Mechanism Of B Cell Activating Transcription Factor On The Airway Inflammation Of Asthmatic Mice

Objective:To investigate the regulation mechanism of B cell activating transcription factor (BATF) on airway inflammation in asthmatic mice induced by ovalbumin, and the relationship between BATF and the retinoic acid orphan nuclear receptors gamma t (ROR γ t), a key transcription factor of asthma. Method:(1) 24 female BALB/c mice (SPF, weight 15-18g,6-8 weeks), were randomly divided into three groups:normal saline (NS) group, asthma (AS) group and dexamethasone (DEX) group,8 mice in each group. The mice in asthma group and DEX group were immunized on days 0,7 and 14 by intraperitoneal injection of 200μl freshly prepared ovalbumin (OVA) and aluminum hydroxide suspended solution (100μg OVA+lmg), and were challenged by ultrasonic atomizing inhalation of 2% OVA solution on day 21 (1 times a day,40 minutes at a time, for five days). The mice in DEX group were intervention by intraperitoneal injection of 1.0 mg/kg dexamethasone at 30 minutes before 2% OVA ultrasonic atomizing inhalation every time. The mice in NS group were given intraperitoneal injection and ultrasonic atomizing inhalation of an equal volume of sterile normal saline in a same manner.24 h after the final challenge, mice were anesthetized and the bronchoalveolar lavage fluid (BALF) and the lung tissue samples were collected. (2) To count the WBC and EOS in BALF. The expression of interleukin 17 (IL-17) in the supernatant was measured by ELISA. The lung morphological changes and the airway inflammation degree were observed with hematoxylin and eosin (HE) staining. Quantitative real-time PCR was used to evaluate BATF, IL-17 and ROR γ t mRNA expression in lung tissue. All date were expressed with mean ± SD. The statistical analyses were performed using SPSS 17.0 statistical data processing software to one-way analysis of variance and linear correlation analysis, p<0.05 was considered significance difference. Results:(1) HE staining:NS group: The airway epithelium of mice were complete, the trachea and bronchial lumen were smooth and regular with no obvious secretions while the airway smooth muscle was thinner, the mucosal folds were low and flat, the alveolar interval was clear, there was also no obvious inflammatory cells infiltration around the bronchi or blood vessels; AS group:The airway epithelium cells of mice were hyperplasia, the epithelial were shedding and incomplete with the airway smooth muscle thickened, bronchial lumen were obviously narrowed, lots of mucus plugs can be seen in the bronchial lumen and alveolar space, mucosal folds were hypertrophy and irregular, the alveolar interval was obviously thickened, there were a large number of inflammatory cells infiltration around the bronchioles and perivascular tissues and most of them were EOS or lymphocyte; In comparison with the AS group, the above changes of DEX group were significantly improved and the alveolar space were largened. (2) The total number of white blood cells, EOS and Polymorphonuclear in BALF of the AS group increased significantly (P< 0.05); Compared with the AS group, the total number of white blood cells, EOS and Polymorphonuclear in BALF of DEX group was obviously reduced (P< 0.05), but still more than those of the NS group (P< 0.05). (3)Results of ELISA shows:The IL-17 protein concentration in BALF of the AS group were significantly higher than those in BALF of the NS group and the DEX group; Compared with the AS group, The IL-17 protein concentration in BALF of DEX group relatively decreased, the difference was statistically significance (P< 0.05). (4) The results of RT-PCR shows:The expression of BATF, IL-17 and ROR y t and mRNA in the lung tissues of the AS group were obviously higher than that of the NS group and the DEX group, the differences were statistically significant (P< 0.05); The expression level of BATF, IL-17 and ROR y t and mRNA in the lung tissues of the DEX group were reduced Compared with AS group, the difference was considered to be statistically significant (P< 0.05). (5) The correlation analysis:The expression of IL-17 in the lung tissue of the AS group was positively correlated with the expression of WBC, EOS and PMN in BALF and BATF,RORγt in the lung tissue (r=0.934, r=0.776,r=0.833, r=0.852, r=0.916, P< 0.05); In the AS group the expression of BATF and ROR y t were significantly positive correlated with each other (r= 0.860, p< 0.05), and the expression of BATF in the lung tissue of the AS group was positively correlated with the expression of WBC, EOS and PMN in BALF (r=0.884, r=0.890, r=0.951, p< 0.05). Conclusions:(1) The expression of BATF, IL-17 and ROR y t in bronchial and lung tissues of asthmatic mice was increased, and they expressed by the positive correlation. (2) The over expression of BATF in lung tissues might be the key point to induce the airway inflammation of asthmatic mice, which would provide a theoretical basis to find new methods to cure asthma by transcription factors. (3) Dexamethasone could down-regulate BATF and ROR y t expression in asthmatic mice, to reduce the secretion of Th17 cells and to alleviate the airway inflammatory and the asthmatic symptoms, which might be one of the important mechanism to inhibit the airway inflammation of asthmatic mice.