Animal models for COVID-19.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the aetiological agent of coronavirus disease 2019 (COVID-19), an emerging respiratory infection caused by the introduction of a novel coronavirus into humans late in 2019 (first detected in Hubei province, China). As of 18 September 2020, SARS-CoV-2 has spread to 215 countries, has infected more than 30 million people and has caused more than 950,000 deaths. As humans do not have pre-existing immunity to SARS-CoV-2, there is an urgent need to develop therapeutic agents and vaccines to mitigate the current pandemic and to prevent the re-emergence of COVID-19. In February 2020, the World Health Organization (WHO) assembled an international panel to develop animal models for COVID-19 to accelerate the testing of vaccines and therapeutic agents. Here we summarize the findings to date and provides relevant information for preclinical testing of vaccine candidates and therapeutic agents for COVID-19.

Differential susceptibility of human motor neurons to infection with Usutu and West Nile virus.

West Nile virus (WNV) and Usutu virus (USUV) are closely related flaviviruses with differing capacities to cause neurological disease in humans. WNV is thought to use a transneural route of neuroinvasion along motor neurons and causes severe motor deficits. The potential for use of transneural routes of neuroinvasion by USUV has not been investigated experimentally, and evidence from the few clinical case reports of USUV-associated neuroinvasive disease is lacking. We hypothesised that, compared with WNV, USUV is less able to infect motor neurons, and therefore determined the susceptibility of human induced pluripotent stem cell (iPSC)-derived spinal cord motor neurons to infection. Both viruses could grow to high titres in iPSC-derived neural cultures. However, USUV could not productively infect motor neurons due to restriction by the antiviral response, which was not induced upon WNV infection. Inhibition of the antiviral response allowed for widespread infection and transportation of USUV along motor neurons within a compartmented culture system. These results show a stark difference in the ability of these two viruses to evade initiation of intrinsic antiviral immunity. Our data suggests that USUV cannot infect motor neurons in healthy individuals but in case of immunodeficiency may pose a risk for motor-related neurological disease and transneural invasion.

West Nile virus, but not Usutu virus, can productively infect human motor neurons as a possible route of neuroinvasion.

Transcriptomic Profiling Reveals Intense Host-Pathogen Dispute Compromising Homeostasis during Acute Rift Valley Fever Virus Infection.

Rift Valley fever virus (RVFV) (family Phenuiviridae) can cause severe disease, and outbreaks of this mosquito-borne pathogen pose a significant threat to public and animal health. Yet many molecular aspects of RVFV pathogenesis remain incompletely understood. Natural RVFV infections are acute, characterized by a rapid onset of peak viremia during the first days post-infection, followed by a rapid decline. Although in vitro studies identified a major role of interferon (IFN) responses in counteracting the infection, a comprehensive overview of the specific host factors that play a role in RVFV pathogenesis in vivo is still lacking. Here, the host in vivo transcriptional profiles in the liver and spleen tissues of lambs exposed to RVFV are studied using RNA sequencing (RNA-seq) technology. We validate that IFN-mediated pathways are robustly activated in response to infection. We also link the observed hepatocellular necrosis with severely compromised organ function, which is reflected as a marked downregulation of multiple metabolic enzymes essential for homeostasis. Furthermore, we associate the elevated basal expression of LRP1 in the liver with RVFV tissue tropism. Collectively, the results of this study deepen the knowledge of the in vivo host response during RVFV infection and reveal new insights into the gene regulation networks underlying pathogenesis in a natural host. IMPORTANCE Rift Valley fever virus (RVFV) is a mosquito-transmitted pathogen capable of causing severe disease in animals and humans. Outbreaks of RVFV pose a significant threat to public health and can result in substantial economic losses. Little is known about the molecular basis of RVFV pathogenesis in vivo, particularly in its natural hosts. We employed RNA-seq technology to investigate genome-wide host responses in the liver and spleen of lambs during acute RVFV infection. We show that RVFV infection drastically decreases the expression of metabolic enzymes, which impairs normal liver function. Moreover, we highlight that basal expression levels of the host factor LRP1 may be a determinant of RVFV tissue tropism. This study links the typical pathological phenotype induced by RVFV infection with tissue-specific gene expression profiles, thereby improving our understanding of RVFV pathogenesis.

