The effects of rhinovirus infections on allergic airway responses

Is asthma an infectious disease? New evidence

The pathogenetic mechanisms leading to asthma are likely to be diverse, influenced by multiple genetic polymorphisms as well as elements of the environment. Recent data on the microbiome of the airway have revealed intriguing differences between the number and diversity of microbial populations in healthy persons and asthmatics. There is convincing evidence that early viral infections, particularly with human rhinovirus and respiratory syncytial virus, are often associated with the development of chronic asthma and with exacerbations. Recent studies suggest that two unrelated types of atypical bacteria, Mycoplasma pneumoniae (Mpn) and Chlamydia pneumoniae, are present in the airways of a substantial proportion of the population, bringing up the possibility that the persistent presence of the organism may contribute to the asthmatic phenotype in a subset of patients. This review will examine the current data regarding a possible role for infection in chronic asthma with a particular focus on atypical bacterial infections.

The human rhinovirus: human-pathological impact, mechanisms of antirhinoviral agents, and strategies for their discovery

As the major etiological agent of the common cold, human rhinoviruses (HRV) cause millions of lost working and school days annually. Moreover, clinical studies proved an association between harmless upper respiratory tract infections and more severe diseases e.g. sinusitis, asthma, and chronic obstructive pulmonary disease. Both the medicinal and socio-economic impact of HRV infections and the lack of antiviral drugs substantiate the need for intensive antiviral research. A common structural feature of the approximately 100 HRV serotypes is the icosahedrally shaped capsid formed by 60 identical copies of viral capsid proteins VP1-4. The capsid protects the single-stranded, positive sense RNA genome of about 7,400 bases in length. Both structural as well as nonstructural proteins produced during the viral life cycle have been identified as potential targets for blocking viral replication at the step of attachment, entry, uncoating, RNA and protein synthesis by synthetic or natural compounds. Moreover, interferon and phytoceuticals were shown to protect host cells. Most of the known inhibitors of HRV replication were discovered as a result of empirical or semi-empirical screening in cell culture. Structure-activity relationship studies are used for hit optimization and lead structure discovery. The increasing structural insight and molecular understanding of viral proteins on the one hand and the advent of innovative computer-assisted technologies on the other hand have facilitated a rationalized access for the discovery of small chemical entities with antirhinoviral (anti-HRV) activity. This review will (i) summarize existing structural knowledge about HRV, (ii) focus on mechanisms of anti-HRV agents from synthetic and natural origin, and (iii) demonstrate strategies for efficient lead structure discovery.

Allergy skin test responses during experimental infection with respiratory syncytial virus

BACKGROUND

Allergy skin testing is one of the most frequently performed physician office procedures. Many factors can affect the results of those tests, including the well-defined suppressive effect of systemic antihistamines. False-positive allergen skin test results are known to occur; however, contributing factors are not well understood.

OBJECTIVE

To determine whether a viral upper respiratory tract infection affects allergy skin test responsiveness.

METHODS

We performed skin tests with histamine and a panel of geographically relevant inhalant allergens on 16 adults before and 3, 6, and 21 days after experimental exposure to respiratory syncytial virus (RSV), a virus that causes signs and symptoms of a cold.

RESULTS

The RSV exposure, with and without documented infection, caused increased wheal and flare areas to histamine and allergen and de novo positive allergen test responses in individuals with no measurable responses at baseline. These were noted as late as 21 days after RSV exposure and may be consistent with mediation by up-regulated neurogenic inflammation during RSV infection.

CONCLUSION

These results may have implications for explaining the cause of such well-known complications of RSV infection as otitis media, bronchiolitis, and asthmatic exacerbation.

