Gene expression of nucleic acid-sensing pattern recognition receptors in children hospitalized for respiratory syncytial virus-associated acute bronchiolitis

The implication of infection with respiratory syncytial virus in pediatric recurrent wheezing and asthma: knowledge expanded post-COVID-19 era

BACKGROUND

Respiratory syncytial virus (RSV) infection has been identified to serve as the primary cause of acute lower respiratory infectious diseases in children under the age of one and a significant risk factor for the emergence and development of pediatric recurrent wheezing and asthma, though the exact mechanism is still unknown.

METHODS AND RESULTS

In this study, we discuss the key routes that lead to recurrent wheezing and bronchial asthma following RSV infection. It is interesting to note that following the coronavirus disease 2019 (COVID-19) epidemic, the prevalence of RSV changes significantly. This presents us with a rare opportunity to better understand the associated mechanism for RSV infection, its effects on the respiratory system, and the immunological response to RSV following the COVID-19 epidemic. To better understand the associated mechanisms in the occurrence and progression of pediatric asthma, we thoroughly described how the RSV infection directly destroys the physical barrier of airway epithelial tissue, promotes inflammatory responses, enhances airway hyper-responsiveness, and ultimately causes the airway remodeling. More critically, extensive discussion was also conducted regarding the potential impact of RSV infection on host pulmonary immune response.

CONCLUSION

In conclusion, this study offers a comprehensive perspective to better understand how the RSV infection interacts in the control of the host's pulmonary immune system, causing recurrent wheezing and the development of asthma, and it sheds fresh light on potential avenues for pharmaceutical therapy in the future.

Nasopharyngeal and Peripheral Blood Type II Interferon Signature Evaluation in Infants during Respiratory Syncytial Virus Infection

Background and Objectives: In this study, we applied one-step real time rt-PCR technology type II INF signature to blood and nasopharyngeal (NPS) swabs of acute early recovery children < 1 years hospitalized for bronchiolitis with laboratory-confirmed RSV infection. Materials and Methods: A prospective observational case-control study was conducted in 2021-2022. The study took place in Children Hospital "Regina Margherita", Torino Italy. The study included 66 infants, of which 30 patients were hospitalized for bronchiolitis due to RSV infection and 36 age-matched controls. Inclusion criteria included a positive RSV test for infants with bronchiolitis. We collected peripheral blood and nasopharyngeal swabs for relative quantification of type II Interferon signature by One-Step Multiplex PCR real time. Results: IFN levels were downregulated in the peripheral blood of bronchiolitis patients; these data were not confirmed in the nasopharyngeal swab. There was no correlation between NPS and the type II IFN score in peripheral blood. Conclusions: our study shows for the first time that type II IFN score was significant reduced in peripheral blood of infants with bronchiolitis by RSV compared to age-matched healthy controls; in the NPS swab this resulted downregulation was not statistically significant and the type II IFN score in the NPS swab can be used as marker of resolution of infection or improvement of clinical conditions.

Pathogenicity and virulence of human respiratory syncytial virus: Multifunctional nonstructural proteins NS1 and NS2

Human respiratory syncytial virus (hRSV) is a major cause of acute lower respiratory tract infections in children under the age of two as well as in the elderly and immunocompromised worldwide. Despite its discovery over 60 years ago and the global impact on human health, limited specific and effective prophylactic or therapeutic options have been available for hRSV infections. Part of the lack of treatment options is attributed to the legacy of vaccine failure in the 1960s using a formalin-inactivated RSV (FI-RSV), which led to enhancement of disease post exposure to hRSV infection and hampered subsequent development of vaccine candidates. Recent FDA approval of a vaccine for older adults and impending approval for a maternal vaccine are major advancements but leaves children between 6 months and 5 years of age unprotected. Part of this limitation can be attributed to a lack of complete understanding of the factors that contribute to hRSV pathogenesis. The nonstructural proteins NS1 and NS2 are multifunctional virulence factors that are unique to hRSV and that play critical roles during hRSV infection, including antagonizing interferon (IFN) signalling to modulate host responses to hRSV infection. However, the molecular mechanisms by which the nonstructural proteins mediate their IFN inhibitory functions have not been completely defined. Current progress on the characterization of NS1 and NS2 during infection provides deeper insight into their roles. Furthermore, reverse genetics systems for hRSV provide a viable strategy to generate attenuated viruses by introduction of select mutations while maintaining immunogenicity required to elicit a long-term protective response. Here we will review the current state of knowledge of the nonstructural proteins, their contributions to RSV pathogenesis, and their potential as targets for therapeutic development.

Innate Immune Evasion by Human Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) is the leading cause of severe respiratory infection in young children. Nearly all individuals become infected in their early childhood, and reinfections with RSV are common throughout life. Primary infection with RSV is usually involved in the symptom of bronchiolitis and pneumonia in the lower respiratory tract, which accounts for over 3 million hospitalizations and approximately 66,000 deaths annually worldwide. Despite the widespread prevalence and high morbidity and lethality rates of diseases caused by RSV infection, there is currently no licensed RSV vaccine. During RSV infection, innate immunity plays the first line of defense to suppress RSV infection and replication. However, RSV has evolved multiple mechanisms to evade the host’s innate immune responses to gain a window of opportunity for efficient viral replication. This review discusses the comprehensive interaction between RSV infection and the host antiviral innate immunity and updates recent findings on how RSV modulates the host innate immune response for survival, which may provide novel insights to find potent drug targets and vaccines against RSV.

How RSV Proteins Join Forces to Overcome the Host Innate Immune Response

Respiratory syncytial virus (RSV) is the leading cause of severe acute lower respiratory tract infections in infants worldwide. Although several pattern recognition receptors (PRRs) can sense RSV-derived pathogen-associated molecular patterns (PAMPs), infection with RSV is typically associated with low to undetectable levels of type I interferons (IFNs). Multiple RSV proteins can hinder the host’s innate immune response. The main players are NS1 and NS2 which suppress type I IFN production and signalling in multiple ways. The recruitment of innate immune cells and the production of several cytokines are reduced by RSV G. Next, RSV N can sequester immunostimulatory proteins to inclusion bodies (IBs). N might also facilitate the assembly of a multiprotein complex that is responsible for the negative regulation of innate immune pathways. Furthermore, RSV M modulates the host’s innate immune response. The nuclear accumulation of RSV M has been linked to an impaired host gene transcription, in particular for nuclear-encoded mitochondrial proteins. In addition, RSV M might also directly target mitochondrial proteins which results in a reduced mitochondrion-mediated innate immune recognition of RSV. Lastly, RSV SH might prolong the viral replication in infected cells and influence cytokine production.

Early innate immune response triggered by the human respiratory syncytial virus and its regulation by ubiquitination/deubiquitination processes

The human respiratory syncytial virus (HRSV) causes severe lower respiratory tract infections in infants and the elderly. An exuberant inadequate immune response is behind most of the pathology caused by the HRSV. The main targets of HRSV infection are the epithelial cells of the respiratory tract, where the immune response against the virus begins. This early innate immune response consists of the expression of hundreds of pro-inflammatory and anti-viral genes that stimulates subsequent innate and adaptive immunity. The early innate response in infected cells is mediated by intracellular signaling pathways composed of pattern recognition receptors (PRRs), adapters, kinases, and transcriptions factors. These pathways are tightly regulated by complex networks of post-translational modifications, including ubiquitination. Numerous ubiquitinases and deubiquitinases make these modifications reversible and highly dynamic. The intricate nature of the signaling pathways and their regulation offers the opportunity for fine-tuning the innate immune response against HRSV to control virus replication and immunopathology.

