“a”决定簇变异对慢性乙型肝炎患者HBsAg与HBsAb表达的影响

目的研究＂a＂决定簇变异对慢性乙型肝炎患者乙型肝炎表面抗原（HBsAg）与表面抗体（HBsAb）表达的影响。方法收集HBsAg阳性持续6个月以上的CHB患者866例，其中789例（91．1％）仅HBsAg阳性，77例（8．9％）患者血清HBsAg与HB-sAb均阳性。从77例血清HBsAg与HBsAb双阳患者中，选择14例血清HBsAg与HBsAb双阳患者为Ⅰ组。789例HBsAg阳性患者中随机选择12例HBsAg单独阳患者为Ⅱ组对照。对HBsAg编码基因进行扩增和克隆，每例样本至少克隆15个后进行测序分析。结果Ⅰ组患者S蛋白氨基酸残基改变数量为Ⅱ组患者的2．7倍[9．52变化量／100残基vs2．43变化量／100残基（9．52％VS2．43％），P〈0．01]，且绝大多数发生在主亲水区（MHR）“a”决定簇。MHR区至少出现2残基改变的在Ⅰ组有10例（71％），Ⅱ组3例（25％）。Ⅰ组患者S蛋白残基改变常见位点为s145、s129、s126、s144和s123。这些S基因位点突变，最终形成病毒的免疫逃逸。结论CHB患者HBsAg和HBsAb共存可能与“a”决定簇变异率升高相关。“a”决定簇变异可能为乙型肝炎病毒免疫逃逸突变的一种选择。HBV免疫逃逸对疫苗接种免疫效应、临床疾病诊断和治疗策略革新等有影响。

The effects of "a" determinant variants in chronic hepatitis B virus patients on the expression of hepatitis B surface antigen and anti-HBs

Objective To investigate the effects of "a determinant variants in chronic hepatitis B(CHB)patients on the expression of hepatitis B surface antigen(HBsAg) and anti-HBs antibodies (HBsAb). Methods Eight hundred sixty-six chronic hepatitis B patients were enrolled, which HBs Ag carriage was beyond a 6 month period.77 patients(8.9%)concomitantly carried both HBs Ag and anti-HBs antibodies,789 patients(91.1%)were only HBs Ag positive. Selection criteria for patients with both HBs Ag and anti-HBs were mainly focused on anti-HBs titers at least three times above the analytical threshold of the technique(10 U/L)on at least three consecutive visits.14 patients were selected from77 patients, who presented both markers(group Ⅰ),and 12 patients from another 789 patients who positive for HBs Ag only(group Ⅱ)were randomly selected as controls. The HBs Ag-encoding gene was amplified and cloned, and at least 15clones per patient were sequenced and analyzed. Results The number of residue changes within the S protein group Ⅰ was 2.7 times more frequently than that in group Ⅱ patients, and "a" determinant of the major hydrophilic region(MHR)occurred mostly. Ten patients (71%)from group Ⅰ and three patients(25%)from group Ⅱ presented at least two residue changes in the MHR. The most frequent changes in group Ⅰ patients were located at positions s145,s129,s126,s144, and s123 as described for immune escape variants. Conclusions In CHB patients, the coexistence of HBsAg and HBsAb is associated with an increase of "a" determinant variability, suggesting a selection of HBV immune escape mutants during chronic carriage. The consequences of this selection process play an important role in vaccine efficacy, diagnosis and clinical therapy.