[Acute viral respiratory tract infections and childhood asthma]

Les infections virales respiratoires sont de très importants facteurs déclenchants des crises d'asthme. Chez l'enfant les études épidémiologiques les plus récentes, utilisant la PCR, leur attribuent le déclenchement de 80 à 85 % des crises, aussi bien pour les crises modérées que les crises nécessitant une hospitalisation. Le virus respiratoire syncytial et les virus parainfluenzae prédominent chez le nourrisson, les rhinovirus et le mycoplasme chez l'enfant plus grand. Les mécanismes précis de l'induction des crises d'asthme par les virus restent mal compris, toutefois de récentes études montrent une augmentation de l'activation des cellules inflammatoires dans le lavage alvéolaire. Les sujets atopiques, en dehors des périodes d'allergie, ne semblent pas avoir plus de manifestations respiratoires viro-induites que les non-atopiques. En revanche, chez le sujet asthmatique, l'infection virale aggrave les réactions immédiate et retardée de l'hypersensibilité immédiate après test de provocation allergénique, en augmentant la libération des médiateurs mastocytaires et le recrutement des éosinophiles dans les voies aériennes inférieures. Les études chez l'homme et l'animal suggèrent que la production locale de cytokines (IL4, IL8, RANTES, MIP-1a...) et l'expression accrue chez l'asthmatique de la molécule d'adhésion ICAM1 aient un rôle important pour le recrutement et l'activation des cellules de l'inflammation dans les voies aériennes. Une hypothèse, qui reste à démontrer serait que dans des situations où, comme dans l'asthme, les lymphocytes Th2 prédominent, un excès d'Il4 pourrait inhiber les CD8 cytotoxiques, les cellules NK et les Th1 et ainsi entraîner une diminution des défenses antivirales et une réaction inflammatoire broncho-pulmonaire plus sévère que chez le non-asthmatique.

[Viral infections and asthma]

Les infections respiratoires à rhinovirus, parainfluenza, influenza, adénovirus et virus syncytial respiratoire sont des causes fréquentes d'exacerbations asthmatiques surtout chez l'enfant. Tous ces virus peuvent induire une inflammation des bronches qui, en se superposant à l'inflammation allergique propre à l'asthme, peut aggraver l'obstruction et l'hyperréactivité bronchiques des asthmatiques. En outre, les infections virales respiratoires peuvent amplifier la réaction allergique bronchique induite par inhalation d'un allergène et favoriser l'éclosion d'un asthme ou d'un état d'atopie. Certains virus peuvent induire la synthèse d'IgE spécifiques et une réponse immunologique privilégiant le phénotype lymphocytaire TH2 promoteur de l'allergie. L'asthme et l'atopie prédisposent aux infections virales de l'organe de choc, peut-être à la faveur de l'inflammation allergique locale (expression d'ICAM-1, desquamation de la muqueuse, mucostase, etc.) et/ou des effets anti-inflammatoires de l'histamine.

[Atopy and infections]

Il existe de toute évidence des relations réciproques et importantes entre atopie et infection. L'atopie prédispose aux infections de l'organe de choc c'est-à-dire le siège de la réaction allergique. Puisque c'est l'inflammation allergique qui fait le lit de ces infections, il importera avant tout de lutter contre celle-ci en éliminant de l'environnement des sujets atopiques les allergènes et les irritants. Dans certains cas, il faudra recourir aux médicaments anti-inflammatoires topiques tels que le cromoglycate ou les corticostéroïdes en spray ou en pommade. Réciproquement, les infections de l'organe de choc aggravent les maladies atopiques en superposant les phénomènes inflammatoires qui leur sont propres à ceux de la réaction allergique, en amplifiant celle-ci et en créant une hyperréactivité de l'organe cible. Le rôle possible des infections à Chlamydia pneumoniae dans la genèse de certains asthmes chroniques sévères pourrait voir attribuer aux macrolides une place dans le traitement voire la prophylaxie de l'asthme.

