Center for AIDS Research, Kumamoto University Kumamoto, Japan.
Front Microbiol. 2013 May 14;4:117. doi: 10.3389/fmicb.2013.00117. eCollection 2013.
The role of antibodies in protecting the host from human immunodeficiency virus type 1 (HIV-1) infection is of considerable interest, particularly because the RV144 trial results suggest that antibodies contribute to protection. Although infection of non-human primates with simian immunodeficiency virus (SIV) is commonly used as an animal model of HIV-1 infection, the viral epitopes that elicit potent and broad neutralizing antibodies to SIV have not been identified. We isolated a monoclonal antibody (MAb) B404 that potently and broadly neutralizes various SIV strains. B404 targets a conformational epitope comprising the V3 and V4 loops of Env that intensely exposed when Env binds CD4. B404-resistant variants were obtained by passaging viruses in the presence of increasing concentration of B404 in PM1/CCR5 cells. Genetic analysis revealed that the Q733stop mutation, which truncates the cytoplasmic tail of gp41, was the first major substitution in Env during passage. The maximal inhibition by B404 and other MAbs were significantly decreased against a recombinant virus with a gp41 truncation compared with the parental SIVmac316. This indicates that the gp41 truncation was associated with resistance to antibody-mediated neutralization. The infectivities of the recombinant virus with the gp41 truncation were 7,900-, 1,000-, and 140-fold higher than those of SIVmac316 in PM1, PM1/CCR5, and TZM-bl cells, respectively. Immunoblotting analysis revealed that the gp41 truncation enhanced the incorporation of Env into virions. The effect of the gp41 truncation on infectivity was not obvious in the HSC-F macaque cell line, although the resistance of viruses harboring the gp41 truncation to neutralization was maintained. These results suggest that viruses with a truncated gp41 cytoplasmic tail were selected by increased infectivity in human cells and by acquiring resistance to neutralizing antibody.
抗体在保护宿主免受人类免疫缺陷病毒 1 型（HIV-1）感染中的作用引起了相当大的关注，特别是因为 RV144 试验结果表明抗体有助于保护。尽管用猴免疫缺陷病毒（SIV）感染非人类灵长类动物通常被用作 HIV-1 感染的动物模型，但尚未鉴定出能诱导针对 SIV 的强效和广泛中和抗体的病毒表位。我们分离出一种单克隆抗体（MAb）B404，该抗体能强烈且广泛地中和各种 SIV 株。B404 靶向一个构象表位，该表位包含Env 的 V3 和 V4 环，当 Env 结合 CD4 时，该表位强烈暴露。通过在 PM1/CCR5 细胞中用逐渐增加的 B404 浓度传代病毒，获得了 B404 抗性变体。遗传分析显示，在传代过程中，Env 中的第一个主要取代是 Q733stop 突变，该突变截断了 gp41 的细胞质尾巴。与亲本 SIVmac316 相比，B404 和其他 MAb 的最大抑制作用对具有 gp41 截断的重组病毒明显降低。这表明 gp41 截断与抗体介导的中和的抗性有关。与 SIVmac316 相比，具有 gp41 截断的重组病毒在 PM1、PM1/CCR5 和 TZM-bl 细胞中的感染性分别高 7900、1000 和 140 倍。免疫印迹分析显示，gp41 截断增强了 Env 掺入病毒粒子。尽管携带 gp41 截断的病毒对中和的抗性得以维持，但在 HSC-F 食蟹猴细胞系中，gp41 截断对感染性的影响并不明显。这些结果表明，具有截断的 gp41 细胞质尾巴的病毒通过在人细胞中增加感染性和获得对中和抗体的抗性而被选择。
