Pathogenesis of respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is recognized as the most important cause of serious lower respiratory tract illness in infants and young children worldwide causing repeat infections throughout life with serious complications occurring in the elderly and immune compromised patient. The level of disease pathogenesis associated with RSV infection is balanced between virus elimination and the nature of the immune response to infection. The innate and adaptive immune responses to RSV infection are not fully elucidated; however, significant progress has been made in understanding the virus-host relationship and mechanisms associated with disease pathogenesis. This review summarizes important aspects of these findings, and provides current perspective on processes that may contribute to RSV disease pathogenesis.     

呼吸道合胞病毒感染的研究进展

呼吸道合胞病毒是在世界范围内引起婴幼儿呼吸道感染的最常见病原微生物,它不仅可以引起呼吸系统的一些常见症状和体征,而且在肺外器官如中枢神经系统、心血管系统、内分泌系统等各器官也可引起一些尚未被人们普遍认识的肺外表现,而这些临床特点的重要性也愈来愈受到人们的重视.     

Replication and clearance of respiratory syncytial virus: apoptosis is an important pathway of virus clearance after experimental infection with bovine respiratory syncytial virus

Human respiratory syncytial virus is an important cause of severe respiratory disease in young children, the elderly, and in immunocompromised adults. Similarly, bovine respiratory syncytial virus (BRSV) is causing severe, sometimes fatal, respiratory disease in calves. Both viruses are pneumovirus and the infections with human respiratory syncytial virus and BRSV have similar clinical, pathological, and epidemiological characteristics. In this study we used experimental BRSV infection in calves as a model of respiratory syncytial virus infection to demonstrate important aspects of viral replication and clearance in a natural target animal. Replication of BRSV was demonstrated in the luminal part of the respiratory epithelial cells and replication in the upper respiratory tract preceded the replication in the lower respiratory tract. Virus excreted to the lumen of the respiratory tract was cleared by neutrophils whereas apoptosis was an important way of clearance of BRSV-infected epithelial cells. Neighboring cells, which probably were epithelial cells, phagocytized the BRSV-infected apoptotic cells. The number of both CD4(+) and CD8+ T cells increased during the course of infection, but the T cells were not found between the epithelial cells of the bronchi up until apoptosis was no longer detected, thus in the bronchi there was no indication of direct contact-dependent T-cell-mediated cytotoxicity in the primary infection.     

Allergy skin test responses during experimental infection with respiratory syncytial virus.

BACKGROUND: Allergy skin testing is one of the most frequently performed physician office procedures. Many factors can affect the results of those tests, including the well-defined suppressive effect of systemic antihistamines. False-positive allergen skin test results are known to occur; however, contributing factors are not well understood. OBJECTIVE: To determine whether a viral upper respiratory tract infection affects allergy skin test responsiveness. METHODS: We performed skin tests with histamine and a panel of geographically relevant inhalant allergens on 16 adults before and 3, 6, and 21 days after experimental exposure to respiratory syncytial virus (RSV), a virus that causes signs and symptoms of a cold. RESULTS: The RSV exposure, with and without documented infection, caused increased wheal and flare areas to histamine and allergen and de novo positive allergen test responses in individuals with no measurable responses at baseline. These were noted as late as 21 days after RSV exposure and may be consistent with mediation by up-regulated neurogenic inflammation during RSV infection. CONCLUSION: These results may have implications for explaining the cause of such well-known complications of RSV infection as otitis media, bronchiolitis, and asthmatic exacerbation.     

Viremia in respiratory syncytial virus infection]

Viremia was demonstrated to occur in experimental respiratory syncytial (RS) virus infection in suckling cotton rats and in natural infection in children. RS virus was isolated from the whole blood of the animals in 3 out of 6 experiments at 2, 5, 6, 7 and 15 days after inoculation, the maximum infectious titer being more than 10(4) TCPD50/0.1 ml. RS virus was also isolated from the blood of 7 out of 15 examined children presenting the typical clinical picture of RS virus disease during the epidemic season of RS virus infection. In 6 patients RS virus was isolated from one blood specimen at 1, 6 and 7 days after the onset, in one patient from 3 blood specimens at 6, 9 and 22 days after the onset. The demonstrated long-term persistence of virus in the blood suggests the possibility of existence of chronic RS virus infection.     

Primary respiratory syncytial virus infection in mice

A mouse model of respiratory syncytial virus (RSV) infection is described. A high-titered, large-volume inoculum results in replication of RSV to a high titer in lungs of BALB/c mice. Mice older than 15 weeks of age are more susceptible to RSV infection. Titers up to 10(6.9) plaque-forming units (pfu)/gram lung can be attained in 32-week-old mice. Older mice experience a clinical illness manifested by ruffled fur, reduced activity, and weight loss. Lung histology of older mice infected with RSV shows bronchiolitis and increased number of lymphocytes and macrophages in alveolar spaces compared with that of mice less than 8 weeks old. This model will serve as the basis for investigating immunodeterminants of recovery and protection from RSV infection.     

