The development of respiratory syncytial virus-specific IgE and the release of histamine in nasopharyngeal secretions after infection

Role of viruses in the pathogenesis of acute otitis media

To date there is ample evidence suggesting a crucial role for respiratory viruses in the pathogenesis of AOM. Respiratory viral infection appears to initiate the cascade of events that finally leads to development of AOM (Fig. 1). The pathogenesis of AOM is complicated, involving a network of factors, some probably not yet identified, which affect each other in a time-dependent manner. Increased knowledge of the detailed mechanisms of viral infection, the host inflammatory response during URI and the interaction between viruses and bacteria could lead to major advances in the prevention of AOM.

Le virus respiratoire syncytial: importance en pathologie, méthodes diagnostiques, traitement et prévention

Les bronchiolites à VRS sont fréquentes, épidémiques et nécessitent parfois l'hospitalisation des nourrissons, voire une réanimation.Le déterminisme des lésions pulmonaires est complexe, lié au virus et à la réaction immunitaire. Le traitement est symptomatique, et l'utilisation de la ribavirine est limitée aux formes sévères. Le diagnostic virologique doit être rapide, et la recherche immunologique directe des protéines virales est la technique la plus utilisée.

Analysis of the phenotypic distribution of HLA class I and class II in atopic and non-atopic asthma patients

In several studies the HLA system has been implicated in the development of asthma, but the importance of the associations between HLA genes and asthma remains unclear. The aim of this study was to determine the HLA class I and II phenotypic frequencies in a population of asthmatics, and to analyse the relationship between these phenotypes and any type of asthma. We typed HLA class I and II antigens in a series of 189 asthmatic individuals (102 atopic and 87 non-atopic), and in a control population of 150 unrelated healthy Caucasoid donors. When the HLA phenotypic frequencies were compared, no statistical differences were found. Therefore, no definitive HLA association could be established with atopic or non-atopic asthma in the studied population. Abbreviations AA, atopic asthma; FEV1, forced expiratory volume in 1 s; NAA, non-atopic asthma; PCR, polymerase chain reaction; SSOP, sequence-specific oligonucleotide probes; SPT, skin prick test.

Increasing importance of viruses in acute otitis media

Acute otitis media is generally considered a simple bacterial infection that can be effectively treated with antibiotics. However, despite the extensive use of broad-spectrum antibiotics, poor clinical response to treatment of acute otitis media is common in children. Numerous studies ranging from animal experiments to extensive clinical studies have clearly demonstrated that respiratory viruses play a crucial role in the aetiology and pathogenesis of acute otitis media. Viral infection of the upper respiratory tract initiates the whole cascade of events that finally leads to the development of acute otitis media as a complication. Respiratory viruses induce a release of inflammatory mediators in the nasopharynx, increase bacterial colonization and adherence, and have a suppressive effect on the host's immune defense. Recent data indicate that at least some types of viruses actively invade the middle ear. Viruses also seem to enhance the inflammatory process in the middle ear and impair the outcome of the disease. Vaccines against the major viruses predisposing to acute otitis media hold a great promise for the prevention of this disease. Major advances in the management of acute otitis media will require further research into the mechanisms of viral infection, viral-bacterial interaction and the host inflammatory response during viral infection.

Bovine respiratory syncytial virus-specific IgE is associated with interleukin-2 and -4, and interferon-gamma expression in pulmonary lymph of experimentally infected calves

OBJECTIVE

To study the local immune response of calves to bovine respiratory syncytial virus (BRSV) infection with emphasis on IgE production and cytokine gene expression in pulmonary lymph.

ANIMALS

Twelve 6- to 8-week-old Holstein bull calves. Six similar control calves were mock infected to obtain control data.

PROCEDURE

Lymphatic cannulation surgery was performed on 12 calves to create a long-term thoracic lymph fistula draining to the exterior. Cannulated calves were exposed to virulent BRSV by aerosol. Lymph fluid collected daily was assayed for BRSV and isotype-specific IgE antibody, total IgG, IgA, IgM, and protein concentrations. Interleukin-4 (IL-4), interleukin-2 (IL-2), and interferon-gamma were semi-quantitated by reverse transcription-polymerase chain reaction (RT-PCR). Cell counts and fluorescence-activated cell scanner (FACSCAN) analysis of T-cell subsets were performed on lymph cells.

RESULTS

Calves had clinical signs of respiratory tract disease during days 5 to 10 after infection and shed virus. Bovine respiratory syncytial virus-specific IgE in infected calves was significantly increased over baseline on day 9 after infection. Mean virus-specific IgE concentrations strongly correlated with increases in severity of clinical disease (r = 0.903). Expression of IL-2, IL-4, and interferon-gamma was variably present in infected and control calves, with IL-4 expression most consistent during early infection.

CONCLUSIONS AND CLINICAL RELEVANCE

Infection with BRSV was associated with production of BRSV-specific IgE, and IL-4 message was commonly found in lymph cells of infected calves. This finding supports the concept that BRSV-induced pathophysiology involves a T helper cell type-2 response. Effective therapeutic and prophylactic strategies could, therefore, be developed using immunomodulation to shift the immune response more toward a T helper cell type-1 response.

