Obdulio García-Nicolás

Vector-free transmission and persistence of Japanese encephalitis virus in pigs

Japanese encephalitis virus (JEV), a main cause of severe viral encephalitis in humans, has a complex ecology, composed of a cycle involving primarily waterbirds and mosquitoes, as well as a cycle involving pigs as amplifying hosts. To date, JEV transmission has been exclusively described as being mosquito-mediated. Here we demonstrate that JEV can be transmitted between pigs in the absence of arthropod vectors. Pigs shed virus in oronasal secretions and are highly susceptible to oronasal infection. Clinical symptoms, virus tropism and central nervous system histological lesions are similar in pigs infected through needle, contact or oronasal inoculation. In all cases, a particularly important site of replication are the tonsils, in which JEV is found to persist for at least 25 days despite the presence of high levels of neutralizing antibodies. Our findings could have a major impact on the ecology of JEV in temperate regions with short mosquito seasons.

Virulence and genotype-associated infectivity of interferon-treated macrophages by porcine reproductive and respiratory syndrome viruses.

The polarization into M1 and M2 macrophages (MΦ) is essential to understand MΦ function. Consequently, the aim of this study was to determine the impact of IFN-γ (M1), IL-4 (M2) and IFN-β activation of MΦ on the susceptibility to genotype 1 and 2 porcine reproductive respiratory syndrome (PRRS) virus (PRRSV) strains varying in virulence. To this end, monocyte-derived MΦ were generated by culture during 72h and polarization was induced for another 24h by addition of IFN-γ, IL-4 or IFN-β. MΦ were infected with a collection of PRRSV isolates belonging to genotype 1 and genotype 2. Undifferentiated and M2 MΦ were highly susceptible to all PRRSV isolates. In contrast, M1 and IFN-β activated MΦ were resistant to low pathogenic genotype 1 PRRSV but not or only partially to genotype 2 PRRSV strains. Interestingly, highly virulent PRRSV isolates of both genotypes showed particularly high levels of infection compared with the prototype viruses in both M1 and IFN-β-treated MΦ (P<0.05). This was seen at the level of nucleocapsid expression, viral titres and virus-induced cell death. In conclusion, by using IFN-γ and IFN-β stimulated MΦ it is possible to discriminate between PRRSV varying in genotype and virulence. Genotype 2 PRRSV strains are more efficient at escaping the intrinsic antiviral effects induced by type I and II IFNs. Our in vitro model will help to identify viral genetic elements responsible for virulence, an information important not only to understand PRRS pathogenesis but also for a rational vaccine design. Our results also suggest that monocyte-derived MΦ can be used as a PRRSV infection model instead of alveolar MΦ, avoiding the killing of pigs.

Cytokines transcript levels in lung and lymphoid organs during genotype 1 Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) infection.

Porcine Reproductive and Respiratory Syndrome (PRRS) is one of the most economically important diseases of swine. PRRS virus (PRRSV) infection in the pig is characterized by a weak or absent host innate immune response. The underlying mechanisms of PRRSV pathogenesis are still unclear. The analysis of transcript levels represents an alternative to immunoassays for the detection of cytokines that sometimes are difficult to detect due to their low amounts. This study sets out to determine the differences in pathogenesis and the immune response between lung, tonsil, tracheobronchial lymph node (Tb-LN) and retropharyngeal LN (Rf-LN) of PRRSV 2982 strain infected pigs. PRRSV strain 2982 avoided the onset of an effective innate immune response, especially in PRRSV main target (lung) and reservoir (tonsil) organs. PRRSV lead to an impaired expression of IFN-α and TNF-α gene expression, which finally induced a weak and delayed adaptive immune response through an inefficient IL-12 and IFN-γ expression. Finally, PRRSV replication favored the expression of the anti-inflammatory IL-10 cytokine in infected pigs.

Activation of extrinsic- and Daxx-mediated pathways in lymphoid tissue of PRRSV-infected pigs

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is a major infectious pathogen in pigs leading to huge economical losses worldwide. PRRSV is able to escape from host immunity and causes transient infections. In the present study, expression of different apoptotic markers and its connection with PRRSV were assessed in tonsil and mediastinal lymph node from PRRSV-infected pigs. Cleaved caspase (CCasp)8, CCasp9, Fas, Daxx, CCasp3 and PRRSV expression were analyzed by immunohistochemistry. An up-regulation of CCasp8, Fas and CCasp3 expression in lymphocytes and macrophages from both organs was found during PRRSV infection, indicating the activation of the extrinsic-mediated pathway of apoptosis. Moreover, Daxx expression was also enhanced in macrophages of both organs, suggesting a simultaneous caspase-independent pathway of apoptosis. A correlation between the expression of the different apoptotic markers and IL-10, IL-6 and TGF-β but not with PRRSV antigen was found in our study, which supports the hypothesis of an indirect mechanism in PRRSV-induced apoptosis.