The immunobiology of respiratory syncytial virus infection

There is increasing evidence that young children with severe respiratory syncytial virus (RSV)-induced bronchiolitis are at high risk of developing allergy and asthma during their later life. The determinants for this association are not well understood. Current studies suggest that both genetic backgrounds and unique characteristics of the virus play critical roles in determining the type of immune responses to RSV infection, leading to altered regulation of airway tone associated with wheezing. In susceptible subjects, RSV may either enhance the Th2 immune response or decrease the Th1 immune response. This altered Th1/Th2 cytokine response associated with RSV infection is not commonly observed among other RNA viruses, suggesting that RSV may have unique characteristics. Multiple clinical studies support the link between severe RSV bronchiolitis and the subsequent development of allergy and asthma. This link will be further tested by the ongoing large studies on the effect of early RSV intervention on the development of allergy. The administration of palivizumab, an anti-RSV monoclonal antibody, seems to be helpful for RSV prevention and treatment at early stage. There are no effective RSV vaccines available, and this is, at least in part, because of the poorly understood immunology and pathogenesis of RSV disease. The use of experimental animal models has led to a better, but not sufficient, understanding of the immunologic basis of RSV-induced disease, particularly asthma. Further studies on the immunopathology of RSV infection with animal models, including the nonhuman primate models, may help develop effective RSV vaccines.     

Otitis and respiratory distress episodes following a respiratory syncytial virus infection

Objective  To document, over two consecutive respiratory syncytial virus (RSV) seasons, the occurrence of acute otitis media (AOM) and recurrence of respiratory distress in children < 2 years of age hospitalized for respiratory distress.
Methods  Patients were examined during hospitalization and at 6 weeks and 6 months after discharge. RSV testing was performed on all patients, and hospitalized patients were evaluated daily for the occurrence of AOM.
Results  In total, 347 children were enrolled; 54.8% were RSV positive, and 45.2% were RSV negative. Children were most frequently diagnosed as having bronchiolitis (71.9%) or asthmatic bronchitis (17.9%); other diagnoses included pneumonia, laryngitis, and rhinitis. During hospitalization, AOM was diagnosed in 16.8% of RSV-positive versus 8.3% of RSV-negative children ( P  < 0.05). Six weeks after discharge, AOM was reported in 10.4% of RSV-positive as compared with 5.8% of RSV-negative patients. Six months later, AOM was reported in 2.9% of the RSV-positive and 7.6% of the RSV-negative patients. A second episode of acute respiratory distress, which either required (9) or did not require (35) hospitalization, occurred in 18.4% of the total population, with similar proportions of RSV-positive and RSV-negative children (17% versus 18.6%).
Conclusion  We conclude that RSV appears to be an important contributing factor for the occurrence of AOM in young children hospitalized with respiratory distress. The occurrence of a second episode of acute respiratory distress did not appear to correlate with the previous RSV infection, but longer-term follow-up is required.     

RhoA is activated during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is an important human pathogen that can cause severe and life-threatening respiratory infections in infants and immunocompromised adults. We have recently shown the RSV F glycoprotein, which mediates viral fusion and entry, interacts with the cellular protein RhoA in two-hybrid and in vitro binding assays. Whether this interaction occurs in living cells remains an open question. However, because RhoA signaling is associated with many cellular functions relevant to RSV pathogenesis such as actin cytoskeleton organization, expression of proinflammatory cytokines, and smooth muscle contraction, we asked whether RhoA activation occurred during RSV infection of HEp-2 cells. We found that the amount of isoprenylated and membrane-bound RhoA in RSV-infected cultures was increased. Further evidence of RhoA activation was demonstrated by downstream signaling activity mediated by RhoA. There was an increase in p130(cas) phosphorylation during RSV infection, which was prevented by Y-27632, a specific inhibitor of Rho kinase, or lovastatin, an HMG-CoA reductase inhibitor that reduces the synthesis of groups needed for isoprenylation. In addition, RSV infection of HEp-2 cells resulted in an increase in the formation of actin stress fibers. Pretreatment of HEp-2 cells with Clostridium botulinum C3 exotoxin, an enzyme that specifically ADP-ribosylates and inactivates RhoA, prevented RSV-induced stress fiber formation. These observations indicate that RhoA and subsequent downstream signaling events are activated during RSV infection, which has implications for RSV pathogenesis.     

