Effects of neonatal Streptococcus pneumoniae pneumonia on airway epithelial injury of mice / 解放军医学杂志

ABSTRACT

Objective To investigate the effects of neonatal Streptococcus pneumoniae pneumonia (S.pp) on airway epithelial injury of mice. Methods Neonatal C57BL/6 (1-week-old) mice were infected intranasally with 2×105 cfu of Streptococcus pneumoniae (S.p) in a volume of 5 μl sterile phosphate buffered saline (PBS) (S.pp group), while the mock-infected controls received the same volume of sterile PBS (control group). Five weeks after the infection, the airway hyperresponsiveness (AHR) was evaluated by invasive body plethysmography system. The lung tissue was harvested, CDH1 and TJP1 mRNA levels were analyzed by RT-PCR. Immunohistochemical method and Western blotting were used to evaluate the expressions of E-cadherin and tight junction protein (ZO-1). Airway inflammation was detected by HE staining, the subcutaneous collagen deposition beneath the airway epithelium was evaluated by Masson staining, and the number of goblet cells was detected by Alcian Blue Periodic Acid Schiff (AB-PAS) staining. Results When the concentration of aerosolized methacholine inhaled by mice ranged from 6.25 to 50 mg/ml, the AHR was obviously higher in S.pp group than that in control group (P<0.001); the levels of CDH1 and TJP1 mRNA in the lung tissue were markedly lower in S.pp group (0.85±0.29 and 0.43±0.16) than those in control group (0.85±0.29 vs. 1.42±0.40, P=0.033; 0.43±0.16 vs. 0.83±0.26, P=0.010, respectively); the expression levels of E-cadherin and ZO-1 in airway epithelium were lower in S.pp group than those in control group (9.66±4.89 vs. 24.52±7.58, P=0.001; 13.54±3.79 vs. 25.53±5.99, P=0.005, respectively); the protein levels of E-cadherin and ZO-1 in lung tissue were remarkably lower in S.pp group than those in control group (0.23±0.06 vs. 0.38±0.06, P=0.019; 0.68±0.12 vs. 0.96±0.16, P=0.032, respectively); the subcutaneous collagen deposition beneath the airway epithelium increased significantly in S.pp group than that in control group (45.54±5.79 vs. 26.3±5.53, P=0.001). The number of goblet cells and inflammatory cell infiltration showed no statistical significance between the two groups. Conclusion Neonatal S.pp may lead to airway epithelial injury and be involved in the formation of AHR.