Sensing of Porcine Reproductive and Respiratory Syndrome Virus-Infected Macrophages by Plasmacytoid Dendritic Cells

Porcine reproductive and respiratory syndrome virus (PRRSV) represents a macrophage (MØ)-tropic virus which is unable to induce interferon (IFN) type I in its target cells. Nevertheless, infected pigs show a short but prominent systemic IFN alpha (IFN-α) response. A possible explanation for this discrepancy is the ability of plasmacytoid dendritic cells (pDC) to produce IFN-α in response to free PRRSV virions, independent of infection. Here, we show that the highly pathogenic PRRSV genotype 1 strain Lena is unique in not inducing IFN-α production in pDC, contrasting with systemic IFN-α responses found in infected pigs. We also demonstrate efficient pDC stimulation by PRRSV Lena-infected MØ, resulting in a higher IFN-α production than direct stimulation of pDC by PRRSV virions. This response was strain-independent, required integrin-mediated intercellular contact, intact actin filaments in the MØ and was partially inhibited by an inhibitor of neutral sphingomyelinase. Although infected MØ-derived exosomes stimulated pDC, an efficient delivery of the stimulatory component was dependent on a tight contact between pDC and the infected cells. In conclusion, with this mechanism the immune system can efficiently sense PRRSV, resulting in production of considerable quantities of IFN-α. This is adding complexity to the immunopathogenesis of PRRSV infections, as IFN-α should alert the immune system and initiate the induction of adaptive immune responses, a process known to be inefficient during infection of pigs.

A Lentiviral Vector Expressing Japanese Encephalitis Virus-like Particles Elicits Broad Neutralizing Antibody Response in Pigs.

Background Japanese encephalitis virus (JEV) is the major cause of viral encephalitis in Southeast Asia. Vaccination of domestic pigs has been suggested as a “one health” strategy to reduce viral disease transmission to humans. The efficiency of two lentiviral TRIP/JEV vectors expressing the JEV envelope prM and E glycoproteins at eliciting protective humoral response was assessed in a mouse model and piglets. Methodology/Principal Findings A gene encoding the envelope proteins prM and E from a genotype 3 JEV strain was inserted into a lentiviral TRIP vector. Two lentiviral vectors TRIP/JEV were generated, each expressing the prM signal peptide followed by the prM protein and the E glycoprotein, the latter being expressed either in its native form or lacking its two C-terminal transmembrane domains. In vitro transduction of cells with the TRIP/JEV vector expressing the native prM and E resulted in the efficient secretion of virus-like particles of Japanese encephalitis virus. Immunization of BALB/c mice with TRIP/JEV vectors resulted in the production of IgGs against Japanese encephalitis virus, and the injection of a second dose one month after the prime injection greatly boosted antibody titers. The TRIP/JEV vectors elicited neutralizing antibodies against JEV strains belonging to genotypes 1, 3, and 5. Immunization of piglets with two doses of the lentiviral vector expressing JEV virus-like particles led to high titers of anti-JEV antibodies, that had efficient neutralizing activity regardless of the JEV genotype tested. Conclusions/Significance Immunization of pigs with the lentiviral vector expressing JEV virus-like particles is particularly efficient to prime antigen-specific humoral immunity and trigger neutralizing antibody responses against JEV genotypes 1, 3, and 5. The titers of neutralizing antibodies elicited by the TRIP/JEV vector are sufficient to confer protection in domestic pigs against different genotypes of JEV and this could be of a great utility in endemic regions where more than one genotype is circulating.

