Increased production of IFN-gamma and cysteinyl leukotrienes in virus-induced wheezing

Mast-cell responses to pathogens

Mast cells have mainly been studied in the setting of allergic disease, but the importance of mast cells for host defence against several pathogens has now been well established. The location of mast cells, which are found closely associated with blood vessels, allows them to have a crucial sentinel role in host defence. The mast cell has a unique 'armamentarium' of receptor systems and mediators for responding to pathogen-associated signals. Studies of this intriguing immune-effector cell provide important insights into the complex mechanisms by which appropriate innate and acquired immune responses are initiated.

Mast cells in innate immunity

Mast cells have been most extensively studied in their traditional role as an early effector cell of allergic disease. However, in the majority of individuals, it might be the role of this cell as a sentinel in host defense that is most important. Mast cells have been repeatedly demonstrated to play a critical role in defense against bacterial infections, and evidence for their involvement in early responses to viral and fungal pathogens is growing. Mast cells are activated during innate immune responses by multiple mechanisms, including well-established responses to complement components. In addition, novel mechanisms have emerged as a result of the explosion of knowledge in our understanding of pattern-recognition receptors. The mast cell shares many features with other innate immune effector cells, such as neutrophils and macrophages. However, a unique role for mast cells is defined not only by their extensive mediator profile but also by their ability to interact with the vasculature, to expedite selective cell recruitment, and to set the stage for an appropriate acquired response.

Innate immune responses in respiratory syncytial virus infections

Respiratory syncytial virus (RSV) is the most important viral respiratory pathogen of early life. Studies of the immune response in general (and the innate response in particular) to this agent are of interest for a number of reasons. First, severe forms of illness may be a result of enhanced immunologic responsiveness to viral constituents at the time of infection. Secondly, the immune response to RSV may consist principally of innate immune responses at the time of maximum severity of illness. Third, RSV infection in infancy may be linked via immune mechanisms to the development of childhood wheezing. Finally there are no meaningfully effective forms of therapy for RSV infection, and elucidation of the immune response may suggest new therapeutic approaches. This review will summarize our current knowledge of innate immune responses to RSV infection. Specifically we will review early interactions of the virus with surfactant proteins and Toll-like receptors, chemokine release from infected cells, cytokine release from activated inflammatory cells, activation of neuroimmune pathways, generation of dendritic cells, the release of soluble mediators of airway obstruction, and genetic polymorphisms associated with RSV-related illness.

Production of interferon gamma in respiratory syncytial virus infection of humans is not associated with interleukins 12 and 18

In order to understand early events in the immune response to respiratory syncytial virus (RSV) infection, we studied the presence of various chemokines and cytokines in respiratory secretions of human infants with RSV infection. Interferon gamma (IFNgamma) was present in 30/39 (76.9%) subjects tested, but the IFNgamma-inducing cytokines interleukin (IL)12 and IL18 were detectable in 6/40 (15%) and 11/38 (28.9%) subjects, respectively. Quantities of IL12 and IL18 did not correlate with those of IFNgamma. IL18, but neither IFNgamma nor IL12 was found in significantly greater concentrations in subjects with mild, nonhypoxic forms of bronchiolitis than in those with upper respiratory illness alone or hypoxic bronchiolitis. The findings suggest that IFNgamma may be induced independently of the activities of IL12 and IL18 during RSV infection. Immune responses characterized by relatively greater release of IL18 may be associated with milder forms of bronchiolitis.

Discrepancy between cytokine production from peripheral blood mononuclear cells and nasal secretions among infants with acute bronchiolitis

BACKGROUND

Many studies have measured cytokine production derived from peripheral blood mononuclear cells (PBMCs) to evaluate the immune response in acute bronchiolitis (AB), but no previous reports have examined the association between PBMC release of cytokines and concomitant airway immune response.

OBJECTIVE

To determine whether interferon-gamma (IFN-gamma), interleukin 4 (IL-4), and IL-10 levels from PBMCs are associated with concurrent cytokine release in the airways of infants with AB.

METHODS

Infants with acute viral-associated first episode of wheezing who required hospitalization between May and September 2002 were recruited. Nasopharyngeal aspirates (NPAs) and PBMC samples were collected simultaneously. The concentrations of IFN-gamma, IL-4, and IL-10 in NPA and PBMC supernatants were determined by enzyme-linked immunosorbent assay.

RESULTS

Twenty infants with AB were enrolled in the study of whom 17 (85%) had positive NPA immunofluorescence results for viral detection and respiratory syncytial virus. Median total cell count and viability from NPA samples were 2.2 x 10(6) cells/mL (SD, 1.7 cells/mL) and 92% (SD, 6.0%), respectively. There was a significant correlation between IL-4 levels from NPA and PBMC samples (r = 0.5, P = .02); however, we did not find an association between IFN-gamma and IL-10 levels.

CONCLUSIONS

Cytokines produced by in vitro PBMCs may not necessarily reflect the concurrent cytokine pattern production at the mucosal surface in the respiratory tract of infants with AB. Further studies are required to determine whether peripheral blood is a reliable sample for airway inflammation evaluation and to explain the discrepancies of cytokine productions found in this study.

Eosinophil activation and cysteinyl leukotriene production in infants with respiratory syncytial virus bronchiolitis

BACKGROUND

It has been suggested that acute infantile bronchiolitis associated with respiratory syncytial virus (RSV) may share some pathogenic features with atopic asthma in that virus-specific IgE is produced and cysteinyl leukotrienes (cLTs) and eosinophil cationic protein (ECP) have been detected in airway secretions. ECP is a specific marker of eosinophil activation although leukotrienes can be released from a variety of cells including mast cells, eosinophils and monocytes.

OBJECTIVE

To test the association between eosinophil activation and cysteinyl leukotriene production in the upper airway secretions of infants with RSV positive (RSV+ve) bronchiolitis.

METHODS

Nasal lavage samples were performed in 78 infants (0.0-11.5 months) admitted to hospital with RSV+ve bronchiolitis soon after admission (0-48 h). Leukotriene C4 (LTC4) was assayed by enzyme immunoassay (EIA) and eosinophil cationic protein (ECP) by fluoroimmunoassay (FIA).

RESULTS

LTC4 was detectable in 51 and ECP in 57 of 78 samples with a significant positive relationship between LTC4 and ECP (r=0.557, P<0.001).

CONCLUSION

In the majority of our subjects with RSV+ve bronchiolitis ECP and LTC4 were detectable in upper airway secretions and were significantly associated with each other. In this clinical setting much of the detected LTC4 within upper airway secretions is likely to originate from the eosinophil, an observation that may have implications for clinical management and for delineation of the underlying mechanisms associated with this illness.

Viral respiratory infection and the link to asthma

BACKGROUND

Acute wheezing secondary to viral infection is common in children. Whereas many children suffer primarily mild to moderate symptoms, others develop severe coughing and wheezing.

