Impaired immune response in severe human lower tract respiratory infection by respiratory syncytial virus

Altered Treg and cytokine responses in RSV-infected infants

BACKGROUND

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and pneumonia in children under 1 y of age in the USA. The host immune response is believed to contribute to RSV-induced disease. We hypothesize that severe RSV infection in infants is mediated by insufficient regulation of the host immune response of regulatory T cells (Tregs) resulting in immunopathology.

METHODS

Blood and nasal aspirates from 23 RSV-infected and 17 control infants under 1 y of age were collected. Treg frequencies were determined by flow cytometry from peripheral blood mononuclear cells. Analysis of 24 cytokines was measured by multiplex assay on nasal aspirates.

RESULTS

We demonstrate that the frequency of activated Tregs is significantly reduced in the peripheral blood of RSV-infected infants compared with age-matched controls. Surprisingly, T helper (Th)17 related cytokines including interleukin (IL)-1β, IL-17A, and IL-23 were associated with a reduction in clinical symptoms of respiratory distress. In addition, the amount of IL-33 protein in nasal washes, a cytokine important in maintaining Treg homeostasis in mucosal tissues, was decreased in RSV-infected children.

CONCLUSION

These results suggest that decreased Treg numbers and an inability to properly control the host inflammatory response results in severe RSV infection.

Baicalin from Scutellaria baicalensis blocks respiratory syncytial virus (RSV) infection and reduces inflammatory cell infiltration and lung injury in mice

The roots of Scutellaria baicalensis has been used as a remedy for inflammatory and infective diseases for thousands of years. We evaluated the antiviral activity against respiratory syncytial virus (RSV) infection, the leading cause of childhood infection and hospitalization. By fractionation and chromatographic analysis, we determined that baicalin was responsible for the antiviral activity of S. baicalensis against RSV infection. The concentration for 50% inhibition (IC₅₀) of RSV infection was determined at 19.9 ± 1.8 μM, while the 50% cytotoxic concentration (CC₅₀) was measured at 370 ± 10 μM. We then used a mouse model of RSV infection to further demonstrate baicalin antiviral effect. RSV infection caused significant lung injury and proinflammatory response, including CD4 and CD8 T lymphocyte infiltration. Baicalin treatment resulted in reduction of T lymphocyte infiltration and gene expression of proinflammatory factors, while the treatment moderately reduced RSV titers recovered from the lung tissues. T lymphocyte infiltration and cytotoxic T lymphocyte modulated tissue damage has been identified critical factors of RSV disease. The study therefore demonstrates that baicalin subjugates RSV disease through antiviral and anti-inflammatory effect.

Cytokine responses in primary and secondary respiratory syncytial virus infections

BACKGROUND

Primary respiratory syncytial virus (RSV) infections are characterized by high levels of IL-8 and an intense neutrophilia. Little is known about the cytokine responses in secondary infections. Preschool children experiencing RSV secondary infections were recruited from the siblings of infants admitted to hospital with RSV acute bronchiolitis.

METHODS

Fifty-one infants with acute bronchiolitis (39 RSV positive, 12 RSV negative) and 20 age-matched control infants were recruited. In addition, seven older siblings of infants from the RSV-positive cohort and confirmed RSV infection were recruited. Samples of nasal secretions were obtained using a flocked swab, and secretions extracted using centrifugation. Cytokine bead array was used to obtain levels of interleukin (IL)-17A, IL-8, IL-6, IL-21, and tumor necrosis factor-α.

RESULTS

Levels of IL-8 and IL-6 were significantly lower in the RSV-positive siblings compared with the RSV-positive infants. There were no significant differences between levels of the other cytokines in the primary and secondary infections.

CONCLUSION

The very high levels of IL-8 and IL-6 response characteristic of the primary RSV infection was not observed in secondary RSV-positive infections and this did not appear to be due to a global reduction in cytokine production.

NK cell immunophenotypic and genotypic analysis of infants with severe respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the leading cause of severe lower respiratory tract infection in infants. Reduced numbers of NK cells have been reported in infants with severe RSV infection; however, the precise role of NK cells during acute RSV infection is unclear. In this study the NK and T cell phenotypes, LILRB1 gene polymorphisms and KIR genotypes of infants hospitalized with RSV infection were analyzed. Compared to controls, infants with acute RSV infection showed a higher proportion of LILRB1+ T cells; in addition, a subgroup of infants with RSV infection showed an increase in LILRB1+ NK cells. No differences in NKG2C, NKG2A, or CD161 expression between RSV infected infants and controls were observed. LILRB1 genotype distribution of the rs3760860 A>G, and rs3760861 A>G single nucleotide polymorphisms differed between infants with RSV infection and healthy donors, whereas no differences in any of the KIR genes were observed. Our results suggest that LILRB1 participates in the pathogenesis of RSV infection. Further studies are needed to define the role of LILRB1+ NK in response to RSV and to confirm an association between LILRB1 polymorphisms and the risk of severe RSV infection.

