Interleukin (IL)-18 polymorphism 133C/G is associated with severe respiratory syncytial virus infection

Genetic variants affecting chemical mediated skin immunotoxicity

The skin is an immune-competent organ and this function may be impaired by exposure to chemicals, which may ultimately result in immune-mediated dermal disorders. Interindividual variability to chemical-induced skin immune reactions is associated with intrinsic individual characteristics and their genomes. In the last 30-40 years, several genes influencing susceptibility to skin immune reactions were identified. The aim of this review is to provide information regarding common genetic variations affecting skin immunotoxicity. The polymorphisms selected for this review are related to xenobiotic-metabolizing enzymes (CYPA1 and CYPB1 genes), antioxidant defense (GSTM1, GSTT1, and GSTP1 genes), aryl hydrocarbon receptor signaling pathway (AHR and ARNT genes), skin barrier function transepidermal water loss (FLG, CASP14, and SPINK5 genes), inflammation (TNF, IL10, IL6, IL18, IL31, and TSLP genes), major histocompatibility complex (MHC) and neuroendocrine system peptides (CALCA, TRPV1, ACE genes). These genes present variants associated with skin immune responses and diseases, as well as variants associated with protecting skin immune homeostasis following chemical exposure. The molecular and association studies focusing on these genetic variants may elucidate their functional consequences and contribution in the susceptibility to skin immunotoxicity. Providing information on how genetic variations affect the skin immune system may reduce uncertainties in estimating chemical hazards/risks for human health in the future.

Interindividual immunogenic variants: Susceptibility to coronavirus, respiratory syncytial virus and influenza virus

The coronavirus disease (Covid-19) pandemic is the most serious event of the year 2020, causing considerable global morbidity and mortality. The goal of this review is to provide a comprehensive summary of reported associations between inter-individual immunogenic variants and disease susceptibility or symptoms caused by the coronavirus strains severe acute respiratory syndrome-associated coronavirus, severe acute respiratory syndrome-associated coronavirus-2, and two of the main respiratory viruses, respiratory syncytial virus and influenza virus. The results suggest that the genetic background of the host could affect the levels of proinflammatory and anti-inflammatory cytokines and might modulate the progression of Covid-19 in affected patients. Notably, genetic variations in innate immune components such as toll-like receptors and mannose-binding lectin 2 play critical roles in the ability of the immune system to recognize coronavirus and initiate an early immune response to clear the virus and prevent the development of severe symptoms. This review provides promising clues related to the potential benefits of using immunotherapy and immune modulation for respiratory infectious disease treatment in a personalized manner.

Respiratory syncytial virus infection: why does disease severity vary among individuals?

Introduction: Respiratory syncytial virus (RSV) is the most common cause of acute lower respiratory tract infections in infancy. While many infants are infected with RSV, the nature and severity of the disease vary among individuals. RSV causes bronchiolitis, pneumonia, and asthma exacerbation. However, most children infected with RSV have only mild upper airways disease and may be asymptomatic.Areas covered: Despite efforts to elucidate mechanisms for the various clinical responses to RSV infection, they remain largely unknown, suggesting that susceptibility and disease are influenced by multiple intrinsic and extrinsic factors. This article reviews the available literature on the field of RSV disease severity and discusses important factors associated to susceptibility and different disease outcome.Expert opinion: The severity of RSV-induced illness is a phenomenon that depends on a variety of graded mechanisms of interaction between the host, virus, and environment. This may lead to differences in the intensity of immune response in the lung and different courses of the disease. By characterizing, classifying, and grading the affecting factors in high-risk patients versus those who do not fall ill by RSV, we may find therapies or point to disease-limiting medications.