METHODS

Review of recent medical literature regarding the correlation between viral illness and increased susceptibility to develop severe respiratory illnesses and subsequent asthma.

DISCUSSION

In infants factors that predispose to severe disease and lower respiratory airway effects include small lung size, passive smoke exposure, virus-induced immune responses, severe disease and infection at a young age. Acute asthma symptoms have been correlated with a variety of viral pathogens, most commonly respiratory syncytial virus bronchiolitis in infancy and rhinovirus in older children. Epidemiologic and biologic factors that influence development of asthma include repeated exposure to infectious disease during early childhood, early exposure to pets, a farming lifestyle, alterations in bacterial flora of the intestine and increased use of antibiotics. Thus the likelihood of asthma is related to the specific pathogen, severity of infection, cumulative number of infections and stage of immunologic development. Progress is also being made in understanding how viruses can adversely affect lung or immune development. In asthmatic children viral infections initiate bronchospasm and airway obstruction. It is hoped that research on virus-induced airway alterations and the host factors that lead to severe clinical illnesses can help clinicians to identify children whose wheezing is an early sign of asthma.

Prior airway exposure to allergen increases virus-induced airway hyperresponsiveness

BACKGROUND

Respiratory syncytial virus (RSV) bronchiolitis in early life can lead to changes in airway function, but there are likely additional predisposing factors, such as prior allergen exposure, determining which children develop wheezing and asthma.

OBJECTIVE

To define the effects of prior airway exposure to sensitizing allergen on the development of airway inflammation and hyperresponsiveness (AHR) to subsequent RSV infection.

METHODS

BALB/c mice were exposed to ovalbumin or PBS exclusively through the airways and subsequently infected with RSV or sham-inoculated. AHR, lung inflammation, and the frequency of cytokine-producing T lymphocytes in the lung were determined.

RESULTS

In PBS-exposed mice, RSV infection induced AHR and an increased proportion of TH1-type (IFN-gamma and IL-12) cytokine-producing cells in the lungs. However, in mice previously exposed to ovalbumin through the airways and subsequently infected with RSV, the degree of AHR was significantly increased and was associated with an increased proportion of TH2 (IL-4, IL-5) cytokine-producing T lymphocytes. This response was also associated with an increased accumulation of eosinophils, neutrophils, and CD8+ T cells in the lungs.

CONCLUSIONS

These data suggest that prior airway exposure to allergen may predispose sensitized hosts to a greater degree of altered airway function upon subsequent respiratory viral infection.

Elevations of local leukotriene C4 levels during viral upper respiratory tract infections

BACKGROUND

One potential mechanism by which respiratory viruses trigger illness and complications is via the local elaboration of inflammatory mediators.

OBJECTIVE

To determine whether there is an increase in local leukotriene C4 (LTC4) levels during experimental infection with influenza A virus (FLU), rhinovirus (RV), or respiratory syncytial virus (RSV).

METHODS

Healthy adults were intranasally inoculated with a safety-tested strain of FLU (n = 29), RV (n = 16), or RSV (n = 21). Nasal lavage samples were collected, symptoms were recorded, and expelled nasal secretions were weighed before and then daily after challenge. Lavage samples were submitted for viral culture and assayed for LTC4 levels by radioimmunoassay. Serum antibody titers to the challenge viruses were assayed at baseline and 21 days after challenge.

RESULTS

All subjects were infected as evidenced by viral shedding and/or seroconversion. Following infection, significant increases (P < 0.05 by analysis of variance) in LTC4 levels were measured for each virus. Furthermore, there was a temporal association between the local LTC4 levels and the development of illness.

CONCLUSIONS

The results of this study, which used an adult experimental model, demonstrate elevations in locally produced LTC4 during respiratory infection with FLU, RV, and RSV. Future studies using antileukotriene agents may help elucidate the precise role of leukotrienes in mediating disease expression.

Reduced interferon gamma production and soluble CD14 levels in early life predict recurrent wheezing by 1 year of age

It is unknown whether reduced production of IFNgamma in early life, before any lower respiratory tract illness, is a risk factor for recurrent wheezing in infancy. We followed 238 infants prospectively from birth to 1 year of age. At birth and at 3 months of age, IFNgamma production from polyclonally stimulated peripheral blood mononuclear cells and soluble CD14 (sCD14) levels in plasma were measured. The odds of developing recurrent wheezing (assessed by questionnaire) in the first year of life were up to 4.5 times higher for children in the lowest quartile of IFNgamma production at 3 months (p = 0.0005) and 3.2 times higher for children in the lowest quartile of sCD14 levels at birth (p = 0.004) as compared with children in the other 3 combined quartiles of IFNgamma and sCD14, respectively. Findings were confirmed in the multivariate analysis. IFNgamma production at 3 months and sCD14 levels at birth were correlated (r = 0.188, p = 0.031). Our findings from a longitudinal cohort suggest that impaired IFNgamma production at 3 months and reduced plasma-sCD14 levels at birth significantly increase the risk of developing recurrent wheezing in the first year of life.

RSV-induced bronchiolitis but not upper respiratory tract infection is accompanied by an increased nasal IL-18 response

The aim of this study was to investigate potential differences in the local nasal immune response between bronchiolitis and upper respiratory tract infection induced by respiratory syncytial virus (RSV). Nasal brush samples were obtained from 14 infants with RSV bronchiolitis and from 8 infants with RSV upper respiratory tract infection. The samples were taken during infection (acute phase) and 2-4 weeks later (convalescent phase). Cytospin preparations were stained immunohistochemically for T cells, macrophages, and eosinophils. Staining also took place for intercellular adhesion molecule-1 (ICAM-1), T-helper 1 (Th1)-like (interleukin-12 [IL-12], interferon-gamma [IFN-gamma]), Th2-like (IL-4, IL-10), and proinflammatory cytokines (IL-6, IL-8, IL-18). During both RSV-induced bronchiolitis and upper respiratory tract infection, cellular inflammation was observed. This was characterised by an increase in the numbers of nasal macrophages, which tended to be higher in bronchiolitis than in upper respiratory tract infection. Numbers of T lymphocytes and ICAM-1 positive cells increased during both bronchiolitis and upper respiratory tract infection. There were no differences between numbers in the groups. Interestingly, a distinct nasal proinflammatory cytokine response was observed in RSV-induced bronchiolitis. This is characterised by an increase in the number of IL-18 positive cells. This increase is specific for bronchiolitis, as a similar increase could not be detected in RSV-induced upper respiratory tract infection. Numbers of IL-6 and IL-12 positive cells were higher in both bronchiolitis and upper respiratory tract infection, and there were no differences between the groups. By contrast, the number of IL-8, IFN-gamma, IL-4, and IL-10-positive cells remained constant. In conclusion, clear differences were found in nasal immune responses of children with RSV-induced upper respiratory tract infection or bronchiolitis. The induction of a strong IL-18 response was typical for bronchiolitis, as this could not be observed in RSV-induced upper respiratory tract infection, and could explain the eosinophilia that is observed frequently during bronchiolitis.