The regulation of rhinovirus infection in vitro by IL-8, HuIFN-alpha, and TNF-alpha

The influence of three important cytokines (IL-8, TNF-alpha, and HuIFN-alpha) on ongoing rhinovirus infections has been examined in vitro, individually or as combinations. TNF-alpha was able to transform traces of HRV infections into full-blown infections. Furthermore, TNF-alpha was able to down-regulate the antiviral action of HuIFN-alpha completely, even at levels of just a few pg/ml. This suggests that the induction of TNF-alpha by HRV may be part of the virus's strategy to minimize the interferon response which is part of the host's immune defence system. However, troxerutin (a flavonoid) was able to neutralize the downregulatory action of TNF-alpha on the HuIFN-alpha system at low levels and re-establish the antiviral activity ascribed to IFN-alpha. IL-8 exerted a minor influence on the interferon system, and had no influence on rhinovirus infections. The in vitro findings are supported, in part, by recent in vivo findings in a common cold pilot study.

Impact of respiratory illness on expiratory flow rates in normal, asthmatic, and allergic children

We examined the effects of current respiratory illness (RI) on pulmonary function (PF) in 1,103 subjects who underwent spirometry at schools twice within a 4-month period. Before spirometry, subjects were asked if they had a "cold or other chest illness" during the previous month, and if so, whether they had fully recovered. Those who had not recovered were considered to have an RI. We found that children without RI at their first PF test who reported RI on retest had significantly lower forced expiratory volume in 1 sec (FEV(1)) (-0.8%), peak expiratory flow rate (PEFR) (-2.2%), forced expiratory flow between 25-75% of vital capacity (FEF(25-75)) (-3.5%), and forced expiratory flow at 75% of vital capacity (FEF(75)) (-5.1%) than those without RI on both test and retest. Restriction of subjects to those without a history of doctor-diagnosed asthma did not appreciably change these findings. Children with hay fever had significantly larger RI-associated decreases for FEV(1), FEF(25-75), and FEF(75), but not PEFR, than those without hay fever. Among asthmatic subjects, those with active asthma had larger RI-associated decreases in FEF(25-75) and FEF(75), but not PEFR, than those without asthma. There was limited evidence that small airway losses were greater in children less than 12.5 years old. We conclude that RI in children who are well enough to attend school may reduce expiratory flow rates. These effects are greater for children with active asthma or hay fever than in those without, and may be inversely related to age.

Expression of tachykinins in nonnociceptive vagal afferent neurons during respiratory viral infection in guinea pigs

Immunohistochemistry was combined with retrograde labeling to characterize the effect of respiratory infection with Sendai virus on the number of Substance P/Neurokinin A-containing vagal afferent neurons whose cell bodies resided in the nodose ganglia and whose receptive fields were located in guinea pig trachea. Of the neurons labeled from the trachea of vehicle-inoculated guinea pigs, few stained positively for Substance P/Neurokinin A (approximately 3% of total labeled neurons). These neurons had small diameter cell bodies (mode = 16-20 microm), a feature of nociceptive-like C-fibers. Viral infection (Day 4 after inoculation) was associated with a significantly greater number of labeled neurons containing Substance P/Neurokinin A (approximately 20% of total labeled neurons). The majority of these had a relatively large cell body diameter (mode = 36- 40 microm), a feature of nonnociceptive afferent neurons. This induction appeared to be reversible as there were significantly fewer Substance P/Neurokinin A positive neurons in nodose ganglia from virus-inoculated guinea pigs at Day 28 after inoculation, a time point when virus-induced airway inflammation had all but resolved. These findings support the hypothesis that viral infection leads to a qualitative change in the vagal afferent innervation of guinea pig airways such that both small diameter nociceptive-like neurons and large diameter nonnociceptive neurons express tachykinins.

Rhinovirus elicits proasthmatic changes in airway responsiveness independently of viral infection

BACKGROUND

Rhinovirus (RV), the principal pathogen responsible for the common cold, is importantly implicated in triggering attacks of asthma secondary to changes in airway responsiveness.

