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

Biomarkers for Disease Severity in Children Infected With Respiratory Syncytial Virus: A Systematic Literature Review

BACKGROUND

Clinical manifestations of respiratory syncytial virus (RSV) infection vary widely from mild, self-limiting illness to severe life-threatening disease. There are gaps in knowledge of biomarkers to objectively define severe disease and predict clinical outcomes.

METHODS

A systematic search was performed, 1945-March 2019 in databases Ovid Medline, Embase, Global health, Scopus, and Web of Science. Risk of bias was assessed using the Cochrane tool.

RESULTS

A total of 25 132 abstracts were screened and studies were assessed for quality, risk of bias, and extracted data; 111 studies met the inclusion criteria. RSV severity was correlated with antibody titers, reduced T and B cells, dysregulated innate immunity, neutrophil mobilization to the lungs and blood, decreased Th1 response, and Th2 weighted shift. Microbial exposures in respiratory tract may contribute to neutrophil mobilization to the lungs of the infants with severe RSV compared with mild RSV disease.

CONCLUSIONS

Although a wide range of biomarkers have been associated with RSV disease severity, robust validated biomarkers are lacking. This review illustrates the broad heterogeneity of study designs and high variability in the definition of severe RSV disease. Prospective studies are required to validate biomarkers. Additional research investigating epigenetics, metabolomics, and microbiome holds promise for novel biomarkers.

Comparing respiratory syncytial virus and rhinovirus in development of post-viral airway disease

OBJECTIVE

Respiratory syncytial virus (RSV) and rhinovirus (RV) are common viral infections that may result in post-viral airway/atopic disease. By understanding the antiviral immune response involved, and the mechanisms that translate/associate with post-viral airway disease, further research can be directed to potential treatments that affect these mechanisms.

DATA SOURCES

Utilized peer-reviewed manuscripts listed in PubMed that had relevance to RSV/RV and development of atopic/airway disease in both humans and mice.

STUDY SELECTIONS

Studies that explained the mechanisms behind antiviral response were selected.

RESULTS

RSV infections have been associated with post-viral airway disease primarily in those without preexisting atopy; however, the mechanistic link connecting the viral infection with atopy is less clear. Mouse models (in particular those using Sendai virus, a virus related to RSV) provide a potential mechanistic pathway that may explain the linkage between RSV and post-viral airway disease. RV infection also can drive post-viral airway disease, but unlike RSV, this seems to occur only in those with preexisting atopy. Studies explore this link by demonstrating an impaired interferon response in atopic individuals, which may make them more susceptible to development of post-viral airway disease with RV infection.

CONCLUSION

Both RSV and RV are associated with a risk for developing post-viral airway disease and atopy. However, the mechanisms that connect these viruses with post-viral disease appear to be disparate, suggesting that treatments to prevent post-viral airway disease may need to be specific to the viral etiology.

Fc-Mediated Antibody Effector Functions During Respiratory Syncytial Virus Infection and Disease

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract infections and hospitalization in infants under 1 year of age and there is currently no market-approved vaccine available. For protection against infection, young children mainly depend on their innate immune system and maternal antibodies. Traditionally, antibody-mediated protection against viral infections is thought to be mediated by direct binding of antibodies to viral particles, resulting in virus neutralization. However, in the case of RSV, virus neutralization titers do not provide an adequate correlate of protection. The current lack of understanding of the mechanisms by which antibodies can protect against RSV infection and disease or, alternatively, contribute to disease severity, hampers the design of safe and effective vaccines against this virus. Importantly, neutralization is only one of many mechanisms by which antibodies can interfere with viral infection. Antibodies consist of two structural regions: a variable fragment (Fab) that mediates antigen binding and a constant fragment (Fc) that mediates downstream effector functions via its interaction with Fc-receptors on (innate) immune cells or with C1q, the recognition molecule of the complement system. The interaction with Fc-receptors can lead to killing of virus-infected cells through a variety of immune effector mechanisms, including antibody-dependent cell-mediated cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP). Antibody-mediated complement activation may lead to complement-dependent cytotoxicity (CDC). In addition, both Fc-receptor interactions and complement activation can exert a broad range of immunomodulatory functions. Recent studies have emphasized the importance of Fc-mediated antibody effector functions in both protection and pathogenesis for various infectious agents. In this review article, we aim to provide a comprehensive overview of the current knowledge on Fc-mediated antibody effector functions in the context of RSV infection, discuss their potential role in establishing the balance between protection and pathogenesis, and point out important gaps in our understanding of these processes. Furthermore, we elaborate on the regulation of these effector functions on both the cellular and humoral side. Finally, we discuss the implications of Fc-mediated antibody effector functions for the rational design of safe and effective vaccines and monoclonal antibody therapies against RSV.

Is IgE or eosinophils the key player in allergic asthma pathogenesis? Are we asking the right question?

