Development of an eosinophilic bronchitis mouse model and the effects of eosinophil activation on airway hyperresponsiveness in eosinophilic bronchitis mice

Abstract

Objective: To develop a mouse model of eosinophilic bronchitis, and explore the effects of eosinophil activation on airway hyperresponsiveness. Methods: A total of 60 female specific pathogen free BALB/c female mice were divided randomly into four groups: polymyxin B group, normal saline group, polymyxin B+ N-methionine leucine phenylalanine (fMLP) group, normal saline+ fMLP group. All the groups were given corresponding nasal drops for 21 days. The former two groups were given 12 μl 0.5% polymyxin B or normal saline once a day by transnasal administration respectively. Besides the above, the latter two groups were given 10 μl fMLP (0.05 mg/ml, dissolved in acetic acid) once by transnasal administration 3 hours after polymyxin B or normal saline administration on the 21st day. Within 24 hours after the last transnasal administration, cells in bronchoalveolar lavage fluid (BALF) were collected and analyzed by absolute different cell counts. Airway responsiveness (inspiratory and expiratory airway resistance and lung compliance) to acetyl choline (Ach) were measured 3 hours after the last transnasal administration in the former two groups and 24 hours after the last transnasal administration in the latter two groups. Eosinophil peroxidase (EPX), eosinophil cationic protein (ECP) and eosinophil chemotactic factor (ECF) levels in serum, BALF and lung tissue were tested by emzyme linked immunosorbent assay (ELISA). HE and Chromotrope 2R staining of lung tissue were used to observe the infiltration of inflammatory cells. The morphology of low-density eosinophils was observed under electron microscope. Results: The total cell counts of BALF in polymyxin B group were significantly higher than the normal saline group [29.50 (3.25)×10(4)/ml vs 15.25 (2.25)×10(4)/ml, P<0.001], especially eosinophil counts [11.76 (6.02)×10(4)/ml vs 0.12 (1.08)×10(4)/ml, P<0.001]. However, no significant differences of inspiratory and expiratory airway resistance and lung compliance existed in the two groups. Inspiratory and expiratory airway resistance in polymyxin B+ fMLP group were significantly higher, lung compliance significantly lower than those in the other three groups (all P<0.001), and the EPX, ECP, ECF levels in serum, BALF and lung tissue of the polymyxin B+ fMLP group were significantly higher than the other three groups (all P<0.001). There were more inflammatory cells, especially eosinophils in lung tissue of polymyxin B and polymyxin B+ fMLP group. Meanwhile, more activated eosinophils in polymyxin B+ fMLP group were observed by electron microscopy. Conclusion: A mouse model of eosinophilic bronchitis can be successfully developed by transnasal administration of polymyxin B, and the eosinophil activation plays an important role in the occurrence of airway hyperresponsiveness.