Progress in defining the role of RSV in allergy and asthma: from clinical observations to animal models

Respiratory syncytial virus (RSV), an RNA virus in the family Paramyxoviridae, causes respiratory disease in humans. A closely related bovine RSV is responsible for a remarkably similar disease syndrome in young cattle. Severe RSV disease is characterized by bronchiolitis. The impact of RSV on human health is demonstrated annually when infants are admitted to the hospital in large numbers. Nearly every child will have been infected with RSV by the age of 3 years. While the disease is most severe in young infants and elderly people, it can re-infect adults causing mild upper respiratory tract disease throughout life. In addition, there is growing evidence that RSV infection may also predispose some children to the development of asthma. This is based on the observation that children who wheeze with RSV-induced bronchiolitis are more likely to develop into allergic asthmatics. Recent studies describe attempts to create an RSV induced asthma model in mice and other species; these have shown some degree of success. Such reports of case studies and animal models have suggested a wide range of factors possibly contributing to RSV induced asthma, these include timing of RSV infection with respect to allergen exposure, prior allergic sensitization, environmental conditions, exposure to endotoxin, and the genetic background of the person or animal. Herein, we primarily focus on the influence of RSV infection and inhalation of extraneous substances (such as allergens or endotoxin) on development of allergic asthma.     

Epidemiologic, experimental, and clinical links between respiratory syncytial virus infection and asthma

Virtually all children experience respiratory syncytial virus (RSV) infection at least once during the first 2 years of life, but only a few develop bronchiolitis and more severe disease requiring hospitalization, usually in the first 6 months of life. Children who recover from RSV-induced bronchiolitis are at increased risk for the development of recurrent wheeze and asthma in later childhood. Recent studies suggest that there is an association between RSV-induced bronchiolitis and asthma within the first decade of life but that this association is not significant after age 13. Despite the considerable progress made in our understanding of several aspects of respiratory viral infections, further work needs to be done to clarify the molecular mechanisms of early interactions between virus and host cell and the role of host gene products in the infection process. This review provides a critical appraisal of the literature in epidemiology and experimental research which links RSV infection to asthma. Studies to date demonstrate that there is a significant association between RSV infection and childhood asthma and that preventing severe primary RSV infections can decrease the risk of childhood asthma.     

Interferon-gamma levels in nasopharyngeal secretions of infants with respiratory syncytial virus and other respiratory viral infections

Respiratory syncytial virus (RSV) infection, one of the most common causes of hospitalization of children in developed countries, has been implicated as a cause of asthma. We aimed to characterize the cytokine profile in nasopharyngeal aspirates (NPAs) taken from infants during upper respiratory tract infection to investigate whether RSV induced a unique immune response as compared with other viruses. Additionally, we sought to determine whether this profile was influenced by the infants' atopic status. A prospective birth cohort of babies at high risk of atopy was recruited. Ratios of a T-helper 1 (Th1) cytokine, interferon gamma (IFN-gamma) and a T-helper 2 (Th2)-like cytokine, interleukin-10 (IL-10), in NPAs were determined during episodes of respiratory tract infections in the first year. The viral aetiology of the respiratory tract infections was determined using polymerase chain reaction (PCR), culture and immunofluorescence. Atopic status was ascertained at 1 year of age using skin prick tests. Participants were recruited antenatally and subsequently followed in the community. Sixty babies with one or both parents atopic were enrolled into the study. IFN-gamma : IL-10 ratios in NPAs during upper respiratory tract infections and their correlation with viral aetiology and atopic status were the main outcome measures. The mean IFN-gamma : IL-10 ratio was significantly lower (due to lower IFN-gamma) during RSV infections than during infections with other viruses (P = 0.035). The cytokine ratio, however, did not differ between infants with or without wheeze during URTIs (P = 0.44), or between infants who were atopic or non-atopic (P = 0.49). This study suggests that RSV is associated with lower IFN-gamma production in young babies, regardless of their atopic status, compared to upper respiratory tract infections where either another virus is detected or where no viral identification is made.     