Type 1 and type 2 cytokine imbalance in acute respiratory syncytial virus bronchiolitis

We examined the in vivo immune response of infants to natural respiratory syncytial virus (RSV) infection through analysis of cytokine levels in nasal lavage fluid and stimulated peripheral blood mononuclear cells. Eighty-eight babies with at least one parent with atopy and asthma were prospectively studied through their first winter. Twenty-eight infants had an upper respiratory tract infection where RSV was detected, of whom nine developed signs of acute bronchiolitis. Nasal lavage specimens were assayed for interferon-gamma, interleukin (IL)-4, IL-10, and IL-12 and the RSV load determined by quantitative polymerase chain reaction. Messenger RNA (mRNA) was extracted from stimulated peripheral blood mononuclear cells and interferon-gamma, IL-4, IL-12, and IL-18 mRNA levels determined by polymerase chain reaction. Cytokine profiles were analyzed in relation to clinical outcome. The IL-4/interferon-gamma ratio for infants with acute bronchiolitis was elevated in nasal lavage fluid on both Days 1-2 (p = 0.014) and Days 5-7 (p = 0.001) of the illness compared with infants with upper respiratory tract infection alone. Those with acute bronchiolitis demonstrated a higher IL-10/IL-12 ratio (p = 0.0015) on Days 1-2. IL-18 mRNA levels were reduced (p = 0.019) and the IL-4/interferon-gamma ratio elevated (p = 0.01) in stimulated peripheral blood mononuclear cells from infants with acute bronchiolitis. There was no difference in initial RSV load. These data strongly implicate excess type 2 and/or deficient type 1 immune responses in the pathogenesis of RSV bronchiolitis.

Association of an early respiratory syncytial virus infection and atopic allergy

BACKGROUND

Respiratory syncytial virus (RSV) causes postbronchiolitic wheezing but its role in allergic sensitization is controversial. The purpose of the study was to examine the effect of an early RSV infection on allergic sensitization.

METHODS

Seventy-six subjects were examined 6-10 years after hospitalization for RSV infection during the first year of life. Fifty-one subjects (68%) attended clinical studies and 25 filled in a questionnaire. The study protocol included lung function, skin-prick and blood tests. The controls were matched for birth date and sex.

RESULTS

Eight per cent of the subjects and 37% of the controls had at least one positive skin-prick test (SPT) (difference -35%, 95% CI -50 to -19%, P < 0.0001). Allergic rhinitis, atopic dermatitis and asthma occurred as often in both groups, but asthma had been diagnosed significantly earlier in the subjects than in the controls [mean age 3.0 years (SD 2.6) and 5.6 years (SD 3.0), difference 2.6 years, 95% CI 0.57-4.65, P = 0.014]. In a logistic regression analysis, RSV infection was associated with negative SPTs.

CONCLUSIONS

An early RSV infection results in reduction of SPT positivity but not of occurrence of atopic diseases. This finding might explain why there is less atopic sensitization in countries with a greater probability of acquiring RSV infection at an early age.

Bronchoalveolar lavage cytokine profiles in acute asthma and acute bronchiolitis

BACKGROUND

The pathogenetic basis for the relationship between acute bronchiolitis and asthma has not yet been completely elucidated.

OBJECTIVE

The aim of this study was to compare these 2 diseases in terms of their patterns of airway cytokine response (T(H)1 or T(H)2).

METHODS

By using a bronchoalveolar lavage (BAL) technique, this study investigated the cytokine levels of BAL fluid in children with acute asthma who had no identifiable respiratory syncytial virus (RSV) infection (n = 18) and in infants with acute bronchiolitis caused by RSV (n = 22). Comparisons were made with normal control subjects (n = 14). IFN-gamma (T(H)1) and IL-4 and IL-5 (T(H)2) levels were measured in concentrated BAL fluids by means of ELISA.

RESULTS

The IL-5 level (P <.001) and IL-5/IFN-gamma ratio (P <.001) were significantly increased in the asthmatic group with no identifiable RSV infection and in the RSV-induced bronchiolitis group compared with values in the control group. When infants in the bronchiolitis group were divided into eosinophil-positive and eosinophil-negative subgroups, the eosinophil-positive subgroup had significantly increased IL-5 levels (P <.001) and IL-5/IFN-gamma ratios (P <.01) compared with those in the control group, but similar cytokine responses were not induced in the eosinophil-negative subgroup. The percentage of BAL eosinophils correlated significantly with levels of BAL IL-5 in both the asthma group (r = 0.80, P =.000) and the bronchiolitis group (r = 0.82, P =.000).

CONCLUSIONS

These findings suggest that a subgroup of the RSV-induced bronchiolitis group results in a T(H)2-type response, and this could provide a valuable framework to explain the link between RSV-induced bronchiolitis and asthma.

Infectious triggers of pediatric asthma

Respiratory infections can cause wheezing illnesses in children of all ages and also can influence the causation and disease activity of asthma. For years it has been recognized that respiratory syncytial virus infections often produce the first episode of wheezing in children who go on to develop chronic asthma. More recently, it has been proposed that repeated infections with other common childhood viral pathogens might help the immune system develop in such a way as to prevent the onset of allergic diseases and possibly asthma. In addition to the effects of viral infections, infections with certain intracellular pathogens, such as chlamydia and mycoplasma, may cause acute and chronic wheezing in some individuals, whereas common cold and acute sinus infections can trigger acute symptoms of asthma. In this article, the epidemiologic, mechanistic, and treatment implications of the association between respiratory infections and asthma are discussed.

Cytokine gene polymorphisms moderate illness severity in infants with respiratory syncytial virus infection

Illness severity and frequency of complications in infants with respiratory syncytial virus (RSV) infection may be influenced by the local elaboration of cytokines. Cytokine gene polymorphisms moderate severity of illness in various inflammatory and infectious diseases. We performed cytokine genotyping on 77 infants hospitalized with confirmed RSV infection to determine whether specific cytokine gene polymorphisms are associated with illness severity or complications. DNA was extracted from buccal brushings and assayed for tumor necrosis factor (TNF)-alpha, interferon (IFN)-gamma, interleukin (IL)-6 and IL-10, and transforming growth factor (TGF)-beta1 genotypes using polymerase chain reaction-sequence-specific primer technology. Clinical outcomes consisted of severity scores of lower respiratory illness, blood oxygen saturation, lengths of oxygen supplementation, and intensive care unit (ICU) and hospital stays, and the presence or absence of pneumonia and otitis media. IFN-gamma genotype was related to severity of lower respiratory illness, duration of ICU stay, and frequency of otitis media. Additionally, IL-6 genotype was related to the length of oxygen (O(2)) supplementation and hospital stay, IL-10 genotype to the frequency of pneumonia, and TGF-beta1 genotype to O(2) saturations at presentation. There were no associations between TNF-alpha genotype and any of the outcome parameters. These results demonstrate that certain cytokine gene polymorphisms contribute to illness severity and complications during RSV infection in infants. If future prospective studies confirm these observations, cytokine genotyping may be a useful tool for identifying "at risk" infants who may benefit from the selective use of preventive or early intervention treatments for RSV.

