The role of the respiratory syncytial virus in airway syndromes in childhood

Early-life pulmonary viral infection leads to long-term functional and lower airway structural changes in the lungs

Early-life respiratory virus infections have been correlated with enhanced development of childhood asthma. In particular, significant numbers of respiratory syncytial virus (RSV)-hospitalized infants go on to develop lung disease. It has been suggested that early-life viral infections may lead to altered lung development or repair that negatively impacts lung function later in life. Our data demonstrate that early-life RSV infection modifies lung structure, leading to decreased lung function. At 5 wk postneonatal RSV infection, significant defects are observed in baseline pulmonary function test (PFT) parameters consistent with decreased lung function as well as enlarged alveolar spaces. Lung function changes in the early-life RSV-infected group continue at 3 mo of age. The altered PFT and structural changes induced by early-life RSV were mitigated in TSLPR-/- mice that have previously been shown to have reduced immune cell accumulation associated with a persistent Th2 environment. Importantly, long-term effects were demonstrated using a secondary RSV infection 3 mo following the initial early-life RSV infection and led to significant additional defects in lung function, with severe mucus deposition within the airways, and consolidation of the alveolar spaces. These studies suggest that early-life respiratory viral infection leads to alterations in lung structure/repair that predispose to diminished lung function later in life.NEW & NOTEWORTHY These studies outline a novel finding that early-life respiratory virus infection can alter lung structure and function long-term. Importantly, the data also indicate that there are critical links between inflammatory responses and subsequent events that produce a more severe pathogenic response later in life. The findings provide additional data to support that early-life infections during lung development can alter the trajectory of airway function.

Saline in acute bronchiolitis RCT and economic evaluation: hypertonic saline in acute bronchiolitis - randomised controlled trial and systematic review

BACKGROUND

Acute bronchiolitis is the most common cause of hospitalisation in infancy. Supportive care and oxygen are the cornerstones of management. A Cochrane review concluded that the use of nebulised 3% hypertonic saline (HS) may significantly reduce the duration of hospitalisation.

OBJECTIVE

To test the hypothesis that HS reduces the time to when infants were assessed as being fit for discharge, defined as in air with saturations of > 92% for 6 hours, by 25%.

DESIGN

Parallel-group, pragmatic randomised controlled trial, cost-utility analysis and systematic review.

SETTING

Ten UK hospitals.

PARTICIPANTS

Infants with acute bronchiolitis requiring oxygen therapy were allocated within 4 hours of admission.

INTERVENTIONS

Supportive care with oxygen as required, minimal handling and fluid administration as appropriate to the severity of the disease, 3% nebulised HS every ± 6 hours.

MAIN OUTCOME MEASURES

The trial primary outcome was time until the infant met objective discharge criteria. Secondary end points included time to discharge and adverse events. The costs analysed related to length of stay (LoS), readmissions, nebulised saline and other NHS resource use. Quality-adjusted life-years (QALYs) were estimated using an existing utility decrement derived for hospitalisation in children, together with the time spent in hospital in the trial.

DATA SOURCES

We searched MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials and other databases from inception or from 2010 onwards, searched ClinicalTrials.gov and other registries and hand-searched Chest, Paediatrics and Journal of Paediatrics to January 2015.

REVIEW METHODS

We included randomised/quasi-randomised trials which compared HS versus saline (± adjunct treatment) or no treatment. We used a fixed-effects model to combine mean differences for LoS and assessed statistical heterogeneity using the I (2) statistic.

RESULTS

The trial randomised 158 infants to HS (n = 141 analysed) and 159 to standard care (n = 149 analysed). There was no difference between the two arms in the time to being declared fit for discharge [median 76.6 vs. 75.9 hours, hazard ratio (HR) 0.95, 95% confidence interval (CI) 0.75 to 1.20] or to actual discharge (median 88.5 vs. 88.7 hours, HR 0.97, 95% CI 0.76 to 1.23). There was no difference in adverse events. One infant developed bradycardia with desaturation associated with HS. Mean hospital costs were £2595 and £2727 for the control and intervention groups, respectively (p = 0.657). Incremental QALYs were 0.0000175 (p = 0.757). An incremental cost-effectiveness ratio of £7.6M per QALY gained was not appreciably altered by sensitivity analyses. The systematic review comprised 15 trials (n = 1922) including our own. HS reduced the mean LoS by -0.36 days (95% CI -0.50 to -0.22 days). High levels of heterogeneity (I (2) = 78%) indicate that the result should be treated cautiously.