Distinct spatial arrangements of ACE2 and TMPRSS2 expression in Syrian hamster lung lobes dictates SARS-CoV-2 infection patterns.

SARS-CoV-2 attaches to angiotensin-converting enzyme 2 (ACE2) to gain entry into cells after which the spike protein is cleaved by the transmembrane serine protease 2 (TMPRSS2) to facilitate viral-host membrane fusion. ACE2 and TMPRSS2 expression profiles have been analyzed at the genomic, transcriptomic, and single-cell RNAseq levels. However, transcriptomic data and actual protein validation convey conflicting information regarding the distribution of the biologically relevant protein receptor in whole tissues. To describe the organ-level architecture of receptor expression, related to the ability of ACE2 and TMPRSS2 to mediate infectivity, we performed a volumetric analysis of whole Syrian hamster lung lobes. Lung tissue of infected and control animals was stained using antibodies against ACE2 and TMPRSS2, combined with SARS-CoV-2 nucleoprotein staining. This was followed by light-sheet microscopy imaging to visualize their expression and related infection patterns. The data demonstrate that infection is restricted to sites containing both ACE2 and TMPRSS2, the latter is expressed in the primary and secondary bronchi whereas ACE2 is predominantly observed in the bronchioles and alveoli. Conversely, infection completely overlaps where ACE2 and TMPRSS2 co-localize in the tertiary bronchi, bronchioles, and alveoli.

Zika virus alters osteogenic lineage progression of human mesenchymal stromal cells.

Arboviruses target bone forming osteoblasts and perturb bone remodeling via paracrine factors. We previously reported that Zika virus (ZIKV) infection of early-stage human mesenchymal stromal cells (MSCs) inhibited the osteogenic lineage commitment of MSCs. To understand the physiological interplay between bone development and ZIKV pathogenesis, we employed a primary in vitro model to examine the biological responses of MSCs to ZIKV infection at different stages of osteogenesis. Precommitted MSCs were infected at the late stage of osteogenic stimulation (Day 7) with ZIKV (multiplicity of infection of 5). We observe that MSCs infected at the late stage of differentiation are highly susceptible to ZIKV infection similar to previous observations with early stage infected MSCs (Day 0). However, in contrast to ZIKV infection at the early stage of differentiation, infection at a later stage significantly elevates the key osteogenic markers and calcium content. Comparative RNA sequencing (RNA-seq) of early and late stage infected MSCs reveals that ZIKV infection alters the mRNA transcriptome during osteogenic induction of MSCs (1251 genes). ZIKV infection provokes a robust antiviral response at both stages of osteogenic differentiation as reflected by the upregulation of interferon responsive genes (n > 140). ZIKV infection enhances the expression of immune-related genes in early stage MSCs while increasing cell cycle genes in late stage MSCs. Remarkably, ZIKA infection in early stage MSCs also activates lipid metabolism-related pathways. In conclusion, ZIKV infection has differentiation stage-dependent effects on MSCs and this mechanistic understanding may permit the development of new therapeutic or preventative measures for bone-related effects of ZIKV infection.

Multimerization- and glycosylation-dependent receptor binding of SARS-CoV-2 spike proteins.

Receptor binding studies on sarbecoviruses would benefit from an available toolkit of recombinant spike proteins, or domains thereof, that recapitulate receptor binding properties of native viruses. We hypothesized that trimeric Receptor Binding Domain (RBD) proteins would be suitable candidates to study receptor binding properties of SARS-CoV-1 and -2. Here we created monomeric and trimeric fluorescent RBD proteins, derived from adherent HEK293T, as well as in GnTI-/- mutant cells, to analyze the effect of complex vs high mannose glycosylation on receptor binding. The results demonstrate that trimeric, complex glycosylated proteins are superior in receptor binding compared to monomeric and immaturely glycosylated variants. Although differences in binding to commonly used cell lines were minimal between the different RBD preparations, substantial differences were observed when respiratory tissues of experimental animals were stained. The RBD trimers demonstrated distinct ACE2 expression profiles in bronchiolar ducts and confirmed the higher binding affinity of SARS-CoV-2 over SARS-CoV-1. Our results show that complex glycosylated trimeric RBD proteins are attractive to analyze sarbecovirus receptor binding and explore ACE2 expression profiles in tissues.