Bronchial asthma (BA) is a chronic inflammatory disease with a marked heterogeneity in pathophysiology and etiology. The heterogeneity of BA may be related to the inducing mechanism(s) (allergic vs non-allergic), the histopathological background (eosinophilic vs non-eosinophilic), and the clinical manifestations, particularly in terms of severity and frequency of exacerbations. Asthma can be divided into at least two different endotypes based on the degree of Th2 inflammation (T2 'high' and T2 'low'). For patients with severe uncontrolled asthma, monoclonal antibodies (mAbs) against immunoglobulin E (IgE) or interleukin (IL)-5 are now available as add-on treatments. Treatment decisions for individual patients should consider the biological background in terms of the "driving mechanisms" of inflammation as this should predict the patients' likely responses to treatment. The question is not whether an anti-IgE or an anti-eosinophilic strategy is more effective, but rather what the mechanism is at the origin of the airway. While IgE is involved early in the inflammatory cascade and can be considered as a cause of allergic asthma, eosinophilia can be considered a consequence of the whole process. This article discusses the different roles of the IgE and IL-5/eosinophil pathways in the pathogenic mechanisms of airway inflammation occurring in allergic asthma, and the possible reasons to choose an anti-IgE mAb or anti-IL-5 treatment.

Respiratory viral infections and atopic development: From possible mechanisms to advances in treatment

Atopic sensitization and allergic diseases are increasing in modernized countries. These diseases affect millions of individuals, but the mechanisms behind their development are not fully understood. One hypothesis relates to early life respiratory viral infections driving the development of atopic disease including asthma. This review presents the current state of the field, focusing on epidemiologic data supporting a role for early life respiratory viruses in the development of specific IgE, both against aeroallergens and the respiratory virus. Our own work using the Sendai mouse model is then summarized to provide a potential mechanistic explanation for how a respiratory viral infection could drive development of atopic sensitization and disease. We then discuss the components of this mechanistic pathway that have and have not been validated in humans. Finally, we discuss areas ripe for research, as well as potential and current therapeutics that might disrupt the link between respiratory viral infections in early life and atopic sensitization/disease.

The Human Immune Response to Respiratory Syncytial Virus Infection

Respiratory syncytial virus (RSV) is an important etiological agent of respiratory infections, particularly in children. Much information regarding the immune response to RSV comes from animal models and in vitro studies. Here, we provide a comprehensive description of the human immune response to RSV infection, based on a systematic literature review of research on infected humans. There is an initial strong neutrophil response to RSV infection in humans, which is positively correlated with disease severity and mediated by interleukin-8 (IL-8). Dendritic cells migrate to the lungs as the primary antigen-presenting cell. An initial systemic T-cell lymphopenia is followed by a pulmonary CD8+ T-cell response, mediating viral clearance. Humoral immunity to reinfection is incomplete, but RSV IgG and IgA are protective. B-cell-stimulating factors derived from airway epithelium play a major role in protective antibody generation. Gamma interferon (IFN-γ) has a strongly protective role, and a Th2-biased response may be deleterious. Other cytokines (particularly IL-17A), chemokines (particularly CCL-5 and CCL-3), and local innate immune factors (including cathelicidins and IFN-λ) contribute to pathogenesis. In summary, neutrophilic inflammation is incriminated as a harmful response, whereas CD8+ T cells and IFN-γ have protective roles. These may represent important therapeutic targets to modulate the immunopathogenesis of RSV infection.

Role of IgE in autoimmunity

There is accumulating evidence to suggest that IgE plays a significant role in autoimmunity. The presence of circulating self-reactive IgE in patients with autoimmune disorders has been long known but, at the same time, largely understudied. However, studies have shown that the increased IgE concentration is not associated with higher prevalence for atopy and allergy in patients with autoimmune diseases, such as systemic lupus erythematosus. IgE-mediated mechanisms are conventionally known to facilitate degranulation of mast cells and basophils and promote TH2 immunity, mechanisms that are not only central to mounting an appropriate defense against parasitic worms, noxious substances, toxins, venoms, and environmental irritants but that also trigger exuberant allergic reactions in patients with allergies. More recently, IgE autoantibodies have been recognized to participate in the self-inflicted damaging immune responses that characterize autoimmunity. Such autoimmune responses include direct damage on tissue-containing autoantigens, activation and migration of basophils to lymph nodes, and, as observed most recently, induction of type 1 interferon responses from plasmacytoid dendritic cells. The importance of IgE as a central pathogenic mechanism in autoimmunity has now been clinically validated by the approval of omalizumab, an anti-IgE mAb, for patients with chronic spontaneous urticaria and for the clinical benefit of patients with bullous pemphigoid. In this review we summarize recent reports describing the prevalence of self-reactive IgE and discuss novel findings that incriminate IgE as central in the pathogenesis of inflammatory autoimmune disorders.

Self-reactive IgE exacerbates interferon responses associated with autoimmunity

Canonically, immunoglobulin E (IgE) mediates allergic immune responses by triggering mast cells and basophils to release histamine and type 2 helper cytokines. Here we found that in human systemic lupus erythematosus (SLE), IgE antibodies specific for double-stranded DNA (dsDNA) activated plasmacytoid dendritic cells (pDCs), a type of cell of the immune system linked to viral defense, which led to the secretion of substantial amounts of interferon-α (IFN-α). The concentration of dsDNA-specific IgE found in patient serum correlated with disease severity and greatly potentiated pDC function by triggering phagocytosis via the high-affinity FcɛRI receptor for IgE, followed by Toll-like receptor 9 (TLR9)-mediated sensing of DNA in phagosomes. Our findings expand the known pathogenic mechanisms of IgE-mediated inflammation beyond those found in allergy and demonstrate that IgE can trigger interferon responses capable of exacerbating self-destructive autoimmune responses.

