Sensitivity to the house dust mite and airway hyperresponsiveness in a young adult population

Background: The pathogenic mechanisms of airway hyperresponsiveness (AHR) in asthma are unknown and only a few studies have examined the importance of sensitivity to antigens in AHR in young adults. Objective: We investigated the correlation between AHR and sensitivity to specific antigens, atopy, history of childhood asthma and spirometry in a young adult population. Methods: Based on the results of interviews with 447 students at our university, 308 non-smoker students were classified into six groups. Group 1 comprised subjects with intermittent mild bronchial asthma; group 2, subjects with history of childhood asthma; group 3, subjects with atopic disease, and a RAST score for Dermatophagoides farinae (Def) of greater than or equal to 2; group 4, normal subjects with a RAST score for Def of greater than or equal to 2; group 5, subjects with cedar pollinosis; and group 6, normal subjects. We measured AHR to methacholine (MCh), spirometry, immunoglobulin E-radioimmunosorbent test (IgE-RIST), IgE-radioallergosorbent test to six common antigens, eosinophil cationic protein (ECP), and eosinophil count in peripheral blood in each subject. Results: Airway hyperresponsiveness to MCh did not correlate with IgE-RIST, eosinophil count, or ECP. The highest AHR to MCh was present in groups 1 and 2 and lowest in groups 5 and 6. Multiple regression analysis showed that sensitivity to Def was the only factor that significantly influenced AHR to MCh. Airway hyperresponsiveness to MCh of groups with a RAST score for Def of 0/1 was lower than groups with a RAST score of 2 to 6. Airway hyperresponsiveness to MCh did not correlate with the degree of positivity to Def antigen among positive sensitized groups (RAST score 2 to 6). Conclusions: Sensitivity to mite antigen may be important in the pathogenesis of AHR and Def is a major contributing antigen in young adults in Japan. Once asthma occurs, AHR remains positive for a long time even after the disappearance of asthma-related symptoms.