OBJECTIVE

Because the airway histopathologic features of RV infection are relatively modest, we tested the hypothesis that RV can directly elicit proasthmatic-like changes in airway smooth muscle (ASM) responsiveness independently of actual viral infection and its associated cytopathic effects.

METHODS

Isolated ASM tissues and cultured ASM cells were inoculated with either infectious or noninfectious (UV-irradiated) RV16 and RV2, the latter serotypes belonging to the "major" and "minor" groups of RV subtypes, respectively. ASM constrictor and relaxant responsiveness, G(i) protein expression, and proinflammatory cytokine release were subsequently compared under the different treatment conditions.

RESULTS

In contrast to RV2, which had no effect, RV16 inoculation elicited enhanced ASM contractility and impaired relaxation to cholinergic and beta-adrenergic agonists, respectively, in association with increased ASM membrane G(i) protein expression and induced release of the proinflammatory cytokines IL-5 and IL-1beta. These proasthmatic-like effects were also observed in ASM exposed to UV-irradiated RV16, wherein viral replication was completely inhibited. In contrast, pretreatment of ASM with a neutralizing antibody directed against ICAM-1, the host receptor for the "major" group of RVs, completely abrogated the proasthmatic effects of RV16.

CONCLUSIONS

The results demonstrate that (1) RV16 elicits proasthmatic changes in ASM responsiveness that can occur independently of actual viral infection of the ASM and (2) the effects of RV16 are attributed solely to binding of the virus to its host receptor (ICAM-1) on the ASM cell surface. Collectively, these findings support the notion that RV-induced exacerbation of wheezing in asthmatic individuals can occur even in the absence of any cytopathology associated with viral infection.

Biochemical and genetic studies of the initiation of human rhinovirus 2 RNA replication: purification and enzymatic analysis of the RNA-dependent RNA polymerase 3D(pol)

The replication of human rhinovirus 2 (HRV2), a positive-stranded RNA virus belonging to the Picornaviridae, requires a virus-encoded RNA polymerase. We have expressed in Escherichia coli and purified both a glutathione S-transferase fusion polypeptide and an untagged form of the HRV2 RNA polymerase 3D(pol). Using in vitro assay systems previously described for poliovirus RNA polymerase 3D(pol) (J. B. Flanegan and D. Baltimore, Proc. Natl. Acad. Sci. USA 74:3677-3680, 1977; A. V. Paul, J. H. van Boom, D. Filippov, and E. Wimmer, Nature 393:280-284, 1998), we have analyzed the biochemical properties of the two different enzyme preparations. HRV2 3D(pol) is both template and primer dependent, and it catalyzes two types of synthetic reactions in the presence of UTP, Mn(2+), and a poly(A) template. The first consists of an elongation reaction of an oligo(dT)(15) primer into poly(U). The second is a protein-priming reaction in which the enzyme covalently links UMP to the hydroxyl group of tyrosine in the terminal protein VPg, yielding VPgpU. This precursor is elongated first into VPgpUpU and then into VPg-linked poly(U), which is identical to the 5' end of picornavirus minus strands. The two forms of the enzyme are about equally active both in the oligonucleotide elongation and in the VPg-primed reaction. Various synthetic mutant VPgs were tested as substrates in the VPg uridylylation reaction.

Mechanism of cooperative effects of rhinovirus and atopic sensitization on airway responsiveness