Structural basis for IFN antagonism by human respiratory syncytial virus nonstructural protein 2

Human respiratory syncytial virus (RSV) nonstructural protein 2 (NS2) inhibits host interferon (IFN) responses stimulated by RSV infection by targeting early steps in the IFN-signaling pathway. But the molecular mechanisms related to how NS2 regulates these processes remain incompletely understood. To address this gap, here we solved the X-ray crystal structure of NS2. This structure revealed a unique fold that is distinct from other known viral IFN antagonists, including RSV NS1. We also show that NS2 directly interacts with an inactive conformation of the RIG-I-like receptors (RLRs) RIG-I and MDA5. NS2 binding prevents RLR ubiquitination, a process critical for prolonged activation of downstream signaling. Structural analysis, including by hydrogen-deuterium exchange coupled to mass spectrometry, revealed that the N terminus of NS2 is essential for binding to the RIG-I caspase activation and recruitment domains. N-terminal mutations significantly diminish RIG-I interactions and result in increased IFNβ messenger RNA levels. Collectively, our studies uncover a previously unappreciated regulatory mechanism by which NS2 further modulates host responses and define an approach for targeting host responses.

Innate Receptor Activation Patterns Involving TLR and NLR Synergisms in COVID-19, ALI/ARDS and Sepsis Cytokine Storms: A Review and Model Making Novel Predictions and Therapeutic Suggestions

Severe COVID-19 is characterized by a “cytokine storm”, the mechanism of which is not yet understood. I propose that cytokine storms result from synergistic interactions among Toll-like receptors (TLR) and nucleotide-binding oligomerization domain-like receptors (NLR) due to combined infections of SARS-CoV-2 with other microbes, mainly bacterial and fungal. This proposition is based on eight linked types of evidence and their logical connections. (1) Severe cases of COVID-19 differ from healthy controls and mild COVID-19 patients in exhibiting increased TLR4, TLR7, TLR9 and NLRP3 activity. (2) SARS-CoV-2 and related coronaviruses activate TLR3, TLR7, RIG1 and NLRP3. (3) SARS-CoV-2 cannot, therefore, account for the innate receptor activation pattern (IRAP) found in severe COVID-19 patients. (4) Severe COVID-19 also differs from its mild form in being characterized by bacterial and fungal infections. (5) Respiratory bacterial and fungal infections activate TLR2, TLR4, TLR9 and NLRP3. (6) A combination of SARS-CoV-2 with bacterial/fungal coinfections accounts for the IRAP found in severe COVID-19 and why it differs from mild cases. (7) Notably, TLR7 (viral) and TLR4 (bacterial/fungal) synergize, TLR9 and TLR4 (both bacterial/fungal) synergize and TLR2 and TLR4 (both bacterial/fungal) synergize with NLRP3 (viral and bacterial). (8) Thus, a SARS-CoV-2-bacterium/fungus coinfection produces synergistic innate activation, resulting in the hyperinflammation characteristic of a cytokine storm. Unique clinical, experimental and therapeutic predictions (such as why melatonin is effective in treating COVID-19) are discussed, and broader implications are outlined for understanding why other syndromes such as acute lung injury, acute respiratory distress syndrome and sepsis display varied cytokine storm symptoms.

Ex vivo peripheral blood mononuclear cell response to R848 in children after supplementation with the probiotic Lactobacillus acidophilus NCFM/Bifidobacterium lactis Bi-07

Several studies have demonstrated a decrease in upper respiratory infection (URI) frequency and severity in subjects taking probiotic supplements. We hypothesised beneficial effects of probiotics on viral URI in children are due to modulation of inflammatory innate immune responses. We tested this hypothesis, providing children with a probiotic combination of Lactobacillus acidophilus/Bidfidobacterium animalis ssp. lactis Bi-07 (NCFM/Bi-07) and measuring levels of cytokines in response to stimulation of peripheral blood mononuclear cells (PBMCs) to toll-like receptor (TLR) 7/8 agonist resiquimod (R848). In this open label study, 21 (2 dropouts) children received probiotic containing 5×10⁹ cfu each of NCFM/(Bi-07) daily for 30 days. Whole blood was taken from each subject at study entry and 30 days for culture of PBMCs. PBMCs stimulated with resiquimod (R848) or unstimulated were incubated and a panel of immune markers was measured. There was a significant decrease in the net (stimulated-null) level of myeloid progenitor inhibitory factor 1 (MPIF-1) (mean decrease 0.1 ng/ml, 95% confidence interval 0.01-0.24, P=0.032) following probiotic supplementation. The change in immune marker levels after supplementation, when analysed together with respect to expected inflammatory/anti-inflammatory effects, was increased for interleukin (IL)-10 and decreased for MPIF-1, IL-8, interferon gamma induced protein 10, macrophage inflammatory protein 3 alpha (MIP-3α) and E-selectin (P=0.01). Adverse events were mild. In conclusion, supplementation with this probiotic combination was safe and resulted in significant modulation of PBMC limited immune response to TLR7/8 agonist R848 and in levels of MPIF-1 and MIP-3α. The anti-inflammatory effect may be one mechanism by which probiotics modulate the immune system however further study is needed.

Current Insights into the Host Immune Response to Respiratory Viral Infections

Respiratory viral infections often lead to severe illnesses varying from mild or asymptomatic upper respiratory tract infections to severe bronchiolitis and pneumonia or/and chronic obstructive pulmonary disease. Common viral infections, including but not limited to influenza virus, respiratory syncytial virus, rhinovirus and coronavirus, are often the leading cause of morbidity and mortality. Since the lungs are continuously exposed to foreign particles, including respiratory pathogens, it is also well equipped for recognition and antiviral defense utilizing the complex network of innate and adaptive immune cells. Immediately upon infection, a range of proinflammatory cytokines, chemokines and an interferon response is generated, thereby making the immune response a two edged sword, on one hand it is required to eliminate viral pathogens while on other hand it's prolonged response can lead to chronic infection and significant pulmonary damage. Since vaccines to all respiratory viruses are not available, a better understanding of the virus-host interactions, leading to the development of immune response, is critically needed to design effective therapies to limit the severity of inflammatory damage, enhance viral clearance and to compliment the current strategies targeting the virus. In this chapter, we discuss the host responses to common respiratory viral infections, the key players of adaptive and innate immunity and the fine balance that exists between the viral clearance and immune-mediated damage.

p53-responsive TLR8 SNP enhances human innate immune response to respiratory syncytial virus

The Toll-like receptor 8 (TLR8) has an important role in innate immune responses to RNA viral infections, including respiratory syncytial virus (RSV). We previously reported that TLR8 expression was increased directly by the tumor suppressor and transcription factor p53 via a single nucleotide polymorphism (SNP) (rs3761624) in the TLR8 promoter, thereby placing TLR8 in the p53/immune axis. Because this SNP is in linkage disequilibrium with other SNPs associated with several infectious diseases, we addressed the combined influence of p53 and the SNP on downstream inflammatory signaling in response to a TLR8 cognate ssRNA ligand. Using human primary lymphocytes, p53 induction by chemotherapeutic agents such as ionizing radiation caused SNP-dependent synergistic increases in IL-6 following incubation with an ssRNA ligand, as well as TLR8 RNA and protein expression along with p53 binding at the TLR-p53 SNP site. Because TLR8 is X-linked, the increases were generally reduced in heterozygous females. We found a corresponding association of the p53-responsive allele with RSV disease severity in infants hospitalized with RSV infection. We conclude that p53 can strongly influence TLR8-mediated immune responses and that knowledge of the p53-responsive SNP can inform diagnosis and prognosis of RSV disease and other diseases that might have a TLR8 component, including cancer.

