detected in the islets of recent-onset type 1 diabetic donors, suggesting the existence of a low-grade EV infection that could become persistent. Increasing evidence in the field shows that a 'viral signature' exists in type 1 diabetes and involves interferon responses that could be sustained during prolonged periods. These include the up-regulation of markers such as protein kinase R (PKR), melanoma differentiation-associated protein 5 (MDA5), retinoic acid inducible gene I (RIG-I), myxovirus resistance protein (MxA) and human leukocyte antigen-I (HLA-I) and the release of chemokines able to attract immune cells to the islets leading to insulitis. In this scenario, the hyperexpression of HLA-I molecules would promote antigen presentation to autoreactive T cells, favoring beta cell recognition and, ultimately, destruction. In this review, an overview is provided of the standing evidence that implicates EVs in beta cell 'murder', the time-line of events is investigated from EV entry in the cell to beta cell death and possible accomplices are highlighted that might be involved in beta cell demise.

A fatal case of enterovirus infection with secondary hemophagocytosis-case report with review of literature

Enterovirus is a common viral infection, which can affect multiple organ systems with an array of clinical presentation such as meningitis, encephalitis, myocarditis, and disseminated infections. The illness is usually asymptomatic and self-limited but few cases can be severe and life-threatening especially when associated with hemophagocytosis. We discuss a fatal case of disseminated enterovirus infection and the histomorphological features of the infection.

Cellular N-myristoyltransferases play a crucial picornavirus genus-specific role in viral assembly, virion maturation, and infectivity

In nearly all picornaviruses the precursor of the smallest capsid protein VP4 undergoes co-translational N-terminal myristoylation by host cell N-myristoyltransferases (NMTs). Curtailing this modification by mutation of the myristoylation signal in poliovirus has been shown to result in severe assembly defects and very little, if any, progeny virus production. Avoiding possible pleiotropic effects of such mutations, we here used pharmacological abrogation of myristoylation with the NMT inhibitor DDD85646, a pyrazole sulfonamide originally developed against trypanosomal NMT. Infection of HeLa cells with coxsackievirus B3 in the presence of this drug decreased VP0 acylation at least 100-fold, resulting in a defect both early and late in virus morphogenesis, which diminishes the yield of viral progeny by about 90%. Virus particles still produced consisted mainly of provirions containing RNA and uncleaved VP0 and, to a substantially lesser extent, of mature virions with cleaved VP0. This indicates an important role of myristoylation in the viral maturation cleavage. By electron microscopy, these RNA-filled particles were indistinguishable from virus produced under control conditions. Nevertheless, their specific infectivity decreased by about five hundred fold. Since host cell-attachment was not markedly impaired, their defect must lie in the inability to transfer their genomic RNA into the cytosol, likely at the level of endosomal pore formation. Strikingly, neither parechoviruses nor kobuviruses are affected by DDD85646, which appears to correlate with their native capsid containing only unprocessed VP0. Individual knockout of the genes encoding the two human NMT isozymes in haploid HAP1 cells further demonstrated the pivotal role for HsNMT1, with little contribution by HsNMT2, in the virus replication cycle. Our results also indicate that inhibition of NMT can possibly be exploited for controlling the infection by a wide spectrum of picornaviruses.

Picornaviruses are important human and animal pathogens. Protective vaccines are only available against very few representatives. Furthermore, antiviral drugs have not made it to the market because of serious side effects and viral mutational escape. We here show that pharmacological inhibition of cellular myristoyltransferases severely decreased myristoylation of enteroviral structural proteins as exemplified by coxsackievirus B3, a prominent pathogen causing virus-induced acute and chronic heart disease. The drug DDD85646 substantially diminished virus yield and almost abolished the infectivity of the residual progeny virus. It is highly effective against several other picornaviruses, except those two included in our study that naturally do not process VP0. Our work provides new insight into the role of myristoylation in the life cycle of picornaviruses and identifies the responsible cellular enzyme as a promising candidate for antiviral therapy.