[Factors associated with the development of atopy in young adults]

BACKGROUND

To determine the risk factors for the development of atopy in Spanish young adults.

SUBJECTS AND METHODS

Case-control study over prevalent cases. Carried out in general population between the ages of 20 to 44 years old. Spanish participants of the ECRHS, a random representative sample of Spanish young adults (n = 16,884), and a 20% randomised subsample made by those who answered to a short respiratory questionnaire and had atopy assessed, was studied. Atopy was defined as having serum specific IgE positivity to the following aeroallergnes: cat dander, Cladosporium herbarum, Dermatophagoides pteronyssinus, Parietaria judaica and Phleum pratense.

RESULTS

Several factors had a statistically significant effect. In addition to male gender and lower age, maternal allergy (OR = 1.63; 95% CI = 1.11-2.40), having allergic siblings (OR = 1.40; 95% CI = 1.06-1.90) and a higher educational level (OR = 1.69; 95% CI = 1.22-2.34) were associated with the presence of high levels of specific IgE in our sample. Moreover, having had older siblings, especially older brothers appears to be a protective factor to the development of atopy but not in a statistically significant way, while having had pet birds during childhood appears to enhance the risk.

CONCLUSIONS

In addition to the familial variables that indicates both environmental and genetic factors, educational level seems to have low degree of association with atopy; this feature shows that variables related with life style are involved in atopy development.

The relevance of allergen exposure to the development of asthma in childhood

Sensitization to 1 or more of the common indoor allergens has been consistently associated with asthma among children and young adults (odds ratios for asthma, 3-18). For dust mite and cockroach allergens, there is a dose response relationship between domestic exposure and sensitization. Given that allergen provocation can induce many of the features of asthma, the findings strongly suggest that there is a causal relationship between allergen exposure in the home and asthma. However, it remains unclear at what time the critical exposure occurs (ie, in infancy or later) and what role allergen exposure has played in the increasing prevalence and severity of asthma. Objective evidence of an immune response to allergens is generally not present until after 2 years of age. Viral infections play several different roles in asthma in childhood. In infancy, respiratory syncytial virus infection can induce bronchiolitis and set up recurrent wheezing over the next few years. However, the risk factors for this are maternal smoking and small lungs at birth, rather than allergy. By contrast, the role of rhinovirus in precipitating attacks in children and young adults is strongly associated with allergy. Thus the likely scenario is that allergen exposure over the first few years of life induces sensitization (ie, T(H2) cells and IgE antibodies). Continuing exposure can maintain inflammation in the nose and lungs. However, many other factors contribute to wheezing such that there is no simple relationship between allergen exposure and asthma. Nonetheless, it is clear that the changes that have increased asthma have acted on allergic children.

Interleukin-4 diminishes CD8(+) respiratory syncytial virus-specific cytotoxic T-lymphocyte activity in vivo

Although interleukin-4 (IL-4) has been implicated in respiratory syncytial virus (RSV)-enhanced disease, the mechanism by which it modulates immune responses to primary RSV infection remains unclear. We have developed a system to investigate the effect of IL-4 on RSV epitope-specific cytotoxic T-lymphocyte (CTL) effector function in vivo, using an H-2K(d)-restricted RSV M2 epitope. BALB/c mice were infected with recombinant vaccinia virus (rVV) constructed to express RSV M2 protein (vvM2) alone or coexpress M2 and IL-4 (vvM2/IL-4). Splenocytes were assessed for M2-specific CTL activity in a direct (51)Cr release assay and intracellular gamma interferon (IFN-gamma) production by fluorescence-activated cell sorting analysis. Mice infected with vvM2/IL-4 had less M2-specific primary CTL activity than those infected with vvM2. M2-specific CTL frequency, as measured by M2 peptide-induced intracellular IFN-gamma production, was diminished in the vvM2/IL-4 group, partially accounting for the reduction of CTL activity. Mice immunized with either construct were challenged intravenously with RSV 4 weeks postimmunization, and direct CTL were measured. These results demonstrate that local expression of IL-4, at the time of antigen presentation, diminishes the cytolytic activity of primary and memory CD8(+) RSV-specific CTL responses in vivo.

Reduced interferon-gamma expression in peripheral blood mononuclear cells of infants with severe respiratory syncytial virus disease

We examined the in vivo cell-mediated immune response in infants with respiratory syncytial virus (RSV) infection in order to gain information about the pathogenesis of severe RSV disease in infancy. Semiquantitative reverse transcription-polymerase chain reaction and three-color flow cytometry were used to determine the levels of messenger RNA (mRNA) for interferon (IFN)-gamma in peripheral blood mononuclear cells, and the distribution of lymphocyte subsets in infants with acute RSV infection. The findings were correlated with the severity of the patients' illness and the production of RSV-specific IgE antibodies (RSV-IgE). Significantly lower IFN-gamma levels and T-lymphocyte counts in the acute phase of illness were observed in infants with severe RSV disease than in those with a milder clinical course of illness. The induction of RSV-IgE was not related to IFN-gamma levels in the acute phase of illness, but rather correlated with IFN-gamma expression during convalescence. The data indicate that reduced IFN-gamma expression may be an important factor in the pathogenesis of severe RSV disease in infancy.

