Cell-free and cell-bound antibody in nasal secretions from infants with respiratory syncytial virus infection.

Twenty-two infants under 9 months of age hospitalized with bronchiolitis or pneumonia due to respiratory syncytial virus (RSV) were serially sampled to determine the pattern of secretory antibody response. Using double labeling techniques, we found several types of immunoglobulin in secretions: cell-free antibody to RSV of the immunoglobulin A (IgA), immunoglobulin G (IgG), and immunoglobulin M (IgM) classes; and immunoglobulins of all three classes bound to RSV-infected cells shed from the nasal epithelium (presumably cell-bound antibody to RSV). IgA attached to RSV-infected epithelial cells was almost always detected in the first available nasal sample (day 1 or 2 of hospitalization). In contrast, cell-free anti-RSV IgA first appeared an average of 3.5 days later at a time when virus antigen was disappearing from the secretion. IgG and IgM attached to RSV-infected cells appeared more irregularly. The titer of cell-free anti-RSV IgM was often higher than that of IgA early in the illness and declined as the infection resolved. Cell-free anti-RSV IgG was usually present earlier than IgA and rose during convalescence.     

Development of interleukin 6 and tumor necrosis factor alpha activity in nasopharyngeal secretions of infants and children during infection with respiratory syncytial virus.

Cytokine (interleukin 6 [IL-6] and tumor necrosis factor alpha [TNF-alpha]) activity in nasopharyngeal secretions of 21 infants and children (19 days to 16 months old) infected with primary respiratory syncytial virus was determined by an enzyme-linked immunosorbent assay. IL-6 and TNF-alpha were detectable in 100% (21 of 21) and 67% (14 of 21) of cases during the course of infection, respectively. Generally, TNF-alpha activity was high in the acute phase and declined thereafter, sometimes to undetectable levels. IL-6 activity was also highest in the acute phase and declined thereafter in infants younger than 5 months, while in patients older than 5 months, it-increased during the course of the disease to peak in the early convalescent phase. These observations suggest that inflammatory cytokines are produced in vivo in infants and children in response to primary respiratory syncytial virus infection and may be involved in disease pathogenesis. However, the mechanism of induction of cytokines may be different for infants and children in different age groups.     

Serum and nasal-wash immunoglobulin G and A antibody response of infants and children to respiratory syncytial virus F and G glycoproteins following primary infection.

An enzyme-linked immunosorbent assay (ELISA) with immunoaffinity-purified fusion (F) or attachment (G) glycoprotein was used to measure the serum and secretory immune responses of 18 infants and children, 4 to 21 months of age, who underwent primary infection with respiratory syncytial virus (RSV). Most of the 10 older individuals (9 to 21 months of age) developed moderate levels of serum and nasal-wash immunoglobin A (IgA) and IgG F and G antibodies. These individuals developed a moderate level of serum or nasal-wash antibodies that neutralized virus infectivity. One of the eight younger individuals (4 to 8 months of age) failed to develop an F antibody response, while three failed to develop a G antibody response. The most notable difference in the responses of the two age groups involved the titer in convalescent sera of G, F, and neutralizing antibodies which were 8- to 10-fold lower in younger individuals. Most of the younger infants failed to develop a rise in serum or nasal-wash neutralizing antibody. It is possible that the presence of maternally derived antibody in the younger infants suppressed the immune response to RSV infection, and that this accounted, in part, for the low level of postinfection antibody titer in this group. This low level and the irregular response of the infants less than 8 months of age may contribute to the severity of their initial infection and may also be responsible, in part, for their failure to develop effective resistance to subsequent reinfection by RSV.     

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.     

Respiratory syncytial virus infection in inbred mice.

Respiratory syncytial virus infected the nose and lungs of each of 20 strains of inbred mice, with viral titers varying 100-fold from least permissive to most permissive strains. Viral titers appeared to be under genetic control, but did not correlate with the H-2 haplotype.     

Detection of respiratory syncytial virus in nasopharyngeal secretions by DNA-RNA hybridization.

We have developed an RNA-cDNA hybridization assay for the detection of respiratory syncytial virus (RSV) RNA in nasopharyngeal samples. We chose to use as probe a cDNA complementary to the nucleocapsid protein gene of RSV, integrated into the plasmid vector pBR322. The lower limit of sensitivity of the assay is 8.2 X 10(2) PFU of the Long strain of RSV. In throat washes with added cell-free virus, the assay can detect 3.3 X 10(3) PFU of RSV. Respiratory secretions were collected from a group of 104 infants in New Orleans, and 73 of the samples were tested for RSV by immunofluorescence (IF). All were then frozen at -70 degrees C for later testing by hybridization, and 67 were tested for RSV antigens by enzyme immunoassay (EIA). A second set of respiratory secretions from 48 infants in Denver were cultured for virus, assayed for RSV antigen by EIA, and then frozen for later testing by hybridization. For those samples on which IF was performed, hybridization, compared with IF, had a sensitivity of 49% and a specificity of 66%. For samples tested by EIA, hybridization had a sensitivity of 60% and a specificity of 81% compared with EIA. Compared with virus isolation, hybridization assay had a sensitivity of 73% and a specificity of 92%. With clinical samples, the sensitivity and specificity of the assay were improved with the addition of a control blot, which was hybridized to the plasmid vector (pBR322). The performance of the hybridization assay can be expected to improve when the assay is used with fresh clinical material rather than frozen samples.     