IgE anti-respiratory syncytial virus antibodies detected in serum of pediatric patients with asthma

Respiratory syncytial virus (RSV) causes lower respiratory tract disease in infants and young children, and is a public health concern, as is the increase in pediatric asthma. Respiratory viral infections may trigger asthma exacerbations. However, it remains unknown whether RSV infection may have a specific association with asthma. Total serum IgE, and IgE- and IgG-anti-RSV Ab responses were studied in older asthmatic compared with non-asthmatic children (M/F, mean age: 14) (N=30, N=43, respectively). We found: (1) total serum IgE was higher in asthmatic compared with non-asthmatics (P<0.001); (2) total serum IgE did correlate with IgE anti-RSV Abs (P<0.001), and with IgG anti-RSV Abs (P=0.008) in all subjects; (3) total serum IgE levels did correlate with IgE anti-RSV in asthmatics (P=0.047), but not in non-asthmatics (P=0.13); (4) IgE anti-RSV Abs did correlate with IgG anti-RSV Abs in all subjects (P=0.001); (5) IgE- and IgG-anti RSV Abs were higher in asthma compared with no asthma (P=0.003; <0.001, respectively); (6) there was a significant association between age and IgE anti-RSV in non-asthma (P=0.008), but not in asthma (P=0.64). Our findings indicate that IgE-anti-RSV Ab responses may play important roles in RSV infection and asthma.

Respiratory syncytial virus--a comprehensive review

Respiratory syncytial virus (RSV) is amongst the most important pathogenic infections of childhood and is associated with significant morbidity and mortality. Although there have been extensive studies of epidemiology, clinical manifestations, diagnostic techniques, animal models and the immunobiology of infection, there is not yet a convincing and safe vaccine available. The major histopathologic characteristics of RSV infection are acute bronchiolitis, mucosal and submucosal edema, and luminal occlusion by cellular debris of sloughed epithelial cells mixed with macrophages, strands of fibrin, and some mucin. There is a single RSV serotype with two major antigenic subgroups, A and B. Strains of both subtypes often co-circulate, but usually one subtype predominates. In temperate climates, RSV infections reflect a distinct seasonality with onset in late fall or early winter. It is believed that most children will experience at least one RSV infection by the age of 2 years. There are several key animal models of RSV. These include a model in mice and, more importantly, a bovine model; the latter reflects distinct similarity to the human disease. Importantly, the prevalence of asthma is significantly higher amongst children who are hospitalized with RSV in infancy or early childhood. However, there have been only limited investigations of candidate genes that have the potential to explain this increase in susceptibility. An atopic predisposition appears to predispose to subsequent development of asthma and it is likely that subsequent development of asthma is secondary to the pathogenic inflammatory response involving cytokines, chemokines and their cognate receptors. Numerous approaches to the development of RSV vaccines are being evaluated, as are the use of newer antiviral agents to mitigate disease. There is also significant attention being placed on the potential impact of co-infection and defining the natural history of RSV. Clearly, more research is required to define the relationships between RSV bronchiolitis, other viral induced inflammatory responses, and asthma.

Cellular and humoral immunity of virus-induced asthma

Asthma inception is associated with respiratory viral infection, especially infection with respiratory syncytial virus (RSV) and/or human rhinovirus (HRV), in the vast majority of cases. However, the reason why RSV and HRV induce the majority of bronchiolitis cases during early childhood and why only a small percentage of children with RSV- and HRV-induced bronchiolitis later develop asthma remains unclear. A genetic association study has revealed the important interaction between viral illness and genetic variants in patients with asthma. Severe RSV- and HRV-induced bronchiolitis may be associated with a deficiency in the innate immune response to RSV and HRV. RSV and HRV infections in infants with deficient innate immune response and the dysfunction of regulatory T cells are considered to be a risk factor for the development of asthma. Sensitization to aeroallergens, beginning in the first year of life, consistently predisposes children to HRV-induced wheezing illnesses, but the converse is not true. Some evidence of virus specificity exists, in that allergic sensitization specifically increased the risk of wheezing in individuals infected with HRV, but not RSV. Administration of Palivizumab, a humanized monoclonal antibody that targets the A antigenic site of the Fusion-protein of RSV, decreases the risk of hospitalization in high-risk infants and the risk of recurrent of wheezing. However, palivizumab did not have any effect on subsequent recurrent wheezing in children with a family history of atopy. These findings suggest that infection with RSV and infection with HRV might predispose individuals to recurrent wheezing through an atopy-independent and an atopy-dependent mechanism, respectively. Respiratory virus-induced wheezing illnesses may encompass multiple sub-phenotypes that relate to asthma in different ways.

Role of viruses in the development of atopic disease in pediatric patients

The prevalence of atopic diseases continues to rise in modernized countries, without a clear explanation for this increase. One potential cause identified from epidemiologic studies of children is respiratory RNA viral infections leading to development of recurrent wheezing, asthma, and allergic sensitization. We review human epidemiologic data that both support and refute the role of viruses in this process. Exploring recent murine models, we document possible immunologic mechanisms that could translate a viral infection into atopic disease. We further discuss evidence for a post-viral "atopic cycle" that could explain the development of multiple allergen sensitization, and we explore available data to suggest a connection between viral infections of the gastrointestinal tract with the development of food allergy. Taken together, this review documents evidence to support the "viral hypothesis", and, in particular, the role of RNA viruses in the development of atopic disease.