Respiratory Syncytial Virus Stimulates Neutrophil Degranulation and Chemokine Release

Neutrophil infiltration of the airways is a common finding in respiratory syncytial virus (RSV) bronchiolitis. Neutrophil-derived chemokines and neutrophil granule contents can cause further inflammation, hyperresponsiveness, and damage of the airways. In this study, peripheral blood neutrophils incubated with RSV (multiplicity of infection (MOI) = 10) induced IL-8, macrophage inflammatory protein (MIP)-1α, MIP-1β, and myeloperoxidase (MPO) release. In contrast, LPS induced only chemokine but not MPO release. RSV-induced chemokine and MPO release was noncytotoxic as assessed by trypan blue exclusion. The mechanism of RSV-induced chemokine release was shown to be transcription dependent since cytokine mRNA synthesis was increased with RSV stimulation and the process was inhibited by actinomycin-D. In addition, the effect of dexamethasone (dex) on mediator release was also studied. Dex significantly inhibited chemokine release but did not inhibit MPO release. The mechanism of inhibition of the release of these chemokines is probably posttranscriptional since the mRNA synthesis was not inhibited by dex. We conclude that the release of chemokines (IL-8, MIP-1α, MIP-1β) and granule enzymes (MPO) by RSV-stimulated neutrophils may contribute to the pulmonary pathology in RSV bronchiolitis. These in vitro findings showing that dex failed to consistently inhibit all the RSV-induced release of neutrophil inflammatory mediators may explain the variable efficacy of corticosteroids in the treatment of RSV bronchiolitis.

Decreased interleukin-12 levels in umbilical cord blood in children who developed acute bronchiolitis

Respiratory syncytial virus (RSV) infection is common in young children, but only a few develop severe bronchiolitis. The relationship between bronchiolitis, asthma, and atopy has been debated for a long time, but the pathogenesis of wheezing remains unclear. A Th1 and Th2-type lymphocyte imbalance seems to be involved in asthma and atopic disease. Serum interleukin-12 (IL-12), IL-10, and soluble CD30 (sCD30) levels were measured by enzyme-linked immunosorbent assay (ELISA) in 23 cord blood samples kept frozen since birth: 11 from normal term newborns who several months later were admitted to the hospital with bronchiolitis, and 12 from newborns who did not develop the disease (controls). The study was also performed on 28 additional children (1-16 months old) suffering an episode of acute bronchiolitis. IL-12 was clearly increased in all cases at birth, but newborns who later developed bronchiolitis showed low IL-12 levels in cord blood compared to newborns who did not develop the disease (median 295 vs. 507 pg/mL; P = 0.001). sCD30 levels were also decreased in the first group (15 vs. 26 U/mL; P = 0.007). During episodes of bronchiolitis, a clear rise of IL-12, IL-10, and sCD30 was observed. None of the factors studied in the acute phase showed statistical differences in children who were later readmitted to the hospital due to repeated wheezing crises. Children who develop acute bronchiolitis with wheezing may have an immunological imbalance that is expressed at the time of delivery by a lower concentration of serum IL-12.

Recognizing early asthma

Asthma symptoms often develop during the first years of life. Longitudinal studies show that at least 40% of children with wheezing lower respiratory illnesses (LRIs) during the first 3 years of life still have wheezing episodes at 6 years of age. Thus, it is important to identify children at risk of developing asthma, and to distinguish these from those in whom early wheezing is likely to be transient. This is complicated, however, by the variable nature of asthma and the lack of specific and sensitive markers. Genetic markers and epidemiologic risk factors for asthma have been identified, but cannot be used to predict the development of asthma in an individual patient. Similarly, infants who subsequently develop asthma in childhood have higher serum immunoglobulin E (IgE) and peripheral eosinophil counts than those who do not develop asthma, but, again, these factors are not sufficiently sensitive and specific to allow identification of children at risk of developing asthma. An algorithm is presented that outlines possible criteria to determine the risk of developing asthma in infants.

PEDIATRIC ALLERGY

The current paradigm of allergy pathogenesis is that allergy develops in individuals with a genetic predisposition only after they are exposed to allergens (Fig. 1). This hypothesis implies that factors in the environment can determine the initiation of allergic sensitization and can potentially influence the clinical manifestations and severity of disease. Because the prevalence of atopic diseases such as allergic rhinitis, asthma, atopic dermatitis, and food allergy have increased worldwide in the past several decades, and there is no mechanism for changes in population genetics over this short period of time, changes in the human environment are most likely responsible for these trends. From this line of reasoning, it follows that if the factors responsible for the increasing prevalence can be identified, then there would be an opportunity to develop strategies to reverse these trends. It also would be helpful to identify infants who are at risk for developing allergy, so that preventive strategies could be used most effectively.

