儿童与成人慢性乙型肝炎患者乙型肝炎病毒Core基因区准种特征及正选择压力差异分析

Distinct quasispecies characteristics and positive selection within the core gene in chronic hepatitis B virus infected child and adult patients

儿童与成人慢性乙型肝炎患者的临床特征差异明显。乙型肝炎病毒(Hepatitis B virus,HBV)病毒准种特征与其致病特性紧密相连,HBV病毒Core基因区富含免疫表位,该区域的准种特征直接反映病毒变异与病毒应对宿主免疫压力间的动态过程。文章通过扩增170名儿童慢性乙型肝炎患者及121名成人慢性乙型肝炎患者病毒Core基因区,按照病毒基因型以及病毒e抗原(Hepatitis B virus e antigen,HBe Ag)状态进行分组,使用序列复杂度、多样性、非同义突变率(Non-synonymous substitution ratio,d N)、同义突变率(Synonymous substitution ratios,d S)等指标衡量不同组别之间的病毒准种特征;使用不同模型计算不同组别中受到正选择压力的位点,进一步结合HBV Core基因区免疫表位信息,进行正选择位点的定位分析。结果发现,儿童乙型肝炎病毒患者体内病毒Core基因区序列复杂性和多样性低于成人患者,且前者Core基因区正选择位点个数显著低于后者,这说明儿童慢性乙型肝炎患者体内病毒受到的选择压力低于成人患者。在儿童及成人慢性感染病人组中,HBe Ag阳性病人体内病毒受到的选择压力低于HBe Ag阴性病人。儿童及成人慢性感染患者体内病毒存在13个正选择位点,大多数正选择位点位于已知的抗原表位上。本研究从分子进化角度揭示了儿童与成人慢性乙型肝炎病例体内病毒Core基因区序列准种差异,为两类病人显著不同的临床表征提供了群体遗传学的解释。

There are significant differences in clinical characteristics between chronic hepatitis B virus infected （CHB） child and adult patients. Viral quasispecies characteristics are associated with its pathogenic properties. For hepatitis B virus （HBV）, its core region is the main immune recognition region for its enriched epitopes. In our study, we discuss the quasispecies characteristics and positive selection within core gene within chronic HBV infected child and adult patients. By analyzing 170 core gene sequences from child CHB patients and 121 core genes sequences from adult CHB patients, quasispecies characteristics were described by sequence complexity, diversity, non-synonymous substitution ratio （dN） and synonymous substitution ratios （dS）. In addition, positive selection sites were also determined by bioinformatics tools. Then, all these parameters were compared between child and adult CHB patient groups. Compared with child patients, adult patients with CHB showed distinct quasispecies characteris- tics within the core region, had a higher sequence complexity and diversity and more positive selection sites, sug- gesting that the adult CHB patients had a higher immune selection pressure on the HBV core gene. Reduced selection pressure on the HBV core gene in hepatitis B e antigen （HBeAg）-positive CHB patients than HBeAg negative CHB patients were observed in both adult and child patient groups. The majority of the screened positive selection sites lay within human leukocyte antigens （HLA）-restricted epitopes. In conclusion, this study analyzed the quasispecies cha- racteristics discrepancy between child and adult patients with CHB, and revealed the possible reason for the dis- tinct clinical characteristics in the perspective of population genetics.