Need for a safe vaccine against respiratory syncytial virus infection

Human respiratory syncytial virus (HRSV) is a major cause of severe respiratory tract illnesses in infants and young children worldwide. Despite its importance as a respiratory pathogen, there is currently no licensed vaccine for HRSV. Following failure of the initial trial of formalin-inactivated virus particle vaccine, continuous efforts have been made for the development of safe and efficacious vaccines against HRSV. However, several obstacles persist that delay the development of HRSV vaccine, such as the immature immune system of newborn infants and the possible Th2-biased immune responses leading to subsequent vaccine-enhanced diseases. Many HRSV vaccine strategies are currently being developed and evaluated, including live-attenuated viruses, subunit-based, and vector-based candidates. In this review, the current HRSV vaccines are overviewed and the safety issues regarding asthma and vaccine-induced pathology are discussed.

Long term persistence of IgE anti-influenza virus antibodies in pediatric and adult serum post vaccination with influenza virus vaccine

The production of IgE specific to different viruses (HIV-1, Parvovirus B19, Parainfluenza virus, Varicella Zoster Virus), and the ability of IgE anti-HIV-1 to suppress HIV-1 production in vitro, strongly suggest an important role for IgE and/or anti viral specific IgE in viral pathogenesis. Nevertheless, the presence and persistence of IgE anti-Influenza virus antibodies has not been studied. Total serum IgE and specific IgE and IgG anti-Influenza virus antibodies were studied in children (N = 3) (m/f 14-16 y/o) and adults (N = 3) (m/f, 41-49 y/o) 2-20 months after vaccination with Influenza virus (Flumist(®) or Fluzone(®)), as well as in non-vaccinated children (N = 2). (UniCAP total IgE Fluoroenzymeimmunoassay, ELISA, Immunoblot). We found that serum of vaccinated children and adults contained IgE and IgG anti-Influenza virus antibodies approaching two years post vaccination. Non-vaccinated children did not make either IgE or IgG anti-Influenza antibodies. Similar levels of IL-2, IFN-γ, IL-4, and IL-10 cytokines were detected in serum of vaccinated compared with non vaccinated subjects (p > 0.05), as well as between vaccinated adults compared with vaccinated children and non vaccinated subjects (p > 0.05). Vaccinated children and adults continue to produce IgE anti-Influenza virus antibodies long term post vaccination. The long term production of IgE anti-Influenza virus antibodies induced by vaccination may contribute to protective immunity against Influenza.

Long Term Persistence of IgE Anti-Varicella Zoster Virus in Pediatric and Adult Serum Post Chicken Pox Infection and after Vaccination with Varicella Virus Vaccine

The production of IgE specific to different viruses (HIV-1, Parvovirus B19, RSV), and the ability for IgE anti-HIV-1 to suppress HIV-1 production in vitro, strongly suggest an important role for IgE and/or anti viral specific IgE in viral pathogenesis. Previous studies in our laboratory were the first to report the presence of IgE anti-varicella zoster virus (VZV) in an adolescent patient with shingles. However, the presence and long term persistence of IgE anti VZV antibodies has not been studied in adults. The presence of serum IgE in addition to IgE and IgG anti-VZV antibody in sera were studied in children (N=12) (0-16 y/o) and adults (N=9) (32-76 y/o) with either a past history of (wild type) chicken pox (N=7 children, 9 adults) or 5 years after vaccination with varicella zoster (N=2 children) (Varicella virus vaccine live, Oka/Merck), as well as in non-infected subjects (N=3 children). Of the patients who had a positive history of chicken pox 13 of 16 (81%) contained IgE anti-VZV antibodies; they were both serum IgEHi (>100 IU/ml) and IgELo (<100 IU/ml). Of the patients who were vaccinated, IgE anti-VZV antibodies were undetected. In contrast, serum from the patients without a history of chicken pox or vaccination did not make either IgE or IgG anti-VZV antibodies. This is the first demonstration of the existence of IgE anti-VZV antibodies, and its long-term persistence in serum of previously infected subjects. Future studies regarding the functional role of anti-viral IgE and its relationship to VZV are warranted.

The immune response to respiratory syncytial virus infection: friend or foe?

The immune response to respiratory syncytial virus (RSV) infection has fascinated and frustrated investigators for decades. After adverse responses to early attempts at vaccination, it became popularly held that disease following infection was related to overly aggressive immune responses. However, recent data illustrate that severe forms of disease are related to inadequate, rather than hyperresponsive, adaptive immune reactions. Thus, recovery from primary (and perhaps later) RSV infection is dependent on the quality of innate immune responses. These findings should have enormous significance to the development of vaccines and antiviral compounds.