Immune biomarkers predicting bronchiolitis disease severity: A systematic review

Bronchiolitis is one of the leading causes of hospitalisation in infancy, with highly variable clinical presentations ranging from mild disease safely managed at home to severe disease requiring invasive respiratory support. Identifying immune biomarkers that can predict and stratify this variable disease severity has important implications for clinical prognostication/disposition. A systematic literature search of the databases Embase, PubMed, ScienceDirect, Web of Science, and Wiley Online Library was performed. English language studies that assessed the association between an immune biomarker and bronchiolitis disease severity among children aged less than 24 months were included. 252 distinct biomarkers were identified across 90 studies. A substantial degree of heterogeneity was observed in the bronchiolitis definitions, measures of disease severity, and study designs. 99 biomarkers showed some significant association with disease severity, but only 18 were significant in multiple studies. However, all of these candidate biomarkers had comparable studies that reported conflicting results. Conclusion: The heterogeneity among included studies and the lack of a consistently significant biomarker highlight the need for consensus on bronchiolitis definitions and severity measures, as well as further studies assessing their clinical utility both in isolation and in combination.

Respiratory syncytial virus nonstructural proteins 1 and 2: Exceptional disrupters of innate immune responses

Human respiratory syncytial virus (RSV) is the most important cause of acute lower respiratory tract disease in infants worldwide. As a first line of defense against respiratory infections, innate immune responses, including the production of type I and III interferons (IFNs), play an important role. Upon infection with RSV, multiple pattern recognition receptors (PRRs) can recognize RSV-derived pathogen-associated molecular patterns (PAMPs) and mount innate immune responses. Retinoic-acid-inducible gene-I (RIG-I) and nucleotide-binding oligomerization domain-containing protein 2 (NOD2) have been identified as important innate receptors to mount type I IFNs during RSV infection. However, type I IFN levels remain surprisingly low during RSV infection despite strong viral replication. The poor induction of type I IFNs can be attributed to the cooperative activity of 2 unique, nonstructural (NS) proteins of RSV, i.e., NS1 and NS2. These viral proteins have been shown to suppress both the production and signaling of type I and III IFNs by counteracting a plethora of key host innate signaling proteins. Moreover, increasing numbers of IFN-stimulated genes (ISGs) are being identified as targets of the NS proteins in recent years, highlighting an underexplored protein family in the identification of NS target proteins. To understand the diverse effector functions of NS1 and NS2, Goswami and colleagues proposed the hypothesis of the NS degradasome (NSD) complex, a multiprotein complex made up of, at least, NS1 and NS2. Furthermore, the crystal structure of NS1 was resolved recently and, remarkably, identified NS1 as a structural paralogue of the RSV matrix protein. Unfortunately, no structural data on NS2 have been published so far. In this review, we briefly describe the PRRs that mount innate immune responses upon RSV infection and provide an overview of the various effector functions of NS1 and NS2. Furthermore, we discuss the ubiquitination effector functions of NS1 and NS2, which are in line with the hypothesis that the NSD shares features with the canonical 26S proteasome.

Toll-like receptor 1 and 10 variations increase asthma risk and review highlights further research directions

AIM

This paper summarises variations in the genes encoding toll-like receptors (TLRs) in relation to the aetiology and outcome of infant bronchiolitis. It compares the literature with research carried out by our group.

METHODS

A mini review was conducted to provide context for a study carried out at the Department of Paediatrics, Tampere University Hospital, Finland. In 2000-2004, 187 infants were hospitalised for bronchiolitis and then followed up: 129 at 1.5 years of age, 166 at 5-7 years of age and 138 at 11-13 years of age.

RESULTS

The review showed that the Finnish bronchiolitis study was the only prospective study on the association between TLRs and the emergence of childhood asthma or lung function reduction after bronchiolitis in infancy. It found that TLR1 and TLR10 variant genotypes were associated with more asthma at 5-7 and 11-13 years, with inconsistent results for the other eight TLR genes. Large population-based studies were also identified that stressed the importance of the TLR2 subfamily members in childhood asthma.

CONCLUSION

Our study found that variations in the TLR1 and TLR10 genes increased the asthma risk after bronchiolitis. The mini review calls for further research on the TLR2 subfamily in bronchiolitis and childhood asthma.

Utility of the Neonatal Calf Model for Testing Vaccines and Intervention Strategies for Use against Human RSV Infection

Respiratory syncytial virus (RSV) is a significant cause of pediatric respiratory tract infections. It is estimated that two-thirds of infants are infected with RSV during the first year of life and it is one of the leading causes of death in this age group worldwide. Similarly, bovine RSV is a primary viral pathogen in cases of pneumonia in young calves and plays a significant role in bovine respiratory disease complex. Importantly, naturally occurring infection of calves with bovine RSV shares many features in common with human RSV infection. Herein, we update our current understanding of RSV infection in cattle, with particular focus on similarities between the calf and human infection, and the recent reports in which the neonatal calf has been employed for the development and testing of vaccines and therapeutics which may be applied to hRSV infection in humans.

Respiratory syncytial virus

Respiratory syncytial virus (RSV) is the most common cause of infant hospitalization and causes a high burden of disease in the elderly, too. This enveloped negative-stranded RNA virus has been recently reclassified in the Pneumoviridae family. Infections of the respiratory cells happens when the two major surface glycoproteins, G and F, take contact with the cell receptor CX3CR1 and mediate entry by fusion, respectively. Viral mRNA transcription, genomic RNA synthesis and nucleocapsid formation occur in large cytoplasmic inclusion bodies to avoid recognition by the host innate immune response. Most progeny virions remain associated to the infected cell surface; fusion of infected with adjacent cells results in the formation of large multinucleated syncytia that eventually undergo apoptosis. Desquamated epithelial cells form the plugs that with mucus and fibrin may cause lower airway obstructions. Pathogenetic mechanism of severe RSV disease likely involve both the extent of viral replication and the host immune response. Regarding the latter, single nucleotide polymorphism analysis and genome-wide association studies showed that genetic susceptibility to severe RSV infection is likely a complex trait, in which many different host genetic variants contribute. Recent studies pointed to the fact that bronchiolitis severity depends more on the specific infecting RSV genotypes than on the amount of viral loads. A population-based surveillance system to better define RSV burden of disease would be of valuable help for implementing future vaccination programs.

Interferon lambda receptor 1 (IFNL1R) transcript is highly expressed in rhinovirus bronchiolitis and correlates with disease severity

BACKGROUND

As the expression of type III IFN receptor is restricted to the mucosal surfaces, its evaluation could be crucial to characterize the role of IFNλs during bronchiolitis.

OBJECTIVES

This study was designed to investigate airway type III IFN receptor (IFNLR1/IL10RB) expression during respiratory syncytial virus (RSV) or human rhinovirus (HRV) bronchiolitis.

STUDY DESIGN

Seventy-one 1-6 month old infants hospitalized with their first episode of acute RSV or HRV bronchiolitis were selected for this study. Expression of IFNLR1, IL10RB and IFN-stimulated genes (ISGs) MxA and ISG56 in cells of nasopharyngeal washings taken within the first 48 h of admission were determined by a real-time hydrolysis probe RT-PCR assay. The ability of types I and III IFNs to induce the expression of both IFNLR1 and IL10RB in vitro was also evaluated.

RESULTS

Airway IFNLR1 transcript levels were significantly higher in HRV bronchiolitis infants compared to those with RSV bronchiolitis. No differences were recorded for IL10RB-mRNA between RSV or HRV infection. IFNLR1 mRNA levels increased significantly in infants infected with the C species of HRV and in those with a higher clinical score index and with an eosinophil count >3%. There were no correlations in vivo between type III IFN receptors and those of ISGs and neither IFNLR1 nor IL10RB were induced in vitro by IFNs.

CONCLUSIONS

These results suggest that IFNLR1 are increased in HRV-infected infants with more severe bronchiolitis and blood eosinophilia and in those infected with the HRVC species.