CONCLUSIONS

In this trial, HS had no clinical benefit on LoS or readiness for discharge and was not a cost-effective treatment for acute bronchiolitis. Claims that HS achieves small reductions in LoS must be treated with scepticism.

FUTURE WORK

Well-powered randomised controlled trials of high-flow oxygen are needed.

STUDY REGISTRATION

This study is registered as NCT01469845 and CRD42014007569.

FUNDING DETAILS

This project was funded by the NIHR Health Technology Assessment (HTA) programme and will be published in full in Health Technology Assessment; Vol. 19, No. 66. See the HTA programme website for further project information.

Macrophages are required for dendritic cell uptake of respiratory syncytial virus from an infected epithelium

We have previously shown that the respiratory syncytial virus [RSV] can productively infect monocyte derived dendritic cells [MoDC] and remain dormant within the same cells for prolonged periods. It is therefore possible that infected dendritic cells act as a reservoir within the airways of individuals between annual epidemics. In the present study we explored the possibility that sub-epithelial DCs can be infected with RSV from differentiated bronchial epithelium and that in turn RSV from DCs can infect the epithelium. A dual co-culture model was established in which a differentiated primary airway epithelium on an Air Liquid Interface (ALI) was cultured on a transwell insert and MoDCs were subsequently added to the basolateral membrane of the insert. Further experiments were undertaken using a triple co-culture model in which in which macrophages were added to the apical surface of the differentiated epithelium. A modified RSV [rr-RSV] expressing a red fluorescent protein marker of replication was used to infect either the MoDCs or the differentiated epithelium and infection of the reciprocal cell type was assessed using confocal microscopy. Our data shows that primary epithelium became infected when rr-RSV infected MoDCs were introduced onto the basal surface of the transwell insert. MoDCs located beneath the epithelium did not become infected with virus from infected epithelial cells in the dual co-culture model. However when macrophages were present on the apical surface of the primary epithelium infection of the basal MoDCs occurred. Our data suggests that RSV infected dendritic cells readily transmit infection to epithelial cells even when they are located beneath the basal layer. However macrophages appear to be necessary for the transmission of infection from epithelial cells to basal dendritic cells.

Respiratory syncytial virus infection modifies and accelerates pulmonary disease via DC activation and migration

In the present studies, we have established that RSV can elicit a more pathogenic environment dependent on improper DC-associated sensitization. Our initial studies demonstrated that RSV, but not influenza, infection during an allergen exposure into the airway induced a more severe allergen response. The RSV-induced exacerbation included an increased Th2 cytokine response and pathophysiology as monitored by AHR and mucus overproduction. DCs played a central role in the allergen-induced responses, as instilling RSV-infected BMDC into the airway could recapitulate a live virus challenge. With the use of CCR6-/- mice that have a primary defect in the recruitment of mDC subsets, reduced exacerbation of disease was observed when RSV was administered along with allergen. Furthermore, sensitization of mice with RSV-infected BMDC into the airway produced a more severe immune response to a live virus challenge. Subsequently, using RSV-infected BMDC from CCR7-/- mice (that do not migrate efficiently to LNs) to sensitize the exacerbated response demonstrated that the response was dependent on DC migration to the LN. Finally, the ability of RSV-infected DCs to elicit an exacerbated, allergen-induced pathogenic response could be maintained for as long as 3 weeks, suggesting that RSV-infected DCs themselves created an altered immune environment that impacts off-target mucosal responses that could have prolonged effects.