IgE, CD8(+)CD60+ T cells and IFN-alpha in human immunity to parvovirus B19 in selective IgA deficiency

Although IgE is implicated in viral immunity, its role in parvovirus B19 immunity and its relationship to other immunological states has not been studied. Total serum immunoglobulin levels, IgG and IgE anti-parvovirus B19, blood lymphocyte numbers, and epsilon and cytokine specific mRNA were determined in pediatric patients with normal serum IgA levels (IgA+) and selective IgA deficiency (IgA-) on days 0 (initial diagnosis) and 14, and 3 years after recovery (nephelometry, Western blot test, flow cytometry, reverse transcriptase-polymerase chain reaction). We found that both patients had serum IgM, IgG, IgE, and IgA levels within normal ranges on day 0 to 3 years, excluding IgG(1) and IgA in the IgA- patient, which were elevated and negative, respectively, and IgE in the IgA+ patient, which was elevated (>100 IU/ml). The serum IgA+ and IgA- patients made IgE (and IgG) anti-parvovirus B19 at all time points. Excluding CD8(+)CD60+ T cells, determinations of T, B, and NK lymphocyte subsets always were within normal ranges. In both patients, CD8(+)CD60+ T-cell numbers were within normal ranges on day 0, but dramatically increased on day 14 (more than fivefold). At 3 years, they had returned to normal in the IgA+ patient, but remained high in the IgA- patient. On day 0 to 3 years, peripheral blood mononuclear cells of both patients expressed epsilon- and interferon (IFN)-alpha-specific mRNA. On day 0, the IgA+ patient expressed interleukin (IL)-4 and IL-10, but not IL-2, IFN-gamma, or IL-6 mRNA; the IgA- patient expressed IL-6 and IL-10 mRNA, but not IL-4, IL-2, or IFN-gamma mRNA. At 3 years, the IgA+ patient expressed mRNA for all cytokines, but the IgA- patient did not express mRNA for any of these cytokines. Our results suggest that IgE is important in parvovirus B19 immunity, and that IFN-alpha and CD8(+)CD60+ T cells may regulate IgE memory responses and isotype switching.

The role of virus-specific immunoglobulin E in airway hyperresponsiveness

Respiratory syncytial virus (RSV) is the most common cause of bronchiolitis during infancy and is associated with subsequent wheezing and asthma, but the nature of this association is not fully understood. We investigated the role of RSV-specific IgE antibodies in the pathophysiology of virus-induced airway dysfunction in a mouse model. Lung infection with RSV resulted in significant increases in mRNA expression for IgE and both of its high- and low-affinity receptors. In serum, virus-specific IgE antibodies reached peak levels by Day 21 after infection. Data from in vitro experiments show that RSV can induce mast cell degranulation, but only if these cells are sensitized with specific IgE. When passively sensitized in vivo with virus-specific IgE, mice developed exaggerated airway responsiveness to methacholine on airway infection, an effect that required the high-affinity receptor of IgE. These data suggest that RSV-specific IgE may contribute to the pathophysiology of airway dysfunction in children who develop this class of specific antibody.

Detection of IgE anti-parvovirus B19 and increased CD23+ B cells in parvovirus B19 infection: relation to Th2 cytokines

The immune profile of a parvovirus B19-infected patient (male, 8 years old) was studied on day 0 (initial presentation) and on days 14 and 210 post symptom presentation (psp). Before infection, the patient was skin test positive to various allergens, including ragweed and tree and grass pollens, and had a serum IgE level of 150 IU/mL. On day 0, the patient was diagnosed as parvovirus B19 infected, as judged by the presence of IgG anti-parvovirus Abs in serum (EIA) and presentation of "slap cheek" rash. The patient's serum IgE level increased from 150 IU/mL before infection to 256 IU/mL on day 0, was 233 IU/mL on day 14, and returned to preinfection levels on day 210. In contrast, there was little change in the levels of serum IgM, IgG, or IgA (nephelometry). IgE anti-parvovirus B19 protein (VP-N) was detected in serum (Western blot) on days 0, 14, and 210, despite the decrease in total IgE on day 210. Although there was no increase in total numbers of blood CD23+ B cells on day 0, by day 14 the numbers of these cells increased dramatically (93%), remaining high on day 210. In contrast, there were virtually no changes in total numbers of CD4+ and CD8+ T cells or CD16/56+ NK precursor cells on days 0-210. On day 0, when IgG and IgE anti-parvovirus were detected in serum, patient's peripheral blood mononuclear cells (PBMC) expressed mRNA for the Th2 cytokines IL-4 and IL-10, but not for the Th1 cytokines IFN-gamma or IL-2. However, by day 14 psp, PBMC expressed mRNA for the Th1 cytokines IFN-gamma and IL-2, as well as for IL-4 and IL-10. This is the first demonstration of the existence of IgE anti-parvovirus B19 Ab. The presence of IgE anti-parvovirus B19 Ab in serum on day 0 and its persistence in serum 7 months psp suggests that IgE anti-parvovirus may be useful in prognosis of parvovirus B19 infection. Our results reinforce the idea that IgE, in general, may play a major role in anti-viral immunity, perhaps in conjunction with CD23+ cells. The results further suggest that clearance of this infection is accompanied by a switch to Th1 cytokines.

Bronchiolitis, respiratory syncytial virus, and recurrent wheezing: what is the relationship?

