The Preventive Effect Of Bacillus Calmette-Guerin Vaccinated In Early Life On Airway Inflammation And Mucus Production In A Juvenile Mouse Model Of Asthma

Background Asthma is a chronic inflammatory disorders of the airways in which many cells such as mast cell, eosinophil(Eos) and T lymphocytic cell play an important role, associated with mucus hypersecretion, variable airway obstruction, airway hyperresponsiveness (AHR) and airway reconstitution . Eos infiltrating in the respiratory tract play a central role in the pathogenesis of asthma . Asthma is charactered with mucus hypersecretion. Thus, the muscus overproduction increases the degree of AHR and airflow limitation, contributing to the airway narrowing combination of smooth muscle contraction and airway wall edema, which attends to crucial pathophysiological process of asthma and results in exacerbations and sudden death. The mechanism of asthma is complex. Increasing evidence suggests that Th₂ lymphocyte play an important role in the mechanism of asthma .They produce TH₂ cytokines such IL-4/IL-5 intiating and sustaining inflammatory process, and leading to Eos recruitment and activation in the airways. Inversely TH₁ lymphocytes which excrete different cytokines such as EFN-? and IL-12 inhibiting the production of Th₂ cytokines and decreasing allergic response. It has been documented that there is a lower typel/type2 cell ratio in asthma. So it has been an attractive idea by regulating the TH1/TH2 balance to reduce allergic response. It has been found that BCG is a strong inducer of a Th1 response ,which promotes IFN-? /IL-12 synthesis and inhibits cytokines from Th2-like cells such as IL-4/IL-5 , airway eosinophilia and AHR toantigens, besides inhibits the GC hyperplasia and metaplasia (GCH/M) and the mucus secretion. Our previous studies have suggests that BCG promoted IFN-? /IL-12 synthesis and inhibited a range of TH2 phenomena including secretion of IL-4/IL-5, airway eosinophilia and the mucus overproduction to antigens in the mouse model of asthma. So, we simulate the pattern of BCG Vaccination preventing tuberculosis to see if BCG vaccinztion in early life can up-regulate the systemic immune response and develop a Thl-type response, preventing the development of asthma of juvenile mouse(5 weeks old) to some extent.Objective Based on a mouse model of asthma we created previously, newborn C57BL/6 mice were vaccinated subcutaneously with BCG early, later sensitized and challenged, then we examine the effects on the airway inflammation and airway mucus production , and level of Thl/Th2 cytokin(IFN-?, IL-4) in BALF and spleen cell culture supernatants.Methods Newborn C57BL/6 mice (in 24 hours after birth) were vaccinated with BCG, which were sensitized and challenged by ovabumin(OVA)when they were 5-week-old. At first we select the times of BCG vaccination is 3, and we select the dose of BCG is 105. So we assigned newborn mice to three groups: Normal saline solution group (group A), asthma model group (group B), BCG-vaccinated group (group C -105, 105, 105), and 48 hours after the last challenge, the bronchoalveolar lavage(BALF) inflammatory cell counts, and the pathomorphological changes in the lung were analyzed. The goblet cell hyperplasia ratio(HR) and the epithelial cell mucus occupying ratio(MOR) also measured;the level of Thl/ Th2 cytokin(EFN-?, IL-4) in BALF and spleen cell culture supernatants were detected. Results1 .the changes of total cells number and Eos in BALFWe found the total leukocytes and Eos increases obviously in BALF after OVA challenge compared with negative group, p<0.01. BCG infection before OVA challenge resulted in reduction in the total leukocytes and Eos within BALF compared with positive group, p<0.01. 2.the influence of the level of IL-4 and IFN-? in BALF and spleen cell culturesuperaatantsThe level of IL-4 increases obviously in BALF and spleen cell culture superaatants compared with negative group, p<0.01, on the contrary, the level of IFN-? decreased obviously, p<0.01. When administration of BCG before OVA challenge, the level of IL-4 in BALF and spleen cell culture superaatants decreased obviously compared with positive group, p<0.01, but the level of IFN-? increased, p<0.01.3 .the change of pulmonary pathology after BCG inflectionIn negative group mice, there are no Eos accumulation around airways and vessels, and no mucus secretion in the epithelial cells. Inversily there are large amount of inflammatory cells and Eos around airways and vessels of the positive group mice, and mucus hypersecretion in the epithelial cells. In BCG-infected mice, there are still a lot of inflammatory cells around airways and vessels, however Eos counts decreased significantly compared with positive mice. Mucus can be seen in the epithelial cells.4.quantitative analysis of airways mucus owing to the effect of BCG HR and MOR of BCG-vaccinated group and positive group increased significantly compared with negative group, p<0.01;but HR and MOR of BCG-vaccinated group is more than positive group obviously, p<0.01. Conclusions:1. Subcutaneous BCG in early life significantly inhibited the accumulation of total cells number and Eos in BALF and reduced eosinophilic influx into the airway lumen.2. Subcutaneous BCG in early life significantly decreased the GCH/M, thus inhibited the mucus production in the airway epithelium.3. Subcutaneous BCG in early life significantly decreased the level of IL-4 in BALF and spleen cell culture supematants , but increased the level of IFN-? compared with positive group.