Bovine Gamma Delta T Cells Contribute to Exacerbated IL-17 Production in Response to Co-Infection with Bovine RSV and Mannheimia haemolytica

Human respiratory syncytial virus (HRSV) is a leading cause of severe lower respiratory tract infection in children under five years of age. IL-17 and Th17 responses are increased in children infected with HRSV and have been implicated in both protective and pathogenic roles during infection. Bovine RSV (BRSV) is genetically closely related to HRSV and is a leading cause of severe respiratory infections in young cattle. While BRSV infection in the calf parallels many aspects of human infection with HRSV, IL-17 and Th17 responses have not been studied in the bovine. Here we demonstrate that calves infected with BRSV express significant levels of IL-17, IL-21 and IL-22; and both CD4 T cells and γδ T cells contribute to this response. In addition to causing significant morbidity from uncomplicated infections, BRSV infection also contributes to the development of bovine respiratory disease complex (BRDC), a leading cause of morbidity in both beef and dairy cattle. BRDC is caused by a primary viral infection, followed by secondary bacterial pneumonia by pathogens such as Mannheimia haemolytica. Here, we demonstrate that in vivo infection with M. haemolytica results in increased expression of IL-17, IL-21 and IL-22. We have also developed an in vitro model of BRDC and show that co-infection of PBMC with BRSV followed by M. haemolytica leads to significantly exacerbated IL-17 production, which is primarily mediated by IL-17-producing γδ T cells. Together, our results demonstrate that calves, like humans, mount a robust IL-17 response during RSV infection; and suggest a previously unrecognized role for IL-17 and γδ T cells in the pathogenesis of BRDC.

Interleukin-15 is associated with disease severity in viral bronchiolitis

Disease severity in viral bronchiolitis in infancy is difficult to predict and has been linked to host innate immunity. The study aimed to investigate the innate cytokine interleukin-15 (IL-15) as a marker of disease severity.A prospective single-centre observational study was conducted in a university-affiliated paediatric teaching hospital, comparing children (0-18 months) hospitalised for viral bronchiolitis, those admitted to the paediatric intensive care unit with severe disease and healthy age-matched controls. IL-15-related parameters were compared between groups. PCR and microRNA (miRNA) sequencing was undertaken on natural killer (NK) cells collected from study participants.Samples from 88 children with viral bronchiolitis and 43 controls enrolled between 2009 and 2012 were analysed. Peripheral blood mononuclear cell (PBMC) IL-15 mRNA expression was significantly higher in those with moderate severity bronchiolitis compared with controls and those with severe disease. Serum IL-15 levels correlated with disease severity. The relative frequency of NK cells in peripheral blood was significantly reduced in participants with bronchiolitis. The NK cell miRNA transcriptome in bronchiolitis was distinct. Targets of de-regulated miRNA were differentially expressed in bronchiolitis, including JAK3, STAT5A and NFKB1 on the IL-15 signalling pathway.IL-15 is associated with disease severity in children hospitalised with viral bronchiolitis.

The role of Th17 and Treg responses in the pathogenesis of RSV infection

The respiratory syncytial virus (RSV) represents the leading cause of viral bronchiolitis and pneumonia in children worldwide and is associated with high morbidity, hospitalization rate, and significant mortality rates. The immune response elicited by RSV is one of the main factors contributing to the pathogenesis of the disease. Two subsets of the cellular immune response, the T helper 17 cell (Th17) and the regulatory T-cell (Treg), and more particularly the balance between these two subsets, might play a significant role in the pathogenesis of the RSV infection. The developmental pathways of Th17 and Treg cells are closely and reciprocally interconnected and plasticity has been demonstrated from Treg toward Th17. During an RSV infection, the functions of both subsets are opposed to one another regarding viral clearance and clinical severity. Th17 and Treg cells offer a promising new view on the pathogenesis of an RSV infection and deserve further exploration.

Pro-Inflammatory Cytokines in Nasopharyngeal Aspirate From Hospitalized Children With Respiratory Syncytial Virus Infection With or Without Rhinovirus Bronchiolitis, and Use of the Cytokines as Predictors of Illness Severity

Respiratory syncytial virus (RSV) and human rhinovirus (HRV) respiratory infection in children induce production of inflammatory interleukins (ILs) in the respiratory epithelium. As IL(s) determine the severity of illness, the purpose of this study was to identify the pro-inflammatory IL(s) that could be predictor(s) of clinical severity. One hundred and fifteen patients <2 years old with bronchiolitis due to RSV and /or HRV and 38 controls were selected from a hospital and an outpatient clinic. Clinical data of all patients were recorded. Severity was defined by the number of days with oxygen need. Nasopharyngeal aspirates (NPA) were collected to perform viral diagnosis by quantitative reverse transcription and polymerase chain reaction (qRT-PCR) and to quantify ILs: TNF-α, IL-10, IL-6, IL-1β, and IL-8, by flow cytometry. Simple and multiple regression and receiver operating characteristic (ROC) curves were used for statistical analysis. Of the patients selected 60 were single RSV, 28 RSV associated to HRV, and 27 single HRV. All patients (115) showed significantly higher IL levels when compared with controls. Levels of IL-6, IL-1β, and IL-8 detected in NPA from RSV single and associated to HRV were significantly higher than HRV infected and positively associated with days requiring O2.Levels of IL-6, IL-1β, and IL-8 detected in NPA from patients infected with RSV only or with both RSV and HRV are increased, and any of those 3 cytokines may have a predictive value for the number of days with need of supplemental oxygen.

New insights on the viral and host factors contributing to the airway pathogenesis caused by the respiratory syncytial virus

The respiratory syncytial virus (RSV) is the most prevalent etiological agent of lower respiratory tract infections and the first cause of hospitalization in infants due to respiratory disease worldwide. However, efforts to develop safe and effective vaccines and antivirals have been challenged by an incomplete understanding of the RSV pathogenesis and the host immune response to RSV infection in the airways. Here, we discuss recent advances in understanding the interaction between RSV and the epithelium to induce pathogenesis in the airways, such as the role of the RSV NS2 protein in the airway epithelium, as well as the events involved in the RSV entry process. In addition, we summarize the cellular factors produced by airway epithelial cells (AECs) in response to RSV infection that lead to the activation of innate and adaptive immune responses, inducing lung inflammation and disease. Further, we discuss the possible contribution of a recently identified cytokine, thymic stromal lymphopoitein (TSLP), in the lung immunopathology caused by RSV.