Predominant type-2 response in infants with respiratory syncytial virus (RSV) infection demonstrated by cytokine flow cytometry

Acute RSV infection in infancy may produce some asthma-like symptoms and may be followed by a recurrent wheeze later in childhood. It has been proposed that RSV infection stimulates type-2 cytokine responses, resembling those found in atopy and asthma. Peripheral blood cells were obtained from RSV-infected infants (n = 30) and healthy controls (n = 10). After in vitro restimulation of the cells, intracellular IL-4 and interferon-gamma (IFN-gamma) were measured by flow cytometry. The cells from RSV-infected infants produced more IL-4 and less IFN-gamma than those from healthy controls. IL-4 production was more frequent in CD8 than in CD4 cells, and the bias toward IL-4 production was greatest in infants with mild infections, whereas IFN-gamma production increased with disease severity. Our conclusions are that RSV infection is associated with IL-4 production in peripheral T cells, and that peripheral blood in infants with severe disease may be depleted of cytokine-producing cells.     

The role of respiratory virus infections in childhood asthma inception

Viral respiratory illnesses associated with wheezing are extremely common during early life and remain a frequent cause of morbidity and hospitalization in young children. Although many children who wheeze with respiratory viruses during infancy outgrow the problem, most children with asthma and reductions in lung function at school age begin wheezing during the first several years of life. Whether symptomatic viral infections of the lower respiratory tract are causal in asthma development or simply identify predisposed children remains a controversial issue. Wheezing illnesses caused by respiratory syncytial virus (RSV), particularly those severe enough to lead to hospitalization, have historically been associated with an increased risk of asthma at school age. However, with the development of molecular diagnostics, human rhinovirus (HRV) wheezing illnesses have been recognized more recently as a stronger predictor of school-age asthma than RSV. In this article, the authors review the impact of virus infections during early life, focusing primarily on RSV and HRV, and their potential roles in asthma inception.     

Uteroglobulin-related protein 1 and severity of respiratory syncytial virus infection in children admitted to hospital

There are several reports suggesting that genetic factors contribute to the severity of infection with the respiratory syncytial virus (RSV). Infants hospitalized with lower respiratory tract infection (LRTI) due to RSV are at a significantly increased risk for both recurrent wheezing and childhood asthma. Uteroglobin-related protein 1 (UGRP1) is a secretory protein expressed in the airways, and speculated to have anti-inflammatory activity. The presence of the -112G/A polymorphism in the UGRP1 promoter was found to have a significant correlation with asthma phenotype. Also plasma UGRP1 levels were shown to be associated both with this polymorphism and the severity of asthma. The study population consisted of 62 previously healthy infants, ≤12 months of age, who were hospitalized with RSV LRTI, and a control group of 99 healthy adults. Genotyping was performed by restriction fragment length polymorphism. UGRP1 serum levels were determined using ELISA. There were no significant differences in the overall distribution of UGRP1 -112G/A polymorphism genotypes or alleles between the hospitalized infants and healthy adults. A comparison of serum UGRP1 concentration measured at the time of admission and discharge between patients with and without the -112A allele revealed that there was no relation between the presence of the -112A allele and serum UGRP1 in hospitalized infants with RSV infection. Furthermore, there was no relationship between severity of RSV infection and genotype or serum UGRP1 concentration. These results suggest that UGRP1 does not have a major role in the development of severe RSV infection.     

Rhinovirus illnesses during infancy predict subsequent childhood wheezing

BACKGROUND: The contribution of viral respiratory infections during infancy to the development of subsequent wheezing and/or allergic diseases in early childhood is not established. OBJECTIVE: To evaluate these relationships prospectively from birth to 3 years of age in 285 children genetically at high risk for developing allergic respiratory diseases. METHODS: By using nasal lavage, the relationship of timing, severity, and etiology of viral respiratory infections during infancy to wheezing in the 3rd year of life was evaluated. In addition, genetic and environmental factors that could modify risk of infections and wheezing prevalence were analyzed. RESULTS: Risk factors for 3rd year wheezing were passive smoke exposure (odds ratio [OR]=2.1), older siblings (OR=2.5), allergic sensitization to foods at age 1 year (OR=2.0), any moderate to severe respiratory illness without wheezing during infancy (OR=3.6), and at least 1 wheezing illness with respiratory syncytial virus (RSV; OR=3.0), rhinovirus (OR=10) and/or non-rhinovirus/RSV pathogens (OR=3.9) during infancy. When viral etiology was considered, 1st-year wheezing illnesses caused by rhinovirus infection were the strongest predictor of subsequent 3rd year wheezing (OR=6.6; P < .0001). Moreover, 63% of infants who wheezed during rhinovirus seasons continued to wheeze in the 3rd year of life, compared with only 20% of all other infants (OR=6.6; P < .0001). CONCLUSION: In this population of children at increased risk of developing allergies and asthma, the most significant risk factor for the development of preschool childhood wheezing is the occurrence of symptomatic rhinovirus illnesses during infancy that are clinically and prognostically informative based on their seasonal nature.     

