目的：探讨卡介菌多糖核酸(BCG-PSN)对毛细支气管炎患儿喘息反复发作的预防作用及机制。方法：40例毛细支气管炎患儿随机分为 干预组和未干预组，并取20例健康体检者作正常对照。干预组(19例)在毛细支气管炎愈后3个月给予BCG-PSN注射液1 ml(含卡介菌多糖 0.35 mg，核酸不低于30 μg)肌注，每周 2次，共24次，而未干预组(21例)在毛细支气管炎愈后未予以干预作空白对照。于干预前及 干预后1年用ELISA法测定3组外周血单个核细胞培养上清中IFN-γ，IL-4及血清IgE含量；并随访1年，观察喘息发作情况。结果：与正常对照组比较，两组毛细 支气管炎患儿干预前IFN-γ水平和IFN-γ/IL4降低，而IL-4，IgE水平增高(P<0 .01)。BCGPSN干预1年后，干预组IFN-γ水平［(986.95±363.20) ng/L］和IFN-γ/IL-4(16.03±7.11)较干预前［(768.43±288.07) ng/L，9.11 ±4.27］升高，而IL-4［(59.73±16.04)ng/L］、IgE［(48.05±1 9.57)kU/L］水平较干预前降低［(81.66±21.92)ng/L，(155.35±76.25)kU/L］(P<0.01)，且IFN-γ水平与正常对照组差异无显著性(P>0.05 )；干预组患儿1年内有两次和/或以上喘息发作者(15.8%) 较未干预组婴儿(52.4% )少(P<0.05)。结论：BCG-PSN具有预防毛细支气管炎反复喘息 的作用，其机制可能与BCG-PSN能提高IFN-γ产生，抑制IL-4分泌，提高IFN-γ/IL-4 ，减少IgE生成有关。

OBJECTIVE: To study the effect and mechanism of early intervention by polysaccharide nucleic acid fraction of BCG (BCG PSN) for prevention of post bronchiolitis wheezing. METHODS: Forty infants with bronchiolitis were randomly assigned into 2 groups: intervention group (n=19) and non intervention group (n=21). Three months after recovering from bronchiolitis, the infants in the intervention group were given BCG PSN injection 1 ml I.M twice a week, 24 times in all. The infants in the non intervention group did not receive any intervention. Twenty healthy children were used as the normal controls. The levels of IFN γ and IL 4 in the supernatant of cultured peripheral blood mononuclear cells, and serum IgE level were measured using ELISA before intervention and one year after intervention. One year following up was done to observe the frequency of the wheezing episodes. RESULTS: The IFN γ level and IFN γ/IL 4 ratio were significantly lower, and the levels of IL 4 and IgE were significantly higher in both intervention group and non intervention group before intervention than those in the normal controls (P< 0.01 ). After one year of BCG PSN intervention, the IFN γ level [( 986.95 ± 363.20 ) ng/L] and IFN γ/IL 4 ratio ( 16.03 ± 7.11 ) were significantly higher than those of before intervention [( 768.43 ± 288.07 ) ng/L and ( 9.11 ± 4.27 ) respectively]; the levels of IL 4 [( 59.73 ± 16.04 ) ng/L] and IgE [( 48.05 ± 19.57 ) kU/L] decreased significantly compared with those of the pre intervention [( 81.66 ± 21.92 ) ng/L and ( 155.35 ± 76.25 ) kU/L, respectively] (P< 0.01 ) and the IFN γ level was not significantly different from the normal controls (P> 0.05 ). In one year of BCG PSN intervention, 3 cases ( 15.8% ) had two or more times wheezing episodes in the intervention group, less than that in the non intervention group [11 cases ( 52.4% )] (P< 0.05 ).CONCLUSIONS: Early intervention with BCG PSN in post bronchiolitis children may be useful in preventing the infants from recurrent wheezing episodes later. The possible explanation is that BCG PSN can increase IFN γ secretion, inhibit IL 4 activity, increase IFN γ/IL 4 ratio and decrease IgE production.