Re-Challenge with Ovalbumin Failed to Induce Bronchial Asthma in Mice with Eosinophilic Bronchitis

OBJECTIVE: To investigate whether eosinophilic bronchitis without airway hyperresponsiveness will develop bronchial asthma in allergic mice. METHODS: Mice were sensitized with OVA on days 0, 7, and 14, challenged on days 21 to 23 (1(st) OVA challenge), and re-challenged on days 46 to 48 (2(nd) OVA challenge), intranasally with 10 (the EB group) and 200 (the AS group) μg OVA. Lung resistance (R(L)) was assessed 24 h after each challenge and on day 45 followed by analysis of leukocyte distribution in the bronchoalveolar lavage (BAL) fluid and histological examination. RESULTS: Twenty-four hours after the 1(st) OVA challenge, aerosolized methacholine caused a dose-dependent increase in R(L) in all groups. At doses ≥1.56 mg/mL, R(L) in the AS group was significantly higher than that of the NS-1 group (P<0.01 or 0.05) and at doses ≥12.5 mg/mL, R(L) was markedly higher in the AS group than that of the EB group (P<0.01). The percentage of eosinophils in both the EB group and the AS group was markedly higher than that of the control group. Twenty-four hours after the 2(nd) OVA challenge, at doses ≤12.5 mg/mL, there was no significant difference in R(L) among all groups (P>0.05). At doses ≥12.5 mg/mL, R(L) in the AS group was significantly higher than that of the control group and EB group (P<0.01 or 0.05). The percentage of eosinophils in the AS group was noticeably higher than that of the EB group(P<0.05). Furthermore, there was apparent infiltration by inflammatory cells, predominantly eosinophils, into the sub-epithelial region of the bronchus and the bronchioles and around the vessels in the EB and AS group. CONCLUSION: Re-challenge with low doses of ovalbumin did not increase airway reactivity and failed to induce bronchial asthma in mice with ovalbumin-induced EB.