Lack of long-term effects of respiratory syncytial virus infection on airway function in mice

Epidemiological data suggests lower respiratory infections (LRI) with respiratory syncytial virus (RSV) are capable of causing long-term abnormalities in airway function. To directly test the effects of RSV LRI, we infected adult and weanling BALB/c mice with RSV (A2) or vehicle. Respiratory system impedance was used to assess baseline airway function and responses to iv methacholine (MCh) at 4, 8, 24 and 34 weeks post infection. In vitro airway responses were measured 24 weeks post infection using electrical field stimulation and MCh. Mice infected as adults showed no alterations in airway function. Mice infected as weanlings had increased MCh responses 24 weeks post infection. However, the increased response was not present 34 weeks post infection nor accompanied by alterations in in vitro responses or airway morphometry. This study did not detect long-lasting changes in airway function following RSV infection in mice. These data do not provide support for alterations in airway structure or function being responsible for the observed relationship between RSV infection in infants and asthma in later life.     

Plasma endothelin-1 in infants and young children with acute bronchiolitis and viral pneumonia

Respiratory syncytial virus (RSV) Infections that occur during the first three years of life have been demonstrated to be associated with the development of childhood asthma. The mechanism of virus-triggered airway inflammation Is not fully understood. Endothelin-1 is a potent bronchoconstrictor involved in many diseases including respiratory tract infections. Infants and young children diagnosed with either viral pneumonia or acute bronchiolitis, their age ranging between 2 months and 3 years, were recruited into this study. Nasopharyngeal aspirates were taken for detection of respiratory virus by antigen immunofluorescence stain, RT-PCR analysis and viral culture. Plasma endothelin-1 (ET-1) was measured by using a commercially available enzyme-linked immunosorbent assay (ELISA). Ten of the nineteen infants and children (52%) were positive for RSV infection, one co-infected with influenza A. Nine Infants (90%) were positive for RSV subtype A. There was only one infant with subtype B. One of the RSV negative individuals was positive for influenza A. In addition, we recruited 10 patients without chronic underlying or respiratory tract illness as controls. ET-1 levels were significantly increased in RSV infection compared to the controls (3.6 +/- 1.2 and 1.2 +/- 1 pg/ml, respectively (p < 0.05). In conclusion, infants and young children who are infected with RSV have an increase in circulating plasma endothelin-1. This in turn may contribute to the subsequent development of childhood asthma.     

Post-viral atopic airway disease: pathogenesis and potential avenues for intervention

Introduction: In early childhood, wheezing due to lower respiratory tract illness is often associated with infection by commonly known respiratory viruses such as respiratory syncytial virus (RSV) and human rhinovirus (RV). How respiratory viral infections lead to wheeze and/or asthma is an area of active research.

Areas covered: This review provides an updated summary of the published information on the development of post-viral induced atopy and asthma and the mechanisms involved. We focus on the contribution of animal models in identifying pathways that may contribute to atopy and asthma following respiratory virus infection, different polymorphisms that have been associated with asthma development, and current options for disease management and potential future interventions.

Expert commentary: Currently there are no prophylactic therapies that prevent infants infected with respiratory viruses from developing asthma or atopy. Neither are there curative therapies for patients with asthma. Therefore, a better understanding of genetic factors and other associated biomarkers in respiratory viral induced pathogenesis is important for developing effective personalized therapies.     