In this article, studies to determine the contributions of genetics and the environment to the development of allergic diseases in childhood are explored. In addition, progress in identifying risk factors for allergy and preventive therapies for those children at risk are also addressed.

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

BACKGROUND

An imbalance of production of T-helper lymphocyte cytokines, favoring overproduction of IL-4, is believed to be important in the pathogenesis of allergic asthma. However, less is known about the cytokine response in virus-induced wheezing, which is a major cause of morbidity in asthma.

OBJECTIVE

We undertook this study to determine the magnitude of IFN-gamma, IL-4 and IL-10, and leukotriene (LT) responses in infants and children with virus-induced wheezing.

METHODS

We measured the concentrations of IFN-gamma, IL-4 and IL-10, and cysteinyl LTs in respiratory secretions of 82 infants and young children during acute episodes of virus-induced wheezing. Control subjects were 47 infants and children with uncomplicated upper respiratory infections and 18 normal healthy infants.

RESULTS

Ratios of IFN-gamma to IL-4 were higher (due to increased quantities of IFN-gamma) in subjects with wheezing than in those with upper respiratory infection alone (P =. 003). Quantities of LTs were also increased in wheezing subjects in comparison with those with upper respiratory infections (P =.009). There was a significant correlation between measured concentrations of IFN-gamma and LTs (correlation coefficient =.451, P =.007). Quantities of IL-4 were slightly suppressed in the wheezing groups.

CONCLUSIONS

An imbalance favoring overproduction of IFN-gamma appears to be associated temporarily with virus-induced wheezing. A possible mechanism is the enhanced release of LTs from eosinophils or mast cells after sensitization by IFN-gamma.

Respiratory syncytial virus infection: immune response, immunopathogenesis, and treatment

Respiratory syncytial virus (RSV) is the single most important cause of lower respiratory tract infection during infancy and early childhood. Once RSV infection is established, the host immune response includes the production of virus-neutralizing antibodies and T-cell-specific immunity. The humoral immune response normally results in the development of anti-RSV neutralizing-antibody titers, but these are often suboptimal during an infant's initial infection. Even when the production of RSV neutralizing antibody following RSV infection is robust, humoral immunity wanes over time. Reinfection during subsequent seasons is common. The cellular immune response to RSV infection is also important for the clearance of virus. This immune response, vital for host defense against RSV, is also implicated in the immunopathogenesis of severe lower respiratory tract RSV bronchiolitis. Many details of the immunology and immunopathologic mechanisms of RSV disease known at present have been learned from rodent models of RSV disease and are discussed in some detail. In addition, the roles of immunoglobulin E, histamine, and eosinophils in the immunopathogenesis of RSV disease are considered. Although the treatment of RSV bronchiolitis is primarily supportive, the role of ribavirin is briefly discussed. Novel approaches to the development of new antiviral drugs with promising anti-RSV activity in vitro are also described.

IL-5 and Eosinophils Are Essential for the Development of Airway Hyperresponsiveness Following Acute Respiratory Syncytial Virus Infection

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

Quantification of cytokines and inflammatory mediators in samples of nasopharyngeal secretions with unknown dilution

In the study of inflammatory mechanisms in the upper respiratory tract, the unknown dilution of collected samples of nasal secretions poses a serious problem for interpretation of the measured concentrations of various substances in the specimens. We investigated the magnitude of the dilution problem in a true clinical research situation and determined the validity of using the levels of total protein, albumin, and secretory IgA in nasal secretions to correct for the unknown dilution. The study samples consisted of simultaneously obtained nasopharyngeal aspirates and nasal lavage specimens from 52 children with upper respiratory tract infection. The dilution factors of the nasal lavage specimens varied widely between 1.8 and 432 (median, 11.2). Of the three proteins studied, total protein had the narrowest inter-subject variation in the nasal secretions of the children and thus seemed to provide the best standardization method for comparing levels of substances between individuals. Concentrations of IL-6 standardized with total protein correlated significantly better with the true IL-6 concentrations in the nasal secretions than did IL-6 levels measured in the nasal lavage specimens without standardization (p = 0.049). These findings suggest that the most common current practice of measuring substances in nasopharyngeal specimens, i.e. measuring without correction for the dilution, may produce "false-negative" results. Potentially important information on inflammatory mechanisms may be undetected if false-negative results mask real differences between groups. The use of exogenous markers of dilution might improve the accuracy of quantifying substances in nasal secretions.

A review of respiratory syncytial virus infection in infants and children

By the age of 2, nearly every child becomes infected with the respiratory syncytial virus (RSV), the most common cause of lower respiratory tract infections (RTIs) in infants and children. Yearly epidemics occur from October to May. Most infections are mild, producing nothing more than a cold, and can be managed at home. Some cases, however, are more severe, leading to bronchiolitis, pneumonitis, pneumonia, and even death.