Mucosal delivery of a vectored RSV vaccine is safe and elicits protective immunity in rodents and nonhuman primates

Respiratory Syncytial Virus (RSV) is a leading cause of severe respiratory disease in infants and the elderly. No vaccine is presently available to address this major unmet medical need. We generated a new genetic vaccine based on chimpanzee Adenovirus (PanAd3-RSV) and Modified Vaccinia Ankara RSV (MVA-RSV) encoding the F, N, and M2-1 proteins of RSV, for the induction of neutralizing antibodies and broad cellular immunity. Because RSV infection is restricted to the respiratory tract, we compared intranasal (IN) and intramuscular (M) administration for safety, immunogenicity, and efficacy in different species. A single IN or IM vaccination completely protected BALB/c mice and cotton rats against RSV replication in the lungs. However, only IN administration could prevent infection in the upper respiratory tract. IM vaccination with MVA-RSV also protected cotton rats from lower respiratory tract infection in the absence of detectable neutralizing antibodies. Heterologous prime boost with PanAd3-RSV and MVA-RSV elicited high neutralizing antibody titers and broad T-cell responses in nonhuman primates. In addition, animals primed in the nose developed mucosal IgA against the F protein. In conclusion, we have shown that our vectored RSV vaccine induces potent cellular and humoral responses in a primate model, providing strong support for clinical testing.

New options in the treatment of respiratory syncytial virus disease

Respiratory syncytial virus (RSV) remains a significant cause of morbidity and mortality in infants, immunocompromised patients and the elderly. Despite the high disease burden, an effective vaccine or specific therapy are lacking which is largely due to our limited understanding of the immune response to RSV and how it relates to clinical disease severity. Current treatment for RSV remains largely supportive and RSV-specific options for prophylaxis and/or treatment are limited to palivizumab and ribavirin. There are a number of promising compounds currently under development, including new monoclonal antibodies and small molecules. These newer antivirals have the potential to impact both the prevention and treatment of RSV disease in the main target populations.

Role of IL-25 in Immunity

IL-25 a 2o KDa protein mostly known as IL-17E, encoded by chromosome 14, and containing 117 amino acids. Cytokine IL-17 family consists of 6 members; IL-17A to IL-17F, among which IL-25 has a unique structure and function. The receptor of IL-25 (IL-17BR) is highly expressed in the main Th2 cells. IL-25 regulates the internal safety of adaptive immune responses which leads to begin allergic diseases and plays a role in stimulation of pulmonary mucosal cells and fibroblasts. IL-25 can also have some effects on production of other cytokines. For instance, production of IL-25 in human and mice or injection of IL-25 to animals has resulted in production of high concentrations of Th2 cytokines, including IL-4, IL-5, and IL-13. Pilot studies have shown that mRNA of IL-25 has a high expression in Th2 cells. However, the mechanism through which IL-25 leads to Th2 immune response is still unknown. Reaction between IL-25 and IL-17BR leads to activation of transcription factors, such as NF-KB, STAT6, GATA3, NF-ATC1, JUNNB, MAPK, and JNK. IL-25 has been used against the kidney damage in mice. A large number of researchers in various countries, including the U.S. and Taiwan, have stated that IL-25 is a strong inflammatory cytokine protein which is involved in allergic inflammations.

Galectin-9 ameliorates respiratory syncytial virus-induced pulmonary immunopathology through regulating the balance between Th17 and regulatory T cells

Respiratory syncytial virus (RSV) infections are characterized by lung inflammation, mucus hypersecretion, and hyperresponsiveness. CD4+ T cells play a pivotal role in the development of RSV-induced lung pathology. Thus targeting the activation of CD4+ T cell subsets and enhancing regulatory functions of CD4+ T cells could be an effectively therapeutic approach. In the present study, we showed that RSV-induced lung inflammation can be suppressed by lectin family member Galectin-9 (Gal-9), which is identified as a T-cell immunoglobulin- and mucindomain-containing molecule-3 (Tim-3) ligand (L) and the Gal-9/Tim-3 interaction acts as a specific inhibitor of T helper(Th)1 and Th17 immune responses. Tim-3 expression was up-regulated in RSV-infected mice compared to non-infected controls. Therefore, we constructed a recombinant adenoviral (rAAV) 9-Gal-9 adenoviral plasmid, and administered it intranasally into RSV-infected mice for five times at every other day until day 8 post-infection. We found that Gal-9 administration significantly decreased viral load, inhibited mucus production, and diminished severity of lung pathology which were all induced by RSV infection. Complicated mechanisms were involved in these inhibitory effects, including inhibition of Th17 cell production, induction of regulatory cell expansion, as well as alteration of CD8 T-cell apoptosis. Our findings suggest that regulating the function of the Gal-9/Tim-3 pathway will be an effective and safe approach to treat RSV infection in lungs.

Impaired gamma delta T cell-derived IL-17A and inflammasome activation during early respiratory syncytial virus infection in infants

Respiratory syncytial virus (RSV) infection remains a significant global health burden disproportionately affecting infants and leading to long-term lung disease. IL-17A has been shown to be involved in regulating viral and allergic lung inflammatory responses, which has led to a more recent interest in its role in RSV infection. Using a neonatal mouse model of RSV, we demonstrate that neonates fail to develop IL-17A responses compared to adult mice; the main immediate IL-17A contributor in adults were γδ T cells. Antibody neutralization of IL-17A in adult mice caused increased lung inflammation and airway mucus from RSV, while exogenous IL-17A administration to RSV-infected neonates caused decreased inflammation but no change in airway mucus. We also observed a lack of pro-inflammatory cytokine production (IL-1β, IL-6) from infected neonates. Using human cord blood mononuclear cells (CBMCs) and adult peripheral blood mononuclear cells (PBMCs), we compared inflammasome activation by direct retinoic acid-inducible gene I (RIG-I) agonism; CBMCs failed to induce pro-inflammatory cytokines or IL-17A⁺ γδ T cells compared to PBMCs. Our results indicate that RSV disease severity is in part mediated by a lack of inflammasome activation and IL-17A production in neonates.

