Abstract: Objective To investigate the effect of early exposure of airway to bacterial allergen on the balance of T-helper-1 cells/T-helper-2 cells(Th1/Th2) and the asthmatic airway inflammation of adult rats and to understand the pathogenic mechanism of asthma.Methods Newborn rats were randomly divided into bacterial allergen exposure group,asthma group and control group.The rats of bacterial allergen exposure group were given 10 μL inactivated Streptococcus pneumoniae via nose drip at 1,3,5 and 7 days after the birth.The asthma group and control group were given 10 μL phosphate buffer solution(PBS) instead.When all rats were kept to adulthood the asthmatic model was made.The pathologic changes of lung tissue,differentiation of bronchoalveolar lavage fluid and serum interleukin-4(IL-4),interferon-γ(IFN-γ) and ovalbuminspecific IgE were observed.Results The airway inflammation in all allergen exposure groups were severe.The ratio of lymphocyte of 10⁷ and 10⁶ allergen exposure groups were 32.94±13.62% and 29.50±8.92%,and were increased significantly compared with those of asthma group(P < 0.05).The serum ovalbumin-specific IgE of 10⁷ allergen exposure group(0.33±0.07) was increased significantly(P < 0.01).While the interferon gamma(IFN-γ)(11.93±2.74 pg/mL) was significantly decreased(P < 0.05).Conclusion Early exposure of the airway to bacterial allergen could aggravate the imbalance of Th1/Th2 and asthmatic airway inflammation in adult rats.