ObjectiveTo establish a murine model of neutrophilic steroid-refractory asthma for a better exploration of its pathogenesis and treatment.

MethodsA mouse model of neutrophilic steroid-refractory asthma was established by intratracheal administration of a mixture of house dust mite (HDM) and lipopolysaccharide (LPS). Eighteen female C57BL/6 mice were randomly divided into a control group, an asthma group (HDM+LPS) and a dexamethasone (Dex) group (HDM+LPS+Dex). The airway resistance was measured by pulmonary function test. Airway inflammation, hypersecretion and inflammatory cell recruitment were observed by HE, PAS and Wright′s staining, respectively. Inflammatory mediators in lung and bronchoalveolar lavage fluid (BALF) were detected by PCR and ELISA. Th17 cell differentiation in the lung was analyzed by flow cytometry.

ResultsHE staining showed a significantly increased airway inflammation in the asthma group than that in the control group ( P<0.05), and a slightly decreased airway inflammation in the Dex group than that in the asthma group ( P>0.05). Cell counts in BALF showed a sharply elevated recruitment of inflammatory cells in the asthma group (except eosinophils) than that in the control group (total number of inflammatory cells (2797±400)×10 ⁶/L vs (105±75)×10 ⁶/L, neutrophils (1151±395)×10 ⁶/L vs (12±6)×10 ⁶/L, lymphocytes(897±135)×10 ⁶/L vs (11±5)×10 ⁶/L, macrophages (215±51)×10 ⁶/L vs (34±16)×10 ⁶/L, P<0.05). Compared with the asthma group, Dex group significantly reduced the recruitment of total number of inflammatory cells and macrophages [total number of inflammatory cells (1140±418)×10 ⁶/L vs (2797±400)×10 ⁶/L, macrophages (117±31)×10 ⁶/L vs (215±51)×10 ⁶/L, all P<0.05]albeit no significances in lymphocytes and neutrophils [lymphocytes (587±208)×10 ⁶/L vs (897±135)×10 ⁶/L, neutrophils (294±134)×10 ⁶/L vs (1151±395)×10 ⁶/L, all P>0.05]. Immunohistochemical staining confirmed that Dex could not effectively alleviate the neutrophilic inflammation in asthmatic mice. Although there was no significant difference in airway hyperreactivity between the asthma group and the Dex group ( P>0.05), both had a higher airway hyperreactivity than that of the control group ( P<0.05). The Dex group exhibited a significantly lower Th2-related inflammatory mediators in the lung than the asthma group (all P<0.05), together with an increased trend in Th17 cell-related inflammatory mediators and no improvement in Th1-related inflammatory mediators. Flow cytometry showed an obviously increased percentage of Th17 cells in the Dex group than that in the asthma group [(5.8±1.9)% vs (2.3±0.8)%, P<0.01].

ConclusionA novel murine model mimicking clinical neutrophilic asthma was elegantly established, in which Dex could not attenuate the neutrophilic airway inflammation and hyperreactivity, but rather augmented Th17 cell differentiation, demonstrating the presence of steroid-resistance.