Inter-individual variation in health and disease associated with pulmonary infectious agents

Respiratory infectious diseases resulting from bacterial or viral pathogens such as Mycobacterium tuberculosis, Streptococcus pneumoniae, respiratory syncytial virus (RSV), or influenza, are major global public health concerns. Lower respiratory tract infections are leading causes of morbidity and mortality, only behind ischemic heart disease and stroke (GBD 2015 LRI Collaborators in Lancet Infect Dis 17(11):1133–1161, 2017). Developing countries are particularly impacted by these diseases. However, while many are infected with viruses such as RSV (> 90% of all individuals are infected by age 2), only sub-populations develop severe disease. Many factors may contribute to the inter-individual variation in response to respiratory infections, including gender, age, socioeconomic status, nutrition, and genetic background. Association studies with functional single nucleotide polymorphisms in biologically plausible gene candidates have been performed in human populations to provide insight to the molecular genetic contribution to pulmonary infections and disease severity. In vitro cell models and genome-wide association studies in animal models of genetic susceptibility to respiratory infections have also identified novel candidate susceptibility genes, some of which have also been found to contribute to disease susceptibility in human populations. Genetic background may also contribute to differential efficacy of vaccines against respiratory infections. Development of new genetic mouse models such as the collaborative cross and diversity outbred mice should provide additional insight to the mechanisms of genetic susceptibility to respiratory infections. Continued investigation of susceptibility factors should provide insight to novel strategies to prevent and treat disease that contributes to global morbidity and mortality attributed to respiratory infections.

Reduced PRF1 enhancer methylation in children with a history of severe RSV bronchiolitis in infancy: an association study

Background

Acute lower respiratory tract infection is the commonest disease affecting children under five worldwide. Respiratory syncytial virus (RSV) is among the most common causative pathogens. Epidemiological data suggest an association between severe viral respiratory infections in infancy and increased incidence of childhood wheeze and asthma. DNA methylation is involved in immune cell differentiation and identity. It provides an avenue for environmental influences on the genome and therefore has potential as a marker for sustained effects of infectious insults. In this study we investigated the association between DNA methylation patterns in the perforin gene (PRF1) in childhood and a history of hospitalisation for severe RSV disease in the first two years of life.

Methods

In this retrospective study, we explored patterns of whole blood DNA methylation at a methylation sensitive region of the proximal PRF1 enhancer in a group of children with a record of hospitalisation for severe RSV disease during infancy (n = 43) compared to healthy controls matched for age and sex with no similar hospitalisation history, no allergy and no persistent wheeze (n = 43). Univariate and bivariate conditional logistic regression analyses were conducted to test the association between PRF1 enhancer methylation and record of hospitalisation for RSV disease.

Results

Children with a record of hospitalisation for severe RSV bronchiolitis demonstrated markedly lower levels of DNA methylation at two cytosine-phosphate-guanine dinucleotide (CpG) loci of the PRF1 proximal enhancer, corresponding to a signal transducer and activator of transcription 5 (STAT5) responsive element, compared to controls, adjusted odds ratios of 0.82 (95% confidence interval [CI] 0.71, 0.94) and 0.73 (95% CI 0.58, 0.92) for each 1% increase in DNA methylation. Smoking in the household showed a significant influence on DNA methylation at the assayed positions.

Conclusions

Our findings support an association between childhood DNA methylation patterns in PRF1 and a record of severe RSV infection in infancy. Longitudinal studies are required to establish the utility of PRF1 methylation as a marker of severe RSV disease.

Genes associated with RSV lower respiratory tract infection and asthma: the application of genetic epidemiological methods to understand causality

Infants with respiratory syncytial virus (RSV) lower respiratory tract infections (LRIs) are at increased risk for childhood asthma. The objectives of this article are to review the genes associated with both RSV LRI and asthma, review analytic approaches to assessing shared genetic risk and propose a future perspective on how these approaches can help us to understand the role of infant RSV infection as both an important risk factor for asthma and marker of shared genetic etiology between the two conditions. The review of shared genes and thus pathways associated with severity of response to RSV infection and asthma risk can help us to understand mechanisms of disease and ultimately propose new and novel targets for primary prevention of both diseases.