To elucidate the mechanistic interplay between rhinovirus (RV) exposure and atopic sensitization in regulating airway smooth muscle (ASM) responsiveness, isolated rabbit ASM tissue and cultured human ASM cells were passively sensitized with sera from atopic asthmatic or nonatopic nonasthmatic (control) subjects in the absence and presence of inoculation with RV serotype 16. Relative to control subjects, atopic asthmatic serum-sensitized and RV-inoculated ASM exhibited significantly increased contractility to acetylcholine, impaired relaxation to isoproterenol, and enhanced release of the proinflammatory cytokine interleukin-1beta. These effects were potentiated in atopic asthmatic serum-sensitized ASM concomitantly inoculated with RV and inhibited by pretreating the tissues with monoclonal blocking antibodies against intercellular adhesion molecule (ICAM)-1 (CD54), the host receptor for RV serotype 16, or lymphocyte function-associated antigen (LFA)-1 (CD11a/CD18), the endogenous counterreceptor for ICAM-1. Moreover, RV inoculation was found to potentiate the induction of mRNA and surface protein expression of FcepsilonRII (CD23), the low-affinity receptor for IgE, in atopic asthmatic serum-sensitized ASM. Collectively, these observations provide new evidence demonstrating that 1) RV exposure and atopic sensitization act cooperatively to potentiate induction of proasthmatic changes in ASM responsiveness in association with upregulated proinflammatory cytokine release and FcepsilonRII expression and 2) the effects of RV exposure and atopic sensitization are mediated by cooperative ICAM-1-coupled LFA-1 signaling in the ASM itself.

The common cold at the turn of the millennium

Upper respiratory tract infections are one of the most common infectious diseases in man and are characterized by transient, relatively mild symptoms. Human rhinoviruses are known to be the major causative agent in adult common colds and their relative importance has further increased with the use of the sensitive RT-PCR technique. Characteristic for a common cold is the selective neutrophil recruitment and time-limited increase in mediator, cytokine, and chemokine concentrations that orchestrate chemotaxis, transmigration, and activation of inflammatory and immunocompetent cells. Common cold symptoms are found to correlate to rhinovirus-induced IL-8 elaboration and neutrophil activation. Treatment of rhinoviral upper respiratory tract infections consists of an inhibition of viral infection by antiviral agents and/or a reduction of symptoms by damping the host inflammatory response.

The role of viral infections in the natural history of asthma

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

Persistence of viruses in upper respiratory tract of children with asthma

OBJECTIVES

Nasopharyngeal swabs of 50 asthmatic children in the symptom-free period were examined for the presence of adenoviruses, rhinoviruses and coronaviruses. A control group of 20 healthy individuals was included in this study.

METHODS

A polymerase chain reaction was used to detect adenovirus DNA and rhinovirus and coronavirus complementary DNA. The fragments of amplified genetic material were visualized with the use of agarose gel electrophoresis.

RESULTS

Adenovirus DNA was found in 78.4% of asthmatic children, rhinovirus RNA in 32.4% and coronavirus RNA in 2.7%. Adenovirus DNA was detected in one of the 20 nasopharyngeal swabs of healthy controls; the rest of the control samples were negative.

CONCLUSIONS

The persistent presence of viruses in the upper respiratory tract of asthmatic children shows a possible connection between viral infections and asthma.

Autocrine cytokine signaling mediates effects of rhinovirus on airway responsiveness

The airway responses to allergen exposure in allergic asthma are qualitatively similar to those elicited by specific viral respiratory pathogens, most notably rhinovirus (RV), suggesting that the altered airway responsiveness seen in allergic asthma and that elicited by viral respiratory tract infection may share a common underlying mechanism. To the extent that T helper cell type 2 (Th2) cytokines have been implicated in the pathogenesis of allergic asthma, this study examined the potential role(s) of Th2-type cytokines in mediating pro-asthmatic-like changes in airway smooth muscle (ASM) responsiveness after inoculation of naive ASM with human RV. Isolated rabbit ASM tissues and cultured human ASM cells were exposed to RV (serotype 16) for 24 h in the absence and presence of monoclonal blocking antibodies (MAbs) or antagonists directed against either the Th2-type cytokines interleukin (IL)-4 and IL-5, intercellular adhesion molecule (ICAM)-1 (the endogenous host receptor for most RVs), or the pleiotropic proinflammatory cytokine IL-1beta. Relative to control (vehicle-treated) tissues, RV-exposed ASM exhibited significantly enhanced isometric contractility to acetylcholine and impaired relaxation to isoproterenol. These pro-asthmatic-like changes in ASM responsiveness were ablated by pretreating the RV-exposed tissues with either IL-5-receptor-alpha blocking antibody or human recombinant IL-1-receptor antagonist, whereas IL-4 neutralizing antibody had no effect. Extended studies further demonstrated that inoculation of ASM cells with RV elicited 1) an increased mRNA expression and release of IL-5 protein, which was inhibited in the presence of anti-ICAM-1 MAb, and 2) an enhanced release of IL-1beta protein, which was inhibited in the presence of IL-5 receptor-alpha antibody. Collectively, these observations provide new evidence demonstrating that RV-induced changes in ASM responsiveness are largely attributed to ICAM-1-dependent activation of a cooperative autocrine signaling mechanism involving upregulated IL-5-mediated release of IL-1beta by the RV-exposed ASM itself.