Complement Evasion Strategies of Viruses: An Overview

Being a major first line of immune defense, the complement system keeps a constant vigil against viruses. Its ability to recognize large panoply of viruses and virus-infected cells, and trigger the effector pathways, results in neutralization of viruses and killing of the infected cells. This selection pressure exerted by complement on viruses has made them evolve a multitude of countermeasures. These include targeting the recognition molecules for the avoidance of detection, targeting key enzymes and complexes of the complement pathways like C3 convertases and C5b-9 formation - either by encoding complement regulators or by recruiting membrane-bound and soluble host complement regulators, cleaving complement proteins by encoding protease, and inhibiting the synthesis of complement proteins. Additionally, viruses also exploit the complement system for their own benefit. For example, they use complement receptors as well as membrane regulators for cellular entry as well as their spread. Here, we provide an overview on the complement subversion mechanisms adopted by the members of various viral families including Poxviridae, Herpesviridae, Adenoviridae, Flaviviridae, Retroviridae, Picornaviridae, Astroviridae, Togaviridae, Orthomyxoviridae and Paramyxoviridae.

Soluble coxsackie- and adenovirus receptor (sCAR-Fc); a highly efficient compound against laboratory and clinical strains of coxsackie-B-virus

Coxsackie-B-viruses (CVB) cause a wide variety of diseases, ranging from mild syndromes to life-threatening conditions such as pancreatitis, myocarditis, meningitis and encephalitis. Especially newborns and young infants develop severe diseases and long-term sequelae may occur among survivors. Due to lack of specific antiviral therapy the current treatment of CVB infection is limited to symptomatic treatment. Here we analyzed the antiviral activity of a soluble receptor fusion protein, containing the extracellular part of the coxsackievirus and adenovirus receptor (CAR) fused to the constant domain of the human IgG - sCAR-Fc - against laboratory and clinical CVB strains. We found a high overall antiviral activity of sCAR-Fc against various prototypic laboratory strains of CVB, with an inhibition of viral replication up to 3 orders of magnitude (99.9%) at a concentration of 2.5 μg/ml. These include isolates that are not dependent on CAR for infection and isolates that are resistant against pleconaril, the currently most promising anti-CVB therapeutic. A complete inhibition was observed using higher concentration of sCAR-Fc. Further analysis of 23 clinical CVB isolates revealed overall high antiviral efficiency (up to 99.99%) of sCAR-Fc. In accordance with previous data, our results confirm the strong antiviral activity of sCAR-Fc against laboratory CVB strains and demonstrate for the first time that sCAR-Fc is also highly efficient at neutralizing clinical CVB isolates. Importantly, during the sCAR-Fc inhibition experiments, no naturally occurring resistant mutants were observed.

Diminished expression of complement regulatory proteins (CD55 and CD59) in lymphocytes from systemic lupus erythematosus patients with lymphopenia

CD55 and CD59 are glycophosphatidylinositol-anchored proteins with complement inhibitory properties. Lymphopenia in systemic lupus erythematosus (SLE) has been associated with autoantibodies targeting nuclear antigens. The aim of this study was to evaluate the surface density of CD55 and CD59 in T and B lymphocytes from patients with SLE and lymphopenia and its possible correlation with the presence of common SLE autoantibodies. Flow cytometric analyses were performed on CD55 and CD59 stained CD3 and CD19 cells from 40 SLE patients, 30 with lymphopenia and 10 without it, and 25 healthy controls. Autoantibodies were detected in the sera by enzyme linked immunosorbent assay. The mean fluorescence intensity of CD55 and CD59 in T and B cells was significantly diminished in SLE patients with lymphopenia when compared with healthy subjects. Interestingly, the opposite was found in T and B cells from non-lymphopenic SLE patients. Although there was no correlation between CD55 and CD59 surface density and the presence of any specificity of the autoantibodies tested, higher titres of anti-dsDNA, anti-SM and anti-ribosomal p antibodies were significantly associated with lymphopenia. The deficiency of CD55 and CD59 expression may play a role in the pathophysiology of lymphopenia, most likely by increasing the susceptibility of cells to complement mediated cytolysis.

The Coxsackievirus and Adenovirus Receptor: Glycosylation and the Extracellular D2 Domain Are Not Required for Coxsackievirus B3 Infection