SARS-CoV-2 Neutralizing Human Antibodies Protect Against Lower Respiratory Tract Disease in a Hamster Model.

Effective clinical intervention strategies for coronavirus disease 2019 (COVID-19) are urgently needed. Although several clinical trials have evaluated use of convalescent plasma containing virus-neutralizing antibodies, levels of neutralizing antibodies are usually not assessed and the effectiveness has not been proven. We show that hamsters treated prophylactically with a 1:2560 titer of human convalescent plasma or a 1:5260 titer of monoclonal antibody were protected against weight loss, had a significant reduction of virus replication in the lungs, and showed reduced pneumonia. Interestingly, this protective effect was lost with a titer of 1:320 of convalescent plasma. These data highlight the importance of screening plasma donors for high levels of neutralizing antibodies. Our data show that prophylactic administration of high levels of neutralizing antibody, either monoclonal or from convalescent plasma, prevent severe SARS-CoV-2 pneumonia in a hamster model, and could be used as an alternative or complementary to other antiviral treatments for COVID-19.

The possible role of cross-reactive dengue virus antibodies in Zika virus pathogenesis.

Zika virus (ZIKV) has been known for decades to circulate in Africa and Asia. However, major complications of a ZIKV infection have recently become apparent for reasons that are still not fully elucidated. One of the hypotheses for the seemingly increased pathogenicity of ZIKV is that cross-reactive dengue antibodies can enhance a ZIKV infection through the principle of antibody-dependent enhancement (ADE). Recently, ADE in ZIKV infection has been studied, but conclusive evidence for the clinical importance of this principle in a ZIKV infection is lacking. Conversely, the widespread circulation of ZIKV in dengue virus (DENV)-endemic regions raises new questions about the potential contribution of ZIKV antibodies to DENV ADE. In this review, we summarize the results of the evidence to date and elaborate on other possible detrimental effects of cross-reactive flavivirus antibodies, both for ZIKV infection and the risk of ZIKV-related congenital anomalies, DENV infection, and dengue hemorrhagic fever.

Performance of Zika Assays in the Context of Toxoplasma gondii, Parvovirus B19, Rubella Virus, and Cytomegalovirus (TORCH) Diagnostic Assays.

Infections during pregnancy that may cause congenital abnormalities have been recognized for decades, but their diagnosis is challenging. This was again illustrated with the emergence of Zika virus (ZIKV), highlighting the inherent difficulties in estimating the extent of pre- and postnatal ZIKV complications because of the difficulties in establishing definitive diagnoses. We reviewed the epidemiology, infection kinetics, and diagnostic methods used for Toxoplasma gondii, parvovirus B19, rubella virus, and cytomegalovirus (TORCH) infections and compared the results with current knowledge of ZIKV diagnostic assays to provide a basis for the inclusion of ZIKV in the TORCH complex evaluations. Similarities between TORCH pathogens and ZIKV support inclusion of ZIKV as an emerging TORCH infection. Our review evaluates the diagnostic performance of various TORCH diagnostic assays for maternal screening, fetal screening, and neonatal screening. We show that the sensitivity, specificity, and positive and negative predictive value of TORCH complex pathogens are widely variable, stressing the importance of confirmatory testing and the need for novel techniques for earlier and accurate diagnosis of maternal and congenital infections. In this context it is also important to acknowledge different needs and access to care for different geographic and resource settings.

Zika Virus Seroprevalence in Urban and Rural Areas of Suriname, 2017.

