Potential therapeutic implications of new insights into respiratory syncytial virus disease

Viral bronchiolitis is the most common cause of hospitalization in infants under 6 months of age, and 70% of all cases of bronchiolitis are caused by respiratory syncytial virus (RSV). Early RSV infection is associated with respiratory problems such as asthma and wheezing later in life. RSV infection is usually spread by contaminated secretions and infects the upper then lower respiratory tracts. Infected cells release proinflammatory cytokines and chemokines, including IL-1, tumor necrosis factor-alpha, IL-6, and IL-8. These activate other cells and recruit inflammatory cells, including macrophages, neutrophils, eosinophils, and T lymphocytes, into the airway wall and surrounding tissues. The pattern of cytokine production by T lymphocytes can be biased toward 'T-helper-1' or 'T-helper-2' cytokines, depending on the local immunologic environment, infection history, and host genetics. T-helper-1 responses are generally efficient in antiviral defense, but young infants have an inherent bias toward T-helper-2 responses. The ideal intervention for RSV infection would be preventive, but the options are currently limited. Vaccines based on protein subunits, live attenuated strains of RSV, DNA vaccines, and synthetic peptides are being developed; passive antibody therapy is at present impractical in otherwise healthy children. Effective vaccines for use in neonates continue to be elusive but simply delaying infection beyond the first 6 months of life might reduce the delayed morbidity associated with infantile disease.     

Cytokine (tumor necrosis factor, IL-6, and IL-8) production by respiratory syncytial virus-infected human alveolar macrophages.

Human alveolar macrophages (AM) are susceptible to infection with respiratory syncytial virus (RSV), but the infection is abortive after the initial cycles of virus replication. We have investigated if RSV infection of AM results in the production of cytokines TNF, IL-6, and IL-8, all of which may modulate inflammatory and immune responses to the virus, as well as may directly protect respiratory epithelial cells against spread of infection. Within 1 h after interaction with RSV, increased mRNA levels were found for all three cytokines. Peak expression of the mRNAs occurred at 3 to 6 h. The virus most effectively induced TNF mRNA expression greater than IL-6 mRNA greater than IL-8 mRNA, as compared to cytokine mRNA expression induced by bacterial endotoxin. Inactivated virus was almost as effective as live virus in inducing and maintaining increased IL-6 and IL-8 mRNA over 16 h, whereas live infectious RSV was necessary for maintaining TNF mRNA expression over the same time. Protein concentrations of the different cytokines in the supernatants of infected AM reflected the increased levels of mRNA in the cells. Despite the high levels of cytokines with possible antiviral activity (TNF and IL-6) in the AM supernatants, neither supernatants nor rTNF when added to bronchial epithelial cells protected them from infection with RSV. However, TNF, IL-1, and RSV, but not IL-6, induced IL-8 and IL-6 mRNA expression by the bronchial epithelial cells suggesting that cytokines produced by RSV-infected AM may be more important in modulating the inflammatory response in infection than directly interfering with virus infection/replication of airway epithelium.     

IL-12-activated NK cells reduce lung eosinophilia to the attachment protein of respiratory syncytial virus but do not enhance the severity of illness in CD8 T cell-immunodeficient conditions

Bronchiolitis caused by respiratory syncytial virus (RSV) infection is a major cause of hospitalization in children under 1 year of age. RSV causes common colds in older children and adults, but can cause serious disease in immunodeficient patients and the elderly. Development of effective vaccines and treatments for RSV infection is therefore a priority. Because bronchiolitis and vaccine-augmented disease are thought to be caused by exuberant T cell activation, attention has focused on the use of immunomodulators that affect T cell responses. In mice, IL-12 treatment down-regulates type 2 cytokine responses to the attachment protein G of RSV, reducing lung eosinophilia but further enhancing illness. We now show that CD8(+) T cells are responsible for enhanced weight loss, whereas IL-12-activated NK cells express high levels of IFN-gamma and inhibit lung eosinophilia without causing illness. Moreover, unlike immunocompetent mice, virus is detected in the mediastinal lymph nodes after elimination of both CD8(+) T cells and NK cells. These studies show that innate immune responses to viral infections direct the pattern of subsequent specific immunity and are critical to the development of nonpathogenic antiviral effects. We speculate that IL-12 treatment might be beneficial and safe in T cell-deficient patients with RSV pneumonitis.     