The coxsackievirus and adenovirus receptor (CAR) is a member of the immunoglobulin superfamily (IgSF) and functions as a receptor for coxsackie B viruses (CVBs). The extracellular portion of CAR comprises two glycosylated immunoglobulin-like domains, D1 and D2. CAR-D1 binds to the virus and is essential for virus infection; however, it is not known whether D2 is also important for infection, and the role of glycosylation has not been explored. To understand the function of these structural components in CAR-mediated CVB3 infection, we generated a panel of human (h) CAR deletion and substitution mutants and analyzed their functionality as CVB receptors, examining both virus binding and replication. Lack of glycosylation of the CAR-D1 or -D2 domains did not adversely affect CVB3 binding or infection, indicating that the glycosylation of CAR is not required for its receptor functions. Deletion of the D2 domain reduced CVB3 binding, with a proportionate reduction in the efficiency of virus infection. Replacement of D2 with the homologous D2 domain from chicken CAR, or with the heterologous type C2 immunoglobulin-like domain from IgSF11, another IgSF member, fully restored receptor function; however, replacement of CAR-D2 with domains from CD155 or CD80 restored function only in part. These data indicate that glycosylation of the extracellular domain of hCAR plays no role in CVB3 receptor function and that CAR-D2 is not specifically required. The D2 domain may function largely as a spacer permitting virus access to D1; however, the data may also suggest that D2 affects virus binding by influencing the conformation of D1.

IMPORTANCE

An important step in virus infection is the initial interaction of the virus with its cellular receptor. Although the role in infection of the extracellular CAR-D1, cytoplasmic, and transmembrane domains have been analyzed extensively, nothing is known about the function of CAR-D2 and the extracellular glycosylation of CAR. Our data indicate that glycosylation of the extracellular CAR domain has only minor importance for the function of CAR as CVB3 receptor and that the D2 domain is not essential per se but contributes to receptor function by promoting the exposure of the D1 domain on the cell surface. These results contribute to our understanding of the coxsackievirus-receptor interactions.

Rhinoviruses and Respiratory Enteroviruses: Not as Simple as ABC

Rhinoviruses (RVs) and respiratory enteroviruses (EVs) are leading causes of upper respiratory tract infections and among the most frequent infectious agents in humans worldwide. Both are classified in the Enterovirus genus within the Picornaviridae family and they have been assigned to seven distinct species, RV-A, B, C and EV-A, B, C, D. As viral infections of public health significance, they represent an important financial burden on health systems worldwide. However, the lack of efficient antiviral treatment or vaccines against these highly prevalent pathogens prevents an effective management of RV-related diseases. Current advances in molecular diagnostic techniques have revealed the presence of RV in the lower respiratory tract and its role in lower airway diseases is increasingly reported. In addition to an established etiological role in the common cold, these viruses demonstrate an unexpected capacity to spread to other body sites under certain conditions. Some of these viruses have received particular attention recently, such as EV-D68 that caused a large outbreak of respiratory illness in 2014, respiratory EVs from species C, or viruses within the newly-discovered RV-C species. This review provides an update of the latest findings on clinical and fundamental aspects of RV and respiratory EV, including a summary of basic knowledge of their biology.

Coxsackie-adenovirus receptor expression is enhanced in pancreas from patients with type 1 diabetes

OBJECTIVES

One of the theories connecting enterovirus (EV) infection of human islets with type 1 diabetes (T1D) is the development of a fertile field in the islets. This implies induction of appropriate proteins for the viral replication such as the coxsackie-adenovirus receptor (CAR). The aim of this study was to investigate to what extent CAR is expressed in human islets of Langerhans, and what conditions that would change the expression.

DESIGN

Immunohistochemistry for CAR was performed on paraffin-embedded pancreatic tissue from patients with T1D (n=9 recent onset T1D, n=4 long-standing T1D), islet autoantibody-positive individuals (n=14) and non-diabetic controls (n=24) individuals. The expression of CAR was also examined by reverse transcription PCR on microdissected islets (n=5), exocrine tissue (n=5) and on explanted islets infected with EV or exposed to chemokines produced by EV-infected islet cells.

RESULTS

An increased frequency of patients with T1D and autoantibody-positive individuals expressed CAR in the pancreas (p<0.039). CAR staining was detected more frequently in pancreatic islets from patients with T1D and autoantibody-positive subjects (15/27) compared with (6/24) non-diabetic controls (p<0.033). Also in explanted islets cultured in UV-treated culture medium from coxsackievirus B (CBV)-1-infected islets, the expression of the CAR gene was increased compared with controls. Laser microdissection of pancreatic tissue revealed that CAR expression was 10-fold higher in endocrine compared with exocrine cells of the pancreas. CAR was also expressed in explanted islets and the expression level decreased with time in culture. CBV-1 infection of explanted islets clearly decreased the expression of CAR (p<0.05). In contrast, infection with echovirus 6 did not affect the expression of CAR.