Autophagy-mediated dendritic cell activation is essential for innate cytokine production and APC function with respiratory syncytial virus responses

The regulation of innate immune responses during viral infection is a crucial step to promote antiviral reactions. Recent studies have drawn attention to a strong relationship of pathogen-associated molecular pattern recognition with autophagy for activation of APC function. Our initial observations indicated that autophagosomes formed in response to respiratory syncytial virus (RSV) infection of dendritic cells (DC). To further investigate whether RSV-induced DC activation and innate cytokine production were associated with autophagy, we used several methods to block autophagosome formation. Using 3-MA, small interfering RNA inhibition of LC3, or Beclin(+/-) mouse-derived DC, studies established a relationship between RSV-induced autophagy and enhanced type I IFN, TNF, IL-6, and IL-12p40 expression. Moreover, autophagosome formation induced by starvation also promoted innate cytokine expression in DC. The induction of starvation-induced autophagy in combination with RSV infection synergistically enhanced DC cytokine expression that was blocked by an autophagy inhibitor. The latter synergistic responses were differentially altered in DC from MyD88(-/-) and TRIF(-/-) mice, supporting the concept of autophagy-mediated TLR signaling. In addition, blockade of autophagy in RSV-infected DC inhibited the maturation of DC as assessed by MHC class II and costimulatory molecule expression. Subsequently, we demonstrated that inhibition of autophagy in DC used to stimulate primary OVA-induced and secondary RSV-infected responses significantly attenuated cytokine production by CD4(+) T cells. Thus, these studies have outlined that autophagy in DC after RSV infection is a crucial mechanism for driving innate cytokine production, leading to altered acquired immune responses.

The host response and molecular pathogenesis associated with respiratory syncytial virus infection

Since the isolation of respiratory syncytial virus (RSV) in 1956, its significance as an important human pathogen in infants, the elderly and the immunocompromised has been established. Many important mechanisms contributing to RSV infection, replication and disease pathogenesis have been uncovered; however, there is still insufficient knowledge in these and related areas, which must be addressed to facilitate the development of safe and effective vaccines and therapeutic treatments. A better understanding of the molecular pathogenesis of RSV infection, particularly the host-cell response and transcription profiles to RSV infection, is required to advance disease intervention strategies. Substantial information is accumulating regarding how RSV proteins modulate molecular signaling and regulation of cytokine and chemokine responses to infection, molecular signals regulating programmed cell death, and innate and adaptive immune responses to infection. This review discusses RSV manipulation of the host response to infection and related disease pathogenesis.

Eosinophils: biological properties and role in health and disease

Eosinophils are pleiotropic multifunctional leukocytes involved in initiation and propagation of diverse inflammatory responses, as well as modulators of innate and adaptive immunity. In this review, the biology of eosinophils is summarized, focusing on transcriptional regulation of eosinophil differentiation, characterization of the growing properties of eosinophil granule proteins, surface proteins and pleiotropic mediators, and molecular mechanisms of eosinophil degranulation. New views on the role of eosinophils in homeostatic function are examined, including developmental biology and innate and adaptive immunity (as well as their interaction with mast cells and T cells) and their proposed role in disease processes including infections, asthma, and gastrointestinal disorders. Finally, strategies for targeted therapeutic intervention in eosinophil-mediated mucosal diseases are conceptualized.

Understanding the mechanisms of viral induced asthma: new therapeutic directions

Asthma is a common and debilitating disease that has substantially increased in prevalence in Western Societies in the last 2 decades. Respiratory tract infections by respiratory syncytial virus (RSV) and rhinovirus (RV) are widely implicated as common causes of the induction and exacerbation of asthma. These infections in early life are associated with the induction of wheeze that may progress to the development of asthma. Infections may also promote airway inflammation and enhance T helper type 2 lymphocyte (Th2 cell) responses that result in exacerbations of established asthma. The mechanisms of how RSV and RV induce and exacerbate asthma are currently being elucidated by clinical studies, in vitro work with human cells and animal models of disease. This research has led to many potential therapeutic strategies and, although none are yet part of clinical practise, they show much promise for the prevention and treatment of viral disease and subsequent asthma.