Immunity to RSV in Early-Life

Respiratory Syncytial Virus (RSV) is the commonest cause of severe respiratory infection in infants, leading to over 3 million hospitalizations and around 66,000 deaths worldwide each year. RSV bronchiolitis predominantly strikes apparently healthy infants, with age as the principal risk factor for severe disease. The differences in the immune response to RSV in the very young are likely to be key to determining the clinical outcome of this common infection. Remarkable age-related differences in innate cytokine responses follow recognition of RSV by numerous pattern recognition receptors, and the importance of this early response is supported by polymorphisms in many early innate genes, which associate with bronchiolitis. In the absence of strong, Th1 polarizing signals, infants develop T cell responses that can be biased away from protective Th1 and cytotoxic T cell immunity toward dysregulated, Th2 and Th17 polarization. This may contribute not only to the initial inflammation in bronchiolitis, but also to the long-term increased risk of developing wheeze and asthma later in life. An early-life vaccine for RSV will need to overcome the difficulties of generating a protective response in infants, and the proven risks associated with generating an inappropriate response. Infantile T follicular helper and B cell responses are immature, but maternal antibodies can afford some protection. Thus, maternal vaccination is a promising alternative approach. However, even in adults adaptive immunity following natural infection is poorly protective, allowing re-infection even with the same strain of RSV. This gives us few clues as to how effective vaccination could be achieved. Challenges remain in understanding how respiratory immunity matures with age, and the external factors influencing its development. Determining why some infants develop bronchiolitis should lead to new therapies to lessen the clinical impact of RSV and aid the rational design of protective vaccines.

Comparison of virological profiles of respiratory syncytial virus and rhinovirus in acute lower tract respiratory infections in very young Chilean infants, according to their clinical outcome

BACKGROUND

Respiratory syncytial virus (RSV) and rhinovirus (HRV) are the main cause of acute lower respiratory tract infections (ALRTIs) in infants. Viral and host-related risk factors for severe disease have also not been clearly established.

OBJECTIVE

To assess whether certain viral features of RSV and, or HRV are associated with severe ALRTI.

STUDY DESIGN

RSV and HRV were studied in nasopharyngeal samples of infants by immunofluorescence, Luminex(®) and/or real-time RT-PCR assays. Quantitation and genotyping of RSV and HRV by PCR were done.

RESULTS

Of 124 virus positive specimens, 74 (59.7%) had RSV; 22 (17.7%) HRV and 28 (22.6%) RSV-HRV co-infection. Hospitalization was required in 57/74 RSV infants (77.0%); in 10/22 HRV cases (45.5%) (p=0.006) and in 15/28 co-infected by both viruses (53.6%) (p=0.003). Severe cases were 33/74 (44.6%) RSV infections, 2/22 HRV cases (9.1%), (p<0.002) and 6/28 (21.4%) patients co-infected by RSV-HRV (p<0.026). Three genotypes (NA1, B7, B9) of RSV circulated during the study. In 33 severe infants, NA1 was detected in 19 cases (57.6%); B7 in 13 (39.4%) and B9 in 1 (3.0%) (p<0.01; OR=10.0). RSV loads were similar between outpatients and hospitalized infants (p=0.7) and among different severities (p=0.7). NA1 loads were higher than other strains (p=0.049). Three geno-groups of HRV circulated homogeneously.

CONCLUSION

In very young infants, RSV cause more severe disease than HRV. Co-infection does not increase the severity of illness. NA1 RSV genotype was associated with major frequency of hospitalization, severe respiratory disease and higher viral load.

Paramyxovirus infection regulates T cell responses by BDCA-1+ and BDCA-3+ myeloid dendritic cells

Respiratory syncytial virus (RSV) and human Metapneumovirus (hMPV), viruses belonging to the family Paramyxoviridae, are the most important causes of lower respiratory tract infection in young children. Infections with RSV and hMPV are clinically indistinguishable, and both RSV and hMPV infection have been associated with aberrant adaptive immune responses. Myeloid Dendritic cells (mDCs) play a pivotal role in shaping adaptive immune responses during infection; however, few studies have examined how interactions of RSV and hMPV with individual mDC subsets (BDCA-1⁺ and BDCA-3⁺ mDCs) affect the outcome of anti-viral responses. To determine whether RSV and hMPV induce virus-specific responses from each subset, we examined co-stimulatory molecules and cytokines expressed by BDCA-1⁺ and BDCA-3⁺ mDCs isolated from peripheral blood after infection with hMPV and RSV, and examined their ability to stimulate T cell proliferation and differentiation. Our data show that RSV and hMPV induce virus-specific and subset-specific patterns of co-stimulatory molecule and cytokine expression. RSV, but not hMPV, impaired the capacity of infected mDCs to stimulate T cell proliferation. Whereas hMPV-infected BDCA-1⁺ and BDCA-3⁺ mDCs induced expansion of Th17 cells, in response to RSV, BDCA-1⁺ mDCs induced expansion of Th1 cells and BDCA-3⁺ mDCs induced expansion of Th2 cells and Tregs. These results demonstrate a virus-specific and subset-specific effect of RSV and hMPV infection on mDC function, suggesting that these viruses may induce different adaptive immune responses.