Respiratory synctial virus infection in BALB/c mice previously immunized with formalin-inactivated virus induces enhanced pulmonary inflammatory response with a predominant Th2-like cytokine pattern.

Vaccination with formalin-inactivated respiratory syncytial virus (FI-RSV) caused excessive disease in infants upon subsequent natural infection with RSV. Recent studies with BALB/c mice have suggested that T cells are important contributors to lung immunopathology during RSV infection. In this study, we investigated vaccine-induced enhanced disease by immunizing BALB/c mice with live RSV intranasally or with FI-RSV intramuscularly. The mice were challenged with RSV 6 weeks later, and the pulmonary inflammatory response was studied by analyzing cells obtained by bronchoalveolar lavage 4 and 8 days after challenge. FI-RSV-immunized mice had an increased number of total cells, granulocytes, eosinophils, and CD4+ cells but a decreased number of CD8+ cells. The immunized mice also had a marked increase in the expression of mRNA for the Th2-type cytokines interleukin-5 (IL-5) and IL-13 as well as some increase in the expression of IL-10 (a Th2-type cytokine) mRNA and some decrease in the expression of IL-12 (a Th1-type cytokine) mRNA. The clear difference in the pulmonary inflammatory response to RSV between FI-RSV- and live-RSV-immunized mice suggests that this model can be used to evaluate the disease-enhancing potential of candidate RSV vaccines and better understand enhanced disease.     

Autocrine regulation of pulmonary inflammation by effector T-cell derived IL-10 during infection with respiratory syncytial virus

Respiratory syncytial virus (RSV) infection is the leading viral cause of severe lower respiratory tract illness in young infants. Clinical studies have documented that certain polymorphisms in the gene encoding the regulatory cytokine IL-10 are associated with the development of severe bronchiolitis in RSV infected infants. Here, we examined the role of IL-10 in a murine model of primary RSV infection and found that high levels of IL-10 are produced in the respiratory tract by anti-viral effector T cells at the onset of the adaptive immune response. We demonstrated that the function of the effector T cell -derived IL-10 in vivo is to limit the excess pulmonary inflammation and thereby to maintain critical lung function. We further identify a novel mechanism by which effector T cell-derived IL-10 controls excess inflammation by feedback inhibition through engagement of the IL-10 receptor on the antiviral effector T cells. Our findings suggest a potentially critical role of effector T cell-derived IL-10 in controlling disease severity in clinical RSV infection.     

Synergistic upregulation of interleukin-8 secretion from pulmonary epithelial cells by direct and monocyte-dependent effects of respiratory syncytial virus infection

Respiratory syncytial virus (RSV) infection is the major cause of severe bronchiolitis in infants. Pathology of this infection is partly due to excessive proinflammatory leukocyte influx mediated by chemokines. Although direct infection of the respiratory epithelium by RSV may induce chemokine secretion, little is known about the role of cytokine networks. We investigated the effects of conditioned medium (CM) from RSV-infected monocytes (RSV-CM) on respiratory epithelial (A549) cell chemokine release. RSV-CM, but not control CM (both at a 1:5 dilution), stimulated interleukin-8 (IL-8) secretion from A549 cells within 2 h, and secretion increased over 72 h to 11,360 +/- 1,090 pg/ml without affecting cell viability. In contrast, RSV-CM had only a small effect on RANTES secretion. RSV-CM interacted with direct RSV infection to synergistically amplify IL-8 secretion from respiratory epithelial cells (levels of secretion at 48 h were as follows: RSV-CM alone, 8,140 +/- 2,160 pg/ml; RSV alone, 12,170 +/- 300 pg/ml; RSV-CM plus RSV, 27,040 +/- 5,260 pg/ml; P < 0.05). RSV-CM induced degradation of IkappaBalpha within 5 min but did not affect IkappaBbeta. RSV-CM activated transient nuclear binding of NF-kappaB within 1 h, while activation of NF-IL6 was delayed until 8 h and was still detectable at 24 h. Promoter-reporter analysis demonstrated that NF-kappaB binding was essential and that NF-IL6 was important for IL-8 promoter activity in RSV-CM-activated cells. Blocking experiments revealed that the effects of RSV-CM depended on monocyte-derived IL-1 but that tumor necrosis factor alpha was not involved in this network. In summary, RSV infection of monocytes results in and amplifies direct RSV-mediated IL-8 secretion from respiratory epithelial cells by an NF-kappaB-dependent, NF-IL6-requiring mechanism.     

