Alain Vanderplasschen

Vaccinia virus immune evasion

Vaccinia virus and other poxviruses express a wide variety of proteins which are nonessential for virus replication in culture but help the virus to evade the host response to infection. Examples include proteins which oppose apoptosis. Synthesise steroids, capture chemokines, counteract complement, interfere with interferon and intercept interleukins. This review provides an overview of such proteins, with an emphasis on work from our laboratory, and illustrates how the study of these proteins can increase our understanding of virus pathogenesis, the function of the immune system and how to make safer and more immunogenic poxvirus‐based vaccines.

Lung interstitial macrophages alter dendritic cell functions to prevent airway allergy in mice

The respiratory tract is continuously exposed to both innocuous airborne antigens and immunostimulatory molecules of microbial origin, such as LPS. At low concentrations, airborne LPS can induce a lung DC-driven Th2 cell response to harmless inhaled antigens, thereby promoting allergic asthma. However, only a small fraction of people exposed to environmental LPS develop allergic asthma. What prevents most people from mounting a lung DC-driven Th2 response upon exposure to LPS is not understood. Here we have shown that lung interstitial macrophages (IMs), a cell population with no previously described in vivo function, prevent induction of a Th2 response in mice challenged with LPS and an experimental harmless airborne antigen. IMs, but not alveolar macrophages, were found to produce high levels of IL-10 and to inhibit LPS-induced maturation and migration of DCs loaded with the experimental harmless airborne antigen in an IL-10-dependent manner. We further demonstrated that specific in vivo elimination of IMs led to overt asthmatic reactions to innocuous airborne antigens inhaled with low doses of LPS. This study has revealed a crucial role for IMs in maintaining immune homeostasis in the respiratory tract and provides an explanation for the paradox that although airborne LPS has the ability to promote the induction of Th2 responses by lung DCs, it does not provoke airway allergy under normal conditions.

Intracellular and extracellular vaccinia virions enter cells by different mechanisms

Vaccinia virus (VV) produces two antigenically distinct infectious virions, intracellular mature virus (IMV) and extracellular enveloped virus (EEV). Structurally, EEV consists of an IMV with an additional outer membrane containing proteins that are absent from IMV. EEV is important for virus dissemination both in vitro and in vivo. Studies of EEV entry have been hampered by having two infectious virions and by the rupture of the EEV outer membrane in the majority of EEV virions during their purification. To overcome these problems, we have developed a novel approach to study VV entry that is based on confocal microscopy and does not require EEV purification. This assay relies on immunofluorescent staining and detection of individual, intracellular, uncoated virus cores. By this method, we show that EEV entry, in contrast to IMV, is dependent on a low-pH pathway and that the IMV enwrapped inside the EEV exhibits a low-pH fusogenic activity. Together with neutralization data demonstrating that exposure to low pH disrupts the EEV outer membrane, this study strongly supports a model for EEV entry which consists of binding, endocytosis, low-pH-induced disruption of the EEV outer membrane and fusion of the exposed IMV with the endosomal membrane releasing the core into the cytosol. The roles of the EEV outer membrane in virus dissemination and virus entry are discussed in relation to this model.

Mechanisms of Persistent Nf-Kappa B Activity in the Bronchi of an Animal Model of Asthma

In most cells trans-activating NF-κB induces many inflammatory proteins as well as its own inhibitor, IκB-α, thus assuring a transient response upon stimulation. However, NF-κB-dependent inflammatory gene expression is persistent in asthmatic bronchi, even after allergen eviction. In the present report we used bronchial brushing samples (BBSs) from heaves-affected horses (a spontaneous model of asthma) to elucidate the mechanisms by which NF-κB activity is maintained in asthmatic airways. NF-κB activity was high in granulocytic and nongranulocytic BBS cells. However, NF-κB activity highly correlated to granulocyte percentage and was only abrogated after granulocytic death in cultured BBSs. Before granulocytic death, NF-κB activity was suppressed by simultaneous addition of neutralizing anti-IL-1β and anti-TNF-α Abs to the medium of cultured BBSs. Surprisingly, IκB-β, whose expression is not regulated by NF-κB, unlike IκB-α, was the most prominent NF-κB inhibitor found in BBSs. The amounts of IκB-β were low in BBSs obtained from diseased horses, but drastically increased after addition of the neutralizing anti-IL-1β and anti-TNF-α Abs. These results indicate that sustained NF-κB activation in asthmatic bronchi is driven by granulocytes and is mediated by IL-1β and TNF-α. Moreover, an imbalance between high levels of IL-1β- and TNF-α-mediated IκB-β degradation and low levels of IκB-β synthesis is likely to be the mechanism preventing NF-κB deactivation in asthmatic airways before granulocytic death.