Induction and Subversion of Human Protective Immunity: Contrasting Influenza and Respiratory Syncytial Virus

Respiratory syncytial virus (RSV) and influenza are among the most important causes of severe respiratory disease worldwide. Despite the clinical need, barriers to developing reliably effective vaccines against these viruses have remained firmly in place for decades. Overcoming these hurdles requires better understanding of human immunity and the strategies by which these pathogens evade it. Although superficially similar, the virology and host response to RSV and influenza are strikingly distinct. Influenza induces robust strain-specific immunity following natural infection, although protection by current vaccines is short-lived. In contrast, even strain-specific protection is incomplete after RSV and there are currently no licensed RSV vaccines. Although animal models have been critical for developing a fundamental understanding of antiviral immunity, extrapolating to human disease has been problematic. It is only with recent translational advances (such as controlled human infection models and high-dimensional technologies) that the mechanisms responsible for differences in protection against RSV compared to influenza have begun to be elucidated in the human context. Influenza infection elicits high-affinity IgA in the respiratory tract and virus-specific IgG, which correlates with protection. Long-lived influenza-specific T cells have also been shown to ameliorate disease. This robust immunity promotes rapid emergence of antigenic variants leading to immune escape. RSV differs markedly, as reinfection with similar strains occurs despite natural infection inducing high levels of antibody against conserved antigens. The immunomodulatory mechanisms of RSV are thus highly effective in inhibiting long-term protection, with disturbance of type I interferon signaling, antigen presentation and chemokine-induced inflammation possibly all contributing. These lead to widespread effects on adaptive immunity with impaired B cell memory and reduced T cell generation and functionality. Here, we discuss the differences in clinical outcome and immune response following influenza and RSV. Specifically, we focus on differences in their recognition by innate immunity; the strategies used by each virus to evade these early immune responses; and effects across the innate-adaptive interface that may prevent long-lived memory generation. Thus, by comparing these globally important pathogens, we highlight mechanisms by which optimal antiviral immunity may be better induced and discuss the potential for these insights to inform novel vaccines.

Host Transcription Profile in Nasal Epithelium and Whole Blood of Hospitalized Children Under 2 Years of Age With Respiratory Syncytial Virus Infection

Background

Most insights into the cascade of immune events after acute respiratory syncytial virus (RSV) infection have been obtained from animal experiments or in vitro models.

Methods

In this study, we investigated host gene expression profiles in nasopharyngeal (NP) swabs and whole blood samples during natural RSV and rhinovirus (hRV) infection (acute versus early recovery phase) in 83 hospitalized patients <2 years old with lower respiratory tract infections.

Results

Respiratory syncytial virus infection induced strong and persistent innate immune responses including interferon signaling and pathways related to chemokine/cytokine signaling in both compartments. Interferon-α/β, NOTCH1 signaling pathways and potential biomarkers HIST1H4E, IL7R, ISG15 in NP samples, or BCL6, HIST2H2AC, CCNA1 in blood are leading pathways and hub genes that were associated with both RSV load and severity. The observed RSV-induced gene expression patterns did not differ significantly in NP swab and blood specimens. In contrast, hRV infection did not as strongly induce expression of innate immunity pathways, and significant differences were observed between NP swab and blood specimens.

Conclusions

We conclude that RSV induced strong and persistent innate immune responses and that RSV severity may be related to development of T follicular helper cells and antiviral inflammatory sequelae derived from high activation of BCL6.

The Human Immune Response to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is an important etiological agent of respiratory infections, particularly in children. Much information regarding the immune response to RSV comes from animal models and in vitro studies. Here, we provide a comprehensive description of the human immune response to RSV infection, based on a systematic literature review of research on infected humans. There is an initial strong neutrophil response to RSV infection in humans, which is positively correlated with disease severity and mediated by interleukin-8 (IL-8). Dendritic cells migrate to the lungs as the primary antigen-presenting cell. An initial systemic T-cell lymphopenia is followed by a pulmonary CD8+ T-cell response, mediating viral clearance. Humoral immunity to reinfection is incomplete, but RSV IgG and IgA are protective. B-cell-stimulating factors derived from airway epithelium play a major role in protective antibody generation. Gamma interferon (IFN-γ) has a strongly protective role, and a Th2-biased response may be deleterious. Other cytokines (particularly IL-17A), chemokines (particularly CCL-5 and CCL-3), and local innate immune factors (including cathelicidins and IFN-λ) contribute to pathogenesis. In summary, neutrophilic inflammation is incriminated as a harmful response, whereas CD8+ T cells and IFN-γ have protective roles. These may represent important therapeutic targets to modulate the immunopathogenesis of RSV infection.

The innate immune response to RSV: Advances in our understanding of critical viral and host factors

Respiratory syncytial virus (RSV) causes mild to severe respiratory illness in humans and is a major cause of hospitalizations of infants and the elderly. Both the innate and the adaptive immune responses contribute to the control of RSV infection, but despite successful viral clearance, protective immunity against RSV re-infection is usually suboptimal and infections recur. Poor understanding of the mechanisms limiting the induction of long-lasting immunity has delayed the development of an effective vaccine. The innate immune response plays a critical role in driving the development of adaptive immunity and is thus a crucial determinant of the infection outcome. Advances in recent years have improved our understanding of cellular and viral factors that influence the onset and quality of the innate immune response to RSV. These advances include the identification of a complex system of cellular sensors that mediate RSV detection and stimulate transcriptome changes that lead to virus control and the discovery that cell stress and apoptosis participate in the control of RSV infection. In addition, it was recently demonstrated that defective viral genomes (DVGs) generated during RSV replication are the primary inducers of the innate immune response. Newly discovered host pathways involved in the innate response to RSV, together with the potential generation of DVG-derived oligonucleotides, present various novel opportunities for the design of vaccine adjuvants able to induce a protective response against RSV and similar viruses.

Human Respiratory Syncytial Virus: Role of Innate Immunity in Clearance and Disease Progression

Human respiratory syncytial virus (HRSV) infections have worldwide records. The virus is responsible for bronchiolitis, pneumonia, and asthma in humans of different age groups. Premature infants, young children, and immunocompromised individuals are prone to severe HRSV infection that may lead to death. Based on worldwide estimations, millions of cases were reported in both developed and developing countries. In fact, HRSV symptoms develop mainly as a result of host immune response. Due to inability to establish long lasting adaptive immunity, HRSV infection is recurrent and hence impairs vaccine development. Once HRSV attached to the airway epithelia, interaction with the host innate immune components starts. HRSV interaction with pulmonary innate defenses is crucial in determining the disease outcome. Infection of alveolar epithelial cells triggers a cascade of events that lead to recruitment and activation of leukocyte populations. HRSV clearance is mediated by a number of innate leukocytes, including macrophages, natural killer cells, eosinophils, dendritic cells, and neutrophils. Regulation of these cells is mediated by cytokines, chemokines, and other immune mediators. Although the innate immune system helps to clear HRSV infection, it participates in disease progression such as bronchiolitis and asthma. Resolving the mechanisms by which HRSV induces pathogenesis, different possible interactions between the virus and immune components, and immune cells interplay are essential for developing new effective vaccines. Therefore, the current review focuses on how the pulmonary innate defenses mediate HRSV clearance and to what extent they participate in disease progression. In addition, immune responses associated with HRSV vaccines will be discussed.

Induction and Antagonism of Antiviral Responses in Respiratory Syncytial Virus-Infected Pediatric Airway Epithelium

Airway epithelium is the primary target of many respiratory viruses. However, virus induction and antagonism of host responses by human airway epithelium remains poorly understood. To address this, we developed a model of respiratory syncytial virus (RSV) infection based on well-differentiated pediatric primary bronchial epithelial cell cultures (WD-PBECs) that mimics hallmarks of RSV disease in infants. RSV is the most important respiratory viral pathogen in young infants worldwide. We found that RSV induces a potent antiviral state in WD-PBECs that was mediated in part by secreted factors, including interferon lambda 1 (IFN-λ1)/interleukin-29 (IL-29). In contrast, type I IFNs were not detected following RSV infection of WD-PBECs. IFN responses in RSV-infected WD-PBECs reflected those in lower airway samples from RSV-hospitalized infants. In view of the prominence of IL-29, we determined whether recombinant IL-29 treatment of WD-PBECs before or after infection abrogated RSV replication. Interestingly, IL-29 demonstrated prophylactic, but not therapeutic, potential against RSV. The absence of therapeutic potential reflected effective RSV antagonism of IFN-mediated antiviral responses in infected cells. Our data are consistent with RSV nonstructural proteins 1 and/or 2 perturbing the Jak-STAT signaling pathway, with concomitant reduced expression of antiviral effector molecules, such as MxA/B. Antagonism of Jak-STAT signaling was restricted to RSV-infected cells in WD-PBEC cultures. Importantly, our study provides the rationale to further explore IL-29 as a novel RSV prophylactic.