CONCLUSIONS

CAR is expressed in pancreatic islets of patients with T1D and the expression level of CAR is increased in explanted islets exposed to proinflammatory cytokines/chemokines produced by infected islets. T1D is associated with increased levels of certain chemokines/cytokines in the islets and this might be the mechanism behind the increased expression of CAR in TID islets.

Differential effects of three echovirus strains on cell lysis and insulin secretion in beta cell derived lines

In an earlier study, infection of human pancreatic islets with epidemic strains of echovirus (E4, E16, E30), with proven but differently ability to induce islet autoimmunity, resulted either in a severe damage (i.e., E16 and E30) or proceeded without visible changes in infected islets (i.e., E4). In this study, the ability of these strains to replicate in beta cells and the consequence of such an infection for beta cell lysis and beta cell function was studied in the pancreatic beta cell lines INS-1, MIN6, and NIT-1. The strains of E16 and E30 did replicate in INS1, MIN6, and NIT1 cells and resulted in a pronounced cytopathic effect within 3 days following infection. By contrast, E4 replicated in all examined insulinoma cells with no apparent cell destruction. The insulin release in response to high glucose stimulation was hampered in all infected cells (P < 0.05) when no evidence of cytolysis was present; however, the adverse effect of E16 and E30 on insulin secretion appeared to be higher than that of the E4 strain. The differential effects of echovirus infection on cell lysis, and beta cell function in the rodent insulinoma INS1, MIN6, and NIT 1 cells reflect those previously obtained in primary human islets and support the notion that the insulin-producing beta cells can harbor a non-cytopathic viral infection.

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.

Blood Groups in Infection and Host Susceptibility

Blood group antigens represent polymorphic traits inherited among individuals and populations. At present, there are 34 recognized human blood groups and hundreds of individual blood group antigens and alleles. Differences in blood group antigen expression can increase or decrease host susceptibility to many infections. Blood groups can play a direct role in infection by serving as receptors and/or coreceptors for microorganisms, parasites, and viruses. In addition, many blood group antigens facilitate intracellular uptake, signal transduction, or adhesion through the organization of membrane microdomains. Several blood groups can modify the innate immune response to infection. Several distinct phenotypes associated with increased host resistance to malaria are overrepresented in populations living in areas where malaria is endemic, as a result of evolutionary pressures. Microorganisms can also stimulate antibodies against blood group antigens, including ABO, T, and Kell. Finally, there is a symbiotic relationship between blood group expression and maturation of the gastrointestinal microbiome.

Pathogenesis of human diffusely adhering Escherichia coli expressing Afa/Dr adhesins (Afa/Dr DAEC): current insights and future challenges

The pathogenicity and clinical pertinence of diffusely adhering Escherichia coli expressing the Afa/Dr adhesins (Afa/Dr DAEC) in urinary tract infections (UTIs) and pregnancy complications are well established. In contrast, the implication of intestinal Afa/Dr DAEC in diarrhea is still under debate. These strains are age dependently involved in diarrhea in children, are apparently not involved in diarrhea in adults, and can also be asymptomatic intestinal microbiota strains in children and adult. This comprehensive review analyzes the epidemiology and diagnosis and highlights recent progress which has improved the understanding of Afa/Dr DAEC pathogenesis. Here, I summarize the roles of Afa/Dr DAEC virulence factors, including Afa/Dr adhesins, flagella, Sat toxin, and pks island products, in the development of specific mechanisms of pathogenicity. In intestinal epithelial polarized cells, the Afa/Dr adhesins trigger cell membrane receptor clustering and activation of the linked cell signaling pathways, promote structural and functional cell lesions and injuries in intestinal barrier, induce proinflammatory responses, create angiogenesis, instigate epithelial-mesenchymal transition-like events, and lead to pks-dependent DNA damage. UTI-associated Afa/Dr DAEC strains, following adhesin-membrane receptor cell interactions and activation of associated lipid raft-dependent cell signaling pathways, internalize in a microtubule-dependent manner within urinary tract epithelial cells, develop a particular intracellular lifestyle, and trigger a toxin-dependent cell detachment. In response to Afa/Dr DAEC infection, the host epithelial cells generate antibacterial defense responses. Finally, I discuss a hypothetical role of intestinal Afa/Dr DAEC strains that can act as "silent pathogens" with the capacity to emerge as "pathobionts" for the development of inflammatory bowel disease and intestinal carcinogenesis.

