VIRUS-INDUCED AIRWAY HYPERRESPONSIVENESS IN MAN

Airway hyperresponsiveness is the most prominent functional abnormalit y in asthma. Although its aetiology is still unclear, it is well-known that allergen exposure and virus infections can temporarily induce or aggravate airway hyperresponsiveness. Among these environmental facto rs, virus infections appear to be clinically most relevant, since rece nt epidemiological studies have shown that most asthma exacerbations i n children are associated with positive nasopharyngeal viral identific ation. The pathogenesis of virus-induced airway hyperresponsiveness ha s been investigated by experimental virus infections in animals and in man. Intranasal inoculation and/or inhalation of live attenuated infl uenza virus, or certain strains of rhinovirus, have been shown to indu ce airway hyperresponsiveness to various bronchoconstrictor stimuli in man. This indicates that experimental virus-infection, like allergen challenge, is an appropriate investigational model of asthma. The mech anisms of virus-induced airway hyperresponsiveness are still unclear, but may, in part, be similar to those involved in the pathogenesis of asthma. Currently investigated hypotheses include: epithelial damage o r dysfunction, immunological responses, inflammatory mediator release, cholinergic and/or noncholinergic reflexes, and impaired beta-adrenoc eptor function. Careful experimental studies, using modern laboratory techniques, are needed to unravel the role of viruses in the developme nt of airway hyperresponsiveness. The results of such studies can pote ntially lead to an improvement of future asthma management