IMPORTANCE

Most respiratory viruses target airway epithelium for infection and replication, which is central to causing disease. However, for most human viruses we have a poor understanding of their interactions with human airway epithelium. Respiratory syncytial virus (RSV) is the most important viral pathogen of young infants. To help understand RSV interactions with pediatric airway epithelium, we previously developed three-dimensional primary cell cultures from infant bronchial epithelium that reproduce several hallmarks of RSV infection in infants, indicating that they represent authentic surrogates of RSV infection in infants. We found that RSV induced a potent antiviral state in these cultures and that a type III interferon, interleukin IL-29 (IL-29), was involved. Indeed, our data suggest that IL-29 has potential to prevent RSV disease. However, we also demonstrated that RSV efficiently circumvents this antiviral immune response and identified mechanisms by which this may occur. Our study provides new insights into RSV interaction with pediatric airway epithelium.

Human Rhinovirus-induced Proinflammatory Cytokine and Interferon-β Responses in Nasal Epithelial Cells From Chronic Rhinosinusitis Patients

Purpose

Asthma exacerbation from human rhinovirus (HRV) infection is associated with deficient antiviral interferon (IFN) secretion. Although chronic rhinosinusitis (CRS), an inflammatory upper airway disease, is closely linked to asthma, IFN-β responses to HRV infections in human nasal epithelial cells (HNECs) from CRS patients remain to be studied. We evaluated inflammatory and antiviral responses to HRV infection in HNECs from CRS patients.

Methods

HNECs, isolated from turbinate tissue of 13 patients with CRS and 14 non-CRS controls, were infected with HRV16 for 4 hours. The HRV titer, LDH activity, production of proinflammatory cytokines and IFN-β proteins, and expression levels of RIG-I and MDA5 mRNA were assessed at 8, 24, and 48 hours after HRV16 infection.

Results

The reduction in viral titer was slightly delayed in the CRS group compared to the non-CRS control group. IL-6 and IL-8 were significantly increased to a similar extent in both groups after HRV infection. In the control group, IFN-β production and MDA5 mRNA expression were significantly increased at 8 and 24 hours after HRV16 infection, respectively. By contrast, in the CRS group, IFN-β was not induced by HRV infection; however, HRV-induced MDA5 mRNA expression was increased, but the increase was slightly delayed compared to the non-CRS control group. The RIG-I mRNA level was not significantly increased by HRV16 infection in either group.

Conclusions

HRV-induced secretion of proinflammatory cytokines in CRS patients was not different from that in the non-CRS controls. However, reductions in viral titer, IFN-β secretion, and MDA5 mRNA expression in response to HRV infection in CRS patients were slightly impaired compared to those in the controls, suggesting that HRV clearance in CRS patients might be slightly deficient.

Innate immune recognition of respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the leading cause of respiratory infection in infants and young children. Severe clinical manifestation of RSV infection is a bronchiolitis, which is common in infants under six months of age. Recently, RSV has been recognized as an important cause of respiratory infection in older populations with cardiovascular morbidity or immunocompromised patients. However, neither a vaccine nor an effective antiviral therapy is currently available. Moreover, the interaction between the host immune system and the RSV pathogen during an infection is not well understood. The innate immune system recognizes RSV through multiple mechanisms. The first innate immune RSV detectors are the pattern recognition receptors (PRRs), including toll-like receptors (TLRs), retinoic acid-inducible gene-I (RIG-I)-like receptors (RLRs), and nucleotide-biding oligomerization domain (NOD)-like receptors (NLRs). The following is a review of studies associated with various PRRs that are responsible for RSV virion recognition and subsequent induction of the antiviral immune response during RSV infection. [BMB Reports 2014; 47(4): 184-191]

MicroRNA-29 family expression and its relation to antiviral immune response and viro-immunological markers in HIV-1-infected patients

Background

Several in vitro studies suggested the microRNA-29 (miRNA-29) family is involved in regulating HIV-1 and modulating the expression of interleukin (IL)-32, an anti-HIV-1 cytokine.

Methods

To investigate the contribution of the miRNA-29 family to HIV-1 infection in vivo, we compared miRNA-29 expression in PBMC collected from 58 HIV-1-infected patients, naïve for antiretroviral therapy, and 21 gender- and age-matched HIV-1 seronegative healthy donors, using RT-Taqman assays. The relation between miRNA-29 levels and HIV-1 viro-immunological markers and the activation rate of antiviral immune response were also evaluated. In addition, we profiled miRNA-29 expression in CD4+ T lymphocytes and CD14+ monocytes collected from 5 antiretroviral treated HIV-1 infected patients.

Results

miRNA-29b levels were higher in HIV-1-infected patients than in the control group (p < 0.001). There were no correlations with either HIV-1 RNA levels or CD4+ T count, whereas a significant correlation was found between miRNA-29-a/c levels and integrated HIV-1 DNA (miRNA-29a: p = 0.009, r = −0.448; miRNA-29c: p = 0.029; r = −0.381). When the HIV-1-infected patients were grouped on the basis of their plasma HIV-1 RNA and CD4+ T cell count, we also found that patients expressing the lowest levels of miRNA-29c showed high viraemia, low CD4+ T cell count and high levels of integrated HIV-1 DNA. Moreover, miRNA-29b levels were correlated with those of IL-32nonα (p = 0.028; r = −0.298). Patients expressing higher levels of miRNA-29b showed lower levels of MxA, an interferon-stimulated gene, also induced by IL-32 (p = 0.006 r = −0.397). Lastly, we found that CD4+ T lymphocytes and CD14+ monocytes shared similar miRNA-29a/b/c expression patterns but the amount of miRNA-29a/b/c, IL-32 isoforms and MxA were highly variable in these two cellular subsets.

Conclusions

The miRNA-29 family could influence the clinical progression of HIV-1 infection, the HIV-1 proviral load and the innate immune response against HIV-1.

Type-I interferons induce lung protease responses following respiratory syncytial virus infection via RIG-I-like receptors

The role of proteases in viral infection of the lung is poorly understood. Thus, we examined matrix metalloproteinases (MMPs) and cathepsin proteases in respiratory syncytial virus (RSV)-infected mouse lungs. RSV-induced gene expression for MMPs -2, -3, -7, -8, -9, -10, -12, -13, -14, -16, -17, -19, -20, -25, -27, and -28 and cathepsins B, C, E, G, H, K, L1, S, W, and Z in the airways of Friend leukemia virus B sensitive strain mice. Increased proteases were present in the bronchoalveolar lavage fluid (BALF) and lung tissue during infection. Mitochondrial antiviral-signaling protein (MAVS) and TIR-domain-containing adapter-inducing interferon-β-deficient mice were exposed to RSV. Mavs-deficient mice had significantly lower expression of airway MMP-2, -3, -7, -8, -9, -10, -12, -13, and -28 and cathepsins C, G, K, S, W, and Z. In lung epithelial cells, retinoic acid-inducible gene-1 (RIG-I) was identified as the major RIG-I-like receptor required for RSV-induced protease expression via MAVS. Overexpression of RIG-I or treatment with interferon-β in these cells induced MMP and cathepsin gene and protein expression. The significance of RIG-1 protease induction was demonstrated by the fact that inhibiting proteases with batimastat, E64 or ribavirin prevented airway hyperresponsiveness and enhanced viral clearance in RSV-infected mice.

