Glycoprotein L sets the neutralization profile of murid herpesvirus 4

Antibodies readily neutralize acute, epidemic viruses, but are less effective against more indolent pathogens such as herpesviruses. Murid herpesvirus 4 (MuHV-4) provides an accessible model for tracking the fate of antibody-exposed gammaherpesvirus virions. Glycoprotein L (gL) plays a central role in MuHV-4 entry: it allows gH to bind heparan sulfate and regulates fusion-associated conformation changes in gH and gB. However, gL is non-essential: heparan sulfate binding can also occur via gp70, and the gB–gH complex alone seems to be sufficient for membrane fusion. Here, we investigated how gL affects the susceptibility of MuHV-4 to neutralization. Immune sera neutralized gL− virions more readily than gL+ virions, chiefly because heparan sulfate binding now depended on gp70 and was therefore easier to block. However, there were also post-binding effects. First, the downstream, gL-independent conformation of gH became a neutralization target; gL normally prevents this by holding gH in an antigenically distinct heterodimer until after endocytosis. Second, gL− virions were more vulnerable to gB-directed neutralization. This covered multiple epitopes and thus seemed to reflect a general opening up of the gH–gB entry complex, which gL again normally restricts to late endosomes. gL therefore limits MuHV-4 neutralization by providing redundancy in cell binding and by keeping key elements of the virion fusion machinery hidden until after endocytosis

Le Quesnoy – Chemin du Vivier à Prêtres

Une opération de diagnostic a été prescrite au nord-ouest du noyau urbain historique du Quesnoy, longeant le Chemin du Vivier à Prêtres (ZAE des Prés du Roy), sur une superficie de 199 481 m2. L’emprise correspond à des parcelles agricoles destinées à l’accueil d’un vaste établissement industriel (usine d’embouteillage). Cinquante et une tranchées et vingt-deux sondages profonds (SP) ont été réalisés sur l’emprise. Ils répondent principalement à deux objectifs : explorer le potentiel archéolo..

In vivo importance of heparan sulfate-binding glycoproteins for murid herpesvirus-4 infection

Many herpesviruses bind to heparan sulfate (HS). Murid herpesvirus-4 (MuHV-4) does so via its envelope glycoproteins gp70 and gH/gL. MuHV-4 gp150 further regulates an HS-independent interaction to make that HS-dependent too. Cell binding by MuHV-4 virions is consequently strongly HS-dependent. Gp70 and gH/gL show some in vitro redundancy: an antibody-mediated blockade of HS binding by one is well tolerated, whereas a blockade of both severely impairs infection. In order to understand the importance of HS binding for MuHV-4 in vivo, we generated mutants lacking both gL and gp70. As expected, gL−gp70− MuHV-4 showed very poor cell binding. It infected mice at high dose but not at low dose, indicating defective host entry. But once entry occurred, host colonization, which for MuHV-4 is relatively independent of the infection dose, was remarkably normal. The gL−gp70− entry deficit was much greater than that of gL− or gp70− single knockouts. And gp150 disruption, which allows HS-independent cell binding, largely rescued the gL−gp70− cell binding and host entry deficits. Thus, it appeared that MuHV-4 HS binding is important in vivo, principally for efficient host entry

Sequencing of bovine herpesvirus 4 v.test strain reveals important genome features

Background Bovine herpesvirus 4 (BoHV-4) is a useful model for the human pathogenic gammaherpesviruses Epstein-Barr virus and Kaposi's Sarcoma-associated Herpesvirus. Although genome manipulations of this virus have been greatly facilitated by the cloning of the BoHV-4 V.test strain as a Bacterial Artificial Chromosome (BAC), the lack of a complete genome sequence for this strain limits its experimental use. Methods In this study, we have determined the complete sequence of BoHV-4 V.test strain by a pyrosequencing approach. Results The long unique coding region (LUR) consists of 108,241 bp encoding at least 79 open reading frames and is flanked by several polyrepetitive DNA units (prDNA). As previously suggested, we showed that the prDNA unit located at the left prDNA-LUR junction (prDNA-G) differs from the other prDNA units (prDNA-inner). Namely, the prDNA-G unit lacks the conserved pac-2 cleavage and packaging signal in its right terminal region. Based on the mechanisms of cleavage and packaging of herpesvirus genomes, this feature implies that only genomes bearing left and right end prDNA units are encapsulated into virions. Conclusions In this study, we have determined the complete genome sequence of the BAC-cloned BoHV-4 V.test strain and identified genome organization features that could be important in other herpesviruses