Molecular concepts of IgE-initiated inflammation in atopic and nonatopic asthma

Atopic and nonatopic (intrinsic) asthmatics were characterized by a broadly conserved bronchial mucosal proeosinophilic cytokine network in which IL-5 appears to play a key role. Inappropriate IgE-mediated mechanisms may occur in asthma, irrespective of its atopic status, as suggested by elevated serum IgE concentrations and bronchial mucosal expression of FcepsilonRI, IL-4, IL-13, Iepsilon, and Cepsilon. In general, these observations support the concept that these subtypes of asthma, despite showing distinct clinical and biologic features, share many common immunopathologic mechanisms. The most promising future directions of research regarding intrinsic asthma concern the possible identification of novel allergens or antigens, the detailed description of local bronchial mucosal IgE production, and the understanding of a possible macrophage dysfunction. Furthermore, a role for infectious (viral?) or autoimmune processes has yet to be firmly identified in intrinsic asthma. Animal models may also help us to understand the role of IgE and atopy in asthma. Although these are largely IgE-mediated mechanisms, allergen-induced bronchial hyperresponsiveness and eosinophilic inflammation can also occur in the absence of IgE (null mutation of the Cepsilon locus), as shown in a mouse model of hypersensitivity to Aspergillus fumigatus (57). Thus, despite the absence of atopy, IgE-mediated mechanisms may operate in intrinsic asthma (Fig. 1).

Does influenza vaccination exacerbate asthma?

A few anecdotal reports have described serious asthma exacerbations following influenza vaccination. However, a causal relationship has not been clearly established since the vaccine is administered at the time of year when the background incidence of asthma exacerbation is high. Some reports describing minor pulmonary function changes or increased bronchial reactivity in patients with asthma receiving influenza vaccination did not include placebo controls and the results as they are reported are difficult to interpret. Results from several placebo-controlled studies, open trials, and US and European postmarketing surveillance data have shown no evidence of asthma exacerbation related to killed influenza vaccination, although 1 recent placebo-controlled study demonstrated a decrease in peak flow in a small number of first-time vaccinees without clinical exacerbation of asthma. A recent report demonstrated that a group of children with acute asthma exacerbation tolerated influenza vaccination to the same degree as patients with stable asthma. Thus, a plethora of evidence indicates that killed-subunit influenza vaccination is well tolerated and does not exacerbate asthma to a clinically significant degree. Limited experience with live influenza vaccine also suggests that it may be safely given to patients with asthma. Although vaccine efficacy has not been unequivocally demonstrated in patients with asthma, the potential benefits from prevention of morbidity associated with influenza infection in these patients outweighs the theoretical concerns over the safety of influenza vaccination.

Cell-specific expression of RANTES, MCP-1, and MIP-1alpha by lower airway epithelial cells and eosinophils infected with respiratory syncytial virus

Respiratory syncytial virus (RSV) is the major cause of acute bronchiolitis in infancy, a syndrome characterized by wheezing, respiratory distress, and the pathologic findings of peribronchial mononuclear cell infiltration and release of inflammatory mediators by basophil and eosinophil leukocytes. Composition and activation of this cellular response are thought to rely on the discrete target cell selectivity of C-C chemokines. We demonstrate that infection in vitro of human epithelial cells of the lower respiratory tract by RSV induced dose- and time-dependent increases in mRNA and protein secretion for RANTES (regulated upon activation, normal T-cell expressed and presumably secreted), monocyte chemotactic protein-1 (MCP-1), and macrophage inflammatory protein-1alpha (MIP-1alpha). Production of MCP-1 and MIP-1alpha was selectively localized only in epithelial cells of the small airways and lung. Exposure of epithelial cells to gamma interferon (IFN-gamma), in combination with RSV infection, induced a significant increase in RANTES production that was synergistic with respect to that obtained by RSV infection or IFN-gamma treatment alone. Epithelial cell-derived chemokines exhibited a strong chemotactic activity for normal human blood eosinophils. Furthermore, eosinophils were susceptible to RSV and released RANTES and MIP-1alpha as a result of infection. Therefore, the inflammatory process in RSV-induced bronchiolitis appears to be triggered by the infection of epithelial cells and further amplified via mechanisms driven by IFN-gamma and by the secretion of eosinophil chemokines.

