Oral administration of Lactobacillus paracasei L9 attenuates PM2.5-induced enhancement of airway hyperresponsiveness and allergic airway response in murine model of asthma

This study investigated allergy immunotherapy potential of Lactobacillus paracasei L9 to prevent or mitigate the particulate matter 2.5 (PM2.5) enhanced pre-existing asthma in mice. Firstly, we used a mouse model of asthma (a 21-day ovalbumin (OVA) sensitization and challenge model) followed by PM2.5 exposure twice on the same day of the last challenge. PM2.5 was collected from the urban area of Beijing and underwent analysis for metals and polycyclic aromatic hydrocarbon contents. The results showed that PM2.5 exposure enhanced airway hyper-responsiveness (AHR) and lead to a mixed Th2/ IL-17 response in asthmatic mice. Secondly, the PM2.5 exposed asthmatic mice were orally administered with L9 (4×107, 4×109 CFU/mouse, day) from the day of first sensitization to the endpoint, for 20 days, to investigate the potential mitigative effect of L9 on asthma. The results showed that L9 ameliorated PM2.5 exposure enhanced AHR with an approximate 50% decrease in total airway resistance response to methacholine (48 mg/ml). L9 also prevented the exacerbated eosinophil and neutrophil infiltration in bronchoalveolar lavage fluid (BALF), and decreased the serum level of total IgE and OVA-specific IgG1 by 0.44-fold and 0.3-fold, respectively. Additionally, cytokine production showed that L9 significantly decreased T-helper cell type 2 (Th2)–related cytokines (IL-4, -5, -13) and elevated levels of Th1 related IFN-γ in BALF. L9 also reduced the level of IL-17A and increased the level of TGF-β. Taken together, these results indicate that L9 may exert the anti-allergic benefit, possibly through rebalancing Th1/Th2 immune response and modulating IL-17 pro-inflammatory immune response. Thus, L9 is a promising candidate for preventing PM exposure enhanced pre-existing asthma.本研究探究了副干酪乳杆菌L9（Lactobacillus paracasei L9）预防或缓解细颗粒物2.5（PM2.5）加剧小鼠已有哮喘的过敏免疫治疗潜力。首先，我们构建了为期21天的卵清蛋白（OVA）致敏-激发哮喘小鼠模型，并在末次激发当日给予两次PM2.5暴露。PM2.5采集自北京市城区，并对其金属与多环芳烃含量进行了检测分析。结果显示，PM2.5暴露可加剧哮喘小鼠的气道高反应性（AHR），并诱发混合的Th2/IL-17免疫应答。随后，我们对PM2.5暴露后的哮喘小鼠灌胃给予L9（剂量分别为4×10^7、4×10^9 CFU/只，每日给药），给药周期为首次致敏当日至实验终点，共计20天，以探究L9对哮喘的潜在缓解作用。结果表明，L9可改善PM2.5暴露诱导的气道高反应性加剧，使乙酰甲胆碱（48mg/ml）激发下的总气道阻力反应降低约50%。L9还可抑制支气管肺泡灌洗液（BALF）中嗜酸性粒细胞与中性粒细胞的过度浸润，并使血清总免疫球蛋白E（IgE）与OVA特异性免疫球蛋白G1（IgG1）水平分别下降0.44倍与0.3倍。此外，细胞因子检测结果显示，L9可显著降低支气管肺泡灌洗液中辅助性T细胞2型（Th2）相关细胞因子（IL-4、IL-5、IL-13）的表达水平，同时升高辅助性T细胞1型（Th1）相关干扰素γ（IFN-γ）的水平；L9还可降低IL-17A的表达水平，并提升转化生长因子β（TGF-β）的表达水平。综合上述结果，本研究表明L9可能通过重塑Th1/Th2免疫平衡、调控IL-17介导的促炎免疫应答发挥抗过敏功效，因此L9有望成为预防PM暴露加剧已有哮喘的候选制剂。