Local cytokine response upon respiratory syncytial virus infection

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

Maternal antibody and respiratory syncytial virus infection in infancy

One hundred newborn infants were studied prospectively for 1 year for evidence of infection with respiratory syncytial virus (RSV). The indirect membrane fluorescence technique was used to determine specific antibody in sera. Infection was shown in 29 cases. In 31 infants exposed to an RSV epidemic season, there was no evidence of infection. Maternal antenatal sera were also tested, and a wide range of IgG antibody to RSV was found. Mean titre of maternal IgG antibody to RSV was significantly higher (P < 0.001) in those mothers whose babies remained uninfected than in those whose babies had proved RSV infection before 6 months of age. Babies born to mothers with high levels of IgG antibody to respiratory syncytial virus were protected against infection with this virus during the first months of life when the risk of severe disease was greatest.     

Prevalence and clinical characteristics of human respiratory syncytial virus in Chinese adults with acute respiratory tract infection

Respiratory syncytial virus (RSV) is a leading cause of respiratory tract illnesses worldwide. Although the prevalence and clinical manifestations of the two subtypes, RSV‐A and RSV‐B, have been studied in some detail in infants and young children, they have not been determined in adults. To evaluate the prevalence of the RSV subtypes and disease severity between RSV‐A and RSV‐B infections in adults, nasal and throat swabs that were collected from patients ≥15 years old who sought medical care for acute respiratory infections at the Fever Clinic of the Peking Union Medical College Hospital in Beijing, China between May 2005 and April 2010. The samples were tested for RSV infection using PCR and sequencing analysis. RSV was detected in 95 (1%) of the adult patients, of whom 53 (55.8%) were positive for RSV‐A and 42 (44.2%) for RSV‐B. The incidence of RSV infections increased with age (χ² = 37.17, P = 1.66E?07). Demographic data and clinical manifestations of RSV‐A were similar to those of RSV‐B. Although RSV‐A and RSV‐B co‐circulated during the 2005–2006 and 2008–2009 seasons, RSV‐A was predominant in the 2006–2008 seasons, whereas RSV‐B was predominant in the 2009–2010 season. Upper respiratory tract infections were diagnosed in most RSV‐infected patients (n = 80, 84.2%), and three patients suffered from pulmonary infection. This is the first study to provide data on the prevalence and clinical manifestations of RSV subgroups among Chinese adults with fever and acute illness, over five successive epidemic seasons. J. Med. Virol. 85:348–353, 2013. © 2012 Wiley Periodicals, Inc.     

Development of cell-mediated cytotoxic activity in the respiratory tract after experimental infection with respiratory syncytial virus.

The development of natural killer cell and other antibody-independent cellular cytotoxic response to RSV were studied in splenic and pulmonary mononuclear effector cells obtained from groups of 6-week-old cotton rats after subcutaneous (SC) or intranasal (IN) immunization with live virulent or ultra-violet (UV) inactivated respiratory syncytial virus (RSV). No virus-induced cytotoxic activity was observed after SC immunization with live virus or IN inoculation of inactivated non-infectious virus. On the other hand significant cytotoxic activity was observed after IN infection with live RSV. The peak responses appeared on day 4 in the pulmonary cells and on day 7 in the splenic mononuclear cells. These cytotoxic activities declined to baseline levels 10 and 15 days after immunization in pulmonary and splenic cells respectively. In addition, the amount of 51Cr released was significantly reduced when unlabelled 'cold' HEp-2 cells were added to 51Cr-labelled RSV-infected CRF target cells and vice versa in the cytotoxic assay. It is suggested that viral replication at the mucosal site is essential for the induction of local as well as systemic cytotoxic activity following RSV infection. The development of such cellular reactivity may be important in the elimination of RSV following human infection.     

The association between MICA/MICB polymorphism and respiratory syncytial virus infection in children

MICA/MICB gene polymorphisms are related to several cancers and infectious diseases, but there are no reports on the association between MICA/MICB gene polymorphisms and respiratory syncytial virus (RSV) infection. To clarify the association between MICA/MICB gene polymorphisms and infection of RSV in children, we collected fresh blood samples from paediatric patients with and without pneumonia after RSV infection. The MICA/MICB alleles were characterized by PCR sequence‐specific primers (PCR‐SSP) and PCR sequence‐based genotyping (PCR‐SBT), and then, the frequency of the MICA/MICB alleles and haplotypes was calculated. The results showed that the frequencies of MICA*002:01 and MICA‐A9 in RSV‐infected patients were significantly lower than in controls (9% vs. 20%, pc = 0.04). The allele frequency of MICA*002:01 in pneumonia patients (8%) and nonpneumonia patients (9%) was significantly lower than in controls (20%, pc = 0.02). MICA*002:01‐MICB*008(Δrel = 0.616), MICA*009‐MICB*016 (Δrel = 0.506), and MICA*045‐MICB*014 (Δrel = 0.700) showed linkage disequilibrium in patients infected with RSV. The haplotype frequency of MICA*002:01‐MICB*005:02 in RSV‐infected patients was significantly lower than in controls (10% vs. 16%, pc = 0.033). In conclusion, allele MICA*002:01/A9 and haplotype MICA*002:01‐MICB*005:02 were negatively associated with RSV respiratory tract infections.     