Analysis of the local and systemic inflammatory response in hospitalized infants with respiratory syncitial virus bronchiolitis

BACKGROUND

Respiratory syncytial virus acute bronchiolitis (RSV-AB) is a major cause of hospital admission among our infants. The immune and inflammatory mechanisms involved in the RSV-AB and factors influencing severity have not been clearly established, although an imbalanced Th1 and Th2 response seems to be crucial.

OBJECTIVES

To assess the local and systemic inflammatory response in RSV-AB. To find a possible marker of clinical severity and/or oxygen requirements.

PATIENTS AND METHODS

Levels of nine cytokines were measured in nasopharyngeal aspirate (NPA) and peripheral blood (PB) of 45 infants with RSV-AB and 27 peer controls, including IFNγ, TNFα, VEGF, interleukins 4, 6 and 10, and chemokines (IL-8 and macrophage inflammatory proteins 1-α and 1-β).

RESULTS

The levels of the analyzed cytokines and chemokines were significantly higher in the NPA of RSV-AB group, with a decrease in IL-4/IFNγ ratio. IL-6 and MIP-1β levels in NPA were directly correlated to oxygen therapy. PB showed an increase in IL-8 and a decrease in MIP-1α and MIP-1β in the RSV-AB group (only MIP-1β associated to the need for oxygen therapy). No correlation was found between cytokines and chemokines levels in NPA and PB.

CONCLUSIONS

This study shows that RSV triggers an inflammatory response fundamentally at the respiratory level, with scant systemic repercussion. This local response is characterized by an increase in Th1 and Th2 cytokines, although with a relative predominance of Th1. The determination upon patient admission of IL-6 and MIP-1β levels in NPA, and of MIP-1β in PB could help predict severe forms and the need for oxygenotherapy.

A genetic model of differential susceptibility to human respiratory syncytial virus (RSV) infection

Respiratory syncytial virus (RSV) is the primary cause of lower respiratory tract infection during childhood and causes severe symptoms in some patients, which may cause hospitalization and death. Mechanisms for differential responses to RSV are unknown. Our objective was to develop an in vitro model of RSV infection to evaluate interindividual variation in response to RSV and identify susceptibility genes. Populations of human-derived HapMap lymphoblastoid cell lines (LCLs) were infected with RSV. Compared with controls, RSV-G mRNA expression varied from ~1- to 400-fold between LCLs. Basal expression of a number of gene transcripts, including myxovirus (influenza virus) resistance 1 (MX1), significantly correlated with RSV-G expression in HapMap LCLs. Individuals in a case-control population of RSV-infected children who were homozygous (n=94) or heterozygous (n=172) for the predicted deleterious A allele in a missense G/A SNP in MX1 had significantly greater risk for developing severe RSV disease relative to those with the major allele (n=108) (χ(2)=5.305, P=0.021; OR: 1.750, 95% CI: 1.110, 2.758, P=0.021). We conclude that genetically diverse human LCLs enable identification of susceptibility genes (e.g., MX1) for RSV disease severity in children, providing insight for disease risk.

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.

Human genetics and respiratory syncytial virus disease: current findings and future approaches