Respiratory syncytial virus infection increases regulated on activation normal T cell expressed and secreted and monocyte chemotactic protein 1 levels in serum of patients with asthma and in human monocyte cultures

BackgroundRespiratory syncytial virus (RSV) infection is associated to episodic exacerbations of asthma involving alveolar macrophages and chemokine production.ObjectiveThe aim of this study was to determine the circulating levels of monocyte chemotactic protein 1 (MCP-1), regulated on activation normal T cell expressed and secreted (RANTES), and substance P (SP) in patients with and without asthma with acute respiratory RSV infection and the chemokine profile in RSV- infected monocyte cultures from normal individuals and individuals with asthma.MethodsIn this regard, 31 adult patients with acute respiratory infection (15 patients with asthma) were studied. MCP-1, RANTES and SP were measured in serum and in supernatants from monocyte cultures by enzyme-linked immunosorbent assay (ELISA).ResultsIncreased levels of MCP-1 and RANTES were observed in serum from patients with asthma related to RSV infection. RSV-infected monocyte cultures from healthy individuals showed increased content of those chemokines, and monocyte cultures from patients with asthma showed increased expression of MCP-1.ConclusionThese data show that RSV infection induces increased circulating level of chemokines in patients with asthma, and this finding could be mediated in part by the interaction virus-monocyte.     

A comparison of epidemiologic and immunologic features of bronchiolitis caused by influenza virus and respiratory syncytial virus

We studied epidemiologic and immunologic factors in infants with bronchiolitis caused by influenza virus. The proportion of these infants who were male and who had an immediate family member with a history of asthma was similar to that of a control group of infants with respiratory syncytial virus (RSV) bronchiolitis. In subjects with influenza virus infection, concentrations of the beta chemokine macrophage inflammatory protein-1alpha (MIP-1alpha), but not other beta chemokines, in nasopharyngeal secretions (NPS) were greater among infants with more severe, hypoxic bronchiolitis than in subjects with mild, nonhypoxic bronchiolitis, or upper respiratory tract infection alone. Quantities of MIP-1alpha were also correlated with lower values of oxygen saturation. These findings point out epidemiologic and immunologic similarities between bronchiolitis caused by influenza and RSV, and suggest that host factors are more important than the nature of the infecting virus in the development of severe forms of bronchiolitis caused by influenza and RSV.     

Identification of biomarkers for disease severity in nasopharyngeal secretions of infants with upper or lower respiratory tract viral infections

Lower respiratory tract infections (LRTIs) produced by viruses are the most frequent cause of morbidity and mortality in children younger than 5 years of age. The immune response triggered by viral infection can induce a strong inflammation in the airways and cytokines could be considered as biomarkers for disease severity as these molecules modulate the inflammatory response that defines the outcome of patients. Aiming to predict the severity of disease during respiratory tract infections, we conducted a 1-year follow-up observational study in infants who presented upper or lower respiratory tract infections caused by seasonal respiratory viruses. At the time of enrollment, nasopharyngeal swabs (NPS) were obtained from infants to measure mRNA expression and protein levels of IL-3, IL-8, IL-33, and thymic stromal lymphopoietin. While all cytokines significantly increased their protein levels in infants with upper and lower respiratory tract infections as compared to control infants, IL-33 and IL-8 showed a significant increase in respiratory syncytial virus (RSV)-infected patients with LRTI as compared to patients with upper respiratory tract infection. We also found higher viral loads of RSV-positive samples with a greater IL-8 response at the beginning of the symptoms. Data obtained in this study suggest that both IL-8 and IL-33 could be used as biomarkers for clinical severity for infants suffering from LRTIs caused by the RSV.     