In 2015-2016, a Zika virus (ZIKV) outbreak occurred in the Americas. In 2017, we conducted a ZIKV serosurvey in Suriname in which 770 participants were recruited from 1 urban area and 2 rural villages in the tropical rainforest. All collected samples were tested for presence of ZIKV antibodies using a ZIKV immunoglobulin G enzyme-linked immunosorbent assay and a virus neutralization assay. We found that 35.1% of the participants had neutralizing antibodies against ZIKV. In 1 remote village in the rainforest, 24.5% of the participants had neutralizing antibodies against ZIKV, suggesting that ZIKV was widely spread across Suriname.

Study protocol for the multicentre cohorts of Zika virus infection in pregnant women, infants, and acute clinical cases in Latin America and the Caribbean: the ZIKAlliance consortium.

BACKGROUND: The European Commission (EC) Horizon 2020 (H2020)-funded ZIKAlliance Consortium designed a multicentre study including pregnant women (PW), children (CH) and natural history (NH) cohorts. Clinical sites were selected over a wide geographic range within Latin America and the Caribbean, taking into account the dynamic course of the ZIKV epidemic. METHODS: Recruitment to the PW cohort will take place in antenatal care clinics. PW will be enrolled regardless of symptoms and followed over the course of pregnancy, approximately every 4 weeks. PW will be revisited at delivery (or after miscarriage/abortion) to assess birth outcomes, including microcephaly and other congenital abnormalities according to the evolving definition of congenital Zika syndrome (CZS). After birth, children will be followed for 2 years in the CH cohort. Follow-up visits are scheduled at ages 1-3, 4-6, 12, and 24 months to assess neurocognitive and developmental milestones. In addition, a NH cohort for the characterization of symptomatic rash/fever illness was designed, including follow-up to capture persisting health problems. Blood, urine, and other biological materials will be collected, and tested for ZIKV and other relevant arboviral diseases (dengue, chikungunya, yellow fever) using RT-PCR or serological methods. A virtual, decentralized biobank will be created. Reciprocal clinical monitoring has been established between partner sites. Substudies of ZIKV seroprevalence, transmission clustering, disabilities and health economics, viral kinetics, the potential role of antibody enhancement, and co-infections will be linked to the cohort studies. DISCUSSION: Results of these large cohort studies will provide better risk estimates for birth defects and other developmental abnormalities associated with ZIKV infection including possible co-factors for the variability of risk estimates between other countries and regions. Additional outcomes include incidence and transmission estimates of ZIKV during and after pregnancy, characterization of short and long-term clinical course following infection and viral kinetics of ZIKV. STUDY REGISTRATIONS: clinicaltrials.gov NCT03188731 (PW cohort), June 15, 2017; clinicaltrials.gov NCT03393286 (CH cohort), January 8, 2018; clinicaltrials.gov NCT03204409 (NH cohort), July 2, 2017.

Contribution of Human Lung Parenchyma and Leukocyte Influx to Oxidative Stress and Immune System-Mediated Pathology following Nipah Virus Infection.