Infection with respiratory syncytial virus (RSV) can result in a wide spectrum of pulmonary manifestations, from mild upper respiratory symptoms to severe bronchiolitis and pneumonia. Although there are several known risk factors for severe RSV disease, namely, premature birth, chronic lung disease, congenital heart disease, and T cell immunodeficiency, the majority of young children who develop severe RSV disease are otherwise healthy children. Genetic susceptibility to RSV infection is emerging as a complex trait, in which many different host genetic variants contribute to risk for distinct disease manifestations. Initially, host genetic studies focused on severe RSV disease using the candidate gene approach to interrogate common single nucleotide polymorphisms (SNPs). Many studies have reported genetic associations between severe RSV bronchiolitis and SNPs in genes within plausible biological pathways, such as in innate host defense genes (SPA, SPD, TLR4, and VDR), cytokine or chemokine response genes (CCR5, IFN, IL6, IL10, TGFB1), and altered Th1/Th2 immune responses (IL4, IL13). Due to the complexity of RSV susceptibility, genome studies done on a larger scale, such as genome-wide association studies have certainly identified more of the host factors that contribute to the development of severe RSV bronchiolitis or excessive pathology. Furthermore, whole-genome approaches can reveal robust associations between genetic markers and RSV disease susceptibility. Recent introduction of 'exome' genotyping or sequencing, which specifically analyzes the majority of coding variants, should be fruitful in sufficiently large, well-powered studies. The advent of new genomic technologies together with improved computational tools offer the promise of interrogating the host genome in search of genetic factors, rare, uncommon, or common that should give new insights into the underlying biology of susceptibility to or protection from severe RSV infection. Careful assessment of novel pathways and further identification of specific genes could identify new approaches for vaccine development and perhaps lead to effective risk modeling.

Characterization of the resistance of SJL/J mice to pneumonia virus of mice, a model for infantile bronchiolitis due to a respiratory syncytial virus

Respiratory syncytial virus (RSV), a prominent cause of airway morbidity in children, maintains an excessive hospitalization rate despite decades of research. Host factors are assumed to influence the disease severity. As a first step toward identifying the underlying resistance mechanisms, we recently showed that inbred mouse strains differ dramatically as regards their susceptibility to pneumonia virus of mice (PVM), the murine counterpart of RSV. PVM infection in mice has been shown to faithfully mimic the severe RSV disease in human infants. This study aimed at dissecting the remarkable PVM-resistance shown by the SJL/J strain. To characterize its genetic component, we assessed clinical, physiopathological, and virological resistance/susceptibility traits in large first (F1) and second (F2) generations obtained by crossing the SJL/J (resistant) and 129/Sv (susceptible) strains. Then, to acquire conclusive in vivo evidence in support of the hypothesis that certain radiosensitive hematopoietic cells might play a significant role in PVM-resistance, we monitored the same resistance/susceptibility traits in mock- and γ-irradiated SJL/J mice. Segregation analysis showed that (i) PVM-resistance is polygenic, (ii) the resistance alleles are recessive, and (iii) all resistance-encoding alleles are concentrated in SJL/J. Furthermore, there was no alteration of SJL/J PVM-resistance after immunosuppression by γ-irradiation, which suggests that adaptive immunity is not involved. We conclude that host resistance to pneumoviruses should be amenable to genetic dissection in this mouse model and that radioresistant lung epithelial cells and/or alveolar macrophages may control the clinical severity of pneumovirus-associated lung disease.

Interleukin-18 Gene Polymorphisms in Egyptian Patients with Allergic Diseases

Background

Allergic diseases, such as allergic rhinitis (AR) and atopic dermatitis (AD), affect a large proportion of people worldwide. Both have environmental and genetic predisposing factors. Single nucleotide polymorphisms (SNPs) in interleukin (IL)-18, may play a direct role in the disease pathogenesis. This study was designed to investigate the association of the IL-18 gene SNPs (-137 G/C [rs187238], and −140 C/G [rs360721]) with AR and AD, as well as their relations to the diseases’ severity.

Methods

Seventy-five individuals were enrolled in the study including, 25 AD children, 25 AR patients, and 25 unrelated healthy adult volunteers who served as controls. Genotyping was performed by polymerase chain reaction and restriction fragment length polymorphism analysis.