冬春季儿童、婴幼儿哮喘急性发作的呼吸道病毒病原学特征及临床研究

目的 了解北京地区冬春季儿童、婴幼儿哮喘急性发作时的呼吸道常见病毒——呼吸道合胞病毒（RSV）、流感病毒（IFA1、IFA3、IFB）、副流感病毒（PIF1、PIF3）、腺病毒（ADV）的感染情况及与临床症状和嗜酸细胞的关系。方法 对2000年11月至2001年3月及2001年11月至2002年3月，来首都儿科研究所哮喘中心就诊的哮喘急性发作的患儿176名，采用病毒分离及间接免疫荧光法，对鼻咽分泌物（nasopharyngeal secretions，NPS）中七种病毒抗原进行监测，并同时记录临床症状和用药情况及进行鼻咽分泌物和外周血中嗜酸细胞计数。结果 176例哮喘急性发作患儿NPS中，79例检测出病毒，阳性率为44．9％。其中RSV 66例，感染率为37．5％、IF7例（4．0％）、ADV6例（3．4％）及PIF4例（2．3％）。RSV占79例病毒感染患儿的83．5％；4例患儿同时测定出RSV和其他病毒混合感染。这些病毒在哮喘急性发作的患儿中检出率与年龄呈反比，小年龄组的患儿病毒感染多；检出病毒的患儿病情重，伴发热的患儿显著多于未检查出病毒的患儿。病毒感染与非感染组的NPS中嗜酸细胞数目检测无明显差别；但血中嗜酸细胞的数目，病毒检出阳性的患儿，较病毒测定阴性的患儿明显减少（t=2．676，P〈0．001）。结论 北京地区冬季近半数哮喘急性发作的患儿呼吸道病毒检测阳性，其中RSV是婴幼儿哮喘发作的主要感染病毒，引起较严重的临床症状；病毒检出阳性的患儿，血中嗜酸细胞的数目明显减少。     

Neutralization of nerve growth factor (NGF) inhibits the Th2 response and protects against the respiratory syncytial virus (RSV) infection

Increasing evidence suggests that respiratory syncytial virus (RSV) infection during the early life is an important risk factor for the development of asthma. RSV infection is associated with neurogenic inflammation in the airways along with the increased expression of nerve growth factor (NGF). However, the role of NGF in RSV infection is not clear. In this study, we infected the rat with RSV and treated these animals with anti-NGF neutralization antibody. We found that anti-NGF treatment significantly alleviated the lung inflammation as evidenced by decreased inflammatory infiltration and decreased airway resistance. Importantly, anti-NGF treatment resulted in increased Th1, but decreased Th2 immune responses, and facilitated the viral control in the tissues and blood. Therefore, NGF inhibited Th2 but increased Th1 responses in RSV infection. Pharmacological intervention of NGF signaling during severe RSV infections could prevent or decrease further asthma symptoms.     

Molecular epidemiological analysis of community circulating respiratory syncytial virus in rural South Africa: Comparison of viruses and genotypes responsible for different disease manifestations

Human respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infection in children in both the industrialized and developing world. Most molecular epidemiological studies have, until now, focused on isolates from hospitalized infants in industrialized countries. Limited data have been available with regard to community circulating RSV, especially from Africa. The present study compares RSV isolates from infants attending rural community clinics in the Northern province of South Africa, with isolates from hospitalized infants in Soweto, near Johannesburg, South Africa, during the same period. A multiplex nested polymerase chain reaction was developed for analyzing the clinical specimens, a technique that permits subtyping and nucleotide sequence analysis of the second variable region of the G-protein gene. Community- and hospital-based isolates from young children in South Africa, as well as isolates from Mozambique were compared phylogenetically. One subgroup B community isolate was identified that had a G-protein truncated by approximately 35 amino acids, however, the other community isolates were not significantly different from hospital isolates. Evidence was found that the same RSV genotypes and viruses could cause mild upper respiratory tract infections or lower respiratory tract infections or severe RSV in young infants.     

Disease severity and viral load are correlated in infants with primary respiratory syncytial virus infection in the community

Respiratory syncytial virus (RSV) is a major cause of respiratory tract infections in infants, with remarkable variability in disease severity. Factors determining severity of disease in previously healthy infants are still unclear. It was hypothesized that disease severity is correlated with viral load in primary RSV infection. Infants of a healthy birth cohort were included at signs of their first respiratory tract infection. Nasopharyngeal aspirate was obtained within 48–96 hr and disease severity was assessed with a previously published severity scoring model. PCR was applied to test the aspirates in a semi‐quantitative way for the presence of 10 respiratory pathogens. In case of multiple infection, the pathogen with the highest load was defined as the primary pathogen. The correlation between disease severity and viral load was analyzed. A total of 82 infants were included over a period of 2 years. Median age at first respiratory tract infection was 3 months. Pathogens were detected in 77 (94%) infants; more than one pathogen was detected in 35 (43%) infants. RSV was present in aspirates of 30 infants; in 16 aspirates RSV was the primary pathogen. A negative correlation between RSV CT‐value and disease severity was found in all RSV cases (ρ = ?0.52, P = 0.003) and in cases with RSV as the primary pathogen (ρ = ?0.54, P = 0.03). In conclusion, this is the first report on viral loads in previously healthy infants with RSV infection in the community. Disease severity correlated positively with viral load during primary RSV infection. J. Med. Virol. 82: 1266–1271, 2010. © 2010 Wiley‐Liss, Inc.     

