乙肝病毒核心蛋白病毒样颗粒表面抗原密度对抗体应答水平的影响

Correlation between antigen density on the surface of hepatitis B virus core protein virus-like particles and their antibody response

摘要:

[目的]为了探究乙肝病毒核心蛋白（Hepatitis B virus core protein，HBc）病毒样颗粒（Virus-like particles，VLPs）表面抗原密度对免疫后抗体应答水平的影响，制备了不同抗原密度的HBc VLPs疫苗，并检测了其在小鼠体内的抗体应答水平。[方法]首先制备了N端带有3个甘氨酸的人巨细胞病毒重组抗原域AD-4作为模式抗原，接着通过Sortase A的介导将AD-4连接到HBc VLPs表面上。将系列浓度梯度AD-4抗原在Sortase A介导下分别与相同浓度的HBc VLPs发生反应，制备不同抗原密度的HBc-AD-4 VLPs。将其分别免疫6-8周龄BALB/c小鼠3次，每次免疫间隔2 w，间接ELISA法检测被免疫小鼠血清的抗体应答水平。[结果]结果表明，当HBc VLPs表面抗原密度为44.4%时，即HBc反应浓度：AD-4反应浓度为1：0.5时，不足以引起高滴度的抗体产生；当HBc VLPs表面抗原密度为64.2%时，即HBc反应浓度：AD-4反应浓度为1：1时，HBc-AD-4 VLPs诱导的AD-4特异性抗体滴度与100%抗原密度的HBc-AD-4 VLPs所引起的抗体滴度相当；当HBc VLPs表面抗原密度大于64.2%时，引起的抗体应答水平不因抗原密度增加而进一步增强。[结论]发现了HBc VLPs表面抗原密度与免疫后抗体滴度呈正相关，然而免疫64.2%抗原密度的HBc VLPs所产生的抗体滴度可达峰值，抗原密度进一步增加，抗体应答水平不会进一步加强。

Abstract:

[Objective] To better understand how antigen density on the surface of hepatitis B virus core protein (HBc) virus-like particles (VLPs) affects their antibody response, we generated HBc VLPs with different antigen densities, and tested their antibody response in mice.[Methods] First, we prepared the recombinant antigen domain 4 (AD-4) of human cytomegalovirus (HCMV) as a model antigen, which contains three glycine molecules at its N-terminus, for Sortase A-mediated ligation onto the HBc VLPs. Displaying different densities of antigens onto the surface of VLPs was achieved by using a serial diluted recombinant AD-4 in ligation reactions. After that, HBc-AD-4 VLPs with different antigen densities were applied to 6-8 weeks old BALB/c mice. Each group was inoculated three times at 2-week intervals and the AD-4-specific IgG was detected by indirect ELISA.[Results] When the reaction concentration ratio between HBc and AD-4 is 1:0.5, which HBc surface antigen density is 44.4%, VLPs couldn't induce a high antibody titer. When the reaction concentration ratio between HBc and AD-4 is 1:1, which HBc surface antigen density is 64.2%, VLPs could induce similar highest humoral immune response compared to 100% antigen density HBc VLPs. When HBc surface antigen density is greater than 64.2%, no further enhancement of antibody response was observed by further increasing the antigen density.[Conclusion] In conclusion, we found that antigen density on HBc VLPs is positively correlated with the antibody response. However, it reaches a peak at 64% antigen density, and no further enhancement of antibody response was observed by further increasing the antigen density.