| Hepatitis B virus (HBV) can be transmitted from HBsAg seropositive preganant woman to her fetus through placenta. It is called HBV intrauterine transmission. The relating study has proved that mother-to-child transmission of HBV could be effectively blocked by the HbsIg. But there is still about 10%-20% high risk children does not product anti-HBs and lead to the immune failure. Intrauterine transmission of HBV is the most important reason of the HBsIg immune failure and also is the most important reason for the large number of HBV carriers in our country. At present, most of the reports about the mechanism of HBV intrauterine transmission are descriptive studies. Since 1993 our department have studied systematically from macroscopical epidemiology to molecular epidemiology according to the mechanism of HBV intrauterine transmission. Our studies suggested that there might be two transmission routes on the mechanism of HBV intrauterine transmission, homogenous by damage of placental vessels andcellular through placental cellular transfer of HBV. Liupengbo has done more deeply research and suggest the mechanism of placenta' s infection of HBV as follows.- HBsAg and anti-HBs were formed as HBsAg-anti-HJBs complexes in peripheral bloodstream of HBV infected woman. Fc fraction of anti-HBs in complexes binded with Fc Y receptor on trophoblast cells and then followed the pit of binding sites. Being formed isolated whole vesicle, HBsAg-anti-HBs complexes entry into trophoblast cells and results in the infection of the first layer cell of placenta barrier.To testify that suggestion, this study used 6 HBsAg seropositive pregnant women and the newborn in Maternal and Children Health Hospital of Shaan' xi Province. Blood specimens from mothers and blood specimens from infants at birth within 24 hours were collected to determine HBsAg> HBeAg in mothers sera. Placentas were collected at the same time. HBsAg> HBeAg in mothers' sera and HBsAg> HBeAg in newborns' sera were determined by ELISA. Fc Y RIT1 and HBsAg were determined by immunohistochemistry staining method. HBsAg-anti-HBs complexes were determined by double-labeling immunofluorescence method.The results are as follows: (D FcYRHI in ten seropositive and seronegative placenta tissues were detected by ABC immunohistochemistry method. Fc Y RHI was found on trophoblast cells and villous meseachymed cells(VMC) (2) ABC immunohistochemistry methods were used to detect HBsAg in HBsAgseropositive placenta tissues. Then those samples were tested HBsAg-anti-HBs complexes by double-labeling immunofluorescence method and visualized with laser scanning confocal microscope. The results show that HBsAg-anti-HBs complexes were distributed in trophoblast cells.According to the present study about the mechanism of HBV intrauterine transmission, this study was carried out on the basis of the hypothesis that HBV antigen-antibody complexes are mediated by Fc Y RIII to entry into trophoblast cells of placenta tissues. The Fc v RIII was tested in this study and its existence has been testified. The detection of HBsAg-anti-HBs complexes also suggests that trophoblast cells may be infected of HBV by HBsAg and anti-HBs complexes. What' s more, the detection of complexes has significant difference between fetal HBsAg seropositive and seronegative placenta tissues. This also suggests that existence of complexes is correlated with intrauterine transmission. But the conclusion still need to be study more according to its small samples.
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