Objective:To detect the frequency of CD4+CD25+CD127low/-regulatory T cell(Treg)in cord blood born from HBsAg positive mother and to determine the relationship between mother’s HBeAg and HBV persistent infection after the children were born.Methods:According to mother’s HBeAg status

63 cord blood of neonates delivered by HBsAg positive mothers were divided into group A(HBeAg positive)and group B(HBeAg negative).22 cases of cord blood of neonates from HBsAg negative mother were served as group C(healthy controls).The frequency of Treg was analyzed by three-color immunofluorescence flow cytometry.HBV serum markers and HBVDNA level both in cord blood and mother’s peripheral blood were detected.Results:In group A

24 of 33 cord blood of neonates were HBeAg positive

but none of them were HBeAg positive in group B and group C.All of the cord blood were HBVDNA negative.There was no relationship about the HBeAg quantity between mother’s peripheral blood and cord blood(P>0.05).Compared with group B and group C

the percentage of Treg significantly increased in group A(P<0.05)

but the number was not dramatically different between group B and group C(P>0.05).The frequency of Treg did not relate to HBVDNA level and HBeAg quantity either in mother’s peripheral blood or in cord blood.Conclusion:HBeAg may have substantial impact on the development of fetal immune system and bring on their immunotolerance to HBV by upregulating Treg in cord blood.