Targeting nanoparticles to M cells with non-peptidic ligands for oral vaccination

The presence of RGD on nanoparticles allows the targeting of beta1 integrins at the apical surface of human M cells and the enhancement of an immune response after oral immunization. To check the hypothesis that non-peptidic ligands targeting intestinal M cells or APCs would be more efficient for oral immunization than RGD, novel non-peptidic and peptidic analogs (RGD peptidomimitic (RGDp), LDV derivative (LDVd) and LDV peptidomimetic (LDVp)) as well as mannose were grafted on the PEG chain of PCL-PEG and incorporated in PLGA-based nanoparticles. RGD and RGDp significantly increased the transport of nanoparticles across an in vitro model of human M cells as compared to enterocytes. RGD, LDVp, LDVd and mannose enhanced nanoparticle uptake by macrophages in vitro. The intraduodenal immunization with RGDp-, LDVd- or mannose-labeled nanoparticles elicited a higher production of IgG antibodies than the intramuscular injection of free ovalbumin or intraduodenal administration of either non-targeted or RGD-nanoparticles. Targeted formulations were also able to induce a cellular immune response. In conclusion, the in vitro transport of nanoparticles, uptake by macrophages and the immune response were positively influenced by the presence of ligands at the surface of nanoparticles. These targeted-nanoparticles could thus represent a promising delivery system for oral immunization.

Glycoprotein G isoforms from some alphaherpesviruses function as broad-spectrum chemokine binding proteins

Mimicry of host chemokines and chemokine receptors to modulate chemokine activity is a strategy encoded by beta‐ and gammaherpesviruses, but very limited information is available on the anti‐chemokine strategies encoded by alphaherpesviruses. The secretion of chemokine binding proteins (vCKBPs) has hitherto been considered a unique strategy encoded by poxviruses and gammaherpesviruses. We describe a family of novel vCKBPs in equine herpesvirus 1, bovine herpesvirus 1 and 5, and related alphaherpesviruses with no sequence similarity to chemokine receptors or other vCKBPs. We show that glycoprotein G (gG) is secreted from infected cells, binds a broad range of chemokines with high affinity and blocks chemokine activity by preventing their interaction with specific receptors. Moreover, gG also blocks chemokine binding to glycosaminoglycans, an interaction required for the correct presentation and function of chemokines in vivo. In contrast to other vCKBPs, gG may also be membrane anchored and, consistently, we show chemokine binding activity at the surface of cells expressing full‐length protein. These alphaherpesvirus vCKBPs represent a novel family of proteins that bind chemokines both at the membrane and in solution.

The Major Portal of Entry of Koi Herpesvirus in Cyprinus carpio Is the Skin

ABSTRACT Koi herpesvirus (KHV), recently designated Cyprinid herpesvirus 3, is the causative agent of a lethal disease in koi and common carp. In the present study, we investigated the portal of entry of KHV in carp by using bioluminescence imaging. Taking advantage of the recent cloning of the KHV genome as a bacterial artificial chromosome (BAC), we produced a recombinant plasmid encoding a firefly luciferase (LUC) expression cassette inserted in the intergenic region between open reading frame (ORF) 136 and ORF 137. Two viral strains were then reconstituted from the modified plasmid, the FL BAC 136 LUC excised strain and the FL BAC 136 LUC TK revertant strain, including a disrupted and a wild-type thymidine kinase (TK) locus, respectively. In vitro, the two recombinant strains replicated comparably to the parental FL strain. The FL BAC 136 LUC TK revertant strain was shown in vitro to induce a bioluminescent signal allowing the detection of single positive cells as early as 24 h postinfection, while in vivo, it induced KHV infection in carp that was indistinguishable from that induced by the parental FL strain. To identify the KHV portal of entry, carp were analyzed by bioluminescence imaging at different times postinfection with the FL BAC 136 LUC TK revertant strain. These analyses demonstrated that the skin of the fish covering the fins and also the body is the major portal of entry for KHV in carp. Finally, to further demonstrate the role of the skin as the KHV portal of entry, we constructed an original system, nicknamed “U-tube,” to perform percutaneous infection restricted to the posterior part of the fish. All the data obtained in the present study demonstrate that the skin, and not the gills, is the major portal of entry for KHV in carp.