Modulation of Respiratory TLR3-Anti-Viral Response by Probiotic Microorganisms: Lessons Learned from Lactobacillus rhamnosus CRL1505

Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract illness in infants and young children. Host immune response is implicated in both protective and immunopathological mechanisms during RSV infection. Activation of Toll-like receptor (TLR)-3 in innate immune cells by RSV can induce airway inflammation, protective immune response, and pulmonary immunopathology. A clear understanding of RSV–host interaction is important for the development of novel and effective therapeutic strategies. Several studies have centered on whether probiotic microorganisms with the capacity to stimulate the immune system (immunobiotics) might sufficiently stimulate the common mucosal immune system to improve defenses in the respiratory tract. In this regard, it was demonstrated that some orally administered immunobiotics do have the ability to stimulate respiratory immunity and increase resistance to viral infections. Moreover, during the last decade scientists have significantly advanced in the knowledge of the cellular and molecular mechanisms involved in the protective effect of immunobiotics in the respiratory tract. This review examines the most recent advances dealing with the use of immunobiotic bacteria to improve resistance against viral respiratory infections. More specifically, the article discuss the mechanisms involved in the capacity of the immunobiotic strain Lactobacillus rhamnosus CRL1505 to modulate the TLR3-mediated immune response in the respiratory tract and to increase the resistance to RSV infection. In addition, we review the role of interferon (IFN)-γ and interleukin (IL)-10 in the immunoregulatory effect of the CRL1505 strain that has been successfully used for reducing incidence and morbidity of viral airways infections in children.

Translational sciences approach to RSV vaccine development

Respiratory syncytial virus (RSV) is a major cause of lower respiratory tract infections in infants and the elderly. Despite its relatively low degree of antigenic variation, it causes frequent reinfection throughout life. Clinical manifestations of RSV disease and the immune response to infection differ in infants and the elderly, suggesting that vaccines designed to protect these two populations may require different attributes. Here, the authors describe the translational approach of utilizing data from epidemiology studies performed in these populations, the use of RSV diagnostics in clinical practice, lessons learned from previous vaccine clinical trials and the success of palivizumab in prevention of RSV disease in premature and high-risk infants to aid the development of safe and effective RSV vaccines.

Local IL-17A potentiates early neutrophil recruitment to the respiratory tract during severe RSV infection

Respiratory syncytial virus (RSV) bronchiolitis triggers a strong innate immune response characterized by excessive neutrophil infiltration which contributes to RSV induced pathology. The cytokine IL-17A enhances neutrophil infiltration into virus infected lungs. IL-17A is however best known as an effector of adaptive immune responses. The role of IL-17A in early immune modulation in RSV infection is unknown. We aimed to elucidate whether local IL-17A facilitates the innate neutrophil infiltration into RSV infected lungs prior to adaptive immunity. To this end, we studied IL-17A production in newborns that were hospitalized for severe RSV bronchiolitis. In tracheal aspirates we measured IL-17A concentration and neutrophil counts. We utilized cultured human epithelial cells to test if IL-17A regulates RSV infection-induced IL-8 release as mediator of neutrophil recruitment. In mice we investigated the cell types that are responsible for early innate IL-17A production during RSV infection. Using IL-17A neutralizing antibodies we tested if IL-17A is responsible for innate neutrophil infiltration in mice. Our data show that increased IL-17A production in newborn RSV patient lungs correlates with subsequent neutrophil counts recruited to the lungs. IL-17A potentiates RSV-induced production of the neutrophil-attracting chemokine IL-8 by airway epithelial cells in vitro. Various lung-resident lymphocytes produced IL-17A during early RSV infection in Balb/c mice, of which a local population of CD4 T cells stood out as the predominant RSV-induced cell type. By removing IL-17A during early RSV infection in mice we showed that IL-17A is responsible for enhanced innate neutrophil infiltration in vivo. Using patient material, in vitro studies, and an animal model of RSV infection, we thus show that early local IL-17A production in the airways during RSV bronchiolitis facilitates neutrophil recruitment with pathologic consequences to infant lungs.

The Innate Immune System of the Perinatal Lung and Responses to Respiratory Syncytial Virus Infection

The response of the preterm and newborn lung to airborne pathogens, particles, and other insults is initially dependent on innate immune responses since adaptive responses may not fully mature and require weeks for sufficient responses to antigenic stimuli. Foreign material and microbial agents trigger soluble, cell surface, and cytoplasmic receptors that activate signaling cascades that invoke release of surfactant proteins, defensins, interferons, lactoferrin, oxidative products, and other innate immune substances that have antimicrobial activity, which can also influence adaptive responses. For viral infections such as respiratory syncytial virus (RSV), the pulmonary innate immune responses has an essential role in defense as there are no fully effective vaccines or therapies for RSV infections of humans and reinfections are common. Understanding the innate immune response by the preterm and newborn lung may lead to preventive strategies and more effective therapeutic regimens.

Th17 lymphocytes in respiratory syncytial virus infection

Infection by respiratory syncytial virus (RSV) affects approximately 33 million infants annually worldwide and is a major cause of hospitalizations. Helper T lymphocytes (Th) play a central role in the immune response during such infections. However, Th lymphocytes that produce interleukin 17 (IL-17), known as Th17 lymphocytes, in addition to been protective can also cause pathology that accompany this type of infection. The protective effects of Th17 is associated with better prognosis in most infected individuals but heightened Th17 responses causes inflammation and pathology in others. Studies employing animal models haves shown that activated Th17 lymphocytes recruit neutrophils and facilitate tertiary lymphoid structure development in infected lungs. However, IL-17 also inhibits the ability of CD8+ lymphocytes to clear viral particles and acts synergistically with the innate immune system to exacerbate inflammation. Furthermore, IL-17 enhances IL-13 production which, in turn, promotes the activation of Th2 lymphocytes and excessive mucus production. Studies of these animal models have also shown that a lack of, or inadequate, responses by the Th1 subset of T lymphocytes enhances Th17-mediated responses and that this is detrimental during RSV co-infection in experimental asthma. The available evidence, therefore, indicates that Th17 can play contradictory roles during RSV infections. The factors that determine the shift in the balance between beneficial and adverse Th17 mediated effects during RSV infection remains to be determined.