Immunization of macaques with formalin-inactivated respiratory syncytial virus (RSV) induces interleukin-13-associated hypersensitivity to subsequent RSV infection

Respiratory syncytial virus (RSV) is a major cause of severe respiratory disease in infants and the elderly. RSV vaccine development has been hampered by results of clinical trials in the 1960s, when formalin-inactivated whole-RSV preparations adjuvated with alum (FI-RSV) were found to predispose infants for enhanced disease following subsequent natural RSV infection. We have reproduced this apparently immunopathological phenomenon in infant cynomolgus macaques and identified immunological and pathological correlates. Vaccination with FI-RSV induced specific virus-neutralizing antibody responses accompanied by strong lymphoproliferative responses. The vaccine-induced RSV-specific T cells predominantly produced the Th2 cytokines interleukin-13 (IL-13) and IL-5. Intratracheal challenge with a macaque-adapted wild-type RSV 3 months after the third vaccination elicited a hypersensitivity response associated with lung eosinophilia. The challenge resulted in a rapid boosting of IL-13-producing T cells in the FI-RSV-vaccinated animals but not in the FI-measles virus-vaccinated control animals. Two out of seven FI-RSV-vaccinated animals died 12 days after RSV challenge with pulmonary hyperinflation. Surprisingly, the lungs of these two animals did not show overt inflammatory lesions. However, upon vaccination the animals had shown the strongest lymphoproliferative responses associated with the most pronounced Th2 phenotype within their group. We hypothesize that an IL-13-associated asthma-like mechanism resulted in airway hyperreactivity in these animals. This nonhuman primate model will be an important tool to assess the safety of nonreplicating candidate RSV vaccines.     

人呼吸道合胞病毒活疫苗研究进展

人呼吸道合胞病毒是引起婴幼儿支气管炎和肺炎的主要原因,也可导致免疫缺陷病人及老年人群显著发病和死亡.人呼吸道合胞病毒疫苗已被世界卫生组织(World Health Organization,WHO)列为全球最优先发展的疫苗之一.经过50多年的研究,尤其是随着重组技术和反向遗传学的出现,对RSV疫苗的研究取得了重要进展,...     

Effects of Formalin-Inactivated Respiratory Syncytial Virus (FI-RSV) in the Perinatal Lamb Model of RSV

Respiratory syncytial virus (RSV) is the most frequent cause of bronchiolitis in infants and children worldwide. There are currently no licensed vaccines or effective antivirals. The lack of a vaccine is partly due to increased caution following the aftermath of a failed clinical trial of a formalin-inactivated RSV vaccine (FI-RSV) conducted in the 1960’s that led to enhanced disease, necessitating hospitalization of 80% of vaccine recipients and resulting in two fatalities. Perinatal lamb lungs are similar in size, structure and physiology to those of human infants and are susceptible to human strains of RSV that induce similar lesions as those observed in infected human infants. We sought to determine if perinatal lambs immunized with FI-RSV would develop key features of vaccine-enhanced disease. This was tested in colostrum-deprived lambs immunized at 3–5 days of age with FI-RSV followed two weeks later by RSV infection. The FI-RSV-vaccinated lambs exhibited several key features of RSV vaccine-enhanced disease, including reduced RSV titers in bronchoalveolar lavage fluid and lung, and increased infiltration of peribronchiolar and perivascular lymphocytes compared to lambs either undergoing an acute RSV infection or naïve controls; all features of RSV vaccine-enhanced disease. These results represent a first step proof-of-principle demonstration that the lamb can develop altered responses to RSV following FI-RSV vaccination. The lamb model may be useful for future mechanistic studies as well as the assessment of RSV vaccines designed for infants.     