Contribution of neuroimmune mechanisms to airway inflammation and remodeling during and after respiratory syncytial virus infection

A number of studies have implicated severe infections early in life as a risk factor for the subsequent development of asthma. In particular it has been suggested that respiratory syncytial virus (RSV) infection may enhance the development of "allergic" inflammatory responses when the host is exposed to allergens after an episode of bronchiolitis. It has also been suggested that neuronal mechanisms are important in RSV infection and subsequent airway hyperreactivity. Recently we advanced the hypothesis that immune and neuronal mechanisms may be linked and that combined neuroimmune responses may be in play. In the airways a dense network of sensory nerve fibers is strategically placed just below the epithelial surface so that any change in the bronchial environment may stimulate the release of the proinflammatory neuropeptide substance P. During RSV infection, stimulation of these nerves causes a marked increase in airway vascular permeability over that in pathogen-free rats and results in an increase in overall inflammatory status. Our work has revealed that these changes are mediated by the high affinity receptor for substance P [neurokinin (NK) 1 receptor], the expression of which is greatly increased by RSV. This up-regulation presumably occurs at the gene expression level, as NK1 receptor mRNA levels increase substantially during RSV infection. We have also shown that T lymphocyte subpopulations within the bronchial-associated lymphoid tissue in the lungs of RSV-infected rats express high levels of the NK1 receptor. As a consequence stimulation of the sensory nerves by any airborne irritant has the potential of causing a new inflammatory cycle mediated by NK1 receptor-expressing T lymphocytes attracted into the airways and activated by substance P. This mechanism may establish important neuroimmune interactions, which undergo long term dysregulation after RSV infection and predispose to airway inflammation and hyperreactivity. Finally our most recent studies show that RSV infection promotes a large increase in the expression of nerve growth factor (NGF) and neurotrophin receptors. RSV-induced release of NGF leads to short and long term changes in the distribution and reactivity of sensory nerves across the respiratory tract, participating to exaggerated inflammatory reactions during and after the infection. NGF and its receptors may also amplify other immunoinflammatory and neuronal pathways contributing to airway inflammation and hyperreactivity. On the basis of these observations, we postulate that changes of neurotrophin expression in the respiratory tract may represent an important link between early life viral infections and childhood asthma.

A randomized trial of montelukast in respiratory syncytial virus postbronchiolitis

Infants often develop reactive airway disease after respiratory syncytial virus (RSV) bronchiolitis. Cysteinyl-leukotrienes (cys-LT) are released during RSV infection and may contribute to the inflammation. We hypothesized that a cys-LT receptor antagonist would ameliorate reactive airway disease subsequent to RSV bronchiolitis. One hundred and thirty infants who were 3 to 36 months old, hospitalized with acute RSV bronchiolitis, were randomized into a double-blind, parallel comparison of 5-mg montelukast chewable tablets or matching placebo given for 28 days starting within 7 days of symptom debut. Infants with a suspected history of asthma were excluded. One hundred sixteen infants provided diary card data for the treatment period. Median age was 9 months. Infants on montelukast were free of any symptoms on 22% of the days and nights compared with 4% of the days and nights in infants on placebo (p = 0.015). Daytime cough was significantly reduced on active treatment (p = 0.04). Exacerbations were significantly delayed from montelukast compared with placebo (p < 0.05). In conclusion, cys-LT antagonist treatment reduces lung symptoms subsequent to RSV bronchiolitis.

Reduced frequency of wheezing respiratory illness in infants with perinatal human immunodeficiency virus-type 1 infection: a model for immunologic and inflammatory mechanisms of airway obstruction?

A multivariate analysis using a logistic regression model evaluated odds ratio (OR) and 95% confidence limits (95% CL) of pediatrician-diagnosed wheezing respiratory illness in 75 infants with perinatal human immunodeficiency virus-type 1 (HIV-1) infection, 205 uninfected infants of HIV-1 infected mothers, and 1780 infants of HIV-1 uninfected mothers. Infants were prospectively followed-up for the first 2 years of life. Covariates were risk factors for wheezing respiratory illness (preterm delivery, low birth weight, maternal smoking, formula feeding, and neonatal respiratory disorders). Maternal use of illicit drugs in pregnancy, antiretroviral treatment in pregnancy, maternal HIV-1-related clinical condition at the time of delivery were also included in the models when infants of HIV-1 infected mothers were taken into account. Although the frequency of risk factors for wheezing respiratory illness was higher in infants of HIV-1 infected than in those of uninfected mothers, HIV-1 infection emerged as a protective factor [OR: 0.001 (95% CL: 0.0001-0.01); p < 0.001]. The frequency of risk factors was similarly high among infants of infected mothers, but OR was lower in HIV-1 infected than in uninfected infants of infected mothers (0.005; 95% CL: 0.0004-0.06; p < 0.001). Finally, OR was higher in uninfected infants of HIV-1 infected mothers (who evidenced a higher frequency of risk factors) than in infants of HIV-1 uninfected mothers (9.97; 95% CL: 4.87-20.40; p < 0.001). Understanding the reason why HIV-1 protects against wheezing respiratory illness could shed light on the immunologic and inflammatory mechanisms of airway obstruction.

Respiratory syncytial virus and other respiratory viruses

Respiratory syncytial virus (RSV), a nonsegmented, single stranded RNA virus, infects one-half of all infants within the first year of life. RSV possesses pathogenetic qualities that may be attributed to the interplay of viral and host-specific factors including virus strains of different virulence, size of the inoculum, family history of asthma or airway hyperreactivity and immunologic anomalies of the host. Inflammatory cell recruitment and activation occur in response to RSV infection of epithelial cells. Epithelial cells initiate the inflammatory response to RSV by elaborating a wide variety of cytokines and chemokines that trigger further inflammatory responses. Helper T lymphocytes mediate the relative balance of cytokine production and also secrete a variety of antiviral and proinflammatory interleukins. Elevated levels of macrophage-inflammatory protein-1-alpha, an attractant of eosinophils, and monocyte chemotactic protein-1 parallel severe forms of bronchiolitis. Macrophage-inflammatory protein-1-alpha and monocyte chemotactic protein-1 levels also are inversely related to oxygen saturation, suggesting that severity of RSV disease may be linked to chemokine release. Children known to be eosinophilic during an episode of bronchiolitis appear more prone to wheeze at an older age. Influenza, parainfluenza and metapneumoviruses share major epidemiologic risk factors for lower respiratory tract infection similar to those of RSV. Like RSV some of these viruses may also promote an exaggerated lymphocyte-proliferative response, and subjects infected with parainfluenza viruses produce elevated levels of virus-specific IgE. Preliminary evidence suggests that severe RSV and influenza viral infections are mediated via chemokine up-regulation.