Various follow-up studies of children hospitalized with bronchiolitis caused by respiratory syncytial virus have demonstrated that a significant proportion of infants (50%) have recurrent wheezing during childhood. Nevertheless, the relationship between these two entities, if any, has not been established. In order to explain this observation, several hypotheses have been proposed. The first suggests that some children could have an individual predisposition to bronchiolitis caused by respiratory syncytial virus and recurrent wheezing. The virus could be a marker of this condition, and the individual predisposition could in turn be related to an individual hypersensitivity to common allergens (atopy), airway hyperreactivity, or to some disorder related to pulmonary anatomy or physiology that was present before the acute episode of bronchiolitis. Another hypothesis proposes that respiratory syncytial virus could be directly responsible for recurrent wheezing. During an episode of bronchiolitis, the damage in the airway mucosa caused by the vital inflammatory response to infection contributes to sensitivity to other allergens or exposes irritant receptors, resulting in recurrent wheezing. For this review, we analyzed the studies that discuss these hypotheses with the purpose of clarifying the mechanisms for the important issue of recurrent wheezing in childhood.

Serum immunoglobulin E levels in human immunodeficiency virus-infected children with pneumonia

Elevated serum immunoglobulin E (IgE) levels have been reported in association with human immunodeficiency virus (HIV) infection in adults, but there is little information in children. The aim of the present study was to compare serum IgE levels in HIV-positive and -negative children hospitalized with pneumonia in South Africa and to investigate whether IgE may be useful as a marker of specific infections or prognosis in HIV-infected children. History, examination, blood tests, and induced sputum or bronchoalveolar lavage were carried out. Of 122 children [45% female, median age 8 months (3-20 months)], 81 were infected with HIV. A history of allergy or asthma was present in three children (two of whom were HIV positive). Serum IgE was higher in HIV-infected children [83 (33-147) vs. 29 (6-113) IU/l; p = 0.011] as was immunoglobulin G (IgG) [49 (37-63) vs. 27.5 (23-34) g/l; p < 0.001]. CD4 lymphocytes [600 (330-1,210) vs. 1,900 (1,500-3,030) cells/ micro l], percentage CD4 cells [13.6 (9.4-20.3) vs. 40.1 (31.1-44.9)] and CD4 : CD8 ratio [0.3 (0.2-0.4) vs. 2 (1.4-2.8)] were lower in HIV-positive children (p < 0.001 for all). Bacteremia occurred in 12 (10%) children; other specific pathogens identified included Mycobacterium tuberculosis in eight (7%) and Pneumocystis carinii in nine (7%). There was no correlation with CD4 count, CD4 : CD8 ratio, or the presence of specific pathogens, and IgE level. In-hospital mortality (11%) did not correlate with IgE levels. HIV-infected children with pneumonia have higher serum IgE compared with seronegative patients. In HIV-positive children, IgE levels did not correlate with the degree of immunosuppression or with outcome.

HIV type 1-specific IgE in serum of long-term surviving children inhibits HIV type 1 production in vitro

We previously identified a group of long-term pediatric survivors who had acquired HIV-1 through maternal transmission; had not received antiretroviral therapy; are now >8 years old, in good health, and with no opportunistic infections; and have not failed to thrive, although they have greatly decreased numbers of blood CD4+ T cells (<500/mm(3)). All the children have elevated total serum IgE levels (210-2475 IU/ml) and make anti-HIV-1 IgE or IgE directed against non-HIV-1 specificities (radioimmunoassay, Western blot assay); they have no detectable antigenemia. We have now studied the ability of anti-HIV-1 IgE in serum obtained from these children to regulate (1) production of HIV-1 by interleukin 2/phytohemagglutinin (IL-2/PHA)-stimulated peripheral blood mononuclear cells (PBMCs) taken from HIV-1-seronegative donors and infected with a T cell-tropic clone of HIV-1, and (2) transmission of a primary HIV-1 strain from adult AIDS patients to uninfected IL-2/PHA-stimulated PBMCs (p24 core antigen production). High levels of HIV-1 production were observed when PBMCs were cultured for 5 days in the presence of HIV-1-seronegative donor serum that was either IgE positive or IgE negative (IgE, >100 or <100 IU/ml, respectively). HIV-1 production also was observed when PBMCs were cultured with HIV-1-infected donor serum that either contained IgE directed against non-HIV-1 specificities or was IgE negative; these levels were 40% less than those seen with sera from the HIV-1-seronegative donors. Far greater inhibition of virus production was observed if the serum in culture contained anti-HIV-1 IgE (>95%). Virus neutralization did not appear to account for the inhibition obtained with anti-HIV-1 IgE-containing serum because virus production was not suppressed in cultures to which serum was added immediately preinfection (<10%), but was strongly suppressed when serum was added 1.5 hr postinfection (>95%). The inhibition of virus production obtained with serum containing anti-HIV-1 IgE was reversed when (1) serum was depleted of IgE (immunoaffinity), but not when it was depleted of IgG (protein G-Sepharose) before inclusion in culture postinfection, (2) anti-IgE, but not anti-IgG, was included in culture, or (3) serum was heat treated before culture. The results indicate that serum from certain HIV-1-infected pediatric long-term survivors contains agents that inhibit HIV-1 production in vitro, and that these agents include anti-HIV-1 IgE. They suggest that a cytotoxic event, rather than virus neutralization, plays an important role in anti-HIV-1 IgE-mediated inhibition of virus production.

Detection of IgA and IgG but not IgE antibody to respiratory syncytial virus in nasal washes and sera from infants with wheezing

BACKGROUND AND OBJECTIVE

The capacity of respiratory syncytial virus (RSV) to stimulate an IgE antibody response and enhance the development of atopy and asthma remains controversial. Nasal washes and sera from 40 infants (20 with wheezing, 9 with rhinitis, and 11 without respiratory tract symptoms) were obtained to measure IgE, IgA, and IgG antibody to the immunodominant, F and G, virion proteins from RSV.