Host-Viral Interactions: Role of Pattern Recognition Receptors (PRRs) in Human Pneumovirus Infections

Acute respiratory tract infection (RTI) is a leading cause of morbidity and mortality worldwide and the majority of RTIs are caused by viruses, among which respiratory syncytial virus (RSV) and the closely related human metapneumovirus (hMPV) figure prominently. Host innate immune response has been implicated in recognition, protection and immune pathological mechanisms. Host-viral interactions are generally initiated via host recognition of pathogen-associated molecular patterns (PAMPs) of the virus. This recognition occurs through host pattern recognition receptors (PRRs) which are expressed on innate immune cells such as epithelial cells, dendritic cells, macrophages and neutrophils. Multiple PRR families, including Toll-like receptors (TLRs), RIG-I-like receptors (RLRs) and NOD-like receptors (NLRs), contribute significantly to viral detection, leading to induction of cytokines, chemokines and type I interferons (IFNs), which subsequently facilitate the eradication of the virus. This review focuses on the current literature on RSV and hMPV infection and the role of PRRs in establishing/mediating the infection in both in vitro and in vivo models. A better understanding of the complex interplay between these two viruses and host PRRs might lead to efficient prophylactic and therapeutic treatments, as well as the development of adequate vaccines.

TLR9 is expressed in human papillomavirus-positive cervical cells and is overexpressed in persistent infections

Control of human papillomavirus (HPV) infection involves the activation of Toll-like receptors (TLRs), key components of the mucosal antiviral response. Available studies on TLR expression in HPV-positive cervical cells are limited and reported conflicting results. This study quantified TLR 2, 3, 4, 7 and 9 transcripts in low-risk (LR) and high-risk (HR) HPV-positive and HPV-negative cervical samples from 154 women attending a gynaecological clinic. Expression levels of TLR 2, 3, 4 and 7 did not differ among samples, whereas TLR9 levels were quite significantly higher in LR and marginally significant in HR HPV-positive samples, with respect to the HPV-negative samples. Interestingly, in a subgroup of women with documented previous HPV-infection, TLR9 levels were extremely higher in patients persistently positive to the same HPV genotype for more than 1 year, with respect to women who cleared HPV infection and to those re-infected with a different genotype. These findings implicate TLR9 in the response to LR and HR HPVs, including HPV 16 known to interfere with TLR9 transcription in cell lines. Elevated TLR9 levels without HPV clearance in persistently infected women could drive inflammation thereby contributing to cervical cancer risk.

Leukemia inhibitory factor protects the lung during respiratory syncytial viral infection

BACKGROUND

Respiratory syncytial virus (RSV) infects the lung epithelium where it stimulates the production of numerous host cytokines that are associated with disease burden and acute lung injury. Characterizing the host cytokine response to RSV infection, the regulation of host cytokines and the impact of neutralizing an RSV-inducible cytokine during infection were undertaken in this study.

METHODS

A549, primary human small airway epithelial (SAE) cells and wild-type, TIR-domain-containing adapter-inducing interferon-β (Trif) and mitochondrial antiviral-signaling protein (Mavs) knockout (KO) mice were infected with RSV and cytokine responses were investigated by ELISA, multiplex analysis and qPCR. Neutralizing anti-leukemia inhibitory factor (LIF) IgG or control IgG was administered to a group of wild-type animals prior to RSV infection.

RESULTS AND DISCUSSION

RSV-infected A549 and SAE cells release a network of cytokines, including newly identified RSV-inducible cytokines LIF, migration inhibitory factor (MIF), stem cell factor (SCF), CCL27, CXCL12 and stem cell growth factor beta (SCGF-β). These RSV-inducible cytokines were also observed in the airways of mice during an infection. To identify the regulation of RSV inducible cytokines, Mavs and Trif deficient animals were infected with RSV. In vivo induction of airway IL-1β, IL-4, IL-5, IL-6, IL-12(p40), IFN-γ, CCL2, CCL5, CCL3, CXCL1, IP-10/CXCL10, IL-22, MIG/CXCL9 and MIF were dependent on Mavs expression in mice. Loss of Trif expression in mice altered the RSV induction of IL-1β, IL-5, CXCL12, MIF, LIF, CXCL12 and IFN-γ. Silencing of retinoic acid-inducible gene-1 (RIG-I) expression in A549 cells had a greater impact on RSV-inducible cytokines than melanoma differentiation-associated protein 5 (MDA5) and laboratory of genetics and physiology 2 (LGP2), and Trif expression. To evaluate the role of LIF in the airways during RSV infection, animals were treated with neutralizing anti-LIF IgG, which enhanced RSV pathology observed with increased airspace protein content, apoptosis and airway hyperresponsiveness compared to control IgG treatment.

CONCLUSIONS

RSV infection in the epithelium induces a network of immune factors to counter infection, primarily in a RIG-I dependent manner. Expression of LIF protects the lung from lung injury and enhanced pathology during RSV infection.

Interferon lambda 1-3 expression in infants hospitalized for RSV or HRV associated bronchiolitis

OBJECTIVES

The airway expression of type III interferons (IFNs) was evaluated in infants hospitalized for respiratory syncytial virus (RSV) or rhinovirus (HRV) bronchiolitis. As an additional objective we sought to determine whether a different expression of IFN lambda 1-3 was associated with different harboring viruses, the clinical course of bronchiolitis or with the levels of well established IFN stimulated genes (ISGs), such as mixovirus resistance A (MxA) and ISG56.

METHODS

The analysis was undertaken in 118 infants with RSV or HRV bronchiolitis. Nasopharyngeal washes were collected for virological studies and molecular analysis of type III IFN responses.

RESULTS

RSV elicited higher levels of IFN lambda subtypes when compared with HRV. A similar expression of type III IFN was found in RSVA or RSVB infected infants and in those infected with HRVA or HRVC viruses. Results also indicate that IFN lambda 1 and IFN lambda 2-3 levels were correlated with each other and with MxA and ISG56-mRNAs. In addition, a positive correlation exists between the IFN lambda1 levels and the clinical score index during RSV infection. In particular, higher IFN lambda 1 levels are associated to an increase of respiratory rate.

CONCLUSIONS

These findings show that differences in the IFN lambda 1-3 levels in infants with RSV or HRV infections are present and that the expression of IFN lambda 1 correlates with the severity of RSV bronchiolitis.

Interleukin-32 isoforms: expression, interaction with interferon-regulated genes and clinical significance in chronically HIV-1-infected patients

Given the growing evidence for a role of interleukin-32 (IL-32) in the immune response to HIV-1 infection and its interplay with type I and III interferons (IFNs), we studied the gene expression of IL-32 isoforms (α and nonα) in untreated chronically HIV-1-infected patients and in gender- and age-matched healthy individuals. To further characterize both the anti-HIV properties of IL-32 and the cytokine's relationship with host antiviral innate immune responses, we evaluated whether IL-32 can induce ex vivo the expression of antiviral IFN-induced genes (ISGs), namely myxovirus resistance A (MxA), and apolipoprotein B mRNA-editing enzyme catalytic (APOBEC)3G and APOBEC3F. We also investigated whether in vivo IL-32 (α and nonα) mRNA levels were correlated with those of MxA and APOBEC3G/3F. Results indicated that IL-32 (α and nonα) mRNA levels were significantly higher in HIV-1-infected patients than in healthy individuals. Furthermore, IL-32 (α and nonα) mRNA levels correlated negatively with HIV RNA levels, but not with the CD4(+) T-cell count. Our ex vivo studies disclosed that ISGs mRNA levels were increased after IL-32γ treatment of peripheral blood mononuclear cells. Interestingly, significant positive correlations were found between transcript levels of both IL-32α and IL-32nonα and those of MxA and APOBEC3G/3F in untreated chronically HIV-1-infected patients. Overall, our results demonstrated that IL-32 isoforms are highly expressed during chronic HIV-1 infection and that IL-32 could have a central role in the antiviral immune response against HIV-1.