Nipah virus (NiV) is a zoonotic emerging paramyxovirus that can cause fatal respiratory illness or encephalitis in humans. Despite many efforts, the molecular mechanisms of NiV-induced acute lung injury (ALI) remain unclear. We previously showed that NiV replicates to high titers in human lung grafts in NOD-SCID/γ mice, resulting in a robust inflammatory response. Interestingly, these mice can undergo human immune system reconstitution by the bone marrow, liver, and thymus (BLT) reconstitution method, in addition to lung tissue engraftment, giving altogether a realistic model to study human respiratory viral infections. Here, we characterized NiV Bangladesh strain (NiV-B) infection of human lung grafts from human immune system-reconstituted mice in order to identify the overall effect of immune cells on NiV pathogenesis of the lung. We show that NiV-B replicated to high titers in human lung grafts and caused similar cytopathic effects irrespective of the presence of human leukocytes in mice. However, the human immune system interfered with virus spread across lung grafts, responded to infection by leukocyte migration to small airways and alveoli of the lung grafts, and accelerated oxidative stress in lung grafts. In addition, the presence of human leukocytes increased the expression of cytokines and chemokines that regulate inflammatory influx to sites of infection and tissue damage. These results advance our understanding of how the immune system limits NiV dissemination and contributes to ALI and inform efforts to identify therapeutic targets.IMPORTANCE Nipah virus (NiV) is an emerging paramyxovirus that can cause a lethal respiratory and neurological disease in humans. Only limited data are available on NiV pathogenesis in the human lung, and the relative contribution of the innate immune response and NiV to acute lung injury (ALI) is still unknown. Using human lung grafts in a human immune system-reconstituted mouse model, we showed that the NiV Bangladesh strain induced cytopathic lesions in lung grafts similar to those described in patients irrespective of the donor origin or the presence of leukocytes. However, the human immune system interfered with virus spread, responded to infection by leukocyte infiltration in the small airways and alveolar area, induced oxidative stress, and triggered the production of cytokines and chemokines that regulate inflammatory influx by leukocytes in response to infection. Understanding how leukocytes interact with NiV and cause ALI in human lung xenografts is crucial for identifying therapeutic targets.

Tick-Borne Encephalitis Virus in Ticks and Roe Deer, the Netherlands.

We report the presence of tick-borne encephalitis virus (TBEV) in the Netherlands. Serologic screening of roe deer found TBEV-neutralizing antibodies with a seroprevalence of 2%, and TBEV RNA was detected in 2 ticks from the same location. Enhanced surveillance and awareness among medical professionals has led to the identification of autochthonous cases.

Hepatitis E virus seroprevalence among the general population in a livestock-dense area in the Netherlands: a cross-sectional population-based serological survey.

BACKGROUND: Recent serological studies indicate that hepatitis E virus (HEV) is endemic in industrialised countries. The increasing trend in the number of autochthonous cases of HEV genotype 3 in Western European countries, stresses the importance to get insight in the exact routes of exposure. Pigs are the main animal reservoir, and zoonotic food-borne transmission of HEV is proven. However, infected pigs can excrete large amounts of virus via their faeces enabling environmental transmission of HEV to humans. This might pose a risk for of neighbouring residents of livestock farming. METHODS: Within a large study on the health of people living in the vicinity of livestock farming we performed a cross-sectional population-based serological survey among 2,494 non-farming adults from the general population in a livestock-dense area in the south of the Netherlands. Participants completed risk factor questionnaires and blood samples of 2,422 subjects (median age 58 years, range 20-72) were tested for anti-HEV IgG using an enzyme immune assay (Wantai). The aim of this study was to determine the HEV seroprevalence and to assess whether seropositivity in adults was associated with living in the vicinity of pig farms. RESULTS: The average seroprevalence of HEV was 28.7% (95% CI: 26.9-30.5). Determinants associated with an increased risk for HEV seropositivity were male gender and low level of education. There was a clear trend of increasing prevalence with increasing age (Chi-square test for linear trend, X2 = 83.1; p < 0.001). A high number of pigs within 1,000 m of the residential address was not a risk factor for seropositivity. CONCLUSIONS: This study confirmed the high HEV seroprevalence (29%) in the general population of the Netherlands, but presence of antibodies was not associated with residential proximity to pig farms. The prevalence increased with age from 10% in adolescents to 33% among those aged 50 and above, supporting the assumption of a cumulative lifetime exposure to HEV in the Netherlands as well as a higher infection pressure in the past. Our findings cannot refute the assumption that transmission is primarily food-borne.

Increasing evidence of tick-borne encephalitis (TBE) virus transmission, the Netherlands, June 2016.

We present a case of endemic tick-borne encephalitis (TBE) occurring in June 2016 in the eastern part of the Netherlands in an area where a strain of TBE virus, genetically different from the common TBE virus strains in Europe, was reported in ticks in 2016. With the start of the tick season in spring, this second autochthonous Dutch TBE case should remind physicians to consider the possibility of endemic TBE in patients with respective symptoms.