Immunopathology of RSV infection: prospects for developing vaccines without this complication

Respiratory syncytial virus is the most important cause of lower respiratory tract infection in infants and young children. RSV clinical disease varies from rhinitis and otitis media to bronchiolitis and pneumonia. An increased incidence of asthma later in life has been associated with the more severe lower respiratory tract infections. Despite its importance as a pathogen, there is no licensed vaccine against RSV. This is due to a number of factors complicating the development of an effective and safe vaccine. The immunity to natural RSV infection is incomplete as re-infections occur in all age groups, which makes it challenging to design a protective vaccine. Second, the primary target population is the newborn infant, which has a relatively immature immune system and maternal antibodies that can interfere with vaccination. Finally, some vaccines have resulted in a predisposition for exacerbated pulmonary disease in infants, which was attributed to an imbalanced Th2-biased immune response, although the exact cause has not been elucidated. This makes it difficult to proceed with vaccine testing in infants. It is likely that an effective and safe vaccine needs to elicit a balanced immune response, including RSV-specific neutralising antibodies, CD8 T-cells, Th1/Th2 CD4 T-cells and preferably secretory IgA. Subunit vaccines formulated with appropriate adjuvants may be adequate for previously exposed individuals. However, intranasally delivered genetically engineered attenuated or vectored vaccines are currently most promising for newborns, as they are expected to induce a balanced immune response similar to that elicited to natural infection and not be subject to interference from maternal antibodies. Maternal vaccination may be the optimal strategy to protect the very young infants.     

呼吸道合胞病毒感染后婴幼儿喘息患者血清leptin水平的变化

目的 通过测量呼吸道合胞病毒肺炎儿童患者瘦素(leptin)的水平,探讨瘦素与呼吸道合胞病毒感染后婴幼儿喘息间的相互关系.方法 43例呼吸道合胞病毒感染后婴幼儿分别于入院后24h内、治疗结束及出院后12周用放射免疫法检测血清leptin水平,并随访2年.根据患儿喘息发作的情况,分为婴儿哮喘组和非哮喘组;另选10名健康儿童血清标本作对照.结果 BSV感染后喘息发作≥3次的婴幼儿患儿,占41.9%.治疗前,哮喘组和非哮喘组血清leptin水平均高于对照组,差异有统计学意义(t=3.41、2.64,P<0.05).治疗后,哮喘组血清leptin水平高于非哮喘组和对照组,差异有统计学意义(t=5.74、6.23,P<0.05).出院12周后复查,哮喘组血清leptin水平仍高于非哮喘组和对照组,差异有统计学意义(t=6.32、6.11,P<0.05);而非哮喘组血清leptin水平和对照组比较,差异无统计学意义(t=0.81,P>0.05).结论 呼吸道合胞病毒感染后喘息发作≥3次的婴幼儿血清leptin水平较健康同龄儿童及非哮喘儿童明显升高,持续高leptin水平可能是BSV感染后婴儿哮喘的高危因素之一.     

In Hot Pursuit of the First Vaccine Against Respiratory Syncytial Virus

Human respiratory syncytial virus (RSV) is the leading cause of severe lower respiratory tract infection, such as bronchiolitis, bronchitis, or pneumonia, in both infants and the elderly. Despite the global burden of diseases attributable to RSV infection, no clinically approved vaccine is available, and a humanized monoclonal antibody for prophylaxis is not readily affordable in developing countries. There are several hurdles to the successful development of RSV vaccines: immune-vulnerable target populations such as premature infants, pregnant women, and immunocompromised people; safety concerns associated with vaccine-enhanced diseases; repeated infection; and waning memory. To develop successful strategies for the prevention of RSV infection, it is necessary to understand the protective and pathologic roles of host immune responses to RSV infection. In this review, we will summarize the positive and negative relationship between RSV infection and host immunity and discuss strategies for the development of the first successful RSV vaccine.