Respiratory syncytial virus infection in mice

The A2 strain of human respiratory syncytial virus replicated in the nose and lung of BALB/c mice, with virus growing to higher titers in older animals than in younger animals. Virus was recovered from the nose between days 2 and 7 with peak titers on days 3 and 4, and from the lungs between days 2 and 9, with peak titers on days 4 through 6. Serum antibody developed 2 weeks after infection. Viral antigen was demonstrated in the alveolar cells of the lung by immunofluorescence. Histopathological changes included infiltration by mononuclear cells of the peribronchiolar and perivascular tissue, some interstitial thickening, and formation of multinucleated giant cells. Virus could not be recovered from the respiratory tract of mice inoculated with bovine strains of respiratory syncytial virus. Growth of the A2 strain of human respiratory syncytial virus in different cell lines affected its infectivity for mice. Infection of BALB/c mice with respiratory syncytial virus provides a highly reproducible model for the study of the pathogenesis of and mechanisms of immunity to this virus.     

Rapid detection of respiratory syncytial virus antigens in nasopharyngeal secretions

The combined use of fluorescein-labelled monoclonal antibody and a cytocentrifuge for preparation of cell spots greatly reduced the time for rapid diagnosis, and improved the sensitivity and ease of detection of respiratory syncytial (RS) virus antigen in specimens of nasopharyngeal secretions.     

Respiratory syncytial virus infection and immunity

Respiratory syncytial virus (RSV) is the leading cause for childhood hospitalization and respiratory distress, being recognized as a major health and economic burden worldwide. RSV can exploit host immunity and cause a strong inflammatory response that leads to lung damage and virus dissemination. Unfortunately, the immune response elicited by RSV normally fails to protect against subsequent exposures to the virus. Despite intense research during the 50 years after the discovery of RSV, scientists are just beginning to understand the mechanisms contributing to pathology and to the inadequate immune response shown by susceptible individuals. Here, we discuss some of the most important advances made in this field that could lead to the development of new prophylactic tools.     

Respiratory syncytial virus infection in adults

Respiratory syncytial virus (RSV) is now recognized as a significant problem in certain adult populations. These include the elderly, persons with cardiopulmonary diseases, and immunocompromised hosts. Epidemiological evidence indicates that the impact of RSV in older adults may be similar to that of nonpandemic influenza. In addition, RSV has been found to cause 2 to 5% of adult community-acquired pneumonias. Attack rates in nursing homes are approximately 5 to 10% per year, with significant rates of pneumonia (10 to 20%) and death (2 to 5%). Clinical features may be difficult to distinguish from those of influenza but include nasal congestion, cough, wheezing, and low-grade fever. Bone marrow transplant patients prior to marrow engraftment are at highest risk for pneumonia and death. Diagnosis of RSV infection in adults is difficult because viral culture and antigen detection are insensitive, presumably due to low viral titers in nasal secretions, but early bronchoscopy is valuable in immunosuppressed patients. Treatment of RSV in the elderly is largely supportive, whereas early therapy with ribavirin and intravenous gamma globulin is associated with improved survival in immunocompromised persons. An effective RSV vaccine has not yet been developed, and thus prevention of RSV infection is limited to standard infection control practices such as hand washing and the use of gowns and gloves.     

Effect of age and preexisting antibody on serum antibody response of infants and children to the F and G glycoproteins during respiratory syncytial virus infection.

The serum antibody response of 50 infants and children infected with respiratory syncytial virus (RSV) was determined by a glycoprotein-specific enzyme-linked immunosorbent assay, and the effects of age and preexisting antibody titer at the time of RSV infection on response to the G and F glycoproteins of RSV were examined. The immune response to the G and F glycoproteins was assessed with anti-human immunoglobulin A to permit measurement of the response of young infants in the presence of maternally derived immunoglobulin G. The findings suggested that age primarily affects the response to the F glycoprotein and that preexisting antibody titer affects the response to the G glycoprotein.     

Respiratory syncytial virus infection in cyclophosphamide-treated cotton rats.

Cotton rats infected intranasally with respiratory syncytial virus and immunosuppressed with cyclophosphamide shed virus for at least 7 weeks. Dissemination of virus beyond the respiratory tract was observed. In contrast, virus was recovered from infected, non-immunosuppressed rats for only 1 week, and only from the respiratory tract.     

Rapid immunoperoxidase assay for detection of respiratory syncytial virus in nasopharyngeal secretions.