Escape From Monoclonal Antibody Neutralization Affects Henipavirus Fitness In Vitro and In Vivo.

Henipaviruses are zoonotic viruses that can cause severe and acute respiratory diseases and encephalitis in humans. To date, no vaccine or treatments are approved for human use. The presence of neutralizing antibodies is a strong correlate of protection against lethal disease in animals. However, since RNA viruses are prone to high mutation rates, the possibility that these viruses will escape neutralization remains a potential concern. In the present study, we generated neutralization-escape mutants, using 6 different monoclonal antibodies, and studied the effect of these neutralization-escape mutations on in vitro and in vivo fitness. These data provide a mechanism for overcoming neutralization escape by use of cocktails of cross-neutralizing monoclonal antibodies that recognize residues within the glycoprotein that are important for virus replication and virulence.

Characterization of Nipah virus infection in a model of human airway epithelial cells cultured at an air-liquid interface.

Nipah virus (NiV) is an emerging paramyxovirus that can cause lethal respiratory illness in humans. No vaccine/therapeutic is currently licensed for humans. Human-to-human transmission was previously reported during outbreaks and NiV could be isolated from respiratory secretions, but the proportion of cases in Malaysia exhibiting respiratory symptoms was significantly lower than that in Bangladesh. Previously, we showed that primary human basal respiratory epithelial cells are susceptible to both NiV-Malaysia (M) and -Bangladesh (B) strains causing robust pro-inflammatory responses. However, the cells of the human respiratory epithelium that NiV targets are unknown and their role in NiV transmission and NiV-related lung pathogenesis is still poorly understood. Here, we characterized NiV infection of the human respiratory epithelium using a model of the human tracheal/bronchial (B-ALI) and small airway (S-ALI) epithelium cultured at an air-liquid interface. We show that NiV-M and NiV-B infect ciliated and secretory cells in B/S-ALI, and that infection of S-ALI, but not B-ALI, results in disruption of the epithelium integrity and host responses recruiting human immune cells. Interestingly, NiV-B replicated more efficiently in B-ALI than did NiV-M. These results suggest that the human tracheal/bronchial epithelium is favourable to NiV replication and shedding, while inducing a limited host response. Our data suggest that the small airways epithelium is prone to inflammation and lesions as well as constituting a point of virus entry into the pulmonary vasculature. The use of relevant models of the human respiratory tract, such as B/S-ALI, is critical for understanding NiV-related lung pathogenesis and identifying the underlying mechanisms allowing human-to-human transmission.

A novel factor I activity in Nipah virus inhibits human complement pathways through cleavage of C3b.

UNLABELLED: Complement is an innate immune system that most animal viruses must face during natural infections. Given that replication and dissemination of the highly pathogenic Nipah virus (NiV) include exposure to environments rich in complement factors, we tested the in vitro sensitivity of NiV to complement-mediated neutralization. Here we show that NiV was completely resistant to in vitro neutralization by normal human serum (NHS). Treatment of purified NiV with NHS activated complement pathways, but there was very little C3 deposition on virus particles. In in vitro reconstitution experiments, NiV particles provided time- and dose-dependent factor I-like protease activity capable of cleaving C3b into inactive C3b (iC3b). NiV-dependent inactivation of C3b only occurred with the cofactors factor H and soluble CR1 but not with CD46. Purified NiV particles did not support C4b cleavage. Electron microscopy of purified NiV particles showed immunogold labeling with anti-factor I antibodies. Our results suggest a novel mechanism by which NiV evades the human complement system through a unique factor I-like activity. IMPORTANCE: Viruses have evolved mechanisms to limit complement-mediated neutralization, some of which involve hijacking cellular proteins involved in control of inappropriate complement activation. Here we report a previously unknown mechanism whereby NiV provides a novel protease activity capable of in vitro cleavage and inactivation of C3b, a key component of the complement cascade. These data help to explain how an enveloped virus such as NiV can infect and disseminate through body fluids that are rich in complement activity. Disruption of the ability of NiV to recruit complement inhibitors could form the basis for the development of effective therapies and safer vaccines to combat these highly pathogenic emerging viruses.