Decreased pattern recognition receptor signaling, interferon-signature, and bactericidal/permeability-increasing protein gene expression in cord blood of term low birth weight human newborns

Background

Morbidity and mortality rates of low birth weight (LBW) newborns at term are higher than rates in normal birth weight (NBW) newborns. LBW newborns are at greater risk to acquire recurrent bacterial and viral infections during their first few weeks of life possibly as an outcome of compromised innate immune functions. As adaptive immunity is in a naive state, increased risk of infection of LBW as compared to NBW newborns may reflect impairments in innate immunity.

Methodology

To characterize the increased susceptibility to infections in LBW newborns we used microarray technology to identify differences in gene expression in LBW newborns (n = 8) compared to NBW newborns (n = 4) using cord blood. The results obtained from the microarray study were validated on a larger number of samples using real time RT-PCR (LBW = 22, NBW = 18) and western blotting (LBW = 12, NBW = 12). The Interferome database was used to identify interferon (IFN) signature genes and ingenuity pathway analysis identified canonical pathways and biological functions associated with the differentially expressed genes in LBW newborns. ELISAs for IFNs and bactericidal/permeability-increasing protein were performed in both LBW and NBW newborns and in adults (LBW = 18, NBW = 18, Adults  = 8).

Principal Findings

Upon microarray analysis, we identified 1,391 differentially expressed genes, of which, 1,065 genes were down-regulated and 326 genes were up-regulated in the LBW compared to NBW newborns. Of note, 70 IFN-signature genes were found to be significantly down-regulated in LBW compared to NBW newborns. Ingenuity pathway analysis revealed pattern recognition receptors signaling including Toll-Like Receptors (TLRs) -1, -5, and -8 genes and IFN signaling as the most significantly impacted pathways. Respiratory infectious diseases were the most significantly affected bio-functions in LBW newborns.

Conclusion and Significance

Diminished PRRs, IFN-signature, and BPI gene expression raises the possibility that impairments in these pathways contribute to the susceptibility of LBW term infants to infection.

Role of human Toll-like receptors in naturally occurring influenza A infections

BACKGROUND

We investigated the roles of Toll-like receptors (TLRs) in naturally occurring influenza.

METHODS

A prospective, case - control study was conducted. Adults hospitalized with virologically confirmed influenza A infections (onset <48 hours, before treatment) were compared with age-/gender-matched controls. TLRs (2, 3, 4, 7, 8, 9) expression in monocytes and dendritic cells (DCs - total, myeloid, plasmacytoid) was quantitated using flow cytometry. Gene expression of RLRs (RIG-1, MDA-5) was evaluated using real-time PCR. Concomitant signaling molecules expression, plasma cytokine/chemokine concentrations, and respiratory tract viral loads were measured. PBMCs were cultured and stimulated ex vivo with TLR-specific ligands for cytokine responses.

RESULTS

Forty two patients with influenza (24 A/H3N2, 18 A/H1N1pdm09) and 20 controls were studied. Patients' mean age was 68 ± 16 years; 81% had respiratory/cardiovascular complications. There were increased cellular expressions of TLR9, TLR8, TLR3, and TLR7 during influenza; TLR2 and TLR4 were suppressed. Results were similar for both virus strains. Higher TLR expression levels at presentation significantly correlated with lower viral loads (Spearman's rho: -0.46 to -0.69 for TLR9, TLR8, and TLR3; P-values <0.05). Multivariate regression models (adjusted for age, comorbidity, disease severity, time from onset) confirmed their independent associations. Increased signaling molecules (phospho-MAPKs, IκB) and inflammatory cytokines (IL-6, sTNFR-1, CCL2/MCP-1; CXCL10/IP-10, IFN-γ) correlated with increased TLR expression. RLRs were upregulated simultaneously. PBMCs of patients with influenza showed significant, dynamic changes in their cytokine responses upon TLR stimulation, compared with controls.

CONCLUSIONS

Our results suggest that TLRs play an important role in early, innate viral inhibition in naturally occurring influenza. Inflammatory cytokine responses are concomitantly induced. These findings support investigation of TLR targeting as a novel intervention approach for prophylaxis against influenza.

Respiratory syncytial virus interaction with human airway epithelium

Although respiratory syncytial virus (RSV) is a major human respiratory pathogen, our knowledge of how it causes disease in humans is limited. Airway epithelial cells are the primary targets of RSV infection in vivo, so the generation and exploitation of RSV infection models based on morphologically and physiologically authentic well-differentiated primary human airway epithelial cells cultured at an air-liquid interface (WD-PAECs) provide timely developments that will help to bridge this gap. Here we review the interaction of RSV with WD-PAEC cultures, the authenticity of the RSV-WD-PAEC models relative to RSV infection of human airway epithelium in vivo, and future directions for their exploitation in our quest to understand RSV pathogenesis in humans.

Innate immune responses to respiratory syncytial virus infection

The innate immune response has a critical role in the initial stages of respiratory syncytial virus (RSV) infection and provides important instructional control that determines the direction of the acquired immune response and the severity of subsequent disease. Contributions to innate immunity include responses initiated in epithelial cells, dendritic cells, and macrophages. The initiation and the intensity of the response depends upon the recognition of pathogen-associated molecular patterns (PAMPs) that activate various pattern recognition receptors (PRRs) such as toll-like receptors (TLR), RIG-I-like receptors (RLR), and NOD-like receptors (NLR), that induce innate cytokines and chemokines that promote inflammation and direct the recruitment of immune cells as well as promote anti-viral responses. In this review, we summarize the results of numerous studies that have characterized the innate immune responses that contribute to the RSV-induced responses and may be important considerations for the development of efficacious vaccine strategies.

Perinatal lamb model of respiratory syncytial virus (RSV) infection

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. Many animal models are used to study RSV, but most studies investigate disease in adult animals which does not address the unique physiology and immunology that makes infants more susceptible. The perinatal (preterm and term) lamb is a useful model of infant RSV disease as lambs have similar pulmonary structure including airway branching, Clara and type II cells, submucosal glands and Duox/lactoperoxidase (LPO) oxidative system, and prenatal alveologenesis. Lambs can be born preterm (90% gestation) and survive for experimentation although both preterm and term lambs are susceptible to ovine, bovine and human strains of RSV and develop clinical symptoms including fever, tachypnea, and malaise as well as mild to moderate gross and histologic lesions including bronchiolitis with epithelial injury, neutrophil infiltration and syncytial cell formation. RSV disease in preterm lambs is more severe than in term lambs; disease is progressively less in adults and age-dependent susceptibility is a feature similar to humans. Innate and adaptive immune responses by perinatal lambs closely parallel those of infants. The model is used to test therapeutic regimens, risk factors such as maternal ethanol consumption, and formalin inactivated RSV vaccines.

Pattern recognition receptors for respiratory syncytial virus infection and design of vaccines

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract illness in infants and young children. Host immune response has been implicated in both the protection and immunopathological mechanisms. Pattern recognition receptors (PRRs) expressed on innate immune cells during RSV infection recognize the RSV-associated molecular patterns and activate innate immune cells as well as mediate airway inflammation, protective immune response, and pulmonary immunopathology. The resident and recruited innate immune cells play important roles in the protection and pathogenesis of an RSV disease by expressing these PRRs. Agonist-binding PRRs are the basis of many adjuvants that are essential for most vaccines. In the present review, we highlight recent advances in the innate immune recognition of and responses to RSV through PRRs, including toll-like receptors (TLRs), retinoic acid-inducible gene (RIG)-I-like receptors (RLRs), and nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs). We also describe the role of PRRs in the design of RSV vaccines.

