Notch1 induces Th1/Th2 imbalance in neonatal mice with Streptococcus pneumoniae infection

Abstract

Objective To investigate the role of Notch1 signaling pathway in Th1/Th2 imbalance induced by neonatal Streptococcus pneumoniae pneumonia (S.pp) infection. Methods Twelve Balb/c neonatal mice (1 week old) were randomly divided into neonatal S.pp group, neonatal S.pp with Notch1 inhibition treatment group (S.pp+DAPT, a γ-secretase inhibitor) and mock-infected control group (control group) (n=4). The S.pp group and the S.pp+DAPT group were infected with 1×107 CFU of S. pneumoniae in 10 μL of PBS intranasally, while the control group received equivalent PBS. In 7 d after infection, the S.pp+DAPT groups were given 0.3 mg/kg DAPT by nasal instillation, and the S.pp and the control groups were instilled equivalent PBS. In 5 weeks after infection, airway hyperresponsiveness (AHR) was evaluated by invasive body plethysmography system. Differential cell counts in bronchoalveolar lavage fluid (BALF) were analyzed. HE staining was used to observe the histopathological changes of the lung tissue. Western blotting was used to detect the protein expression of Notch1 protein, and RT-PCR to measure the mRNA levels of T-bet and GATA3. And the percentages of Th1 and Th2 cells in the lung tissue were determined by flow cytometry and Th1/Th2 ratio was calculated. Results Notch1 expression was significantly lower in the S.pp+ DAPT group than the S.pp group (0.23±0.09 vs 1.94±0.78, P < 0.01). The total cell count and counts of neutrophils, monocytes and lymphocytes in the BALF from the S.pp+DAPT group were remarkably lower than those in the S.pp group (P < 0.01). The S.pp+DAPT mice had obviously lower histologic scores of pulmonary peribronchiolitis, pulmonary perivasculitis and pulmonary alveolitis in lung tissue than the S.pp group (0.55±0.17 vs 1.52±0.27, P < 0.01; 0.05±0.10 vs 0.88±0.25, P < 0.01; 0.18±0.35 vs 1.57±0.25, P < 0.01). The mRNA level of GATA3 and percentage of Th2 cells were significantly lower in the S.pp+DAPT group than the S.pp group [19.11±9.79 vs 177.56±65.95, P < 0.01; (0.16±0.02)% vs (0.28±0.04)%, P < 0.01]. While the mRNA level of T-bet and percentage of Th1 cells were similar between the 2 groups. The S.pp+DAPT group had significantly higher Th1/Th2 when compared with the S.pp group (14.67±2.60 vs 7.89±0.82, P < 0.01). The AHR in the S.pp+DAPT group mice was significantly decreased when inhaled different concentrations of acetylcholine (3.125~50 mg/mL) as compared with the S.pp group (P < 0.01). Conclusion Neonatal S.pp may induce Th1/Th2 imbalance by activating Notch1 signal, and thus promote airway hyperreactivity and airway inflammation.

Keywords

• streptococcus pneumoniae pneumonia
• notch
• th1/th2
• neonatal mice