Relationship Between Expression Of Interferon Regulatory Factor-1 And Th1/Th2 Cytokines Balance In Rats Lung Infected By Respiratory Syncytial Virus

Objective To observe the airway responsiveness and airway inflammation in SD rates infected by respiratory syncytial virus(RSV), and study the relationship between expression of interferon regulatory factor-1(IRF-1) and Th1/Th2 cytokines balance in rats lung infected by RSV.Methods RSV were inoculated on confluent Hela cell in culture flask. RSV were harvested and stored at-70℃as affection reached to 100%. Same protocol was performed to obtain the virus-free medium which were used as a negative control.To measure virulence,the virus stock was titrated and diluted for final titer of 5×10⁴ 50%tissue culture infective dose(TCID₅₀) per 0.1ml.Sixteen 1-week-old SD rates(Hunan agriculture university,China) were randomly divided into two groups:1. RSV-infected group(eight rats),A volume of 0.4μl/g(body weight) of RSV suspension was intranasated into each nostril while the rats were anaesthed under pentobarbital sodium(40mg/kg).2.Control group(eight rats),Same volume of virus-free medium were administrated to control rats.These process were repeated once a week.The airway responsiveness were observed eighth week after virus inoculation.Lung tissue of SD rats were stained with HE,Pathologic examinations of lung tissue-stained were made.IRF-1 expressions in lung tissue were detected by immunohistochemistry and western-blots,respectively.Interleukin-4 (IL-4) and Interferon-γ(IFN-γ) in lung hemogenous were detected by ELISA.Results(1) Clinical manifestations,par example,catarrhalic rhinitis, breathlessness,mussy hair,and decreased activity gradually emerged in RSV-infected group.There were no significant differences in the average body weight between RSV-infected group and control group. RSV-infected group have little effect on general state of health.But there were significant differences in body temperature.(2) Lung biopsy from RSV-infected group showed typical inflammation under light microscope. Airway resistance in RSV-infected group was higher than in control group.It is suggested that RSV-infected models were successful.(3) Compared with control group,the expression and positive immunologic makers of IRF-1 significant decreased in RSV-infected group (t=-3.361,P＜0.01).The expression of IRF-1 by western-blots in RSV-infected group were also less than in control group(t=-18.246,P＜0.01).(4) The levels of IL-4 enhanced.The levels of IFN-γsignificant decreased in RSV-infected group(P＜0.01).(5) There was a positive correlation between protein level of IRF-1 and IFN-γin lung tissue(r=0.828, P＜0.01).There was a negative correlation between protein level of IRF-1 and IL-4 in lung tissue(r=-0.732,P＜0.01).There was a positive correlation between protein level of IRF-1 and IFN-γ/IL-4(r=0.749, P＜0.01).Conclusion(1) one-week-old SD rats initial infected by RSV may present typical high secretion of Th2 cytokine and low secretion of Th1 cytokine 8 weeks after repeated RSV infection.It is showed that Th1/Th2 imbalance in RSV-infected group similar to asthma.(2) RSV-infection may down regulate the expression of IRF-1 in lung.decrease the ratio of IFN-γ/IL-4,and result in Th1/Th2 cytokines imbalance.