Induced sputum analysis in asymptomatic young adults with bronchial hyperresponsiveness to methacholine

BHR is a clinical feature of asthma and factors crucial to the development of BHR remain to be elucidated. Asymptomatic BHR also occurs in the general population. This study examined the prevalence of asymptomatic BHR in a population of young Japanese atopic individuals to identify whether airway inflammation is present in asthmatic patients but not in asymptomatic subjects with BHR.

Fifty atopic volunteers (aged 18-23 years) without lower respiratory symptoms were recruited and their bronchial responsiveness to methacholine was measured in order to categorize them into two groups, those with BHR (PC(20) below 8 mg/mL) and those without BHR. We evaluated the inflammatory cell profiles and measured IL-5 and IL-13 levels in sputum from subjects of each group by ELISA. Results were compared with those for young adult asthmatic patients.

In the young atopic group, 17 subjects (34.0%) exhibited BHR. Compared with asthmatic patients sputum from asymptomatic subjects with BHR contained significantly lower numbers of eosinophils (P < 0.001) and had significantly lower levels of IL-5 (P = 0.088) and IL-13 (P = 0.032). There were no significant differences in each inflammatory parameter between the two asymptomatic groups.

In young adult atopic subjects with asymptomatic BHR, airway inflammation does not necessarily play a determining role in the development of BHR to methacholine itself, though it might be an important factor in the onset of asthma.