Samples of nasopharyngeal secretions obtained from 70 infants and young children with acute respiratory disease were examined for the presence of respiratory syncytial virus by immunoperoxidase assay (IPA). The IPA was compared with the immunofluorescence assay and with cell culture isolation. Respiratory syncytial virus antigen-positive cells were detected by both IPA and immunofluorescence assay in 28 specimens; 25 samples were positive in cell culture. The agreement between virus isolation and IPA and IFA was 89%. The applicability of IPA to rapid viral diagnosis of respiratory syncytial virus infection is discussed.     

Detection of respiratory syncytial virus in nasopharyngeal secretions by shell vial technique.

A shell vial technique was used to recover respiratory syncytial virus (RSV) from frozen nasopharyngeal specimens previously tested by rapid diagnostic methods. With specimens determined to be positive by direct fluorescence assay (DFA), the shell vial technique was at least as sensitive as conventional tissue culture (92 versus 90%). The majority of RSV isolates were detected within 16 h postinoculation, versus an average of 4.5 days by conventional techniques. Also, the shell vial method recovered RSV from 16 of 17 specimens (94%) which had previously tested positive by enzyme immunoassay (EIA). In addition, the shell vial method detected RSV in 4 and 11% of specimens previously determined to be negative by DFA and EIA, respectively. Therefore, we recommend the use of the shell vial technique for specimens testing negative by the rapid methods of DFA or EIA.     

Respiratory syncytial virus infection in children with severe motor and intellectual disabilities

Children with severe motor intellectual disabilities (SMID) are at high risk of death from acute viral lower respiratory tract infections (LRTI). Although respiratory syncytial virus (RSV) is the most common cause of viral LRTI in children, there have been a few reports on the relationship between SMID and the severity of RSV-LRTI. The aim of the present study is to assess the influence of RSV-LRTI in children with SMID. A case–control study composed of children with SMID (n?=?18) and previously healthy children (n?=?43) less than 16 years old hospitalized for RSV-LRTI was performed during five consecutive RSV seasons. The clinical presentation and the laboratory data in the SMID group were compared with those in the non-SMID group. In the bivariate analysis, the median age of the SMID group was higher than that of the non-SMID group (p?=?0.002). Children with SMID had an increased risk for ventilation support (p?=?0.057). The count of neutrophils in the SMID group was significantly increased (p?=?0.012), whereas the proportion of bacterial co-infection was lower than that in the non-SMID group (p?=?0.005). Multivariate logistic analysis showed that SMID was associated with longer oxygen usage [>7 days: odds ratio (OR) 5.309, p?=?0.033]. The present study revealed that children with SMID were prone to developing hypoxia by RSV-LRTI. The strategies for the treatment and prevention of RSV infection need to be improved in SMID children.     

Respiratory syncytial virus infection in the elderly

Respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infections in infants and children throughout the world. Respiratory syncytial virus infections in the elderly represent reinfections in hosts who have had many prior episodes. Thus, RSV infections are usually not considered serious in adults, since reinfections are generally known to result in mild disease. Nevertheless, in adults, as in children, the infection has been reported to cause altered airway resistance and exacerbation of chronic obstructive lung disease. In people over 60 years of age, RSV usually causes mild nasal congestion, but can also result in fever, anorexia, pneumonia, bronchitis, and even death. Diagnosis of RSV infection in the elderly by the standard methods used in children is not as successful as in the latter group. This may be due to a combination of factors such as shorter shedding phase, lower viral titers, and dry mucosa. An alternative, rapid, and direct viral diagnostic method, the polymerase chain reaction, has recently been introduced in the diagnosis of RSV infections.     

Respiratory syncytial virus infection in Syrian hamsters. II. Regulation of the immune response

The dynamics of immune cell responsiveness in the process of development of primary and secondary immune responses after infection of adult Syrian hamsters with native respiratory syncytial virus (RSV) was studied. In primary immune response, the enhancement of functional responsiveness of lymphocytes to mitogens and the maximum level of their spontaneous proliferative activity were found to precede the optimal level of antibody synthesis. Regulation of the dynamics of immunogenesis after reinfection of animals showed typical features of the secondary immune response.     

Evaluation of immunoglobulin E-specific antibodies and viral antigens in nasopharyngeal secretions of children with respiratory syncytial virus infections.

Enzyme immunoassays were developed to detect the presence of specific immunoglobulin E (IgE) antibodies and respiratory syncytial (RS) virus structural proteins in nasopharyngeal secretions in order to improve the knowledge on some aspects of the pathogenesis of severe acute lower respiratory tract infections caused by RS virus. These assays were used to analyze clinical specimens from children with RS virus-associated infections (bronchiolitis and pneumonia), and the findings were correlated with the patients' clinical symptoms. The results indicate the presence of specific IgE against the two external glycoproteins (G and F) and the absence of detectable IgE levels for the internal viral antigens. There was a correlation between the levels of IgE-specific antibodies and the amount of viral protein F in the secretions, indicating that the IgE response against the viral glycoproteins might be related to the antigen load. In addition, a correlation was found between higher levels of both viral protein F-specific IgE and F antigen with higher respiratory rates in children with pneumonia. These findings may be relevant because they suggest an association between the virus load and the immune response in the pathogenesis of RS virus infections.