Respiratory Syncytial Virus-Infected Pulmonary Epithelial Cells Induce Eosinophil Degranulation by a CD18-Mediated Mechanism

Respiratory syncytial virus (RSV)-induced bronchiolitis in infants is characterized by wheezing, respiratory distress, and the histologic findings of necrosis and sloughing of airway epithelium. High concentrations of eosinophil cationic protein (ECP), a cytotoxic protein contained in the granules of eosinophils, have been found in the airways of RSV-infected infants. The mechanisms of eosinophil degranulation in vivo remain largely unknown. Since RSV-infected respiratory epithelial cells are a rich source of cytokines with eosinophil-activating properties, our studies were designed to mimic in vitro the interaction between RSV, pulmonary epithelial cells (A549), and eosinophils in the airway mucosa. We report in this work that, in the absence of epithelial cells, neither RSV, in the form of purified virions, nor UV-irradiated culture supernatant of RSV-infected epithelial cells (RSV-CM) induced eosinophil degranulation. On the other hand, eosinophils released significant amount of ECP when cultured with RSV-infected A549 cells. Uninfected A549 cells, which failed to induce eosinophil degranulation, were equally effective in triggering ECP release if they were cultured with eosinophils in the presence of RSV-CM. Although RSV-CM induced the up-regulation of the β2 integrin CD11b on eosinophils and the expression of ICAM-1 on A549 cells, release of ECP was inhibited significantly by anti-CD18 mAb, but not by anti-ICAM-1 mAb. These results suggest a novel mechanism by which respiratory viruses may trigger the detrimental release of eosinophil granule proteins in the airway mucosa.

VIRUS-INDUCED WHEEZING IN CHILDREN

The strong association between infantile wheezing and respiratory tract infections caused by the respiratory syncytial virus (RSV) has been well established. In studies of older children, rhinovirus becomes the major virus associated with asthma. These relationships are outlined in the box on page 36. In the past, this relationship was more difficult to appreciate, because rhinovirus does not always grow well in culture. In addition, the linkage between asthma and atopy during childhood has raised the question whether viral infections alone can precipitate exacerbations of asthma. Use of the polymerase chain reaction (PCR) to measure viral nucleic acid material has provided the opportunity to study virus-induced wheezing among children in greater detail, and investigations of experimental rhinovirus infections in adults have demonstrated how this virus can augment both the early and late phase manifestations of airway hyperreactivity. This article reviews recent advances that have enhanced our understanding of virus-induced wheezing, along with new information indicating that interactions between viral infections and allergic inflammation may be critical to the pathogenesis of acute symptoms.

The role of IgE-mediated immunity in otitis media: fact or fiction?

As both OME and allergic rhinitis are common among young children, these disorders are occasionally seen in the same patients. Many clinical and experimental studies have denied the allergic etiology of OME, although type I allergic reactions in the nose cause tubal obstruction without inducing MEE because the induced obstruction remains for a short duration. An animal model study demonstrated that allergy-induced tubal obstruction disturbs the clearance of MEE significantly. Since a clinical and an experimental study showed the efficacy of allergic treatment in patients or animals having both diseases, allergy and OME should be treated simultaneously in patients with both diseases. Viral infections of the upper respiratory tract induce viral-specific IgE antibodies, which may cause mucosal inflammatory reactions similar to those seen in type I allergy. Viral infection also triggers bacterial infection. Consequently, viral infection is a critical factor in the etiopathogenesis of OME.

Prevention and treatment recommendations for respiratory syncytial virus infection. Background and clinical experience 40 years after discovery

Though 40 years have passed since its discovery, respiratory syncytial virus (RSV), one of the most ubiquitous viruses known, continues to evade most of our efforts to prevent or treat the clinical disease it causes. Long recognised as the most common cause of lower respiratory tract infections in virtually all children in the first 2 years of life, it has been increasingly recognised as a cause of more serious disease in several 'high risk' populations. These populations include infants with cardiac or pulmonary disease and infants and adults with immunodeficiencies, particularly those undergoing bone marrow transplantation. Early attempts to immunise children with a simple formalin-inactivated vaccine led to severe disease in vaccinated children who subsequently were infected with RSV from the community. Other vaccine constructs have failed for a variety of reasons, although surface glycoprotein subunit vaccines may hold promise. For years, ribavirin, a synthetic nucleoside analogue administered by constant aerosol, has been felt by many to lead to more rapid improvement in clinical disease caused by RSV, but it is still unclear whether its benefits are truly significant. An intravenous immunoglobulin product prepared from donors screened for the presence of high titres of RSV neutralising antibody (known as RSVIG) appears to be well tolerated and relatively effective in protecting high-risk infants against serious RSV disease, although therapeutic use has proven less dramatic. At least one monoclonal antibody undergoing current testing may prove easier to use in similar immunoprophylactic use. Results on the use of corticosteroids as supportive therapy have not been conclusive. In short, RSV will continue to be a challenge for clinicians and researchers well into the next century.

LOWER RESPIRATORY TRACT INFECTIONS IN ELDERLY PATIENTS WITH ASTHMA

Infection plays a significant role in the morbidity and mortality of the elderly. One population in which infection has not been adequately studied is the elderly asthmatic. This article examines the problems of lower respiratory tract infections in elderly asthmatics in the context of their host defenses, the severity of infection, and their risk of infection with specific organisms. The role of infection in the pathogenesis of asthma and consideration of prophylaxis and therapy are presented.