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.     

抗生素诱导的呼吸道菌群缺失对小鼠RSV感染的影响

目的探究抗生素雾化暴露引起的呼吸道菌群缺失对小鼠呼吸道合胞病毒(RSV)感染的影响,为临床合理使用抗生素提供指导意见。方法32只BALB/c小鼠分为2组:雾化ddH₂O对照组和雾化ABX组合抗生素组,处理6 d后,进行细菌16S rRNA基因PCR检测,构建呼吸道菌群缺失小鼠模型。上述2组组内再随机分为2小组,即PBS对照组(ddH₂O+PBS,ABX+PBS)和RSV感染组(ddH₂O+RSV,ABX+RSV),饲养至第14天。检测和分析各组小鼠支气管肺泡灌洗液(BALF)中的炎症细胞和相关细胞因子(TNF-α、IL-8、IL-10及MCP-1)的数量和水平,观察肺组织病理学状况及检测病毒载量。结果BALF中细菌DNA提取和16S rRNA基因PCR检测显示,雾化ABX组合抗生素处理能够有效地剔除呼吸道菌群。BALF中炎症细胞和相关细胞因子检测显示,ABX+RSV组炎症细胞总数明显增多(P<0.05),分类以巨噬细胞和淋巴细胞为主;且细胞因子TNF-α、IL-8、MCP-1及IL-10水平显著升高(均P<0.05)。肺部HE染色显示,感染RSV后ddH₂O+RSV组和ABX+RSV组小鼠肺部损伤明显加重(均P≤0.01),与ddH₂O+RSV组相比较,ABX+RSV组的病毒载量明显升高(t=2.7160,P=0.0217)。结论雾化ABX组合抗生素不仅能够有效地剔除呼吸道菌群,而且明显增加了小鼠感染RSV的风险,导致呼吸道炎症加重,以及病毒载量升高。     

IL-5 and eosinophils are essential for the development of airway hyperresponsiveness following acute respiratory syncytial virus infection

Viral respiratory infections can cause bronchial hyperresponsiveness and exacerbate asthma. In mice, respiratory syncytial virus (RSV) infection, which induces an immune response dominated by IFN-gamma, results in airway hyperresponsiveness (AHR) and eosinophil influx into the airways, both of which are prevented by pretreatment with anti-IL-5 Ab. To delineate the role of IL-5, IL-4, and IFN-gamma in the development of RSV-induced AHR and lung eosinophilia, we tested the ability of mice deficient in each of these cytokines to develop these symptoms of RSV infection. Mice deficient in either IL-5, IL-4, or IFN-gamma were administered infectious RSV intranasally, and 6 days later, airway responsiveness to inhaled methacholine was assessed by barometric body plethysmography, and numbers of lung eosinophils and production of IFN-gamma, IL-4, and IL-5 by mononuclear cells from peribronchial lymph nodes were monitored. RSV infection resulted in airway eosinophilia and AHR in both IL-4- and IFN-gamma-deficient mice, but not in IL-5-deficient mice. Reconstitution of IL-5-deficient mice with IL-5 restored these responses and enhanced the responses in IL-4-deficient mice. Anti-VLA-4 (very late Ag-4) treatment prevented lung eosinophilia and AHR following RSV infection and IL-5 reconstitution. We conclude that in response to RSV, IL-5 is essential for the influx of eosinophils into the lung and that eosinophils in turn are critical for the development of AHR. IFN-gamma and IL-4 are not essential for these responses to RSV infection.     