Results

AR and AD patients showed no significant differences in the genotype distribution and allele frequencies of −137 G/C and −140 C/G SNPs when compared independently with the control group. However, the −140 GG genotype and the −140 G allele were more often associated with severe AD compared with mild and moderate phenotypes (p = 0.01 and 0.001, respectively; odds ratios [ORs], 14.25 [95% CI, 1.48–143.2] and 16 [95% CI, 2.8–90.46], respectively). Moreover, the −137 G allele was associated with moderate/severe AR (p = 0.019; OR, 6.1 [95% CI, 1.34–28.1]).

Conclusion

This preliminary study indicates that the studied polymorphisms do not confer susceptibility to allergy in Egyptian patients but may be related to the disease phenotype. However, the role of IL-18 in allergy may be too complex to be reflected in a simple association study.

Inflammatory responses to respiratory syncytial virus (RSV) infection and the development of immunomodulatory pharmacotherapeutics

Respiratory syncytial virus (RSV; Family Paramyxoviridae, Genus Pneumovirus) is a major respiratory pathogen of infants and children and an emerging pathogen of the elderly. Current management of RSV disease includes monoclonal antibody prophylaxis for infants identified as high risk and supportive care for those with active infection; there is no vaccine, although several are under study. In this manuscript, we review published findings from human autopsy studies, as well as experiments that focus on human clinical samples and mouse models of acute pneumovirus infection that elucidate basic principles of disease pathogenesis. Consideration of these data suggests that the inflammatory responses to RSV and related pneumoviral pathogens can be strong, persistent, and beyond the control of conventional antiviral and anti-inflammatory therapies, and can have profound negative consequences to the host. From this perspective, we consider the case for specific immunomodulatory strategies that may have the potential to alleviate some of the more serious sequelae of this disease.

Evidence for a causal relationship between respiratory syncytial virus infection and asthma

Respiratory syncytial virus (RSV) infects all children early in life, is the most common cause of infant lower respiratory tract infections, and causes disease exacerbations in children with asthma. Episodes of lower respiratory tract infection in early life are associated with asthma development. Whether RSV infection early in life directly causes asthma or simply identifies infants who are genetically predisposed to develop subsequent wheezing is debatable. Recent studies suggest that these two explanations are not mutually exclusive, and are likely both important in asthma development. An open-label study of RSV immunoprophylaxis administered to preterm infants reduced recurrent wheezing by 50%. Clinical trials of infant RSV prevention, delay or severity reduction on the outcome of childhood asthma would confirm the causal relationship between RSV infection and asthma, and offer a primary prevention strategy.

Pattern recognition receptors and genetic risk for rsv infection: value for clinical decision-making?

Respiratory syncytial virus (RSV) causes respiratory tract infections, especially among young infants. Practically, all infants are infected during epidemics and the clinical presentation ranges from subclinical to fatal infection. Known risk factors for severe RSV infection include prematurity, age of <2 months, underlying chronic lung or heart diseases, serious neurological or metabolic disorders, immune deficiency (especially a disorder of cellular immunity), crowded living conditions, and indoor smoke pollution. Twin studies indicate that host genetic factors affect susceptibility to severe RSV infection. Pattern recognition receptors (PRRs) are the key mediators of the innate immune response to RSV. In the distal respiratory tract, RSV is recognized by the transmembrane Toll-like receptor 4 (TLR4) and adapter proteins, which lead to production of proinflammatory cytokines and subsequent activation of the adaptive immune response. Surfactant proteins A and D are able to bind both RSV and TLR4, modulating the inflammatory response. Genetic variations in TLR4, SP-A, and SP-D have been associated with the risk of severe RSV bronchiolitis, but the results have varied between studies. Both the homozygous hyporesponsive 299Gly genotype of TLR4 and the non-synonymous SP-A and SP-D polymorphism influence the presentation of RSV infection. The reported relative risks associated with these markers are not robust enough to justify clinical use. However, current evidence indicates that innate immune responses including pattern recognition receptors (PRRs) and other components in the distal airways and airspaces profoundly influence the innate immune responses, playing a key role in host resistance to RSV in young infants. This information is useful in guiding efforts to develop better means to identify the high-risk infants and to treat this potentially fatal infection effectively.

