RESULTS: After RSV infection, the Tol group developed the re-emergence of symptoms of asthma, such as increased airway pressure, elevated serum IgE and total number of inflammatory cells in BALF compared with non-infected tolerance group. Quantitative PCR showed that in Tol+RSV group, the mRNA expressions of IL-4, IL-5, IL-13 and IL-17A were significantly up-regulated, especially IL-17A. Pathological results showed that inflammatory responses of the lung reappeared again. Th2, Th17 subsets of hilar lymph nodes in infected mice and non-infected were 2.45±0.06% and 2.19%±0.05% respectively, significantly higher than control group (P <0.05). IL-17A neutralizing antibodies administrated to RSV infection mice significantly reduced airway hyperresponsiveness, serum IgE production and pathological inflammatory responses. Th2, Th17 subsets were also significantly lower than those of the infected control group.