Means R E, Matthews T, Hoxie J A, Malim M H, Kodama T, Desrosiers R C
Department of Microbiology and Molecular Genetics, New England Regional Primate Research Center, Harvard Medical School, Southborough, Massachusetts 01772-9102, USA.
J Virol. 2001 Apr;75(8):3903-15. doi: 10.1128/JVI.75.8.3903-3915.2001.
To better define the effects of sequence variation and tropism on the ability of the simian immunodeficiency virus SIVmac V3 loop to act as a target of antibody-mediated neutralization, a series of experiments were performed. Three SIV strains, SIVmac239, SIVmac316, and SIVmac155/T3, each with defined differences in env sequence and tropism, were used to construct a panel of viruses chimeric for a portion of envelope that includes the V2 and V3 regions. Peptides with sequences corresponding to the V3 loops of the parental viruses were used to immunize rabbits. The polyclonal rabbit antibodies and plasma from SIVmac239-infected animals were then used to assess the neutralization sensitivity of the parental and chimeric viruses. One of the parental viruses, SIVmac316, which is able to replicate to high titer in alveolar macrophages and can infect cells in a CD4-independent fashion, was highly sensitive to neutralization by plasma from SIVmac-infected rhesus macaques, with average 50% neutralization titers of 1:20,480; this same strain was also sensitive to neutralization by the anti-V3 loop peptide sera. Other parental and chimeric viruses were less sensitive to neutralization with this same panel of antibodies, but as seen with SIVmac316, those viruses that were able to productively replicate in alveolar macrophages were more sensitive to antibody-mediated neutralization. To further define the amino acids involved in increased sensitivity to neutralization, a panel of viruses was constructed by changing envelope residues in SIVmac316 to the corresponding SIVmac239 amino acids. The increased neutralization sensitivity observed for SIVmac316 was mapped principally to three amino acid changes spread throughout gp120. In addition, the increased sensitivity to neutralization by V3-directed antibodies correlated with the ability of the various viruses to replicate to high levels in alveolar macrophage cultures and a CD4-negative cell line, BC7/CCR5. These results demonstrate that the V3 loop of SIVmac Env can act as an efficient target of neutralizing antibodies in a fashion that is highly dependent on sequence context. In addition, these studies suggest a correlation between decreased dependence on CD4 and increased sensitivity to antibody-mediated neutralization.
为了更好地确定序列变异和嗜性对猿猴免疫缺陷病毒SIVmac V3环作为抗体介导中和作用靶点能力的影响，进行了一系列实验。使用三种SIV毒株，即SIVmac239、SIVmac316和SIVmac155/T3，它们在env序列和嗜性方面各有明确差异，构建了一组在包括V2和V3区域的包膜部分具有嵌合性的病毒。使用与亲本病毒V3环序列对应的肽免疫兔子。然后使用来自SIVmac239感染动物的多克隆兔抗体和血浆来评估亲本病毒和嵌合病毒的中和敏感性。亲本病毒之一SIVmac316能够在肺泡巨噬细胞中高滴度复制，并且能够以不依赖CD4的方式感染细胞，它对来自感染SIVmac的恒河猴的血浆中和高度敏感，平均50%中和滴度为1:20,480；同一毒株对抗V3环肽血清的中和也敏感。其他亲本病毒和嵌合病毒对同一组抗体的中和不太敏感，但正如在SIVmac316中所见，那些能够在肺泡巨噬细胞中有效复制的病毒对抗体介导的中和更敏感。为了进一步确定参与中和敏感性增加的氨基酸，通过将SIVmac316中的包膜残基改变为相应的SIVmac239氨基酸构建了一组病毒。观察到的SIVmac316中和敏感性增加主要定位到整个gp120中的三个氨基酸变化。此外，对V3导向抗体中和敏感性的增加与各种病毒在肺泡巨噬细胞培养物和CD4阴性细胞系BC7/CCR5中高水平复制的能力相关。这些结果表明，SIVmac Env的V3环可以以高度依赖序列背景的方式作为中和抗体的有效靶点。此外，这些研究表明对CD4的依赖性降低与对抗体介导中和的敏感性增加之间存在相关性。