Mucosal gene expression vaccine: a novel vaccine strategy for respiratory syncytial virus

A number of approaches have been used in attempts to develop a safe and effective vaccine for respiratory syncytial virus (RSV) infection. This article describes an effective prophylactic intranasal gene transfer strategy utilizing chitosan-DNA nanospheres [the mucosal gene expression vaccine (MGXV)], containing a mixture of plasmid DNAs encoding RSV antigens. In a mouse model of RSV infection, a single administration of MGXV (25 microg/mouse) results in a significant reduction of viral titers and viral antigen load after acute RSV infection of these mice. MGXV-treated mice show no significant change in airway reactivity to methacholine and no apparent pulmonary inflammation. Together these results demonstrate the potential of MGXV against acute RSV infection.

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--viral biology and the host response

Respiratory syncytial virus (RSV) is the most important cause of respiratory tract infection in infants. We have an incomplete understanding of the reasons why some infants are more severely affected by RSV than others. There is no effective antiviral treatment for the infection. Advances in our understanding of the biology of RSV, particularly in relation to the attachment protein G and the fusion protein F, have revealed potential targets for new antiviral therapies and vaccine development. In response to RSV infection an intense inflammatory response is triggered, mediated initially by the infected airway epithelial cells. Cell mediated responses are important in controlling the extent of infection and in viral clearance. Humoral responses are important in protection. There is early evidence that genetic variation of the host response can influence the outcome of RSV-induced bronchiolitis.

Leukotrienes mediate neurogenic inflammation in lungs of young rats infected with respiratory syncytial virus

Respiratory syncytial virus (RSV) infection potentiates neurogenic inflammation in rat airways. Because some vascular effects of sensory nerves are mediated by cysteinyl leukotrienes (cysLTs), we studied whether the receptor antagonist montelukast inhibits neurogenic plasma extravasation in RSV-infected rats. Pathogen-free rats were inoculated at 2 wk (weanlings) or 12 wk (adults) of age with RSV or virus-free medium and treated with montelukast or its vehicle starting 1 day before inoculation. Five days postinoculation, we measured the extravasation of Evans blue-labeled albumin in the respiratory tract after stimulation of sensory nerves with capsaicin. Montelukast had no effect in the extrapulmonary airways but abolished albumin extravasation in the intrapulmonary airways of RSV-infected rats, with a larger effect in weanlings than in adults. Increased concentrations of 5-lipoxygenase-encoding mRNA and cysLTs, as well as numerous mast cells, were detected in the lung tissues of RSV-infected weanling rats. These observations suggest that the release of neuropeptides from capsaicin-sensitive sensory nerves and nonneuronal cells in the lungs of RSV-infected young rats increases vascular permeability by promoting the release of leukotrienes from mast cells.

Infection with influenza a virus leads to flu antigen-induced cutaneous anaphylaxis in mice

It is well established, that viral infections may trigger urticaria or allergic asthma; however, as viral infections induce T helper 1 polarized responses, which lead to the inhibition of T helper 2 cell development, the opposite would be plausible. We wanted to investigate how viral infections may mediate allergic symptoms in a mouse model; therefore, we infected BALB/C mice with influenza A virus intranasally. Histologic analyses of lung sections and bronchoalveolar lavages were performed. In addition, cells from the mediastinal lymph nodes were restimulated in vitro to analyze which types of cytokines were induced by the flu infection. Furthermore, flu-specific antibody titers were determined and local anaphylaxis was measured after rechallenge with flu antigen. We found that airways inflammation consisted predominately of macrophages and lymphocytes, whereas only a few eosinophils were observed. interferon-gamma but no interleukin-4 and little interleukin-5 could be detected in the culture supernatants from in vitro restimulated T cells from the draining lymph nodes. The antibody response was characterized by high levels of virus-specific IgG2a, IgG2b, and IgG1 and, surprisingly, low levels of virus-specific IgE antibodies. Interestingly, flu-infected mice developed active and passive cutaneous anaphylaxis after rechallenge with flu-antigen. As the passive cutaneous anaphylaxis reaction persisted over 48 h and was significantly lower after passive transfer of the serum, which was IgE depleted, local anaphylaxis seemed to be mediated predominately by specific IgE antibodies. Taken together, our results demonstrate that mice infected with flu virus develop virus-specific mast cell degranulation in the skin. Our results may also have implications for the pathogenesis of urticaria or other atopic disorders in humans.

The increase in allergic respiratory diseases: survival of the fittest?

The prevalence of allergic respiratory diseases, asthma and allergic rhinoconjunctivitis, has increased since the advent of industrialization. The inverse relationship between the number of infections early in life and atopy has been interpreted as the "hygiene hypothesis." That is, many infections early in life promote the development of T helper type 1 cytokines, while fewer infections early in life favor the development of T helper type 2 (Th2) cytokines and atopy. An alternate interpretation of the same data, that atopy is protective against infections early in life, is rarely considered. With epidemiologic, historical, and immunologic data, I suggest that human evolution has favored individuals with an atopic predisposition. Th2 immune responses promote parity, and ensure successful pregnancy and term birth; provide the infant protection against infections and the inflammation induced by common pathogens in the first years of life until the immune system matures; and protect young adults exposed to viral respiratory pathogens. These traits are of particular value with the advent of industrialization, especially so in the era prior to the development of antibiotics. This theory contradicts the assumption that there is no biological or evolutionary advantage for allergic disease to exist in humans and has significant implications for our current and future treatments of allergic diseases.

The pathogenesis of respiratory syncytial virus disease in childhood

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory infection in infants and children. RSV is an RNA virus whose genome encodes 10 proteins. The G protein is responsible for viral attachment to cells whilst the F protein promotes syncytia formation. These proteins are also important in the immune response to RSV. Both the innate and adaptive arms of the cellular immune system are involved in the immunological response to RSV. The cytopathic effects of the virus explain many of the pathological findings in RSV disease. However, there is compelling evidence to suggest that the host cell immune response also has a prominent role in disease pathogenesis. Non-immunological factors may also be important.

