C3d增强基因免疫诱导的小鼠抗乙型肝炎病毒特异性免疫应答

目的探讨C3d对乙型肝炎病毒(HBV)基因免疫诱导的特异性免疫应答的调节作用,为增强HBV基因疫苗免疫效果寻求新途径。方法将HBVpreS2/S编码基因分别插入真核表达载体TR421和含有三拷贝C3d编码基因的TR421C3d3质粒,构建重组质粒TR421preS2/S和TR421preS2/SC3d3。采用肌肉注射法对BALB/c小鼠实施基因免疫,以空质粒TR421为对照,定期采集血清。ELISA法检测免疫小鼠血清特异性抗HBsIgG,3HTdR掺入法检测其特异性淋巴细胞增殖活性。结果TR421preS2/SC3d3重组质粒免疫组诱导的特异性抗HBsIgG水平明显高于TR421preS2/S重组质粒免疫组(P<005),而且TR421preS2/SC3d3重组质粒基因免疫诱导的特异性淋巴细胞增殖活性也显著高于TR421preS2/S重组质粒组(P<005)。结论C3d可增强基因免疫诱导的HBV特异性体液和细胞免疫应答,为提高HBV基因疫苗的免疫效果提供了新的途径。

C3d enhances the immune response against HBV-preS2/S following gene immunization in mice

OBJECTIVE: To investigate whether C3d can enhance the immune response to HBV-preS2/S induced by direct injecting naked plasmid containing three copies of C3d and HBV-preS2/S in fusion form. METHODS: HBV-preS2/S coding sequence was introduced into the eukaryotic expression vectors TR421 and TR421-C3d3 containing 3 copies of C3d respectively. PCR was used to identify the direction of insertion, DNA sequencing analysis was used on the positive clones. The recombinant plasmids TR421-preS2/S and TR421-preS2/S-C3d3 were transfected into the human breast cancer cells of the line 4T1 as a transient expression system. Semi-quantitative RT-PCR was used to detect the expression of HBV-preS2/S protein. TR421-preS2/S and TR421-preS2/S-C3d3 were injected into the anterior tibial muscles of female BALB/c mice, 6 in each group, 3 times at an interval of 3 weeks. Six mice were injected with blank plasmid TR421 as controls. The total blood was collected from the mice. ELISA was used to detect the level of specific anti-HBs antibody. The splenocytes of the immunized mice were collected and stimulated with HbsAg protein and then harvested to analyze the specific lympho-proliferative response by (3)H-thymidine incorporation assay. CR2 positive Raji cells were added with plasmid transfected and mouse anti-HBs serum. Flow cytometry was used to detect the integration of preS2/S-C3d3 fusion protein. RESULTS: The 4T1 cells transfected with TR421-preS2/S and TR421-preS2/S-C3d3 effectively expressed HBV-preS2/S, with the expression level of TR421-preS2/S-C3d3 lower by 15.25% than that of TR421-preS2/S. Twelve weeks after immunization, the specific anti-HBs-IgG level (A(490nm)) was 0.81 +/- 0.09 in the TR421-preS2/S primed mice, significantly higher than that in the blank plasmid injected mice (0.49 +/- 0.02, P < 0.05); and the specific anti-HBs-IgG level (A(490nm)) was 1.24 +/- 0.29 in the TR421-preS2/S-C3d3 immunized mice, significantly higher than that of the TR421-preS2/S primed mice (P < 0.001). The lympho-proliferative response of the TR421-preS2/S primed mice was significantly stronger than that of the blank plasmid injected mice (P < 0.05) and the lympho-proliferative response of the TR421-preS2/S-C3d3 primed mice was significantly stronger than that of the TR421-preS2/S primed mice (P < 0.05). Surface binding of protein could be detected only in the TR421-preS2/S-C3d3 transfected supernatant. About 43.19% of the CR2 positive Raji cells integrated C3d fusion protein. TR421-preS2/S transfected supernatant and negative control did not show obvious integration. CONCLUSION: C3d enhances the humoral and cell-mediated immune responses against HBV induced by gene immunization.