经母婴传播获得乙型肝炎病毒(HBV)感染儿童及其母亲体内HBV前S/S基因变异特点研究

目的 通过对经母婴传播获得HBV感染的子女及其母亲慢性携带者体内HBV前S／S序列研究,了解不同程度病毒血症下,来源相同HBV变异特点。方法根据HBV病毒血症高低分为3组,每组5对母子。应用T-A克隆技术构建重组质粒pGEM-前S／S、双酶切鉴定并分析。结果 每对母子HBV亚型相同,各组5对母子中4对为B／adw2、1对为C／adrq 亚型。每组中B／adw2亚型HBV分析显示：高病毒血症组间或低病毒血症组间HBV前S／S基因变异数目及位点差异均无显著性,低病毒血症病人变异数目及位点明显高于高病毒血症病人。两低病毒血症组的13／16个克隆存在较多位点变异,每个克隆86—94个;11／13克隆的86个、2／13克隆的90个核苷酸变异相同,分别引起37、38个氨基酸改变、大多位于免疫表位内或附近;这两个变异序列有62个核苷酸变异位点相同、可致28个氨基酸变异。变异与年龄无关。结论 HBV变异可能与感染的时间长短无关;抗-HBe阳性的低病毒血症病人体内HBV前S／S出现较多的变异,其变异是有规律的,可能与病毒逃避免疫攻击有关。

A study of the characteristics of pre S/S gene mutation of hepatitis B virus (HBV) in mothers and HBV-infected children via mother-to-infant transmission

OBJECTIVE: To investigate the characteristics of mutations in pre S/S gene of HBV in asymptomatic carrier (AsC) children infected through mother-to-infant transmission and their AsC mothers with different degree of viremia. METHODS: According to the levels of viremia in every pair of mother and child, 15 pairs of child and mother were divided into three groups 5 pairs in each group in this study: group I (both children and mothers had high viremia), group II (children had high and mothers had low viremia) and group III (children had low and mothers had high viremia). pre S/S gene was amplified by PCR and cloned into pGEM-T vector with T-A cloning technique. The recombinant plasmid pGEM- preS/S was confirmed by digestion with restriction enzyme ApaI and SacI. Tow clones were selected to be sequenced in each patient. The mutations of preS/S were compared with HBV DNA consensus sequence of Chongqing. RESULTS: In each group the subtypes of HBV were B/adw2 in 4 pairs and C/adrq+ in one pair. The preS/S clones in patients infected with subtype B/adw2 HBV were analyzed. It was shown that there was no difference among the four high viremic groups or between the two low viremic groups in the number of mutation and the mutational position. However, there was significant difference between the high viremic group and low viremic group. The mutation was not related to age. In the two low viremic groups (the mothers of group II and the children of group III), there were 86-94 mutational positions in 13/16 clones. There were 86 same mutational positions causing 37 amino acid changes in 11/13 clones and 90 same mutational positions causing 38 amino acid changes in 2/13 clones. Most of the changed amino acids were located within T and B cell epitopes of the envelope protein or/and the surrounding regions. Sixty-two mutational positions that resulted in 28 amino acid changes were same in these two mutational sequences. CONCLUSIONS: The mutation of HBV is not associated with the duration of infection. There are many differences of mutation when HBV comes from a same strain in hosts with different degrees of viremia. There are some regular patterns in the mutation of HBV after occurrence of HBeAg seroconversion. The mutation could be related to the escape of the attack of host's immunity.