Persistent wheezing in very young children is associated with lower respiratory inflammation

Despite advances in understanding the pathophysiology of asthma, morbidity and mortality in pediatrics continue to rise. Little is known about the initiation and chronicity of inflammation resulting in asthma in this young population. We evaluated 20 "wheezing" children (WC) (median age 14.9 mo) with a minimum of two episodes of wheezing or prolonged wheezing > or = 2 mo in a 6-mo period with bronchoscopy and bronchoalveolar lavage (BAL). Comparisons were made with six normal controls (NC) (median age 23.3 mo) undergoing general anesthesia for elective surgery. BAL fluid cell counts and differentials were determined. The eicosanoids, leukotriene (LT) B(4), LTE(4), prostaglandin (PG)E(2), and 15-hydroxyeicosatetraenoic acid (HETE) and the mast cell mediators, beta-tryptase and PGD(2), were evaluated by enzyme immunoassay (EIA). WC had significant elevations in total BAL cells/ml (p = 0.01), as well as, lymphocytes (LYMPH, p = 0.007), macrophages/monocytes (M&M, p = 0.02), polymorphonuclear cells (PMN, p = 0.02), epithelial cells (EPI, p = 0.03), and eosinophils (EOS, p = 0.04) compared with NC. Levels of PGE(2) (p = 0.0005), 15-HETE (p = 0.002), LTE(4) (p = 0.04), and LTB(4) (p = 0.05) were also increased in WC compared with NC, whereas PGD(2) and beta-tryptase were not. This study confirms that inflammation is present in the airways of very young WC and may differ from patterns seen in adults with asthma.

SCF-induced airway hyperreactivity is dependent on leukotriene production

Stem cell factor (SCF) is directly involved in the induction of airway hyperreactivity during allergen-induced pulmonary responses in mouse models. In these studies, we examined the specific mediators and mechanisms by which SCF can directly induce airway hyperreactivity via mast cell activation. Initial in vitro studies with bone marrow-derived mast cells indicated that SCF was able to induce the production of bronchospastic leukotrienes, LTC4and LTE4. Subsequently, when SCF was instilled in the airways of naive mice, we were able to observe a similar induction of LTC4and LTE4in the bronchoalveolar lavage (BAL) fluid and lungs of treated mice. These in vivo studies clearly suggested that the previously observed SCF-induced airway hyperreactivity may be related to the leukotriene production after SCF stimulation. To further investigate whether the released leukotrienes were the mediators of the SCF-induced airway hyperreactivity, an inhibitor of 5-lipoxygenase (5-LO) binding to the 5-LO activating protein (FLAP) was utilized. The FLAP inhibitor MK-886, given to the animals before intratracheal SCF administration, significantly inhibited the release of LTC4and LTE4into the BAL fluid. More importantly, use of the FLAP inhibitor nearly abrogated the SCF-induced airway hyperreactivity. In addition, blocking the LTD4/E4, but not LTB4, receptor attenuated the SCF-induced airway hyperreactivity. In addition, the FLAP inhibitor reduced other mast-derived mediators, including histamine and tumor necrosis factor. Altogether, these studies indicate that SCF-induced airway hyperreactivity is dependent upon leukotriene-mediated pathways.

[Viral infection and asthma: immunologic mechanisms]

The role of viral respiratory infections in lactating infants and other children continues to generate controversy. The debate concerns the difference, or the apparent differences, in the natural history of wheezing. Viral infections frequently provoke wheezing episodes in non-asthmatic small children but in the majority of these the wheezing disappears without the child subsequently developing asthma. In some cases, however, the wheezing persists and in others the child has asthma. Both the role of viral infection and the mechanisms by which wheezing can be produced in a previously healthy child or exacerbated in asthmatic children are unknown. Several hypotheses have been put forward to explain the relationship between viral infections and persistent wheezing and asthma: 1. Altered immune response to various allergens, whether producing sensitization to these allergens or inhibiting tolerance response to airborne allergens. The number of such patients is increasing, among them those with bronchiolitis, asthma, positive skin tests and specific IgE antibodies. Although there is no unanimity on the matter, these patients also present elevated IL-4 levels and reduced IFN-gamma levels. 2. Induction of inflammation typical of allergic asthma. This occurs when the virus interacts with T lymphocytes; (the natural response to viral infection is Th0 and Th1 lymphocyte differentiation and release of IFN-gamma, which has antiviral properties. In children infected with respiratory syncytial virus Th2 lymphocyte differentiation is produced, which is characteristic of allergic reactions, to the detriment of Th1); epithelial cells (in these cells active viral infection activates nuclear transcription kappa-beta and nuclear IL-6 factor, producing the release of numerous pro-inflammatory cytokines and chemokines as well as expression of adhesion molecules); eosinophils (inducing variable eosinophilia which, to a certain degree, has predictive value for the persistence of wheezing) and other inflammatory cells such as neutrophils and macrophages. In the same context, during viral respiratory infection, the presence of mediators (leukotrienes, especially LTC4, histamine, prostaglandins and tryptase) are observed in respiratory secretions and a correlation between levels of specific IgE mediators can be observed. 3. Increased allergic inflammation--producing bronchial hyperreactivity, mediator release by the various inflammatory cells and neuropeptides from C-sensitive fibers, and even interfering with nitric oxide bronchodilators. In spite of all of the above, it seems that recurrent wheezing after childhood bronchiolitis is not exclusively the result of viral infection and that other factors also play a role in this disease.

Pathogenesis of RSV lower respiratory tract infection: implications for vaccine development

Respiratory syncytial virus (RSV) infection is the most prevalent cause of severe respiratory disease in infants. It also causes considerable morbidity in older children and adults with underlying risk factors. RSV vaccine development has been complicated by the need to administer the vaccine at a very young age and by enhanced disease observed after vaccination with formalin inactivated RSV. For infants live attenuated vaccines, which may not be expected to predispose for vaccine induced enhanced pathology, hold the greatest promise. However, the balance between attenuation and immunogenicity appears to be delicate. For older risk groups, results with subunit vaccines are most promising.