Tissue tropism, pathology and pathogenesis of enterovirus infection

Enteroviruses are very common and cause infections with a diverse array of clinical features. Enteroviruses are most frequently considered by practising pathologists in cases of aseptic meningitis, encephalitis, myocarditis and disseminated infections in neonates and infants. Congenital infections have been reported and transplacental transmission is thought to occur. Although skin biopsies during hand, foot and mouth disease are infrequently obtained, characteristic dermatopathological findings can be seen. Enteroviruses have been implicated in lower respiratory tract infections. This review highlights histopathological features of enterovirus infection and discusses diagnostic modalities for formalin-fixed paraffin-embedded tissues and their associated pitfalls. Immunohistochemistry can detect enterovirus antigen within cells of affected tissues; however, assays can be non-specific and detect other viruses. Molecular methods are increasingly relied upon but, due to the high frequency of asymptomatic enteroviral infections, clinical-pathological correlation is needed to determine significance. Of note, diagnostic assays on central nervous system or cardiac tissues from immunocompetent patients with prolonged disease courses are most often negative. Histopathological, immunohistochemical and molecular studies performed on clinical specimens also provide insight into enteroviral tissue tropism and pathogenesis.

Expression of human decay-accelerating factor on intestinal epithelium of transgenic mice does not facilitate infection by the enteral route

In vitro, infection of polarized human intestinal epithelial cells by coxsackievirus B3 (CVB3) depends on virus interaction with decay-accelerating factor (DAF), a receptor expressed on the apical cell surface. Although mice are highly susceptible to CVB3 infection when virus is delivered by intraperitoneal injection, infection by the enteral route is very inefficient. Murine DAF, unlike human DAF, does not bind virus, and we hypothesized that the absence of an accessible receptor on the intestinal surface is an important barrier to infection by the oral route. We generated transgenic mice that express human DAF specifically on intestinal epithelium and measured their susceptibility to infection by a DAF-binding CVB3 isolate. Human DAF permitted CVB3 to bind to the intestinal surface ex vivo and to infect polarized monolayers of small-intestinal epithelial cells derived from DAF transgenic mice. However, expression of human DAF did not facilitate infection by the enteral route either in immunocompetent animals or in animals deficient in the interferon alpha/beta receptor. These results indicate that the absence of an apical receptor on intestinal epithelium is not the major barrier to infection of mice by the oral route.

IMPORTANCE

CVB3 infection of human intestinal epithelial cells depends on DAF at the apical cell surface, and expression of human DAF on murine intestinal epithelial cells permits their infection in vitro. However, expression of human DAF on the intestinal surface of transgenic mice did not facilitate infection by the oral route. Although the role of intestinal DAF in human infection has not been directly examined, these results suggest that DAF is not the critical factor in mice.

Platelets interact with Coxsackieviruses B and have a critical role in the pathogenesis of virus-induced myocarditis

BACKGROUND

To further understand the role of platelets in the pathogenesis of viral infections we explored platelet interaction with Coxsackieviruses B (CVB) 1 and 3. CVB is a group of viruses that cause the majority of human enterovirus-related viral myocarditis; their receptor (CAR) is expressed on the platelet surface and there is a well-characterized CVB3-induced myocarditis murine model.

METHODS

Human platelets were infected with CVB1 and 3 and viruses were detected in pellets and in supernatants. C57BL/6J mice with or without platelet depletion were inoculated with CVB3 and peripheral blood and heart samples collected at different times post-infection.

RESULTS

CVB1 and 3 RNA and a capsid protein were detected in infected platelets. Despite the fact that titration assays in Vero cells showed increasing infectivity titers over time, supernatants and pellets from infected platelets showed similar levels, suggesting that platelets were not susceptible to a replicative infectivity cycle. CVB binding was CAR-independent and resulted in P-selectin and phosphatidylserine (PS) exposure. CVB3-infected mice showed a rapid thrombocytopenia that correlated with an increase in platelet PS exposure and platelet-leukocyte aggregates without modification of platelet P-selectin expression or von Willebrand factor levels. Mortality, viremia, heart viral titers and myocarditis were significantly higher in platelet-depleted than normal animals. Type I IFN levels were not changed but IgG levels were lower in infected and platelet-depleted mice.

CONCLUSIONS

Our data reveal that platelets play a critical role in host survival and immune response against CVB3 infection.

