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目的分析乙型肝炎患者体内ＨＢＶＳ基因的变异情况及对乙型肝炎的免疫预防的现实意义。方法采用巢式聚合酶链反应（ＰＣＲ）、Ｍ１３噬菌体克隆和核苷酸序列分析方法对一例乙型肝炎免疫失败儿童患者体内ＨＢＶＳ基因序列进行分析。结果发现该患儿所感染ＨＢＶ的Ｓ基因上有一个重要的点突变，即第５５１位碱基由野生型的Ａ变为Ｇ。该突变使乙型肝炎表面抗原（ＨＢｓＡｇ）１３３位氨基酸由甲硫（ＡＴＧ）变为缬（ＧＴＧ）。这一氨基酸替换恰恰发生在ＨＢｓＡｇ中和性α抗原决定簇区段（ａａ１２４～ａａ１４７）内。结论鉴于该患者接种乙型肝炎疫苗，其血清呈抗－ＨＢｓ阳性和ＨＢｓＡｇ阴性，推测其体内的ＨＢＶ为一个新的疫苗诱导的免疫逃避株
Objective To analyze the variation of HBV S gene in patients with hepatitis B and its practical significance in the prevention of hepatitis B infection. Methods The sequence of HBV S gene in one child with hepatitis B immune failure was analyzed by nested polymerase chain reaction (PCR), M13 phage cloning and nucleotide sequence analysis. The results found that the children infected with HBV S gene has an important point mutation, that the 551 base from wild-type A to G. This mutation changed the amino acid at position 133 of hepatitis B surface antigen (HBsAg) from methylthio (ATG) to valine (GTG). This amino acid replacement occurs precisely in the HBsAg-neutralizing alpha epitope segment (aa124-aa147). Conclusions In view of the hepatitis B vaccine inoculated with this patient, the serum of the patient is anti-HBs positive and negative for HBsAg, and the in vivo HBV is presumed to be a new vaccine-induced immune evasion strain