Glycoprotein B switches conformation during murid herpesvirus 4 entry

Herpesviruses are ancient pathogens that infect all vertebrates. The most conserved component of their entry machinery is glycoprotein B (gB), yet how gB functions is unclear. A striking feature of the murid herpesvirus 4 (MuHV-4) gB is its resistance to neutralization. Here, we show by direct visualization of infected cells that the MuHV-4 gB changes its conformation between extracellular virions and those in late endosomes, where capsids are released. Specifically, epitopes on its N-terminal cell-binding domain become inaccessible, whilst non-N-terminal epitopes are revealed, consistent with structural changes reported for the vesicular stomatitis virus glycoprotein G. Inhibitors of endosomal acidification blocked the gB conformation switch. They also blocked capsid release and the establishment of infection, implying that the gB switch is a key step in entry. Neutralizing antibodies could only partially inhibit the switch. Their need to engage a less vulnerable, upstream form of gB, because its fusion form is revealed only in endosomes, helps to explain why gB-directed MuHV-4 neutralization is so difficult

Viral glycoprotein gp150 promotes sexual transmission of Murid Herpesvirus-4

Gammaherpesviruses are important pathogens in human and veterinary medicine. During co-evolution with their hosts, they developed many strategies allowing them to shed infectious particles in presence of immune response. Understanding these strategies is likely to be important to control infection. Interestingly, we recently observed that Murid herpesvirus 4 (MuHV-4), a gammaherpesvirus infecting laboratory mice, could be sexually transmitted between mice. This model offers therefore the opportunity to understand the mechanisms underlying natural transmission. Some of these mechanisms could rely on the glycoprotein 150 (gp150), which could limit virus neutralization and promote the release of infectious particles from cells. In this study, we tested therefore the importance of gp150 in the context of MuHV-4 sexual transmission. Briefly, female mice were infected with WT or gp150- strains expressing luciferase. They were imaged with an in vivo imaging system to follow infection. When lytic replication was observed in the genital tract, infected females were mated with naïve males to compare the capacity of transmission of the two strains. Our results show that, while the gp150- strain has no deficit in reaching and replicating in the female genital tract, it displays a major deficit of sexual transmission in comparison with WT virions. Interestingly, this deficit appears to reflect a deficit of virions release from vaginal epithelial cells. Altogether, our results show that, while gp150 is not required for efficient dissemination and maintenance of MuHV-4 within its host, it is essential for efficient transmission, by promoting the releasing of infectious particles from the mucosal cells

Murid herpesvirus 4 infection protects mice from the development of an anti-pneumovirus vaccine-induced TH2 immunopathology

Gammaherpesvirus imprintin

Shaping of the alveolar landscape by respiratory infections and long-term consequences for lung immunity

Respiratory infections and especially viral infections, along with other extrinsic environmental factors, have been shown to profoundly affect macrophage populations in the lung. In particular, alveolar macrophages (AMs) are important sentinels during respiratory infections and their disappearance opens a niche for recruited monocytes (MOs) to differentiate into resident macrophages. Although this topic is still the focus of intense debate, the phenotype and function of AMs that recolonize the niche after an inflammatory insult, such as an infection, appear to be dictated in part by their origin, but also by local and/or systemic changes that may be imprinted at the epigenetic level. Phenotypic alterations following respiratory infections have the potential to shape lung immunity for the long-term, leading to beneficial responses such as protection against allergic airway inflammation or against other infections, but also to detrimental responses when associated with the development of immunopathologies. This review reports the persistence of virus-induced functional alterations in lung macrophages, and discusses the importance of this imprinting in explaining inter-individual and lifetime immune variation

Anchoring tick salivary anti-complement proteins IRAC I and IRAC II to membrane increases their immunogenicity

Tick salivary proteins are promising targets for the development of anti-tick vaccines. Recently, we described two paralogous anti-complement proteins, called Ixodes ricinus anti-complement (IRAC) proteins I and II, that are co-expressed in tick I. ricinus salivary glands. However, our previous attempts to immunize rabbits against IRAC via infection with recombinant Bovine herpesvirus 4 (BoHV-4) vectors invariably failed although both recombinants expressed high levels of functional IRAC proteins in vitro. As IRAC are soluble monovalent antigens, one of the possible explanations is that monovalent ligation of the B-cell receptor induces receptor activation but fails to promote antigen presentation, a phenomenon that is thought to induce a state of B-cell tolerance. In the present study, we tried to increase IRAC immunogenicity by expressing them as oligovalent antigens. To this end, IRAC were fused to membrane anchors and BoHV-4 vectors expressing these recombinant forms were produced. The immunization potentials of recombinant viruses expressing either secreted or transmembrane IRAC proteins were then compared. While the former did not induce a detectable immune response against IRAC, the latter led to high titres of anti-IRAC antibodies that only marginally affected tick blood feeding. All together, the data presented in this study demonstrate that the immunogenicity of a soluble antigen can be greatly improved by anchoring it in membrane