Nonenveloped capsid: mechanisms of viral entry

ABSTRACT 

Viruses are a diverse class of nanoparticles. However, they have evolved a few common mechanisms that enable successful infection of their host cells. The first stage of this process involves entry into the cell. For enveloped viruses this process has been well characterized. For nonenveloped viruses, the focus of this review, the entry mechanisms are less well understood. For these viruses, a typical pathway involves receptor attachment followed by internalization into cellular vesicles and subsequent viral escape to the cytosol and transport to the site of genome replication. Significantly, these viruses have evolved numerous mechanisms to fulfill this seemingly simple infection scheme. We focus on the latest observations for several families of nonenveloped viruses and highlight specific members for eukaryotic families: Adenoviridae, Papillomaviridae, Parvoviridae, Picornaviridae, Polyomaviridae and Reoviridae; and prokaryotic families: Microviridae, Myoviridae, Podoviridae and Siphoviridae.

RNase L interacts with Filamin A to regulate actin dynamics and barrier function for viral entry

The actin cytoskeleton and its network of associated proteins constitute a physical barrier that viruses must circumvent to gain entry into cells for productive infection. The mechanisms by which the physical signals of infection are sensed by the host to activate an innate immune response are not well understood. The antiviral endoribonuclease RNase L is ubiquitously expressed in a latent form and activated upon binding 2-5A, a unique oligoadenylate produced during viral infections. We provide evidence that RNase L in its inactive form interacts with the actin-binding protein Filamin A to modulate the actin cytoskeleton and inhibit virus entry. Cells lacking either RNase L or Filamin A displayed increased virus entry which was exacerbated in cells lacking both proteins. RNase L deletion mutants that reduced Filamin A interaction displayed a compromised ability to restrict virus entry, supporting the idea of an important role for the RNase L-Filamin A complex in barrier function. Remarkably, both the wild type and a catalytically inactive RNase L mutant were competent to reduce virus entry when transfected into RNase L-deficient cells, indicating that this novel function of RNase L is independent of its enzymatic activity. Virus infection and RNase L activation disrupt its association with Filamin A and release RNase L to mediate its canonical nuclease-dependent antiviral activities. The dual functions of RNase L as a constitutive component of the actin cytoskeleton and as an induced mediator of antiviral signaling and effector functions provide insights into its mechanisms of antiviral activity and opportunities for the development of novel antiviral agents.

Cells constantly face and sample pathogens on their outer surface. The actin cytoskeleton and interacting proteins associate with the cell membrane and constitute a barrier to infection. Disruption of the actin cytoskeleton allows viruses to enter the cell and induces innate immune responses to clear infections. The molecular mechanisms that link virus-induced physical perturbations to host defense pathways remain unclear. Our studies identified a novel interaction between the antiviral endoribonuclease RNase L and the actin-binding protein Filamin A that enhances host defense by preventing viral entry into naive cells. This role for RNase L is independent of its enzymatic function. Virus infection alters actin dynamics, disrupts the RNase L-Filamin A complex, and releases RNase L to mediate antiviral signaling and effector functions via its established nucleolytic activities. These dual roles for RNase L provide an efficient strategy to protect cells from infection and rapidly respond upon pathogen exposure.

Study of Coxsackie B viruses interactions with Coxsackie Adenovirus receptor and Decay-Accelerating Factor using Human CaCo-2 cell line

Background

Decay Accelerating Factor (DAF) and Coxsackievirus-Adenovirus Receptor (CAR) have been identified as cellular receptors for Coxsackie B viruses (CV-B). The aim of this study is to elucidate the different binding properties of CV-B serotypes and to find out if there are any amino acid changes that could be associated to the different phenotypes.

Twenty clinical CV-B isolates were tested on CaCo-2 cell line using anti-DAF (BRIC216) and anti-CAR (RmcB) antibodies. CV-B3 Nancy prototype strain and a recombinant strain (Rec, CV-B3/B4) were tested in parallel. The P1 genomic region of 12 CV-B isolates from different serotypes was sequenced and the Trans-Epithelial Electrical Resistance (TEER) along with the virus growth cycle was measured.

Results

Infectivity assays revealed clear differences between CV-B isolates with regard to their interactions with DAF and CAR. All tested CV-B isolates showed an absolute requirement for CAR but varied in their binding to DAF. We also reported that for some isolates of CV-B, DAF attachment was not adapted. Genetic analysis of the P1 region detected multiple differences in the deduced amino acid sequences.