Bronchiolite del lattante

La bronchiolite è un’infezione virale stagionale delle vie respiratorie basse del lattante. Il suo agente causale principale è il virus respiratorio sinciziale. La comparsa di un distress respiratorio è legata all’intensità della risposta infiammatoria delle vie aeree. Benché si tratti di una malattia frequente, le cause della suscettibilità dei lattanti a questa infezione non sono conosciute. La diagnosi è clinica. Il trattamento è sintomatico in assenza di misure specifiche. I rapporti a medio e a lungo termine di un primo episodio di bronchiolite con le recidive e con l’asma non sono spiegati. Essi potrebbero dipendere dalla natura del virus in causa al momento del primo episodio e da fattori genetici individuali.

Surfactant protein A2 polymorphisms and disease severity in a respiratory syncytial virus-infected population

OBJECTIVE

To examine whether genetic variations within the surfactant protein A2 (SP-A2) gene are associated with respiratory syncytial virus (RSV) disease severity in infected children.

STUDY DESIGN

Naturally infected children aged < or =24 months were prospectively enrolled in 3 RSV seasons. SP-A2 genotyping was performed. Independent clinical predictors of disease severity were analyzed. The association of SP-A2 genetic diversity and disease severity was tested by using multivariate logistic regression models and 4 levels of disease gradation as outcome measures.

RESULTS

Homozygosity of the 1A(0) allele was protective against hospitalization (odds ratio [OR] = 0.15, P = .0010). This remained significant in African American patients (OR = 0.24, P = .042) and Caucasian patients (OR = 0.05, P = .021) after adjustment for other co-variates. Hospitalized children with the 1A(2) allele demonstrated significant protection from severe disease with univariate analyses, but only a trend for protection with multivariate analyses. Patients homozygous or heterozygous for an asparagine at amino acid position 9 were twice or more likely to need intensive care unit admission (OR = 2.15, P = .022), require intubation (OR = 3.04, P = .005), and have a hospitalization lasting > or =4 days (OR = 1.89, P = .02) compared with children homozygous for a threonine at this position.

CONCLUSIONS

SP-A2 polymorphisms are associated with the severity of RSV infection in infants.

Interleukin 18 coexpression during respiratory syncytial virus infection results in enhanced disease mediated by natural killer cells

Respiratory syncytial virus (RSV) causes bronchiolitis, the main cause of infantile hospitalization. Immunity against reinfection is poor, and there is great interest in boosting vaccine responses using live vectors expressing host cytokines. We therefore constructed a recombinant RSV expressing murine interleukin 18 (RSV/IL-18), a cytokine capable of inducing strong antiviral immune responses. In vitro RSV/IL-18 replicated at wild-type levels and produced soluble IL-18. In naïve BALB/c mice, RSV/IL-18 infection significantly increased both IL-18 mRNA and protein and attenuated the peak viral load 3-fold. Despite a reduced viral load, RSV/IL-18 infection caused a biphasic weight loss at days 2 and 6 postinfection that was not seen in wild-type infection. Day 2 disease was associated with enhanced pulmonary natural killer (NK) cell numbers and activity and was prevented by NK cell depletion during infection; day 6 disease was correlated with CD8 T-cell recruitment and was enhanced by NK cell depletion. IL-18 expression during priming also enhanced RSV-specific antibody responses and T-cell responses on secondary RSV infection. Therefore, while IL-18 boosted antiviral immunity and reduced the viral load, its coexpression worsened disease. This is the first recombinant RSV with this property, and these are the first studies to demonstrate that NK cells can induce pathology during pulmonary viral infections.