STUDY DESIGN

Children (aged 6 weeks to 2 years) were enrolled in the emergency department during the mid-winter months and seen at follow-up when they were asymptomatic. All nasal washes were tested for RSV antigen. Determinations of antibody isotypes (IgE, IgA, and IgG) to RSV antigens were done in nasal washes and sera by using an enzyme-linked immunosorbent assay. In a subset of nasal washes, IgE to RSV was also evaluated by using a monoclonal anti-F(c)E antibody-based assay.

RESULTS

Fifteen patients with wheezing, two with rhinitis, and one control subject tested positive for RSV antigen at enrollment. Thirteen patients with wheezing were <6 months old, and most (77%) were experiencing their first attack. Among the children with positive test results for RSV antigen, an increase in both nasal wash and serum IgA antibody to RSV-F(a) and G(a) was observed at the follow-up visit. However, there was no evidence for an IgE antibody response to either antigen.

CONCLUSION

Both IgA and IgG antibodies to the immunodominant RSV-F(a) and G(a) antigens were readily detected in the nasal washes and sera from patients in this study. We were unable to demonstrate specific IgE antibody to these antigens and conclude that the production of IgE as a manifestation of a T(H)2 lymphocyte response to RSV is unlikely.

[Relationship between respiratory syncytial virus bronchiolitis and asthma]

Data of the literature over the last 20 years indicate that infantile asthma, although heterogeneous, often appears following RSV bronchiotitis, especially when sufficiently severe to justify hospitalisation. The risk of developing episodes of wheezing (bronchial obstruction syndrome) over the following 2 to 3 years is higher than 50%, but estimations vary according to the authors. Functional disturbances (pulmonary distension, nonspecific bronchial hypperreactivity, hypoxia), with or without associated clinical symptoms, may be observed several months to several years after hospitalisation for bronchiolitis. On the other hand, mild bronchiolitis, and most of the recurrent expiratory obstructive syndromes with asymptomatic free intervals between episodes do not appear to carry a risk of functional sequelae. Children suffering from severe bronchiolitis usually develop a severe bronchial obstruction syndrome. In asthma, the percentage of IgE-dependent sensitization is less than 20% before the age of 4 years. The presence of positive skin tests and/or specific serum IgE directed against the usual allergens are associated with the persistence of asthma during the childhood. Similarly, the appearance of wheezing after the age of 3 years (or recurrence after this age) is associated with the persistence of asthma. Prospective studies of cohorts followed since birth show that pre-existing functional abnormalities can promote the appearance of bronchiolitis and bronchial obstruction syndrome. Asthma in infants comprises several phenotypes with very different prognoses.

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.

Immune responses of infants to infection with respiratory viruses and live attenuated respiratory virus candidate vaccines

Respiratory viruses such as respiratory syncytial virus (RSV), the parainfluenza viruses (PIV), and the influenza viruses cause severe lower respiratory tract diseases in infants and children throughout the world. Experimental live attenuated vaccines for each of these viruses are being developed for intranasal administration in the first weeks or months of life. A variety of promising RSV, PIV-3, and influenza virus vaccine strains have been developed by classical biological methods, evaluated extensively in preclinical and clinical studies, and shown to be attenuated and genetically stable. The ongoing clinical evaluation of these vaccine candidates, coupled with recent major advances in the ability to develop genetically engineered viruses with specified mutations, may allow the rapid development of respiratory virus strains that possess ideal levels of replicative capacity and genetic stability in vivo. A major remaining obstacle to successful immunization of infants against respiratory virus associated disease may be the relatively poor immune response of very young infants to primary virus infection. This paper reviews the immune correlates of protection against disease caused by these viruses, immune responses of infants to naturally-acquired infection, and immune responses of infants to experimental infection with candidate vaccine viruses.

Objective measures of allergic disease in children with human immunodeficiency virus infection

BACKGROUND

Available information suggests that IgE levels are elevated in adults infected with human immunodeficiency virus (HIV), and that increased IgE levels correlate with allergic disease, with decreased CD4 counts, and with a poor prognosis. Data with respect to these factors in children are scant.

OBJECTIVE

We investigated whether serum IgE levels are elevated in children with HIV and, if so, whether the serum IgE level correlates with the degree of immunodeficiency and/or objective indicators of allergic disease.

METHODS

Serum IgE levels, CD4 counts, absolute eosinophil counts, and immediate hypersensitivity skin test (IHST) results were collected from 43 children with symptomatic HIV infection (mean age 7.2 years). Associations between serum IgE levels, CD4 counts, and eosinophil counts were investigated by multiple stepwise linear regression analysis. Data were stratified according to IHST positivity, and analysis of variance was used to compare mean values for age, CD4 counts, IgE levels, and eosinophil counts between the two groups.

RESULTS

Serum IgE values were elevated more than 2 SDs above control age-matched mean values in 17 of 43 patients (40%). IHST results were positive in 12 of 43 patients (28%). CD4 counts were less than 200/mm3 in 17 of 43 patients (40%). Stepwise linear regression failed to demonstrate any correlation between serum IgE levels and either CD4 or eosinophil counts. With data divided into two groups according to IHST results (positive vs negative), analysis of variance failed to reveal significant differences between means for patient age, CD4 counts, IgE levels, or eosinophil counts.