Respiratory syncytial virus infection and recurrent wheezing in Chilean infants: a genetic background?

Respiratory syncytial virus (RSV) infection has been associated to recurrent wheezing, but pathogenic mechanisms are unclear. Interleukin-4/Interleukin-13 (IL-4/IL-13) pathway is involved in both conditions. A common host genetic susceptibility may exist in patients whom RSV will trigger severe illness and those who develop recurrent wheezing.

OBJECTIVE

To assess, by a candidate-gene approach, whether genetic polymorphisms in IL-4/IL-13 pathway are associated with RSV infection severity and its outcome in Chilean children. A cohort of 118 RSV-infected infants was analyzed and followed for one year. Severity of acute infection and later recurrent wheezing were characterized. Alleles and genotypes frequencies were determined for two SNP in each of the genes IL-4, IL-13 and IL-4Rα. Association tests and interaction analyses were performed. Enrollment included 60 moderate and 58 severe cases. Two SNP were found associated to severity during acute infection in IL-4Rα gene (Gln551Arg, Ile50Val). The follow up was completed in 71% of patients (84/118). Later recurrent wheezing was 54% in severe group, versus 31% in moderate cases (p=0.035). In relation to outcome, allele Ile50 in IL-4Rα was more frequent in patients with moderate disease and no wheezing outcome. A common protector genotype is proposed for Chilean children: IL-4Rα Ile/Ile.

CONCLUSION

Genetic variations in the host are associated to infection severity and outcome. A common genetic background might be influencing both pathologies.

CD4+ T-cell counts and interleukin-8 and CCL-5 plasma concentrations discriminate disease severity in children with RSV infection

BACKGROUND

Current tools to predict the severity of respiratory syncytial virus (RSV) infection might be improved by including immunological parameters. We hypothesized that a combination of inflammatory markers would differentiate between severe and mild disease in RSV-infected children.

METHODS

Blood and nasopharyngeal samples from 52 RSV-infected children were collected during acute infection and after recovery. Retrospectively, patients were categorized into three groups based on disease severity: mild (no supportive treatment), moderate (supplemental oxygen and/or nasogastric feeding), and severe (mechanical ventilation). Clinical data, number of flow-defined leukocyte subsets, and cytokine concentrations were compared.

RESULTS

Children with severe RSV infection were characterized by young age; lymphocytopenia; increased interleukin (IL)-8, granulocyte colony-stimulating factor (G-CSF), and IL-6 concentrations; and decreased chemokine (C-C motif) ligand (CCL-5) concentrations in plasma. The combination of plasma levels of IL-8 and CCL-5, and CD4+ T-cell counts, with cutoff values of 67 pg/ml, 13 ng/ml, and 2.3 × 10(6)/ml, respectively, discriminated severe from mild RSV infection with 82% sensitivity and 96% specificity.

CONCLUSION

This study demonstrates that the combination of CD4+ T-cell counts and IL-8 and CCL-5 plasma concentrations correlates with disease severity in RSV-infected children. In addition to clinical features, these immunological markers may be used to assess severity of RSV infection and guide clinical management.

Innate immune dysfunction is associated with enhanced disease severity in infants with severe respiratory syncytial virus bronchiolitis

BACKGROUND

Most patients with respiratory syncytial virus (RSV) bronchiolitis requiring admission to the pediatric intensive care unit (PICU) have no risk factors for severe disease. We sought to investigate the relationship between serum cytokine concentrations, innate immune responsiveness, and RSV disease severity.

METHODS

Previously healthy infants (median age, 2.6 months) with RSV bronchiolitis (PICU, n = 20; floor, n = 46) and healthy matched controls (n = 14) were enrolled, and blood samples were obtained within 24 hours of admission to measure plasma tumor necrosis factor α (TNF-α), interleukin 6 (IL-6), interleukin 8 (IL-8), and interleukin 10 (IL-10) concentrations and, whole blood lipopolysaccharide-stimulated cytokine production capacity.

RESULTS

Plasma IL-6, IL-8, and IL-10 concentrations were comparable between PICU and floor patients, but higher than in healthy controls (P < .05). In contrast, TNF-α, IL-6, and IL-8 production capacity was significantly decreased in PICU compared with both floor patients and healthy controls. In adjusted analyses, only impaired TNF-α and IL-8 production capacity were associated with longer length of stay (P = .035) and greater disease severity scores (P = .001).

CONCLUSIONS

Infants with severe RSV bronchiolitis had increased plasma cytokine concentrations and yet impaired innate immunity cytokine production capacity, which predicted worse disease outcomes. Immune monitoring of otherwise healthy infants with RSV lower respiratory tract infection could help identify patients at risk for severe disease at the time of hospitalization.