The relationship between respiratory syncytial virus infections and the development of wheezing and asthma in children

PURPOSE OF REVIEW: The relationship between respiratory syncytial virus lower-respiratory-tract infections in early childhood and asthma has been the subject of much debate. Most, but not all, previous cohort studies have failed to identify a link between early respiratory syncytial virus infection and atopic asthma. Recent studies have helped clarify some apparently contradictory findings. RECENT FINDINGS: Cohort studies focusing on wheezing in early childhood have indicated that this is associated with an increased incidence of atopic asthma but that this risk is not increased by respiratory syncytial virus infection. Indeed, wheeze associated with rhinovirus infection may be a better marker for possible asthma. In contrast, there is no increased risk of atopic disease in infants with respiratory syncytial virus 'acute bronchiolitis', a phenotype characterized by widespread crepitation. Post-bronchiolitic symptoms are associated with intercurrent viral infections in particular and the incidence of symptoms falls rapidly during infancy. SUMMARY: These studies confirm earlier suggestions that the phenotype of respiratory illness and hence the host response rather than the infecting organism is the best predictor of the future pattern of respiratory illness. Such considerations must be central to the design of any future intervention or cohort studies.     

Immune responses and disease enhancement during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is one of the commonest and most troublesome viruses of infancy. It causes most cases of bronchiolitis, which is associated with wheezing in later childhood. In primary infection, the peak of disease typically coincides with the development of specific T- and B-cell responses, which seem, in large part, to be responsible for disease. Animal models clearly show that a range of immune responses can enhance disease severity, particularly after vaccination with formalin-inactivated RSV. Prior immune sensitization leads to exuberant chemokine production, an excessive cellular influx, and an overabundance of cytokines during RSV challenge. Under different circumstances, specific mediators and T-cell subsets and antibody-antigen immune complex deposition are incriminated as major factors in disease. Animal models of immune enhancement permit a deep understanding of the role of specific immune responses in RSV disease, assist in vaccine design, and indicate which immunomodulatory therapy might be beneficial to children with bronchiolitis.     

Chemokine-receptor upregulation and disease severity in respiratory syncytial virus infection

Respiratory Syncytial Virus (RSV) infection is an important cause of severe infant bronchiolitis, partly due to lower airway inflammation orchestrated by virus-induced chemokine secretion. Chemokine receptors may therefore be therapeutic targets. We investigated RSV-induced chemokine receptor (CCR) 1, 2 and 5 surface expressions in a cellular model and in infants. RSV infection increased human monocytic CCR1, 2 and 5 expression, as assessed by FACS, via replication-dependent mechanisms. CCR1 and CCR5 levels peaked at 36 h and CCR2 levels at 48 h. Monocytes from infants with RSV-bronchiolitis significantly increased CCR1 expression after ex vivo RSV infection compared to controls. Expression of CCR5 also increased, and correlated with CCR1 expression (r=0.78, p<0.0001). CCR1 upregulation correlated with disease severity markers. Monocyte CCR1 receptors were functionally active as stimulation resulted in calcium influx. CCR1/5 blocking strategies may be useful in decreasing cellular inflammation in RSV infection.     

婴幼儿呼吸道合胞病毒感染分子流行病学研究

目的　探讨婴幼儿呼吸道合胞病毒(RSV)感染的分子流行病学情况。方法　采用随机扩增多态DNA(RAPD)技术,对长春市儿童医院1992～1994年分离并鉴定的96株RSV和一株标准RSV进行RAPD分析。结果　所有RSV毒株都有扩增带,共有四种带型。不同疾病来源的RSV基因型不同。来源毛细支气管炎的RSV有8714%为R1型。结论　RAPD技术能从分子水平了解婴幼儿RSV感染情况;R1型RSV可能为引起婴幼儿毛细支气管炎的主要病原。     

Immunofluorescence for routine diagnosis of respiratory syncytial virus infection

A comparison of immunofluorescent tests for the diagnosis of respiratory syncytial (RS) virus infections was carried out on 42 hospitalized cases of respiratory infection in childhood. Respiratory syncytial virus was detected in 22 (52%) cases, the most sensitive method of detection being by indirect immunofluorescence of Bristol HeLa tissue cultures inoculated with nasopharyngeal aspirates. The highest detection rate was in bronchiolitis cases (92%). Detection of antibody rises in paired sera, eight days apart, confirmed RS virus infection in 13 of 16 cases, the most sensitive test being detection of a specific rise in IgG antibody by indirect immunofluorescence. A serodiagnosis was made in all 10 non-bronchiolitis cases. Recommendations are made for the application ofimmunofluorescence to routine diagnosis of RS virus infection.