Evaluation of interleukin 28B single nucleotide polymorphisms in infants suffering from bronchiolitis

The genetic diversity of the host is believed to be the key of the diversity in the clinical presentation of bronchiolitis. The aim of this study was to determine whether the known rs12979860 and rs8099917 single nucleotide polymorphisms (SNPs) in interleukin (IL)28B region, influence clinical features and natural history of bronchiolitis. Both SNPs showed no significant association with the risk of hospitalization for respiratory syncytial virus (RSV), viral load, disease severity, and other clinical features of patients. Interestingly infants carrying IL28B rs12979860 TT genotype had lower age at hospital admission than that of infants carrying CC/CT genotypes. Overall our results indicate that both IL28B SNPs had no impact on the clinical course of bronchiolitis with the only exception of the IL28B rs12979860 SNP which increased the risk of hospitalization for bronchiolitis at early age.

Reduced inflammation and altered innate response in neonates during paramyxoviral infection

Background

Human infants are frequently hospitalized due to infection with the paramyxovirus respiratory syncytial virus (RSV). However, very little is known about the neonatal response to paramyxoviral infection. Here, a neonatal model of paramyxoviral infection is developed using the mouse pathogen Sendai virus (SeV).

Results

Adult mice infected with SeV developed a predominantly neutrophilic inflammatory cell influx and a concomitant reduction in lung function, as determined by oxygen saturation. In contrast, neonates with SeV had significantly reduced inflammation and normal lung function. Surprisingly, infected neonates had similar viral loads as adult mice. A reduced neutrophil influx in the neonates may be due in part to reduced expression of both CXCL2 and intracellular adhesion molecule-1 (ICAM-1). Expression of IFN-γ and TNF-α increased in a dose-dependent manner in adult lungs, but neonates did not increase expression of either of these cytokines, even at the highest doses. Importantly, the expression of the RIG-I-like receptors (RLRs) was delayed in the neonatal mice, which might have contributed to their reduced inflammation and differential cytokine expression.

Conclusions

Neonatal mice developed similar SeV titers and cleared the virus with similar efficiency despite developing a dramatically lower degree of pulmonary inflammation compared to adults. This suggests that inflammation in the lung may not be required to control viral replication. Future studies will be needed to determine any effect the reduced inflammation may have on the development of a protective memory response in neonates.

Type-III interferon, not type-I, is the predominant interferon induced by respiratory viruses in nasal epithelial cells

As an innate immune response against diverse viral infections, a host induces two types of interferon (IFN), type-I (IFN-β/α) and type-III (IFN-λ). We investigated IFN inductions by respiratory viruses, including respiratory syncytial virus (RSV), measles virus and mumps virus in human nasal epithelial cells (NECs). IFN-λ, but not IFN-β/α, was induced by respiratory virus infection in primary NECs and immortalized NECs through transfection with the human telomerase reverse transcriptase gene (hTERT-NECs). In contrast, both IFN-λ and IFN-β/α were induced by RSV infection in human bronchiolar carcinoma cell line A549. Suppression of retinoic acid-inducible gene-I (RIG-I) expression using siRNA significantly reduced IFN-λ1 production in RSV-infected hTERT-NECs, while suppression of melanoma differentiation-associated gene 5 (MDA5) expression did not. Exogenous IFN-λ1 treatment suppressed RSV replication and chemokine induction in hTERT-NECs. These data indicate that IFN-λ, but not IFN-β/α, contributes to the main first line defense via RIG-I-dependent pathway against respiratory virus infection in NECs.

Advances in the diagnosis of respiratory tract infections: role of the Luminex xTAG respiratory viral panel

Clinical laboratories providing an etiological diagnosis of respiratory tract infections (RTI) have increasingly relied on nucleic acid amplification tests. Polymerase chain reaction‐based methods are becoming more standardized, and several have undergone the scrutiny of regulatory agencies mandated to assess the risks and benefits of implementing pathogen‐detection assays into diagnostic algorithms. Respiratory viruses lead to both upper and lower RTI and are implicated in exacerbations of chronic pulmonary conditions. Viruses from different taxonomic families present with overlapping clinical signs and symptoms, necessitating an accurate laboratory diagnosis. The clinical utility of diagnostic algorithms incorporating tests for respiratory viruses will depend on the breadth of pathogen coverage and the time to reliable and actionable results. This review covers strategies for detecting a panel of respiratory viruses employed over the last decade that have enabled an etiological diagnosis of RTI in a cost‐effective manner.

Local cytokine response upon respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the leading cause of childhood hospitalization and respiratory distress and has been recognized for several decades as a major health and economic burden worldwide. This virus has developed several virulence mechanisms to impair the establishment of a protective immune response to re-infection. Accordingly, inefficient immunological memory is usually generated after exposure to this pathogen. Furthermore, it has been shown that RSV can actively promote the induction of an inadequate cellular immune response at the site of infection that causes exacerbated inflammation in the respiratory tract. Such an inflammatory response is both inefficient for clearing the virus and can be responsible for detrimental symptoms, such as asthma and wheezing. Recent data suggest that RSV possesses molecular mechanisms to induce the secretion of pro-inflammatory cytokines that modulate the immune response and impair viral clearance by reducing IFN-γ production. Here, we discuss recent research leading to the identification of RSV virulence factors that are responsible of promoting a pro-inflammatory environment at the airways and their implications on pathogenicity.

TLR4 Asp299Gly and Thr399Ile polymorphisms: no impact on human immune responsiveness to LPS or respiratory syncytial virus

Background

A broad variety of natural environmental stimuli, genotypic influences and timing all contribute to expression of protective versus maladaptive immune responses and the resulting clinical outcomes in humans. The role of commonly co-segregating Toll-like receptor 4 (TLR4) non-synonymous single nucleotide polymorphisms Asp299Gly and Thr399Ile in this process remains highly controversial. Moreover, what differential impact these polymorphisms might have in at risk populations with respiratory dysfunction, such as current asthma or a history of infantile bronchiolitis, has never been examined. Here we determine the importance of these polymorphisms in modulating LPS and respiratory syncytial virus (RSV) - driven cytokine responses. We focus on both healthy children and those with clinically relevant respiratory dysfunction.

Methodology

To elucidate the impact of TLR4 Asp299Gly and Thr399Ile on cytokine production, we assessed multiple immune parameters in over 200 pediatric subjects aged 7–9. Genotyping was followed by quantification of pro- and anti-inflammatory cytokine responses by fresh peripheral blood mononuclear cells upon acute exposure to LPS or RSV.

Principal Findings

In contrast to early reports, neither SNP influenced immune responses evoked by LPS exposure or RSV infection, as measured by the intermediate phenotype of pro- and anti-inflammatory cytokine responses to these ubiquitous agents. There is no evidence of altered sensitivity in populations with “at risk” clinical phenotypes.

Conclusions/Significance

Genomic medicine seeks to inform clinical practice. Determination of the TLR4 Asp299Gly/Thr399Ile haplotype is of no clinical benefit in predicting the nature or intensity of cytokine production in children whether currently healthy or among specific at-risk groups characterized by prior infantile broncholitis or current asthma.

Respiratory viral infections in infants: causes, clinical symptoms, virology, and immunology

In global terms, respiratory viral infection is a major cause of morbidity and mortality. Infancy, in particular, is a time of increased disease susceptibility and severity. Early-life viral infection causes acute illness and can be associated with the development of wheezing and asthma in later life. The most commonly detected viruses are respiratory syncytial virus (RSV), rhinovirus (RV), and influenza virus. In this review we explore the complete picture from epidemiology and virology to clinical impact and immunology. Three striking aspects emerge. The first is the degree of similarity: although the infecting viruses are all different, the clinical outcome, viral evasion strategies, immune response, and long-term sequelae share many common features. The second is the interplay between the infant immune system and viral infection: the immaturity of the infant immune system alters the outcome of viral infection, but at the same time, viral infection shapes the development of the infant immune system and its future responses. Finally, both the virus and the immune response contribute to damage to the lungs and subsequent disease, and therefore, any prevention or treatment needs to address both of these factors.