Human parainfluenza virus serotypes differ in their kinetics of replication and cytokine secretion in human tracheobronchial airway epithelium

Human parainfluenza viruses (PIVs) cause acute respiratory illness in children, the elderly, and immunocompromised patients. PIV3 is a common cause of bronchiolitis and pneumonia, whereas PIV1 and 2 are frequent causes of upper respiratory tract illness and croup. To assess how PIV1, 2, and 3 differ with regard to replication and induction of type I interferons, interleukin-6, and relevant chemokines, we infected primary human airway epithelium (HAE) cultures from the same tissue donors and examined replication kinetics and cytokine secretion. PIV1 replicated to high titer yet did not induce cytokine secretion until late in infection, while PIV2 replicated less efficiently but induced an early cytokine peak. PIV3 replicated to high titer but induced a slower rise in cytokine secretion. The T cell chemoattractants CXCL10 and CXCL11 were the most abundant chemokines induced. Differences in replication and cytokine secretion might explain some of the differences in PIV serotype-specific pathogenesis and epidemiology.

Increased expression of the glucocorticoid receptor β in infants with RSV bronchiolitis

OBJECTIVES

The majority of studies on glucocorticoid treatment in respiratory syncytial virus (RSV) bronchiolitis concluded that there are no beneficial effects. We hypothesized that RSV-infected patients may have an increased glucocorticoid receptor (GR) β expression, the isoform that is unable to bind cortisol and exert an antiinflammatory action.

METHODS

By using real-time polymerase chain reaction, we studied the expression of α and β GR in the peripheral blood mononuclear cells obtained from 49 RSV-infected infants (<1 year of age) with severe (n = 29) and mild to moderate (n = 20) illness. In plasma, we analyzed the level of cortisol by radioimmunoassay and inflammatory cytokines interleukin (IL)-10, IL-6, tumor necrosis factor-α, IL-1β, IL-8, IL-12p70, IL-2, IL-4, IL-5, interferon-γ, and IL-17 by cytometric beads assay. Statistical analysis was performed by nonparametric analysis of variance.

RESULTS

We found a significant increase of β GR expression in patients with severe illness compared with those with mild disease (P < .001) and with a group of healthy controls (P < .01). The α:β GR ratio decreased significantly in infants with severe disease compared with those with mild illness (P < .01) and with normal controls (P < .001). The expression of β GR was positively correlated with the clinical score of severity (r = .54; P < .0001).

CONCLUSIONS

The decrease of the α:β GR ratio by an increase of β receptors expression is related to illness severity and may partly explain the insensitivity to corticoid treatment in RSV-infected infants. The increased expression of β GR could be a marker of disease severity.

Specific increase in local IL-17 production during recovery from primary RSV bronchiolitis

Although Respiratory syncytial virus (RSV) bronchiolitis is the most important cause of hospital admission for infants during the winter season, the pathogenesis is largely unknown. Interleukin-17 (IL-17) concentrations were studied in nasopharyngeal aspirates from 21 non-ventilated and 17 ventilated infants admitted to hospital with RSV bronchiolitis at time of admission and discharge from the hospital. On admission, nasopharyngeal concentrations of most cytokines and chemokines were lower in non-ventilated infants than in ventilated infants, reaching statistical significance for Eotaxin, IL-1α, and IL-6. During course of disease, nasopharyngeal concentrations of most cytokines and chemokines decreased, reaching statistical significance for IL-6 and IP-10. However, nasopharyngeal IL-17 concentrations were higher at discharge than at admission in children with non-ventilated RSV disease (209-101 pg/ml, P = 0.008), a response pattern not observed in ventilated RSV patients nor for other cytokines or chemokines. It is speculated that local IL-17 production may be involved during convalescence from RSV bronchiolitis in non-ventilated patients by facilitating innate and adaptive antiviral immune responses. The role of IL-17 in the pathogenesis of RSV bronchiolitis is to be explored further.

Stimulation of immature lung macrophages with intranasal interferon gamma in a novel neonatal mouse model of respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is the leading cause of bronchiolitis and viral death in infants. Reduced CD8 T-cells and negligible interferon gamma (IFNγ) in the airway are associated with severe infant RSV disease, yet there is an abundance of alveolar macrophages (AM) and neutrophils. However, it is unclear, based on our current understanding of macrophage functional heterogeneity, if immature AM improve viral clearance or contribute to inflammation and airway obstruction in the IFNγ-deficient neonatal lung environment. The aim of the current study was to define the age-dependent AM phenotype during neonatal RSV infection and investigate their differentiation to classically activated macrophages (CAM) using i.n. IFNγ in the context of improving viral clearance. Neonatal and adult BALB/cJ mice were infected with 1×10(6) plaque forming units (PFU)/gram (g) RSV line 19 and their AM responses compared. Adult mice showed a rapid and robust CAM response, indicated by increases in major histocompatibility complex class II (MHC II), CD86, CCR7, and a reduction in mannose receptor (MR). Neonatal mice showed a delayed and reduced CAM response, likely due to undetectable IFNγ production. Intranasal (i.n.) treatment with recombinant mouse IFNγ (rIFNγ) increased the expression of CAM markers on neonatal AM, reduced viral lung titers, and improved weight gain compared to untreated controls with no detectable increase in CD4 or CD8 T-cell infiltration. In vitro infection of J774A.1 macrophages with RSV induced an alternatively activated macrophage (AAM) phenotype however, when macrophages were first primed with IFNγ, a CAM phenotype was induced and RSV spread to adjacent Hep-2 cells was reduced. These studies demonstrate that the neonatal AM response to RSV infection is abundant and immature, but can be exogenously stimulated to express the antimicrobial phenotype, CAM, with i.n. rIFNγ.