Respiratory virus-induced regulation of asthma-like responses in mice depends upon CD8 T cells and interferon-gamma production

Respiratory virus infections can significantly influence the development of airway disease by both predisposing and exacerbating the developing lung immune environment. In contrast, the initiation of a more desirable anti-viral response may better prepare the local environment and protect it from developing an adverse long-term disease phenotype. BALB/c or C57BL/6 mice exposed to respiratory syncytial virus (RSV) infection at the same time as allergen sensitization were assessed for airway function, cytokine responses, and inflammatory parameters. Depending on the genetic strain of mouse used, BALB/c versus C57BL/6, RSV could differentially protect against the development of airway allergen responses. Although RSV was able to block allergen sensitization and induction of airway hyperresponsiveness and eosinophilic inflammation in C57BL/6 mice, the infection did not reduce the allergic responses in BALB/c mice. The alteration of airway responsiveness did not depend on the timing of RSV infection in C57BL/6 mice in conjunction to the allergen sensitization protocol. Neutralization experiments demonstrated that interferon-gamma contributed significantly to the RSV-induced airway attenuation of the allergic responses, whereas transfer of CD8 T cells from RSV-infected animals suggested that they were partially responsible for the altered environment. These data suggest that a respiratory viral infection impacts on the local lung environment and may reflect specific aspects of the hygiene hypothesis. However, the outcome of this interaction depends on the immunological response of the host.

Eosinophils contribute to innate antiviral immunity and promote clearance of respiratory syncytial virus

Eosinophils are recruited to the lungs in response to respiratory syncytial virus (RSV) infection; however, their role in promoting antiviral host defense remains unclear. Here, we demonstrate that eosinophils express TLRs that recognize viral nucleic acids, are activated and degranulate after single-stranded RNA (ssRNA) stimulation of the TLR-7-MyD88 pathway, and provide host defense against RSV that is MyD88 dependent. In contrast to wild-type mice, virus clearance from lung tissue was more rapid in hypereosinophilic (interleukin-5 transgenic) mice. Transfer of wild-type but not MyD88-deficient eosinophils to the lungs of RSV-infected wild-type mice accelerated virus clearance and inhibited the development of airways hyperreactivity. Similar responses were observed when infected recipient mice were MyD88 deficient. Eosinophils isolated from infected hypereosinophilic MyD88-sufficient but not MyD88-deficient mice expressed greater amounts of IFN regulatory factor (IRF)-7 and eosinophil-associated ribonucleases EAR-1 and EAR-2. Hypereosinophilia in the airways of infected mice also correlated with increased expression of IRF-7, IFN-beta, and NOS-2, and inhibition of NO production with the NOS-2 inhibitor L-NMA partially reversed the accelerated virus clearance promoted by eosinophils. Collectively, our results demonstrate that eosinophils can protect against RSV in vivo, as they promote virus clearance and may thus limit virus-induced lung dysfunction.

Tissue-specific regulation of CD8+ T-lymphocyte immunodominance in respiratory syncytial virus infection

Cytotoxic T lymphocytes (CTLs) are critical for control of respiratory syncytial virus (RSV) infection in humans and mice. To investigate cellular immune responses to infection, it is important to identify major histocompatibility complex (MHC) class I-restricted CTL epitopes. In this study, we identified a new RSV-specific, H-2K(d)-restricted subdominant epitope in the M2 protein, M2(127-135) (amino acids 127 to 135). This finding allowed us to study the frequency of T lymphocytes responding to two H-2K(d)-presented epitopes in the same protein following RSV infection by enzyme-linked immunospot (ELISPOT) and intracellular cytokine assays for both lymphoid and nonlymphoid tissues. For the subdominant epitope, we identified an optimal nine-amino-acid peptide, VYNTVISYI, which contained an H-2K(d) consensus sequence with Y at position 2 and I at position 9. In addition, an MHC class I stabilization assay using TAP-2-deficient RMA-S cells transfected with K(d) or L(d) indicated that the epitope was presented by K(d). The ratios of T lymphocytes during the peak CTL response to RSV infection that were specific for M2(82-90) (dominant) to T lymphocytes specific for M2(127-135) (subdominant) were approximately 3:1 in the spleen and 10:1 in the lung. These ratios were observed consistently in primary or secondary infection by the ELISPOT assay and in secondary infection by MHC/peptide tetramer staining. The number of antigen-specific T lymphocytes dropped in the 6 weeks after infection; however, the proportions of T lymphocytes specific for the immunodominant and subdominant epitopes were maintained to a remarkable degree in a tissue-specific manner. These studies will facilitate investigation of the regulation of immunodominance of RSV-specific CTL epitopes.