A comparison of mediators released or generated by IFN-gamma-treated human mast cells following aggregation of Fc gamma RI or Fc epsilon RI

The high affinity receptor for IgG (Fc gamma RI, CD64) is expressed on human mast cells, where it is up-regulated by IFN-gamma and, thus, may allow mast cells to be recruited through IgG-dependent mechanisms in IFN-gamma-rich tissue inflammation. However, the mediators produced by human mast cells after aggregation of Fc gamma RI are incompletely described, and it is unknown whether these mediators are distinct from those produced after activation of human mast cells via Fc epsilon RI. Thus, we investigated the release of histamine and arachidonic acid metabolites and examined the chemokine and cytokine mRNA profiles of IFN-gamma-treated cultured human mast cells after Fc gamma RI or Fc epsilon RI aggregation. Aggregation of Fc gamma RI resulted in histamine release and PGD(2) and LTC(4) generation. These responses were qualitatively indistinguishable from responses stimulated via Fc epsilon RI. Aggregation of Fc epsilon RI or Fc gamma RI led to an induction or accumulation of 22 cytokine and chemokine mRNAs. Among them, seven cytokines (TNF-alpha, IL-1beta, IL-5, IL-6, IL-13, IL-1R antagonist, and GM-CSF) were significantly up-regulated via aggregation of Fc gamma RI compared with Fc epsilon RI. TNF-alpha mRNA data were confirmed by quantitative RT-PCR and ELISA. Furthermore, we confirmed histamine and TNF-alpha data using IFN-gamma-treated purified human lung mast cells. Thus, aggregation of Fc gamma RI on mast cells led to up-regulation and/or release of three important classes of mediators: biogenic amines, lipid mediators, and cytokines. Some cytokines, such as TNF-alpha, were released and generated to a greater degree after Fc gamma RI aggregation, suggesting that selected biologic responses of mast cells may be preferentially generated through Fc gamma RI in an IFN-gamma-rich environment.

IL-13-induced airway hyperreactivity during respiratory syncytial virus infection is STAT6 dependent

Airway damage and hyperreactivity induced during respiratory syncytial virus (RSV) infection can have a prolonged effect in infants and young children. These infections can alter the long-term function of the lung and may lead to severe asthma-like responses. In these studies, the role of IL-13 in inducing and maintaining a prolonged airway hyperreactivity response was examined using a mouse model of primary RSV infection. Using this model, there was evidence of significant airway epithelial cell damage and sloughing, along with mucus production. The airway hyperreactivity response was significantly increased by 8 days postinfection, peaked during days 10-12, and began to resolve by day 14. When the local production of Th1- and Th2-associated cytokines was examined, there was a significant increase, primarily in IL-13, as the viral response progressed. Treatment of RSV-infected mice with anti-IL-13 substantially inhibited airway hyperreactivity. Anti-IL-4 treatment had no effect on the RSV-induced responses. Interestingly, when IL-13 was neutralized, an early increase in IL-12 production was observed within the lungs, as was a significantly lower level of viral Ags, suggesting that IL-13 may be regulating an important antiviral pathway. The examination of RSV-induced airway hyperreactivity in STAT6(-/-) mice demonstrated a significant attenuation of the response, similar to the anti-IL-13 treatment. In addition, STAT6(-/-) mice had a significant alteration of mucus-producing cells in the airway. Altogether, these studies suggest that a primary factor leading to chronic RSV-induced airway dysfunction may be the inappropriate production of IL-13.

IL-18 might reflect disease activity in mild and moderate asthma exacerbation

BACKGROUND

IL-18, identified as an IFN-gamma-inducing factor, is a proinflammatory cytokine that plays an important role in TH1 cell activation. Recently, it was reported that histamine induced IL-18 and that IL-18 might act as a coinducer of TH1 and TH2 cytokines.

OBJECTIVE

The aim was to evaluate the contribution of IL-18 to asthma exacerbation.

METHODS

Serum IL-18, soluble IL-2 receptor, eosinophil cationic protein, and plasma IFN-gamma levels, as well as peak expiratory flow were measured in patients with stable asthma (n = 28), acute mild or moderate asthma (n = 23), or pulmonary sarcoidosis (n = 35) and in healthy subjects (n = 26). We compared the serum IL-18 levels between patients with acute asthma and those in remission and examined the time course in acute exacerbation after asthma therapy.

RESULTS

Significantly higher serum IL-18 levels were found in patients with acute asthma (215 +/- 33 pg/mL, mean +/- SE; P = .02) and pulmonary sarcoidosis (239 +/- 27 pg/mL, P = .008) than in control subjects (127 +/- 11 pg/mL), but the plasma IFN-gamma level was significantly elevated in only pulmonary sarcoidosis (P < .001). In pulmonary sarcoidosis the IL-18 values significantly correlated with the IFN-gamma levels (r = 0.61, P < .001), but in acute asthma they did not. The IL-18 levels during acute asthma exacerbation were significantly higher (P = .01) than on remission days. In acute asthma, circulating IL-18 levels significantly correlated with serum soluble IL-2 receptor levels (r = 0.77, P < .0001) but not with serum eosinophil cationic protein levels. The IL-18 level had a tendency to inversely correlate with peak expiratory flow. The elevated IL-18 levels in acute asthma quickly decreased on day 3 (P = .02) and day 7 (P = .002) after therapy.

CONCLUSION

It was suggested that IL-18 may play a potential role to activate immunologic responses and may reflect disease activity in mild and moderate asthma exacerbation.

[Childhood asthma and viral infection: interactions and therapeutic possibilities]

Rhinovirus infections are the main cause of wheezing in children and adults. Studies carried out with experimental infections report that at least in certain conditions, this infection may spread to the lower respiratory tract as the virus acts on the respiratory epithelium. In vitro experiments with cells from the immune system and lower respiratory tract suggest that the mechanisms of action are directly linked to the production of pro-inflammatory cytokines. Both in vivo and in vitro evidence shows that rhinoviruses may stimulate bronchial epithelial cells to produce cytokines and pro-inflammatory chemokines. They may also stimulate the cholinergic and non-cholinergic nervous system, increasing the production of ICAM-1 and may give rise to a T-lymphocyte non-specific response or to T-lymphocyte replication in direct relation with viral infection. In addition, greater production of cysteinyl leukotrienes has been observed in the secretions of patients with bronchospasm. Experimental infection with Rhinovirus increases clinical symptomatology and bronchial hyperreactivity. The latter is associated with increased eosinophils and cationic proteins in sputum. The above findings suggest that multiple cellular pathways are involved in the induction of exacerbations of asthma induced by the virus. In addition, the possible stimulating role of exposure to allergens in sensitized patients would also increase allergic inflammation. Because of the limited therapeutic efficacy of steroids in reducing exacerbations, new treatment strategies based on greater insight into the physiopathology of the role of viruses in asthma are needed.

Expression of the cysteinyl leukotriene 1 receptor in normal human lung and peripheral blood leukocytes

The cysteinyl leukotrienes (CysLTs) are important mediators of human asthma. Pharmacologic and clinical studies show that the CysLTs exert most of their bronchoconstrictive and proinflammatory effects through activation of a putative, 7-transmembrane domain, G-protein-coupled receptor, the CysLT1 receptor. The initial molecular characterization of the CysLT1 receptor showed by in situ hybridization, the presence of CysLT1 receptor messenger RNA (mRNA) in human lung smooth-muscle cells and lung macrophages. We confirmed the results of these in situ hybridization analyses for the CysLT1 receptor, and produced the first immunohistochemical characterization of the CysLT1 receptor protein in human lung. The identification of the CysLT1 receptor in the lung is consistent with the antibronchoconstrictive and antiinflammatory actions of CysLT1 receptor antagonists. We also report the expression of CysLT1 receptor mRNA and protein in most peripheral blood eosinophils and pregranulocytic CD34+ cells, and in subsets of monocytes and B lymphocytes.