Respiratory viral infections in infants: causes, clinical symptoms, virology, and immunology

In global terms, respiratory viral infection is a major cause of morbidity and mortality. Infancy, in particular, is a time of increased disease susceptibility and severity. Early-life viral infection causes acute illness and can be associated with the development of wheezing and asthma in later life. The most commonly detected viruses are respiratory syncytial virus (RSV), rhinovirus (RV), and influenza virus. In this review we explore the complete picture from epidemiology and virology to clinical impact and immunology. Three striking aspects emerge. The first is the degree of similarity: although the infecting viruses are all different, the clinical outcome, viral evasion strategies, immune response, and long-term sequelae share many common features. The second is the interplay between the infant immune system and viral infection: the immaturity of the infant immune system alters the outcome of viral infection, but at the same time, viral infection shapes the development of the infant immune system and its future responses. Finally, both the virus and the immune response contribute to damage to the lungs and subsequent disease, and therefore, any prevention or treatment needs to address both of these factors.

Genomewide association analysis of respiratory syncytial virus infection in mice

Respiratory syncytial virus (RSV) is the major cause of lower respiratory tract infection in infants, with about half being infected in their first year of life. Yet only 2 to 3% of infants are hospitalized for RSV infection, suggesting that individual susceptibility contributes to disease severity. Previously, we determined that AKR/J (susceptible) mice developed high lung RSV titers and showed delayed weight recovery, whereas C57BL/6J (resistant) mice demonstrated low lung RSV titers and rapid weight recovery. In addition, we have reported that gene-targeted mice lacking the cystic fibrosis transmembrane conductance regulator (Cftr; ATP-binding cassette subfamily C, member 7) are susceptible to RSV infection. For this report, recombinant backcross and F2 progeny derived from C57BL/6J and AKR/J mice were infected with RSV, their lung titers were measured, and quantitative trait locus (QTL) analysis was performed. A major QTL, designated Rsvs1, was identified on proximal mouse chromosome 6 in both recombinant populations. Microarray analysis comparing lung transcripts of the parental strains during infection identified several candidate genes that mapped to the Rsvs1 interval, including Cftr. These findings add to our understanding of individual RSV susceptibility and strongly support a modifier role for CFTR in RSV infection, a significant cause of respiratory morbidity in infants with cystic fibrosis.

The year in review

Over the last year there have been more studies determining predisposition to severe bronchiolitis and its consequences. Studies have highlighted various single-nucleotide polymorphisms (SNPs) to be significantly associated with respiratory syncytial virus (RSV) hospitalisation, and a candidate gene approach demonstrated that innate immune gene SNPs had the strongest association with bronchiolitis. The impact of 'other' viruses (RSV, influenza, adenovirus, parainfluenza, rhinovirus, human metapneumovirus [hMPV], coronavirus, boca-virus, enterovirus, paraechovirus) has been investigated. In one series only children with RSV infection experienced recurrent wheezing and in another only RSV infection was associated with respiratory complications (hypoxia correlated with prolonged hospitalisation). Others have examined the long-term outcome of viral infection in infancy. The above studies and others published in the last year will be discussed.

Gene-environmental interaction in the development of atopic asthma: new developments

PURPOSE OF REVIEW

Over recent years, major advances have occurred in understanding of the role of atopy in asthma. To accommodate these advances requires a revision in the paradigm that asthma is an atopic disease. In turn, a revision in the focus of gene-environment studies is now needed. The aim of this review, therefore, is to provide a new perspective to the topic of the role of genes and environment in the development of symptoms in atopic asthma.

RECENT FINDINGS

Recent data from prospective birth-cohort studies has shown that atopic events appear to play a limited role in the development of asthma and even less of a role in significant acute wheeze in children. Overwhelmingly, acute respiratory viral infection, not acute allergen exposure, is the major environmental cause of acute wheezing episodes in asthmatic children. This knowledge has led to the examination of the genetics of the immune system, particularly genes controlling innate immune responses, with respect to viral defences - an important area of gene-environment interaction in asthma.