Overexpression of interleukin-4 delays virus clearance in mice infected with respiratory syncytial virus

Although interleukin-4 (IL-4) expression has been implicated in vaccine-enhanced respiratory syncytial virus (RSV) disease, its role in mediating the immune response to primary RSV infection remains unclear. To assess the effect of IL-4 production on typical RSV infection, transgenic mice which either overexpress or fail to express IL-4 were challenged intranasally with RSV and their responses were compared to those of the parent strains. IL-4-deficient mice eliminated virus from the lung as quickly as did C57BL/6 controls. In contrast, mice which constitutively overexpress IL-4 showed delayed virus clearance compared with mice of the FVB/N control strain, although peak viral titers did not differ. IL-4 overexpression increased the magnitude of the subsequent antibody response. Lung lymphocytes harvested from IL-4-overexpressing mice post-RSV challenge showed diminished RSV-specific cytolytic activity compared with controls. Both IL-4-deficient and IL-4-overexpressing strains resisted rechallenge. These data imply that constitutive IL-4 expression delays or suppresses the development of a virus-specific cytotoxic lymphocyte population important in clearing primary RSV infection.

Nasopharyngeal eosinophil cationic protein in bronchiolitis: relation to viral findings and subsequent wheezing

A prospective 4-month follow-up of children hospitalized with bronchiolitis revealed that high concentrations of eosinophil cationic protein (ECP) in nasopharyngeal aspirates (NPA) are predictive of wheezing after bronchiolitis. In the 29 patients who received no anti-inflammatory therapy the median concentration of NPA ECP was 882 ng/g in those with physician-diagnosed wheezing (P = 0.02). The NPA ECP concentration of the whole study group of 88 children with and without subsequent hospital admissions for wheezing were 531 and 299 ng/g, respectively (P = 0.02). At entry the children with negative viral findings had significantly higher concentrations of respiratory tract ECP than those with positive viral findings (515 vs. 240 ng/g; P = 0.01). The concentration of ECP in respiratory secretions decreased significantly after bronchiolitis (P = 0.01) provided that no new viral or mycoplasmal infection occurred. NPA ECP values decreased in relation to time regardless of whether anti-inflammatory therapy was used or not. Children with high concentrations of respiratory tract ECP seemed to benefit from anti-inflammatory therapy with nebulized cromolyn sodium or budesonide; both drugs significantly decreased the number of subsequent physician-diagnosed bronchial obstruction (P = 0.0006), and they tended to decrease the number of hospital admissions for wheezing (P = 0.08). Our results suggest that high concentrations of ECP in respiratory tract secretions in children with bronchiolitis reflect the presence of eosinophilic inflammation also seen in asthma.

Respiratory syncytial virus infection in infants is associated with predominant Th-2-like response

Viral infections have been associated with cellular immune responses and production of Th-1 cytokines. Respiratory syncytial virus (RSV), however, induces virus-specific IgE, which might be a consequence of a Th-2-like activation. To test this hypothesis we quantified interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) in the supernatant of peripheral blood mononuclear cells cultured for 24 and 48 h in the presence or absence of phytohemaglutinin and pokeweed mitogen and the lymphocyte phenotypes to analyze subsets and their activation markers, from 15 hospitalized infants during an acute lower respiratory infection caused by RSV and 17 healthy control infants from 1 to 15 mo of age. Compared with the control infants, those infected with RSV had an increase in the number of B-cells (p < 0.02) and decreases in both CD8+ T-cells (p < 0.01) and activated CD8+/CD25+ suppressor/ cytotoxic T-cells (p < 0.007). In RSV-infected infants, IFN-gamma production was subtotally suppressed, whereas IL-4 production was decreased to a lesser degree, giving significantly (p < 0.001) increased IL-4/IFN-gamma ratio compared with that in the control infants. These findings suggest a predominant Th-z-like response in RSV-infected infants, which could explain some aspects of the immunopathogenesis of RSV infection and the RSV-specific and nonspecific IgE antibody responses observed.

Serum eosinophil cationic protein as a predictor of wheezing after bronchiolitis

We have evaluated the role of eosinophil cationic protein (ECP) concentrations in serum in predicting wheezing after bronchiolitis, during infancy and early childhood. A prospective study at a university hospital serving all pediatric patients in a defined area was designed. Serum ECP concentrations were measured in 92 infants under the age of 2 years on admission for acute bronchiolitis, and 6 and 16 weeks after hospitalization. Nebulized anti-inflammatory therapy was initiated during hospitalization: 32 patients received cromolyn sodium and 32 patients received budesonide for 16 weeks; 30 control patients received no maintenance therapy. The numbers of subsequent physician-diagnosed wheezing episodes and hospital admissions for obstructive airway disease were recorded during 16 weeks of follow-up. At entry, 14 of 92 (15%) children had high (> or = 16 micrograms/L) levels of ECP in their serum. During the 16-week follow-up period, this group of patients had significantly more physician-diagnosed episodes of wheezing (86% vs. 43%, P < 0.01) and hospital admissions for wheezing (64% vs. 19%, P = 0.001) than those with serum levels of ECP < 16 micrograms/L. The number of patients with serum ECP > or = 8 micrograms/L was 25 (27%); 76% of this group developed physician-diagnosed wheezing (P < 0.01), and 48% had hospital admissions for wheezing (P < 0.01). Serum ECP levels decreased significantly with respect to time after bronchiolitis and did not differ among the three intervention groups. We conclude that a high serum ECP concentration during the acute phase of bronchiolitis is a specific but insensitive predictor of wheezing after bronchiolitis.