The influence of infections on the development and severity of allergic disorders

The frequency and severity of atopic disorders are steadily increasing, particularly in developing countries. The reason for this observation is not clear. Recent studies indicate that infections with viruses and especially with bacteria early in life may help to inhibit allergic Th2 responses by skewing the immune system towards Th1 responses. However, infections can also lead to the exacerbation of atopic disorders.

Role of interferon gamma in the pathogenesis of primary respiratory syncytial virus infection in BALB/c mice

Immunologic mechanisms are thought to contribute to the pathogenesis of respiratory syncytial virus (RSV) bronchiolitis in humans. RSV-infected BALB/c mice exhibit tachypnea and signs of outflow obstruction, similar to symptoms in humans. Interferon gamma (IFNgamma) has been found to be the predominant cytokine produced in humans and mice with RSV infection. We therefore undertook this study to evaluate the role of IFNgamma in the development of respiratory illness in RSV-infected mice. BALB/c mice were infected with RSV, and lung function was assessed by plethysmography. Bronchoalveolar lavage (BAL) fluids were analyzed for the concentration of interferon gamma (IFNgamma) and the presence of inflammatory cells, and lung tissue sections were examined for histopathologic changes. The role of IFNgamma was further addressed in studies of IFNgamma knock-out mice (IFNgamma(-/-)) and of mice depleted of IFNgamma by in vivo administration of a neutralizing antibody. After infection, mice developed respiratory symptoms that were strongly associated with the number of inflammatory cells in BAL, as well as with the concentrations of IFN-gamma. Both IFN-gamma(-/-) mice and mice treated with anti-IFNgamma developed more extensive inflammation of the airways than control mice. However mice lacking IFNgamma exhibited less severe signs of airway obstruction. Together these data suggest a protective role of IFNgamma in RSV infection in terms of limiting viral replication and inflammatory responses but also a pathogenic role in causing airway obstruction.

Soluble intercellular adhesion molecule-1 (sICAM-1) and interferon-gamma in bronchoalveolar lavage fluid from children with airway diseases

We have previously described that in bronchoalveolar lavage fluid (BALF), eosinophils characterize asthma and neutrophils are more prominent in infantile wheeze. In this study, we hypothesized that intercellular adhesion molecule 1 (ICAM-1) and interferon-gamma (IFN-gamma) would have a role in promoting migration of both cell types into the airway. To investigate this, we measured soluble (s) ICAM-1 in 68 BALFs from infants and young children with various respiratory problems. Children with asthma were characterized by significantly raised sICAM compared with those with chronic cough without wheeze (p = 0.05) or control subjects with no lower airway pathology (p = 0.045). The levels correlated with disease severity (evaluated with a symptom score) and with lymphocyte numbers. IFN-gamma levels were also raised in children with asthma compared with those with chronic cough (p = 0.05), but there was no correlation with disease activity. Infantile wheeze was characterized by a linear correlation between sICAM-1 and IFN-gamma (r = 0.55; p = 0.002). sICAM-1 levels in infantile wheeze correlated with the severity of the disease and lymphocyte numbers. IFN-gamma levels were elevated in the wheezers treated with inhaled steroids compared with untreated infants (p = 0.03). Although sICAM-1 levels were increased in those with severe cough, no characteristic inflammatory profile was found in the group with chronic cough. Our study suggests that ICAM-1 and IFN-gamma play a role in the activity of the inflammatory process in asthma in childhood and possibly in some infant wheezers, in whom IFN-gamma may be one of the factors increasing the expression of ICAM-1. The role of IFN-gamma, a T helper-1 cytokine, in children with asthma remains to be fully understood.

The role of viral infections in the natural history of asthma

Viral infections have been related to the inception of recurrent wheezing illnesses and asthma in infants and are probably the most frequent cause of exacerbations of established disease in older children and adults. The well-recognized clinical effects of viral infections are mainly caused by virus-induced immune responses. Clinical studies of natural and experimentally induced viral infections have led to the identification of mechanisms of inflammation that could be involved in producing airway obstruction and lower airway symptoms. In addition, host factors that are associated with more vigorous viral replication or severe clinical illness are beginning to be identified. Advances in molecular virology and our understanding of immune responses to viral infections may lead to the development of new strategies for the prevention and treatment of virus-induced respiratory disorders.

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.

Novel pathways in the pathogenesis of respiratory syncytial virus disease

Respiratory syncytial virus (RSV) is a leading cause of severe respiratory infections in infants and children. Extensive research in past decades has expanded our knowledge regarding the specific mechanisms involved in the pathogenesis of RSV bronchiolitis and subsequent chronic obstructive airway disease. Studies of RSV infection are performed in humans, cell culture models, and animal models, each with their own specific limitations. A recently developed murine model in which pulmonary dysfunction can be monitored and quantified appears to add a powerful tool for the study of specific pathogenic mechanisms of experimental RSV infections. Both immunologic and nonimmunologic factors have been implicated in the pathogenesis of RSV-induced diseases. Recently, a hypothesis that RSV bronchiolitis may be the result of production of Th2-type cytokines has become popular. There are, however, studies in human infants with RSV as well as in RSV-infected mice that suggest this theory is incorrect, or at least an oversimplification. There is compelling evidence that cells producing interferon gamma may contribute to RSV-induced wheezing, possibly through induction of leukotriene release. Among the nonimmunologic factors, pulmonary surfactant has recently attracted attention, especially because of the therapeutic implications for infants with severe bronchiolitis. A better understanding of the pathogenesis of RSV-induced diseases will be of considerable help in developing specific therapeutic strategies and in vaccine development.

The role of respiratory viruses in acute and chronic asthma

Respiratory infections can have dual effects related to asthma. First, there is increasing evidence that severe infections with RSV and PIV in infancy can alter lung development and physiology to increase the risks of subsequent wheezing and asthma. Second, infections with common cold viruses and influenza commonly precipitate wheezing symptoms in children and adults who already have established asthma, and RV appears to be the most important virus in producing exacerbations of the disease. The principal mechanisms by which this occurs appears to be viral replication in epithelial cells, triggering a cascade of inflammation involving granulocytes, macrophages, T cells, and secreted cytokines and mediators. The inflammatory process, although essential to clear the infection, augments pre-existing airway inflammation in asthma, leading to increased airway obstruction and lower respiratory tract symptoms. Greater understanding of virus-induced changes in inflammation and corresponding changes in airway physiology may lead to new therapeutic approaches to the treatment and prevention of virus-induced airway dysfunction.