Mechanical Ventilation Drives Inflammation in Severe Viral Bronchiolitis

Introduction

Respiratory insufficiency due to severe respiratory syncytial virus (RSV) infection is the most frequent cause of paediatric intensive care unit admission in infants during the winter season. Previous studies have shown increased levels of inflammatory mediators in airways of mechanically ventilated children compared to spontaneous breathing children with viral bronchiolitis. In this prospective observational multi-center study we aimed to investigate whether this increase was related to disease severity or caused by mechanical ventilation.

Materials and Methods

Nasopharyngeal aspirates were collected <1 hour before intubation and 24 hours later in RSV bronchiolitis patients with respiratory failure (n = 18) and non-ventilated RSV bronchiolitis controls (n = 18). Concentrations of the following cytokines were measured: interleukin (IL)-1α, IL-1β, IL-6, monocyte chemotactic protein (MCP)-1 and macrophage inflammatory protein (MIP)-1α.

Results

Baseline cytokine levels were comparable between ventilated and non-ventilated infants. After 24 hours of mechanical ventilation mean cytokine levels, except for MIP-1α, were elevated compared to non-ventilated infected controls: IL-1α (159 versus 4 pg/ml, p<0.01), IL-1β (1068 versus 99 pg/ml, p<0.01), IL-6 (2343 versus 958 pg/ml, p<0.05) and MCP-1 (174 versus 26 pg/ml, p<0.05).

Conclusions

Using pre- and post-intubation observations, this study suggests that endotracheal intubation and subsequent mechanical ventilation cause a robust pulmonary inflammation in infants with RSV bronchiolitis.     

TLR4 polymorphisms mediate impaired responses to respiratory syncytial virus and lipopolysaccharide

Severe bronchiolitis following respiratory syncytial virus (RSV) infection occurs in only a small subset of infected infants and the basis for variations in disease severity is not understood. Innate immune responses to RSV are mediated by TLR-4, and the (299)Gly and (399)Ile alleles of the TLR4 gene have been linked epidemiologically with increased severity of RSV disease in children. We hypothesized that cellular immune responses to RSV mediated by these variant forms of the receptor are defective relative to responses mediated via the common form of the receptor. Human bronchial epithelial cells were transfected with TLR4 constructs encoding the common TLR4 gene sequence ((299)Asp/(399)Thr), or the (299)Gly or (399)Ile alleles, and cytokine responses to in vitro RSV challenge were analyzed in the different transfected cells. Follow-up studies compared RSV-induced responses in PBMC from children expressing these same TLR4 genotypes. Human bronchial epithelial expressing (299)Gly or (399)Ile displayed normal levels of intracellular TLR4 but failed to efficiently translocate the receptor to the cell surface. This was associated with reduced NF-kappaB signaling post-TLR4 engagement, reduced production of IFNs, IL-8, IL-10, IL-12p35, IL-18, and CCL8, and the absence of acute-phase TNF-alpha. These findings were mirrored by blunted PBMC responses to RSV in children expressing the same TLR4 variants. Compromised first-line defense against RSV at the airway-epithelial surface of children expressing these TLR4 variants may thus confer increased susceptibility to severe infections with this virus.     

Interleukin 18 Coexpression during Respiratory Syncytial Virus Infection Results in Enhanced Disease Mediated by Natural Killer Cells