Association between pronounced IgA response in RSV bronchiolitis and development of allergic sensitization

Forty-five children who had been hospitalized with bronchiolitis caused by respiratory syncytial virus (RSV) at a mean age of 4 months, and 90 matched control children, were tested for occurrence of RSV antibodies at one year of age. Of the children who had suffered from bronchiolitis, forty had demonstrable IgG antibodies, whereas the remaining five only had IgA antibodies against RSV. In the control group, 42% were RSV seropositive. The anti-RSV IgA antibody titres tended to be higher in patients with bronchiolitis than in controls and a larger proportion of the seropositive children in the former than in the latter group had demonstrable IgG antibodies. These findings suggest that RSV infections causing bronchiolitis are more often associated with a strong antibody response than are mild cases of the infection. Follow-up of the children at 3 years of age showed that allergic sensitization and development of asthma had occurred much more frequently in children with past RSV bronchiolitis than in controls. Children with past RSV bronchiolitis who later developed allergic sensitization had elevated RSV IgA antibody titres at one year of age more frequently than children with past RSV-bronchiolitis, who were not sensitized (p = 0.015). No significant differences regarding IgG antibody titres were observed. Since IgA, similarly as IgE, antibody formation is strongly Th2 cell dependent, the results are compatible with other findings suggesting that RSV has an unusual propensity to activate the Th2 cell system. This may contribute to the pathological picture of bronchiolitis in small children and at the same time render the infected child predisposed for later development of allergic sensitization. RSV bronchiolitis may thus be an important risk factor for later development of atopic disease although it cannot be excluded that the bronchiolitis simply serves as a marker that predict later development of atopy.

Immunopathology in virus disease

Immunopathology contributes to almost all virus infections, and can be the cause of death. The formation of immune complexes in tissues induces inflammation. Circulating immune complexes are often harmless, but when deposited in tissues can lead to glomerulonephritis, arthritis and vasculitis. Classic examples are provided by certain persistent virus infections, in which antibody responses are of low affinity or directed against non-critical sites on the virus particles, and in which complexes are deposited over long periods. Cytotoxic T cells show powerful effectsin vitro, but have rarely been proved to cause serious tissue damagein vitro. Destruction of cells by antibody plus complement, by antibody and K cells or by NK cells plays an ill-defined role in viral pathology. Delayed hypersensitivity T cells are more obviously important in immunopathology, inducing inflammation, cell infiltration and macrophage-mediated damage. Viral immunopathology could be of major importance in certain chronic diseases of unknown aetiology if damaging autoimmune responses were triggered by virus infection. Possible mechanisms are discussed.

Transcriptional activation of the interleukin-8 gene by respiratory syncytial virus infection in alveolar epithelial cells: nuclear translocation of the RelA transcription factor as a mechanism producing airway mucosal inflammation

The most common cause of epidemic pediatric respiratory disease, respiratory syncytial virus (RSV), stimulates interleukin-8 (IL-8) synthesis upon infecting airway epithelium, an event necessary for the development of mucosal inflammation. We investigated the mechanism for enhanced IL-8 production in human A549 type II pulmonary epithelial cells. Infection with sucrose-purified RSV (pRSV) produced a time-dependent increase in the transcriptional initiation rate of the IL-8 gene. Transient transfection of the human IL-8 promoter mutated in the binding site for nuclear factor-kappaB (NF-kappaB) demonstrated that this sequence was essential for pRSV-activated transcription. Gel mobility shift assays demonstrated pRSV induction of sequence-specific binding complexes; these complexes were supershifted only by antibodies directed to the potent NF-kappaB transactivating subunit RelA. Both Western immunoblot and indirect immunofluorescence assays showed that cytoplasmic RelA in uninfected cells became localized to the nucleus after pRSV infection. RelA activation requires replicating RSV, because neither conditioned medium nor UV-inactivated pRSV was able to stimulate its translocation. We conclude that RelA undergoes changes in subcellular distribution in airway epithelial cells upon pRSV infection. The ability of replicating RSV to activate RelA translocation may play an important role in activating IL-8 and other inflammatory gene products necessary for airway mucosal inflammation seen in RSV disease.

Bronchiolitis

Bronchiolitis is a commonly encountered disease of infants and young children. Mortality is low, but morbidity is significant. Treatment requires considerable commitment of time from medical and nonmedical personnel. Decisions about treatment modalities remain controversial. Patients may remain susceptible to pulmonary problems for years and may be predisposed to the development of asthma. Much is known about this disease, but much remains to be learned.