SUMMARY

Advances in knowledge of the genetics of viral defence have contributed to improved insight into asthma in children and could lead to effective new antiviral asthma therapies.

Genetic diversity of the host and severe respiratory syncytial virus-induced lower respiratory tract infection

Respiratory syncytial virus (RSV)-induced lower respiratory tract disease is a common problem in children and adults in Western societies. The clinical range of RSV infection from asymptomatic to respiratory distress syndrome is believed to be the outcome of viral and host immunity interactions. Genes associated with immune response are of particular interest regarding genetic predisposition to severe RSV infection. Several investigators have sought to identify genetic markers for high-risk patients, and more than 20 independent studies in the medical literature assess the impact of genetic variations-mostly single nucleotide polymorphisms-on the clinical presentation of RSV-induced disease. Several candidate gene loci have been tested in association studies based on the concept that a particular allele is a significant risk factor for a phenotype of interest. Despite the wealth of information available, we are still far from evolving a practical and cost-effective screening tool; certain flaws in association studies first need to be overcome. The development of haplotype-based analysis for candidate loci across the genome, along with advances in biostatistics and bioinformatics, would facilitate the assessment of the relative contribution of genetic markers to disease susceptibility in RSV infection.

Human genetic factors and respiratory syncytial virus disease severity

SUMMARY

To explain the wide spectrum of disease severity caused by respiratory syncytial virus (RSV) and because of the limitations of animal models to fully parallel human RSV disease, study of genetic influences on human RSV disease severity has begun. Candidate gene approaches have demonstrated associations of severe RSV in healthy infants with genetic polymorphisms that may alter the innate ability of humans to control RSV (surfactants, Toll-like receptor 4, cell surface adhesion molecules, and others) and those that may control differences in proinflammatory responses or enhanced immunopathology (specific cytokines and their receptors). These studies are reviewed. They are valuable since an understanding of the direction of a polymorphism's effect can help construct a meaningful human RSV disease pathogenesis model. However, the direction, degree, and significance of the statistical association for any given gene are equivocal among studies, and the functional significance of specific polymorphisms is often not even known. Polymorphism frequency distribution differences associated with RSV infection arising from diversity in the genetic background of the population may be confounded further by multiple-hypothesis testing and publication bias, as well as the investigator's perceived importance of a particular pathogenic disease process. Such problems highlight the limitation of the candidate gene approach and the need for an unbiased large-scale genome-wide association study to evaluate this important disease.

Identification of diagnostic biomarkers for infection in premature neonates

Infection is a leading cause of neonatal morbidity and mortality worldwide. Premature neonates are particularly susceptible to infection because of physiologic immaturity, comorbidity, and extraneous medical interventions. Additionally premature infants are at higher risk of progression to sepsis or severe sepsis, adverse outcomes, and antimicrobial toxicity. Currently initial diagnosis is based upon clinical suspicion accompanied by nonspecific clinical signs and is confirmed upon positive microbiologic culture results several days after institution of empiric therapy. There exists a significant need for rapid, objective, in vitro tests for diagnosis of infection in neonates who are experiencing clinical instability. We used immunoassays multiplexed on microarrays to identify differentially expressed serum proteins in clinically infected and non-infected neonates. Immunoassay arrays were effective for measurement of more than 100 cytokines in small volumes of serum available from neonates. Our analyses revealed significant alterations in levels of eight serum proteins in infected neonates that are associated with inflammation, coagulation, and fibrinolysis. Specifically P- and E-selectins, interleukin 2 soluble receptor alpha, interleukin 18, neutrophil elastase, urokinase plasminogen activator and its cognate receptor, and C-reactive protein were observed at statistically significant increased levels. Multivariate classifiers based on combinations of serum analytes exhibited better diagnostic specificity and sensitivity than single analytes. Multiplexed immunoassays of serum cytokines may have clinical utility as an adjunct for rapid diagnosis of infection and differentiation of etiologic agent in neonates with clinical decompensation.