The Time-effect Relationship Of Mycobacterium Vaccae Nebulization In Preventing Asthma Mice

Objective: The study aimed to investigate the time-effect relationship of nebulizing inhaled Mycobacterium vaccae(M.vaccae)in preventing asthma mouse models.Methods: 48 female Balb/c mice were randomly divided into six groups of eight mice each: normal control group(group A),asthma model group(group B),prevention groups(group C2,C3,C4 and C5).Group B and prevention groups were sensitized and stimulated with ovalbumin(OVA)to establish asthmatic mice model,while group A received phosphate-buffered saline(PBS)instead.Prevention groups were administered with continuous M.vaccae nebulization for 2 to 5 days once daily two weeks prior to establishment of asthmatic model with ovalbumin(OVA).All mice were sacrificed at the end of 24 hours after noninvasive pulmonary function detection of airway responsiveness.Lung tissues were performed with hematoxylin and eosin(HE)staining and periodic acid-schiff(PAS)stainining to examine airway inflammation.The levels of cytokines IFN-?,IL-4,IL-5 and IL-17 A in serum and ??TCR in lung tissue were detected by Enzyme-linked immunosorbent assay(ELISA)and immunohistochemistry.Results: The airway inflammation and the level of ??TCR were decreased in prevention groups.There was lower airway inflammation in group C5 than group C2,C3 and C4.Group C3,C4 and C5 had lower level of ??TCR compared with group C2.Airway hyperresponsiveness was decreased in group C4 and C5,especially group C5.The concentrations of IL-4,IL-5,IL-17 A were decreased,while IFN-? concentration increased in group C4 and C5.The levels of serum IL-4 and IL-5 were lower in group C5 than that in group C4.There was no significant difference between group C5 and the normal group in levels of IL-4,IL-5,IL-17 A and IFN-?.Serum IL-17 A was positively correlated with AHR stimulated by Mch in asthmatic mice.Conclusion: Serum IL-17 A level is associated with AHR in asthmatic mice.The study demonstrates that nebulization of M.vaccae can prevent OVA-induced asthma mice in a time dependent manner.Along with the nebulization time extension,the effect of M.vaccae preventing asthma is more obvious.The mechanism could involve reducing ??T cells in lung and IL-17 A level in serum,mediating Th1/Th2 and Th2/Th17 balance.