Rhinovirus-mediated changes in airway smooth muscle responsiveness: induced autocrine role of interleukin-1beta

An important interplay exists between specific viral respiratory pathogens, most commonly rhinovirus (RV), and altered airway responsiveness in the development and exacerbations of asthma. Given that RV infection reportedly induces the release of various cytokines in different cell types and that the reported effects of RV on airway smooth muscle (ASM) responsiveness are highly comparable to those obtained in ASM exposed to the proinflammatory cytokine interleukin (IL)-1beta, this study examined whether RV (serotype 16)-mediated pertubations in ASM responsiveness are mechanistically coupled to altered induced expression and action of IL-1beta in RV-exposed isolated rabbit and human ASM tissue and cultured cells. Relative to control tissues, ASM inoculated with RV exhibited significantly increased maximal isometric contractility to ACh (P < 0.01) and attenuated relaxation to isoproterenol (P < 0. 005). In extended studies, we found that 1) the RV-induced changes in ASM responsiveness were ablated by pretreating the tissues with the IL-1 recombinant human receptor antagonist; 2) in contrast to their respective controls, RV-inoculated ASM tissue and cultured cells exhibited progressively induced expression of IL-1beta mRNA and elaboration of IL-1beta protein at 6 and 24 h after viral exposure; and 3) the latter effect of RV was inhibited in the presence of a monoclonal antibody to intercellular adhesion molecule-1, the endogenous receptor for most RV. Collectively, these observations provide new evidence demonstrating that "pro-asthmatic-like" pertubations in agonist responsiveness elicited in RV-exposed ASM are largely attributed to the induced autologous expression and autocrine action of IL-1beta in the virus-infected ASM.

Rhinovirus infections: induction and modulation of airways inflammation in asthma

There is renewed interest in the role of respiratory virus infections in the pathogenesis of asthma and in the development of exacerbations in pre-existing disease. This is due to the availability of new molecular and experimental tools. Circumstantial evidence points towards a potentially causative role as well as to possibly protective effects of certain respiratory viruses in the cause of allergic asthma during early childhood. In addition, it now has become clear that exacerbations of asthma, in children as well as adults, are mostly associated with respiratory virus infections, with a predominant role of the common cold virus: rhinovirus. Careful human in vitro and in vivo experiments have shown that rhinovirus can potentially stimulate bronchial epithelial cells to produce pro-inflammatory chemokines and cytokines, may activate cholinergic- or noncholinergic nerves, increase epithelial-derived nitric oxide synthesis, upregulate local ICAM-1 expression, and can lead to nonspecific T-cell responses and/or virus-specific T-cell proliferation. Experimental rhinovirus infections in patients with asthma demonstrate features of exacerbation, such as lower airway symptoms, variable airways obstruction, and bronchial hyperresponsiveness, the latter being associated with eosinophil counts and eosinophilic cationic protein levels in induced sputum. This suggests that multiple cellular pathways can be involved in rhinovirus-induced asthma exacerbations. It is still unknown whether these mechanisms are a distinguishing characteristic of asthma. Because of the limited effects of inhaled steroids during asthma exacerbations, new therapeutic interventions need to be developed based on the increasing pathophysiological knowledge about the role of viruses in asthma.