The use of a neonatal mouse model to study respiratory syncytial virus infections

Respiratory syncytial virus (RSV) infection is the most significant cause of viral death in infants worldwide. The significant morbidity and mortality associated with this disease underscores the urgent need for the development of an RSV vaccine. The development of an RSV vaccine has been hampered by our limited understanding of the human host immune system, which plays a significant role in RSV pathogenesis, susceptibility and vaccine efficacy. As a result, animal models have been developed to better understand the mechanisms by which RSV causes disease. Within the past few years, a revolutionary variation on these animal models has emerged--age at time of initial infection--and early studies in neonatal mice (aged <7 days at time of initial infection) indicate the validity of this model to understand RSV infection in infants. This article reviews available information on current murine and emerging neonatal mouse RSV models.

The role of cytokines and chemokines in severe respiratory syncytial virus infection and subsequent asthma

Respiratory syncytial virus (RSV) is the primary cause of serious lower respiratory tract illness in infants and young children worldwide. The mechanism is largely unknown. RSV stimulates airway epithelial cells and resident leukocytes to release cytokines. Cytokines and chemokines involved in host response to RSV infection are thought to play a central role in the pathogenesis. In addition, RSV infection early in life has been associated with the development of asthma in later childhood. It is likely that the persistence of cytokines and chemokines in fully recovered patients with RSV in the long term can provide a substratum for the development of subsequent asthma. This review describes the genetic factors in cytokines and chemokines associated with severity of RSV disease, cytokines and chemokines synthesis in RSV infection, and the role of these innate immune components in RSV-associated asthma.

Decreased Toll-like receptor 8 expression and lower TNF-α synthesis in infants with acute RSV infection

BACKGROUND

Toll-like receptors (TLRs) are part of the innate immune system, able to recognize pathogen-associated molecular patterns and activate immune system upon pathogen challenge. Respiratory syncytial virus (RSV) is a RNA virus particularly detrimental in infancy. It could cause severe lower respiratory tract disease and recurrent infections related to inadequate development of anti-viral immunity. The reason could be inadequate multiple TLRs engagement, including TLR8 in recognition of single-stranded viral RNA and diminished synthesis of inflammatory mediators due to a lower expression.

METHODS

Intracellular TLR8 expression in peripheral blood monocytes from RSV-infected infants was profiled and compared to healthy adults and age matched controls. Whether the observed difference in TLR8 expression is a transitory effect, infants in convalescent phase (4-6 weeks later) were retested. Specific TLR8-mediated TNF-α production in monocytes during an acute and convalescent phase was analyzed.

RESULTS

RSV-infected and healthy infants had lower percentage of TLR8-expressing monocytes than healthy adults whereas decreased of TLR8 protein levels were detected only for RSV-infected infant group. Lower protein levels of TLR8 in monocytes from RSV-infected infants, compared to healthy infants, negatively correlated with respiratory frequency and resulted in lower TNF-α synthesis upon a specific TLR8 stimulation. In the convalescent phase, levels of TLR8 increased, accompanied by increased TNF-α synthesis compared to acute infection.

CONCLUSIONS

Lower TLR8 expression observed in monocytes, during an acute RSV infection, might have a dampening impact on early anti-viral cytokine production necessary to control RSV replication, and subsequently initiate an adaptive Th1 type immune response leading to severe disease in infected infants.

NK cell deficiency predisposes to viral-induced Th2-type allergic inflammation via epithelial-derived IL-25

Severe respiratory syncytial virus (RSV) infection has long been associated with an increased risk for the development of childhood asthma and exacerbations of this disorder. Despite much research into the induction of Th2 responses by allergens and helminths, the factors associated with viral infection that predispose to Th2-regulated asthma remain unknown. Recently, clinical studies have shown reduced numbers of NK cells in infants suffering from a severe RSV infection. Here we demonstrate that NK cell deficiency during primary RSV infection of BALB/c mice results in the suppression of IFN-γ production and the development of an RSV-specific Th2 response and subsequent allergic lung disease. The outgrowth of the Th2 responses was dependent on airway epithelial cell-derived IL-25, which induced the upregulation of the notch ligand Jagged1 on dendritic cells. This study identifies a novel pathway underlying viral-driven Th2 responses that may have functional relevance to viral-associated asthma.

α-Galactosylceramide protects mice from lethal Coxsackievirus B3 infection and subsequent myocarditis

Myocarditis is an inflammation of the myocardium which often follows virus infections. Coxsackievirus B3 (CVB3), as a marker of the enterovirus group, is one of the most important infectious agents of virus-induced myocarditis. Using a CVB3-induced myocarditis model, we show that injection α-galactosylceramide (α-GalCer), a ligand for invariant natural killer (NK) T (iNK T) cells, can protect the mice from viral myocarditis. After the systemic administration of α-GalCer in CVB3 infected mice, viral transcription and titres in mouse heart, sera and spleen were reduced, and the damage to the heart was ameliorated. This is accompanied by a better disease course with an improved weight loss profile. Compared with untreated mice, α-GalCer-treated mice showed high levels of interferon (IFN)-γ and interleukin (IL)-4, and reduced proinflammatory cytokines and chemokines in their cardiac tissue. Anti-viral immune response was up-regulated by α-GalCer. Three days after CVB3 infection, α-GalCer-administered mice had larger spleens. Besides NK T cells, more macrophages and CD8(+) T cells were found in these spleens. Upon stimulation with phorbol myristate acetate plus ionomycin, splenocytes from α-GalCer-treated mice produced significantly more cytokines [including IFN-γ, tumour necrosis factor-α, IL-4 and IL-10] than those from untreated mice. These data suggest that administration of α-GalCer during acute CVB3 infection is able to protect the mice from lethal myocarditis by local changes in inflammatory cytokine patterns and enhancement of anti-viral immune response at the early stage. α-GalCer is a potential candidate for viral myocarditis treatment. Our work supports the use of anti-viral treatment early to reduce the incidence of virus-mediated heart damage.