Silent infection of human dendritic cells by African and Asian strains of Zika virus

While Zika virus (ZIKV) circulated for decades (African lineage strains) without report of outbreaks and severe complications, its emergence in French Polynesia and subsequently in the Americas (Asian lineage strains) was associated with description of severe neurological defects in newborns/neonates and adults. With the aim to identify virus lineage-dependent factors, we compared cell susceptibility, virus replication, cell death and innate immune responses following infection with two African and three contemporary Asian lineage strains of ZIKV. To this end, we used green monkey Vero and Aedes albopictus C6/36 cells and human monocyte-derived dendritic cells (DCs). The latter are involved in the pathogenesis of several mosquito-borne Flavivirus infections. In Vero and C6/36 cells, we observed strain- but not lineage-dependent differences in infection profiles. Nevertheless, in human DCs, no significant differences in susceptibility and virus replication were found between lineages and strains. ZIKV induced antiviral interferon type I/III in a limited fashion, with the exception of one African strain. None of the strains induced cell death or DC maturation in terms of MHC II, CD40, CD80/86 or CCR7 expression. Taken together, our data suggest that a large collection of virus isolates needs to be investigated before conclusions on lineage differences can be made.

A Japanese Encephalitis Virus Vaccine Inducing Antibodies Strongly Enhancing In Vitro Infection Is Protective in Pigs

The Japanese encephalitis virus (JEV) is responsible for zoonotic severe viral encephalitis transmitted by Culex mosquitoes. Although birds are reservoirs, pigs play a role as amplifying hosts, and are affected in particular through reproductive failure. Here, we show that a lentiviral JEV vector, expressing JEV prM and E proteins (TRIP/JEV.prME), but not JEV infection induces strong antibody-dependent enhancement (ADE) activities for infection of macrophages. Such antibodies strongly promoted infection via Fc receptors. ADE was found at both neutralizing and non-neutralizing serum dilutions. Nevertheless, in vivo JEV challenge of pigs demonstrated comparable protection induced by the TRIP/JEV.prME vaccine or heterologous JEV infection. Thus, either ADE antibodies cause no harm in the presence of neutralizing antibodies or may even have protective effects in vivo in pigs. Additionally, we found that both pre-infected and vaccinated pigs were not fully protected as low levels of viral RNA were found in lymphoid and nervous system tissue in some animals. Strikingly, the virus from the pre-infection persisted in the tonsils throughout the experiment. Finally, despite the vaccination challenge, viral RNA was detected in the oronasal swabs in all vaccinated pigs. These latter data are relevant when JEV vaccination is employed in pigs.

System immunology-based identification of blood transcriptional modules correlating to antibody responses in sheep

Lacking immunogenicity, inactivated vaccines require potent adjuvants. To understand their effects, we used a system immunology-based analysis of ovine blood transcriptional modules (BTMs) to dissect innate immune responses relating to either antibody or haptoglobin levels. Using inactivated foot-and-mouth disease virus as an antigen, we compared non-adjuvanted to liposomal-formulated vaccines complemented or not with TLR4 and TLR7 ligands. Early after vaccination, BTM relating to myeloid cells, innate immune responses, dendritic cells, and antigen presentation correlated positively, whereas BTM relating to T and natural killer cells, as well as cell cycle correlated negatively with antibody responses. Interestingly, BTM relating to myeloid cells, inflammation and antigen presentation also correlated with haptoglobin, but in a reversed manner, indicating that acute systemic inflammation is not beneficial for early antibody responses. Analysis of vaccine-dependent BTM modulation showed that liposomal formulations induced similar responses to those correlating to antibody levels, while addition of TLR ligands reduced myeloid cells, inflammation and antigen presentation BTM expression despite promoting antibody responses. Furthermore, this vaccine was more potent at downregulating T and natural killer cell BTM. When pre-vaccination BTM were analyzed, we found that high vaccine responders expressed higher levels of cell cycle and myeloid cell BTMs as compared with low responders. In conclusion, we have transferred human BTM to sheep and identified early vaccine-induced responses associated with antibody levels or unwanted inflammation. Such readouts are applicable to other veterinary species and very useful to identify efficient vaccine adjuvants, their mechanism of action, and factors related to low responders.Gene expression: developing a platform to identify vaccine effectsA next-generation method to identify genetic changes in response to vaccination opens up the detailed study of vaccine and adjuvant effects. Researchers led by the Swiss University of Bern’s Artur Summerfield inoculated sheep with foot-and-mouth disease (FMD) virus antigens, either alone, adjuvanted (in an immunity-boosting formulation), or adjuvanted with molecules speculated to help generate long-term immunity against FMD. The team found only the latter group stimulated host immunity to a level considered protective, albeit with high variability. Differences in gene expression were identified that correlated to virus-neutralizing responses. The team used a powerful bioinformatics tool, measuring ‘blood transcriptional modules (BTM),’ to identify ovine specific immune processes. The BTM approach offers an advantageous way to identify vaccine and adjuvant effects down to the genetic level. This study also offers data to inform future FMD vaccine development efforts.