Differences between asthma exacerbations and poor asthma control

BACKGROUND

Increased variation in peak expiratory flow (PEF) is characteristic of poorly controlled asthma, and measurement of diurnal variability of PEF has been recommended for assessment of asthma severity, including during exacerbations. We aimed to test whether asthma exacerbations had the same PEF characteristics as poor asthma control.

METHODS

Electronic PEF records from 43 patients with initially poorly controlled asthma were examined for all exacerbations that occurred after PEF reached a plateau with inhaled corticosteroid treatment. Diurnal variability of PEF was compared during exacerbations, run-in (poor asthma control), and the period of stable asthma before each exacerbation.

FINDINGS

Diurnal variability was 21.3% during poor asthma control and improved to 5.3% (stable asthma) with inhaled corticosteroid treatment. 40 exacerbations occurred in 26 patients over 2-16 months; 38 (95%) of exacerbations were associated with symptoms of clinical respiratory infection. During exacerbations, consecutive PEF values fell linearly over several days then improved linearly. However, diurnal variability during exacerbations (7.7%) was not significantly higher than during stable asthma (5.4%, p=0.1). PEF data were consistent with impaired response to inhaled beta2-agonist during exacerbations but not during poorly controlled asthma.

INTERPRETATION

Asthmatics remain vulnerable to exacerbations during clinical respiratory infections, even after asthma is brought under control. Calculation of diurnal variability may fail to detect important changes in lung function. PEF variation is strikingly different during exacerbations compared with poor asthma control, suggesting differences in beta2-adrenoceptor function between these conditions.

Association of rhinovirus infections with asthma

Rhinoviruses are the most common cause of the common cold, but they can cause more severe illnesses in people with underlying lung disorders such as asthma, chronic obstructive pulmonary disease, or cystic fibrosis. Epidemiologic studies with sensitive detection methods such as PCR have identified rhinovirus infection as a major source of asthma exacerbations in both children and adults, especially during the spring and fall. Since rhinoviruses cause little tissue destruction, it is presumed that the immune response to the infection may play an important role in the pathogenesis of rhinovirus-induced exacerbations of asthma. This review examines the epidemiologic association between rhinovirus infections and exacerbations of asthma and outlines current information on immune responses to rhinovirus infection and potential connections between antiviral responses and preexisting allergic inflammation. Finally, current and future strategies for treating rhinovirus infections and virus-induced exacerbations of asthma are discussed.

Mechanism of rhinovirus-induced changes in airway smooth muscle responsiveness

An important interplay exists between specific viral respiratory infections and altered airway responsiveness in the development and exacerbations of asthma. However, the mechanistic basis of this interplay remains to be identified. This study addressed the hypothesis that rhinovirus (RV), the most common viral respiratory pathogen associated with acute asthma attacks, directly affects airway smooth muscle (ASM) to produce proasthmatic changes in receptor-coupled ASM responsiveness. Isolated rabbit and human ASM tissue and cultured ASM cells were inoculated with human RV (serotype 16) or adenovirus, each for 6 or 24 h. In contrast to adenovirus, which had no effect, inoculation of ASM tissue with RV induced heightened ASM tissue constrictor responsiveness to acetylcholine and attenuated the dose-dependent relaxation of ASM to beta-adrenoceptor stimulation with isoproterenol. These RV-induced changes in ASM responsiveness were largely prevented by pretreating the tissues with pertussis toxin or with a monoclonal blocking antibody to intercellular adhesion molecule-1 (ICAM-1), the principal endogenous receptor for most RVs. In extended studies, we found that the RV-induced changes in ASM responsiveness were associated with diminished cAMP accumulation in response to dose-dependent administration of isoproterenol, and this effect was accompanied by autologously upregulated expression of the Gi protein subtype, Gialpha3, in the ASM. Finally, in separate experiments, we found that the RV-induced effects on ASM responsiveness were also accompanied by autologously induced upregulated mRNA and cell surface protein expression of ICAM-1. Taken together, these findings provide new evidence that RV directly induces proasthmatic phenotypic changes in ASM responsiveness, that this effect is triggered by binding of RV to its ICAM-1 receptor in ASM, and that this binding is associated with the induced endogenously upregulated expression of ICAM-1 and enhanced expression and activation of Gi protein in the RV-infected ASM.