Respiratory syncytial virus (RSV) causes bronchiolitis, the main cause of infantile hospitalization. Immunity against reinfection is poor, and there is great interest in boosting vaccine responses using live vectors expressing host cytokines. We therefore constructed a recombinant RSV expressing murine interleukin 18 (RSV/IL-18), a cytokine capable of inducing strong antiviral immune responses. In vitro RSV/IL-18 replicated at wild-type levels and produced soluble IL-18. In naïve BALB/c mice, RSV/IL-18 infection significantly increased both IL-18 mRNA and protein and attenuated the peak viral load 3-fold. Despite a reduced viral load, RSV/IL-18 infection caused a biphasic weight loss at days 2 and 6 postinfection that was not seen in wild-type infection. Day 2 disease was associated with enhanced pulmonary natural killer (NK) cell numbers and activity and was prevented by NK cell depletion during infection; day 6 disease was correlated with CD8 T-cell recruitment and was enhanced by NK cell depletion. IL-18 expression during priming also enhanced RSV-specific antibody responses and T-cell responses on secondary RSV infection. Therefore, while IL-18 boosted antiviral immunity and reduced the viral load, its coexpression worsened disease. This is the first recombinant RSV with this property, and these are the first studies to demonstrate that NK cells can induce pathology during pulmonary viral infections.Human respiratory syncytial virus (RSV) is the major cause of infantile viral bronchiolitis worldwide (27). RSV infection results in lower respiratory tract illness (LRTI) in 25 to 40% of children, with 0.5 to 2% requiring hospitalization. Immunity against RSV is short-lived and incomplete, and reinfection with the same strain can occur regularly throughout life. In elderly persons, RSV causes morbidity and mortality that match those resulting from influenza A virus infection in those vaccinated against seasonal influenza; there is currently no RSV vaccine. The relative roles of the virus and the immune response in causing disease are much debated (9).The proinflammatory cytokine interleukin 18 (IL-18) is produced by a wide range of cells, including macrophages, neutrophils, and airway epithelial cells, and is a potent promoter of immune responses. It induces gamma interferon (IFN-γ) production from T cells without the requirement for T-cell receptor (TCR) engagement, an effect that is greatly enhanced by the presence of IL-12. Together, these cytokines enhance T helper cell type 1 (Th1) responses (15, 25, 32). IL-18 also directly promotes NK cell activation and proliferation and has been shown to drive antiviral immunity in a number of situations (18, 24, 26). In the presence of IL-12, IL-18 is also capable of preventing IgE production (34), but in the absence of IL-12 (or with an abundance of IL-2 or IL-4), it promotes the differentiation of Th2 cells and induces nonspecific IgE production (33, 35). Increased RSV titers are seen in IL-18 knockout mice (2), and polymorphisms in the IL-18 promoter are associated with increased risk of severe bronchiolitis (23).To enhance and redirect immune responses upon RSV infection, we inserted various cytokine genes into the RSV genome for coexpression during infection in vitro and in vivo (3-7, 13). In the present study, we used this technique to investigate whether the potent immune-modulating capacity of IL-18 could be used to boost virus-specific immunity as a vaccine candidate; in addition, we aimed to examine how IL-18 expression influenced lung immune responses and disease severity. We found that both innate and adaptive immune responses were boosted by the coexpression of IL-18 from a recombinant RSV during respiratory tract infection of BALB/c mice. This resulted in a reduced primary viral load and enhanced memory responses with enhanced immunity on secondary infection. Unfortunately IL-18 expression also enhanced illness during primary infection, characterized by weight loss and increased pulmonary cellular infiltration. The unexpected and novel pattern of enhanced disease was accompanied by the excess recruitment of NK cells and then CD8 cells into the airways and lungs. Further investigation of this effect led us to identify NK cells as critical mediators of early disease and determinants of later CD8 T-cell responses. These results show that boosting the responses that reduce the viral load can increase disease severity in RSV infection.     

Expression of interleukin-4 by recombinant respiratory syncytial virus is associated with accelerated inflammation and a nonfunctional cytotoxic T-lymphocyte response following primary infection but not following challenge with wild-type virus