CONCLUSIONS

Our findings confirm that serum IgE levels are increased in children infected with HIV, just as in adults. However, an elevated serum IgE level did not correlate with allergic disease as measured by IHST results and eosinophil counts, nor with the degree of immune dysfunction as approximated by CD4 counts. The mechanism and significance of elevated serum IgE levels remain unclear in children with HIV, and warrant further investigation.

Influence of maternal infections with viral agents or Toxoplasma gondii during pregnancy on fetal IgE production

The importance of maternal infections with Toxoplasma gondii, cytomegalovirus (CMV), Parvovirus B19, respiratory syncytial virus (RSV), and influenza A and B on fetal IgE synthesis was studied in 153 pregnant women. No case of specific IgM activity or viral DNA in cord blood, indicating a congenital infection, was found. From gestational week 15 to delivery, maternal IgG-Ab seroconversion to Parvovirus B19, RSV, influenza A, or influenza B occurred in 47 women. At delivery, serologic signs of past infection with T. gondii were observed in 29 (19%) women, and the corresponding figure for CMV was 117 (77%). The number of women with positive IgG seroconversion during pregnancy or positive IgG-Ab activity toward the studied infectious agents at delivery did not differ significantly among infants with an increased (> or = 1.3 kU/l; n = 51) or with an undetectable (< 0.1 kU/l; n = 102) cord-blood IgE level. These results show that genetic and other environmental factors probably have a greater influence on fetal IgE synthesis than do maternal infections during pregnancy.

IgE against HIV proteins in clinically healthy children with HIV disease

Elevated serum Ige was detected in 26% (7 of 30) of children with HIV infection. The majority of children with elevated IgE were of one ethnic group (Puerto Rican) (4 of 7), compared with only 9% (2 of 23) in the normal to low IgE group (p = 0.02). Most of the children with elevated IgE had decreased circulating CD4+ T cells (5 of 7 or 71%); but none had opportunistic infections, and none failed to thrive. Although similar numbers of children with normal to low IgE had decreased circulating CD4+ T cells (19 of 23 or 83%), this group had opportunistic infections (6 of 23 or 26%) and failure to thrive (7 of 30 or 30%). There was no difference in incidence of allergic symptoms between groups. IgE antibody against HIV protein was detected by Western blot technique in the sera of three children with elevated serum IgE. Thus we have identified a group of children with HIV infection and elevated serum IgE of predominantly one ethnic group, who are without opportunistic infections or failure to thrive, some of whom produce HIV-specific IgE. This suggests that IgE may play a protective (perhaps late compensatory) role in HIV disease in genetically predisposed individuals.

Undetectable IgE responses after respiratory syncytial virus infection

Sequential nasopharyngeal secretions were collected from 81 infants from one day to three months after admission to hospital with respiratory syncytial virus (RSV) infection. Samples from 21 infants were assayed for anti-RSV IgE in an antigen capture ELISA assay. No IgE antibodies were detected although an assay of IgA antibodies carried out in parallel by a similar technique detected IgA antibodies in the secretions of all patients tested. Neither prior absorption of IgA or IgG, concentration of the secretions by freeze drying, nor enzyme amplification of the assay revealed any virus specific IgE. Using an antibody capture ELISA with a sensitivity of 0.85 IU/ml, IgE could be detected in sequential secretions of only one of the 81 RSV infected infants studied. Further testing of the secretions from 12 of these patients and those of a further 15 using an enzyme amplified assay with a sensitivity of 0.1 IU/ml revealed no further positives. Low concentrations of IgE were found in the sera of the majority of infants with RSV infection but they did not differ from those of virus negative children of a similar age collected between RSV epidemics. No rise in mean serum IgE concentrations between acute and convalescent samples was observed. No virus specific IgE was detected in the sera of any infant using the enzyme amplified antigen capture ELISA.

Eosinophil cationic protein in nasal secretion and in serum and myeloperoxidase in serum in respiratory syncytial virus bronchiolitis: relation to asthma and atopy

Eosinophil cationic protein (ECP) in nasal secretions was determined in 34 infants with respiratory syncytial virus (RSV) bronchiolitis during the acute infection stage and one and six months later. ECP in serum was determined in 19 of these children at the same time. Myeloperoxidase (MPO) was determined in the same 19 children at the acute infection stage and after one month. All children were followed prospectively for two years after the infection with regard to the development of bronchial obstructive symptoms. Asthma, defined as three or more episodes of bronchial obstruction verified by a physician, developed in 18% of children and less severe obstructive symptoms in 29%. A screening test for food IgE antibodies in serum was performed six months and a skin prick test two years after the acute infection. Nasal ECP/albumin ratios after six months were significantly higher than during the acute RSV infection. MPO, but not ECP, levels in serum were significantly elevated at the time of acute infection compared with levels after one month. Nasal ECP/albumin ratios at the acute infection were compared to a control group of 27 infants with non-RSV upper respiratory tract infections and did not differ. It was not possible to predict, either from ECP/albumin ratios in nasal secretion or from ECP and MPO in serum, which children would develop asthma, other bronchial obstructive symptoms or positive IgE tests.