Relationships among respiratory infections, triggers of attacks, and asthma severity in children

The present study of asthmatic children examined relationships among the frequencies of prior respiratory infections (i.e., those prior to the development of asthma) and recent (past year) respiratory infections, asthma severity, and the impacts of 12 common asthma triggers: air pollution, allergy problems, anger, cigarette smoke, excitement, high humidity, high or low environmental temperature, laughter, nighttime hours, physical activity, respiratory infection, and stress or worry. Data on these variables were obtained through a survey in which 325 families completed questionnaires; 121 families had asthmatic children who were 2-20 years of age. Pearson correlational analyses revealed many significant positive correlations: The frequencies of prior and recent infections were correlated. The frequency of prior infections was correlated with the impacts of all asthma triggers except allergy problems, but the frequency of recent infections was correlated only with the impacts of air pollution, cigarette smoke, respiratory infection, and nighttime hours as triggers of asthma attacks. Asthma severity was correlated with the frequencies of prior and recent respiratory infections and with the impact of respiratory infection as an asthma trigger.

Serious respiratory illness associated with rhinovirus infection in a pediatric population

BACKGROUND

Rhinoviruses have long been associated with mild upper respiratory illness in both adults and children. However, the role of rhinoviruses as lower respiratory tract pathogens has not been fully characterized. Previous data suggests that rhinoviruses may cause severe lower respiratory illness in young children or infants.

OBJECTIVES

The present study describes the clinical presentations, severity of illness and outcomes for a large cohort of pediatric patients with documented rhinovirus infections.

SUBJECTS AND METHODS

A retrospective chart review was done on 93 pediatric patients from whom 101 nasopharyngeal or endotracheal specimens were positive by viral culture for a rhinovirus. All patients were hospitalized or seen in the pediatric emergency department at The Children's Hospital of Philadelphia between 1 January, 1990 and 31 May, 1996.

RESULTS

Of the 93 patients, 52 were male and 41 female. The age range was 0 days to 18 years with 25 (27%) less than 3 months, 42 (45%) between 3 and 12 months and 26 (28%) over the age of 12 months. Clinical presentations on evaluation in the emergency department or admission included 78 (84%) patients with acute respiratory illness, 13 (17%) with fever and suspected sepsis and 11 (12%) with other complaints. Reported physical findings on examination included one or more lower respiratory symptoms or signs of acute distress and fever greater than or equal to 38.1 degrees C. A total of 64 (69%) children were noted to have significant past medical histories, including 28 (44%) with prematurity or complicated neonatal courses, 11 (17%) with prior reactive airways, 8 (12%) with congenital cardiac disease and 7 (11%) with neurologic disorders. Of the patients, 29 (31%) were considered to be otherwise healthy children with no underlying dysfunctions. The mean duration of hospitalization for 69 patients admitted with respiratory illness who did not develop subsequent unrelated complications was 3.7 days. No significant bacterial or fungal pathogens were identified in 91% of the cases.

CONCLUSIONS

This study shows that rhinoviruses were associated with severe lower respiratory illness and hospitalization in a large pediatric population and that rhinovirus infection was a complicating factor in those patients with underlying or predisposing conditions.

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.