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目的 :研究丙型肝炎病毒 (HCV)螺旋酶N端HLA A2限制性细胞毒性T细胞 (CTL)表位的变异及其增殖反应。方法 :对两例慢性HCV感染者随访 7年 ,用第 1年和第 5年的外周血提取病毒RNA ,再以RT PCR扩增HCV螺旋酶N端基因 ,并亚克隆及测序。根据测序结果 ,合成CTL抗原表位肽段。用血清学方法进行HLA分型。从感染者第 7年外周血中分离淋巴细胞 ,检测CTL对抗原肽的增殖反应。结果 :在具有HLA A2表型的感染者中 ,第 1年病毒抗原表位的起始氨基酸均存在琥珀突变 ,5年后该突变消失。在无HLA A2表型的感染者中 ,其感染后 5年病毒抗原表位肽段既无共有序列的变异 ,也无琥珀突变。HCV感染后 7年 ,两例感染者的淋巴细胞对该抗原表位肽段均无增殖反应。结论 :螺旋酶N端抗原表位出现的无义突变 ,可能与病毒的免疫逃避有关。在慢性感染的后期 ,病毒感染者对螺旋酶N端的CTL表位肽不出现免疫应答。
Objective: To investigate the variation of the epitope of HLA A2-restricted cytotoxic T lymphocyte (CTL) on the N-terminus of hepatitis C virus (HCV) helicase and its proliferative response. Methods: Two patients with chronic HCV infection were followed up for 7 years. The viral RNA was extracted from the peripheral blood of the first year and the fifth year. The N-terminal gene of HCV helicase was amplified by RT PCR and subcloned and sequenced. According to the sequencing results, CTL epitope peptides were synthesized. HLA typing using serological methods. Lymphocytes were isolated from the 7th year of infection and the proliferative response of CTL to antigenic peptides was detected. Results: In the patients with HLA A2 phenotype, there was an amber mutation in the starting amino acid of the first year of virus epitope, and disappeared after 5 years. In those with no HLA A2 phenotype, the virus epitopes at 5 years after infection had neither a consensus sequence nor an amber mutation. Seven years after HCV infection, lymphocytes from two infected patients showed no proliferative response to the epitope peptides. Conclusion: The nonsense mutation in the N-terminal epitope of helicase may be related to the immune evasion of the virus. In the late stages of chronic infection, the virus-infected individuals do not develop an immune response to the helicase N-terminal CTL epitope peptide.