Conclusion

Within a given serotype, variations exist in the capacity of virus isolates to bind to specific receptors, and variants with different additional ligands may arise during infection in humans as well as in tissue culture.

Interspecies differences in virus uptake versus cardiac function of the coxsackievirus and adenovirus receptor

The coxsackievirus and adenovirus receptor (CAR) is a cell contact protein with an important role in virus uptake. Its extracellular immunoglobulin domains mediate the binding to coxsackievirus and adenovirus as well as homophilic and heterophilic interactions between cells. The cytoplasmic tail links CAR to the cytoskeleton and intracellular signaling cascades. In the heart, CAR is crucial for embryonic development, electrophysiology, and coxsackievirus B infection. Noncardiac functions are less well understood, in part due to the lack of suitable animal models. Here, we generated a transgenic mouse that rescued the otherwise embryonic-lethal CAR knockout (KO) phenotype by expressing chicken CAR exclusively in the heart. Using this rescue model, we addressed interspecies differences in coxsackievirus uptake and noncardiac functions of CAR. Survival of the noncardiac CAR KO (ncKO) mouse indicates an essential role for CAR in the developing heart but not in other tissues. In adult animals, cardiac activity was normal, suggesting that chicken CAR can replace the physiological functions of mouse CAR in the cardiomyocyte. However, chicken CAR did not mediate virus entry in vivo, so that hearts expressing chicken instead of mouse CAR were protected from infection and myocarditis. Comparison of sequence homology and modeling of the D1 domain indicate differences between mammalian and chicken CAR that relate to the sites important for virus binding but not those involved in homodimerization. Thus, CAR-directed anticoxsackievirus therapy with only minor adverse effects in noncardiac tissue could be further improved by selectively targeting the virus-host interaction while maintaining cardiac function.

IMPORTANCE

Coxsackievirus B3 (CVB3) is one of the most common human pathogens causing myocarditis. Its receptor, the coxsackievirus and adenovirus receptor (CAR), not only mediates virus uptake but also relates to cytoskeletal organization and intracellular signaling. Animals without CAR die prenatally with major cardiac malformations. In the adult heart, CAR is important for virus entry and electrical conduction, but its nonmuscle functions are largely unknown. Here, we show that chicken CAR expression exclusively in the heart can rescue the otherwise embryonic-lethal CAR knockout phenotype but does not support CVB3 infection of adult cardiomyocytes. Our findings have implications for the evolution of virus-host versus physiological interactions involving CAR and could help to improve future coxsackievirus-directed therapies inhibiting virus replication while maintaining CAR's cellular functions.

Complement protective epitopes and CD55-microtubule complexes facilitate the invasion and intracellular persistence of uropathogenic Escherichia coli

BACKGROUND

 Escherichia coli-bearing Dr-adhesins (Dr+ E. coli) cause chronic pyelonephritis in pregnant women and animal models. This chronic renal infection correlates with the capacity of bacteria to invade epithelial cells expressing CD55. The mechanism of infection remains unknown.

METHODS

 CD55 amino acids in the vicinity of binding pocket-Ser155 for Dr-adhesin were mutated to alanine and subjected to temporal gentamicin-invasion/gentamicin-survival assay in Chinese hamster ovary cells. CD55/microtubule (MT) responses were studied using confocal/electron microscopy, and 3-dimensional structure analysis.

RESULTS

 Mutant analysis revealed that complement-protective CD55-Ser165 and CD55-Phe154 epitopes control E. coli invasion by coregulating CD55-MT complex expression. Single-point CD55 mutations changed E. coli to either a minimally invasive (Ser165Ala) or a hypervirulent pathogen (Phe154Ala). Thus, single amino acid modifications with no impact on CD55 structure and bacterial attachment can have a profound impact on E. coli virulence. While CD55-Ser165Ala decreased E. coli invasion and led to dormant intracellular persistence, intracellular E. coli in CD55-Phe154Ala developed elongated forms (multiplying within vacuoles), upregulated CD55-MT complexes, acquired CD55 coat, and escaped phagolysosomal fusion.

CONCLUSIONS

 E. coli target complement-protective CD55 epitopes for invasion and exploit CD55-MT complexes to escape phagolysosomal fusion, leading to a nondestructive parasitism that allows bacteria to persist intracellularly.