胎盘滋养层细胞的乙型肝炎病毒感染与宫内感染机制

Mechanism of hepatitis B virus infection of trophoblast cells and hepatitis B virus intrauterine infection

目的：检测HBV对胎盘、胎肝和滋养层细胞的感染情况，探讨HBV的宫内感染机制。方法：研究对象包括20例孕妇胎盘组织、6例引产胎儿胎肝组织及体外培养的胎盘滋养层细胞。ELISA法检测孕妇外周血、胎儿脐血和6个月婴儿外周血HBV标志物；荧光定量PCR法检测血清和滋养层细胞中的HBV DNA；免疫组织化学法和免疫荧光法检测胎盘、胎肝组织及滋养层细胞中HBV标志物的表达；末端脱氧核糖核酸转移酶介导的缺口标记法（TUNEL）检测胎盘和滋养层细胞凋亡情况。结果：孕妇血清HBV DNA水平与胎儿脐血HBV DNA水平相关，脐血HBV DNA阳性者其母血HBV DNA〉1.0×10^7拷贝／mL；6例胎盘组织和3例引产胎儿胎肝组织中可见HBsAg免疫组织化学染色阳性细胞，其中1例胎肝组织中发现HBcAg阳性细胞；体外培养滋养层细胞与HBV DNA阳性血清共孵育后，可检测到HBsAg的表达，亦可检测到HBV DNA。体内和体外实验均检测到HBV感染后滋养层细胞凋亡呈增加趋势，且胎盘细胞的凋亡与脐血HBV DNA水平相关。体外实验结果显示，随感染时间的延长，滋养层细胞凋亡呈增加趋势。6个月后，12例新生儿有1例血清HBsAg、HBeAg和抗-HBc阳性，6例抗-HBs阳性。结论：HBV宫内感染的机制可能是通过HBV感染胎盘屏障而使胎儿发生HBV宫内感染。HBV在胎儿组织器官内的定位和复制可能是新生儿发生慢性HBV感染的重要因素。滋养层细胞凋亡可能是胎盘屏障阻断HBV宫内传播的一种保护性机制。

Objective To explore the mechanism of intrauterine infection by investigating hepatitis B virus（HBV） infection status of 20 placental tissues, 6 hepatic tissue elicited fetus and in vitro cultured placental trophoblastic cells in vivo and in vitro. Methods Enzyme-linked immunosorbent assay（ELISA） method was used to detect the HBV markers of maternal blood, cord blood and the peripheral blood of the newborns. Real time-polymerase chain reaction（RT-PCR） assay was used to detect HBV DNA in the serum and trophoblastic cells. Immunohistochemical method （IHC） and immunofluorescence were used to detect the expressions of HBV markers in the placenta, fetus liver tissue and trophoblastic cells. Terminal deoxynucle-otidyltransferase dUTP nick end labeling （TUNEL） was employed to test the apoptotic cells in the placenta and in trophoblastic cells. Results The HBV DNA levels in pregnant women＇s serum and fetal cord blood were correlated. For those HBV DNA positive in cord blood, their maternal blood levels of HBV DNA〉 1.0 × 10^7 copies/mL.The HBsAg IHC staining positive cells could be observed in 6 placental tissues and 3 fetus＇ liver tissues, and HBcAg was also positive in 1 case of fetus＇ liver tissue. After co-incubating the tropho- blastic cells and HBV DNA positive serum in vitro, HBsAg expression and HBV DNA could be detected. Apoptosis of HBV-infected trophoblastic cells increased, which was demonstrated by in vivo and in vitro experiments and the apoptosis of placental cells was correlated with the cord blood HBV DNA level, The results of in vitro experiments showed that the apoptosis of trophoblastic cells increased with the elongation of infection time. After 6 months, 1 of 12 newborns was positive for HBsAg, HBeAg and anti-HBc, 6 was positive for anti-HBs. Conclusions The mechanism of HBV intra-uterine infection may be that HBV breaches the placental barrier and infects the fetus. The localization and replication of HBV in fetal tissues and organs are probably the important factors of chronic HBV infections in neonates. The apoptosis of trophoblastic cells may be the protective mecha- nism for the placental barrier to block the HBV intra-uterine transmission.