The outcome of a viral infection or of immunization with a vaccine can be influenced by the local cytokine environment. In studies of experimental vaccines against respiratory syncytial virus (RSV), an increased stimulation of Th2 (T helper 2) lymphocytes was associated with increased immunopathology upon subsequent RSV infection. For this study, we investigated the effect of increased local expression of the Th2 cytokine interleukin-4 (IL-4) from the genome of a recombinant RSV following primary infection and after a challenge with wild-type (wt) RSV. Mice infected with RSV/IL-4 exhibited an accelerated pulmonary inflammatory response compared to those infected with wt RSV, although the wt RSV group caught up by day 8. In the first few days postinfection, RSV/IL-4 was associated with a small but significant acceleration in the expansion of pulmonary T lymphocytes specific for an RSV CD8(+) cytotoxic T-lymphocyte (CTL) epitope presented as a major histocompatibility complex class I tetramer. However, by day 7 the response of tetramer-positive T lymphocytes in the wt RSV group caught up and exceeded that of the RSV/IL-4 group. At all times, the CTL response of the RSV/IL-4 group was deficient in the production of gamma interferon and was nonfunctional for in vitro cell killing. The accelerated inflammatory response coincided with an accelerated accumulation and activation of pulmonary dendritic cells early in infection, but thereafter the dendritic cells were deficient in the expression of B7-1, which governs the acquisition of cytolytic activity by CTL. Following a challenge with wt RSV, there was an increase in Th2 cytokines in the animals that had previously been infected with RSV/IL-4 compared to those previously infected with wt RSV, but the CD8(+) CTL response and the amount of pulmonary inflammation were not significantly different. Thus, a strong Th2 environment during primary pulmonary immunization with live RSV resulted in early inflammation and a largely nonfunctional primary CTL response but had a minimal effect on the secondary response.     

Local interleukin-10 production during respiratory syncytial virus bronchiolitis is associated with post-bronchiolitis wheeze

Background

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis in infants. Following RSV bronchiolitis, 50% of children develop post-bronchiolitis wheeze (PBW). Animal studies have suggested that interleukin (IL)-10 plays a critical role in the pathogenesis of RSV bronchiolitis and subsequent airway hyperresponsiveness. Previously, we showed that ex vivo monocyte IL-10 production is a predictor of PBW. Additionally, heterozygosity of the single-nucleotide polymorphism (SNP) rs1800872 in the IL10 promoter region was associated with protection against RSV bronchiolitis.

Methods

This study aimed to determine the in vivo role of IL-10 in RSV pathogenesis and recurrent wheeze in a new cohort of 235 infants hospitalized for RSV bronchiolitis. IL-10 levels in nasopharyngeal aspirates (NPAs) were measured at the time of hospitalization and the IL10 SNP rs1800872 genotype was determined. Follow-up data were available for 185 children (79%).

Results

Local IL-10 levels during RSV infection turned out to be higher in infants that later developed physician diagnosed PBW as compared to infants without PBW in the first year after RSV infection (958 vs 692 pg/ml, p = 0.02). The IL10 promoter SNP rs1800872 was not associated with IL-10 concentration in NPAs.

Conclusion

The relationship between high local IL-10 levels during the initial RSV infection and physician diagnosed PBW provides further evidence of the importance of the IL-10 response during RSV bronchiolitis.     

Human metapneumovirus induces a profile of lung cytokines distinct from that of respiratory syncytial virus

Lung cytokine and chemokine production by BALB/c mice infected with human metapneumovirus (hMPV) was compared to respiratory syncytial virus (RSV)-infected mice. hMPV infection induced lower levels of the inflammatory cytokines interleukin-1 (IL-1), IL-6 and tumor necrosis factor alpha but was a more potent inducer of granulocyte-macrophage colony-stimulating factor and triggered a more sustained production of the CXC chemokine KC compared to RSV. hMPV was a stronger inducer of both alpha interferon (IFN-alpha) and IFN-gamma responses than RSV. In regard to immunomodulatory cytokines, hMPV failed to induce detectable IL-10 or IL-12p70 but was a potent inducer of IL-12 p40 subunit. The implications for hMPV pathogenesis are discussed.     

沈阳地区婴幼儿RSV感染的病原学调查研究

查明冬春季沈阳地区婴幼儿RSV感染流行情况.采用APAAP法和IFA法对65例临床诊断为急性病毒性下呼吸道感染的婴幼儿进行了检查.在RSV感染的高发季节由RSV引起婴幼儿的急性下呼吸道感染的阳性率为44.60%(29/65),0～6个月婴幼儿感染率最高,为74.07%(20/27),并有明显的喘息倾向.以上结果表明RSV仍是引起婴幼儿急性下呼吸道感染,特别是肺炎和毛细支气管炎的重要病原体,沈阳地区仍有流行.为防止和控制RSV的流行及为RSV的防治提供了依据.