Role of hydrogen sulfide in paramyxovirus infections.

UNLABELLED: Hydrogen sulfide (H2S) is an endogenous gaseous mediator that has gained increasing recognition as an important player in modulating acute and chronic inflammatory diseases. However, its role in virus-induced lung inflammation is currently unknown. Respiratory syncytial virus (RSV) is a major cause of upper and lower respiratory tract infections in children for which no vaccine or effective treatment is available. Using the slow-releasing H2S donor GYY4137 and propargylglycin (PAG), an inhibitor of cystathionine-γ-lyase (CSE), a key enzyme that produces intracellular H2S, we found that RSV infection led to a reduced ability to generate and maintain intracellular H2S levels in airway epithelial cells (AECs). Inhibition of CSE with PAG resulted in increased viral replication and chemokine secretion. On the other hand, treatment of AECs with the H2S donor GYY4137 reduced proinflammatory mediator production and significantly reduced viral replication, even when administered several hours after viral absorption. GYY4137 also significantly reduced replication and inflammatory chemokine production induced by human metapneumovirus (hMPV) and Nipah virus (NiV), suggesting a broad inhibitory effect of H2S on paramyxovirus infections. GYY4137 treatment had no effect on RSV genome replication or viral mRNA and protein synthesis, but it inhibited syncytium formation and virus assembly/release. GYY4137 inhibition of proinflammatory gene expression occurred by modulation of the activation of the key transcription factors nuclear factor κB (NF-κB) and interferon regulatory factor 3 (IRF-3) at a step subsequent to their nuclear translocation. H2S antiviral and immunoregulatory properties could represent a novel treatment strategy for paramyxovirus infections. IMPORTANCE: RSV is a global health concern, causing significant morbidity and economic losses as well as mortality in developing countries. After decades of intensive research, no vaccine or effective treatment, with the exception of immunoprophylaxis, is available for this infection as well as for other important respiratory mucosal viruses. This study identifies hydrogen sulfide as a novel cellular mediator that can modulate viral replication and proinflammatory gene expression, both important determinants of lung injury in respiratory viral infections, with potential for rapid translation of such findings into novel therapeutic approaches for viral bronchiolitis and pneumonia.

A human lung xenograft mouse model of Nipah virus infection.

Nipah virus (NiV) is a member of the genus Henipavirus (family Paramyxoviridae) that causes severe and often lethal respiratory illness and encephalitis in humans with high mortality rates (up to 92%). NiV can cause Acute Lung Injury (ALI) in humans, and human-to-human transmission has been observed in recent outbreaks of NiV. While the exact route of transmission to humans is not known, we have previously shown that NiV can efficiently infect human respiratory epithelial cells. The molecular mechanisms of NiV-associated ALI in the human respiratory tract are unknown. Thus, there is an urgent need for models of henipavirus infection of the human respiratory tract to study the pathogenesis and understand the host responses. Here, we describe a novel human lung xenograft model in mice to study the pathogenesis of NiV. Following transplantation, human fetal lung xenografts rapidly graft and develop mature structures of adult lungs including cartilage, vascular vessels, ciliated pseudostratified columnar epithelium, and primitive "air" spaces filled with mucus and lined by cuboidal to flat epithelium. Following infection, NiV grows to high titers (10(7) TCID50/gram lung tissue) as early as 3 days post infection (pi). NiV targets both the endothelium as well as respiratory epithelium in the human lung tissues, and results in syncytia formation. NiV infection in the human lung results in the production of several cytokines and chemokines including IL-6, IP-10, eotaxin, G-CSF and GM-CSF on days 5 and 7 pi. In conclusion, this study demonstrates that NiV can replicate to high titers in a novel in vivo model of the human respiratory tract, resulting in a robust inflammatory response, which is known to be associated with ALI. This model will facilitate progress in the fundamental understanding of henipavirus pathogenesis and virus-host interactions; it will also provide biologically relevant models for other respiratory viruses.