Antibodies against vaccinia virus do not neutralize extracellular enveloped virus but prevent virus release from infected cells and comet formation

Vaccinia virus (VV) produces two antigenically and structurally distinct infectious virions, intracellular mature virus (IMV) and extracellular enveloped virus (EEV). EEV is important for the efficient dissemination of virus both in vivo and in vitro where it causes formation of comet-shaped virus plaques. Here, we show that EEV, in contrast to IMV, is resistant to neutralization by antibodies bound to its surface. However, antibodies against EEV can prevent comet formation in cell culture. To explain this apparent paradox, we investigated the mechanism by which antibodies inhibit comet formation and demonstrated that antibodies prevent EEV release from infected cells, and consequently comet formation, by agglutination of the virus on the cell surface. Two complementary observations allow this conclusion: first, electron microscopy showed that infected cells incubated with medium containing anti-vaccinia virus antibodies have virus aggregates on their surface; second, culture medium from these cells contained a 4 log10 fold reduction in the physical particle/ml titre in comparison with control culture. A mechanism by which antibodies to EEV proteins provide immunological protection is thus restriction of EEV release rather than neutralization of free EEV particles.

Novel norovirus recombinants and GII.4 sub-lineages associated with outbreaks between 2006 and 2010 in Belgium

BackgroundNoroviruses (NoVs) are an important cause of acute gastroenteritis in humans worldwide. To gain insight into the epidemiologic patterns of NoV outbreaks and to determine the genetic variation of NoVs strains circulating in Belgium, stool samples originating from patients infected with NoVs in foodborne outbreak investigations were analysed between December 2006 and December 2010.ResultsNoVs were found responsible of 11.8% of all suspected foodborne outbreaks reported in the last 4 years and the number of NoV outbreaks reported increased along the years representing more than 30% of all foodborne outbreaks in 2010. Genogroup II outbreaks largely predominated and represented more than 90% of all outbreaks. Phylogenetic analyses were performed with 63 NoV-positive samples for the partial polymerase (N = 45) and/or capsid gene (N = 35) sequences. For 12 samples, sequences covering the ORF1-ORF2 junction were obtained. A variety of genotypes was found among genogroups I and II; GII.4 was predominant followed in order of importance by GII.2, GII.7, GII.13, GI.4 and GI.7. In the study period, GII.4 NoVs variants 2006a, 2006b, 2007, 2008 and 2010 were identified. Moreover, phylogenetic analyses identified different recombinant NoV strains that were further characterised as intergenotype (GII.e/GII.4 2007, GII.e/GII.3 and GII.g/GII.1) and intersub-genotype (GII.4 2006b/GII.4 2007 and GII.4 2010/GII.4 2010b) recombinants.ConclusionsNoVs circulating in the last 4 years in Belgium showed remarkable genetic diversity either by small-scale mutations or genetic recombination. In this period, GII.4 2006b was successfully displaced by the GII.4 2010 subtype, and previously reported epidemic GII.b recombinants seemed to have been superseded by GII.e recombinants in 2009 and GII.g recombinants in 2010. This study showed that the emergence of novel GII.4 variants together with novel GII recombinants could lead to an explosion in NoV outbreaks, likewise to what was observed in 2008 and 2010. Among recombinants detected in this study, two hitherto unreported strains GII.e/GII.3 and GII.g/GII.1 were characterised. Surveillance will remain important to monitor contemporaneously circulating strains in order to adapt preventive and curative strategies.

Ixodes ticks belonging to the Ixodes ricinus complex encode a family of anticomplement proteins.

The alternative pathway of complement is an important innate defence against pathogens including ticks. This component of the immune system has selected for pathogens that have evolved countermeasures. Recently, a salivary protein able to inhibit the alternative pathway was cloned from the American tick Ixodes scapularis (Valenzuela et al., 2000; J. Biol. Chem. 275, 18717–18723). Here, we isolated two different sequences, similar to Isac, from the transcriptome of I. ricinus salivary glands. Expression of these sequences revealed that they both encode secreted proteins able to inhibit the complement alternative pathway. These proteins, called I. ricinus anticomplement (IRAC) protein I and II, are coexpressed constitutively in I. ricinus salivary glands and are upregulated during blood feeding. Also, we demonstrated that they are the products of different genes and not of alleles of the same locus. Finally, phylogenetic analyses demonstrate that ticks belonging to the Ixodes ricinus complex encode a family of relatively small anticomplement molecules undergoing diversification by positive Darwinian selection.