Institut Pasteur, Unité d'Immunologie Moléculaire des Parasites, Paris, France.
PLoS One. 2011 Jan 27;6(1):e16544. doi: 10.1371/journal.pone.0016544.
The clonally variant Plasmodium falciparum PfEMP1 adhesin is a virulence factor and a prime target of humoral immunity. It is encoded by a repertoire of functionally differentiated var genes, which display architectural diversity and allelic polymorphism. Their serological relationship is key to understanding the evolutionary constraints on this gene family and rational vaccine design. Here, we investigated the Palo Alto/VarO and IT4/R29 and 3D7/PF13_003 parasites lines. VarO and R29 form rosettes with uninfected erythrocytes, a phenotype associated with severe malaria. They express an allelic Cys2/group A NTS-DBL1α(1) PfEMP1 domain implicated in rosetting, whose 3D7 ortholog is encoded by PF13_0003. Using these three recombinant NTS-DBL1α(1) domains, we elicited antibodies in mice that were used to develop monovariant cultures by panning selection. The 3D7/PF13_0003 parasites formed rosettes, revealing a correlation between sequence identity and virulence phenotype. The antibodies cross-reacted with the allelic domains in ELISA but only minimally with the Cys4/group B/C PFL1955w NTS-DBL1α. By contrast, they were variant-specific in surface seroreactivity of the monovariant-infected red cells by FACS analysis and in rosette-disruption assays. Thus, while ELISA can differentiate serogroups, surface reactivity assays define the more restrictive serotypes. Irrespective of cumulated exposure to infection, antibodies acquired by humans living in a malaria-endemic area also displayed a variant-specific surface reactivity. Although seroprevalence exceeded 90% for each rosetting line, the kinetics of acquisition of surface-reactive antibodies differed in the younger age groups. These data indicate that humans acquire an antibody repertoire to non-overlapping serotypes within a serogroup, consistent with an antibody-driven diversification pressure at the population level. In addition, the data provide important information for vaccine design, as production of a vaccine targeting rosetting PfEMP1 adhesins will require engineering to induce variant-transcending responses or combining multiple serotypes to elicit a broad spectrum of immunity.
无性变异型恶性疟原虫 PfEMP1 黏附素是一种毒力因子和体液免疫的主要靶标。它由一系列功能分化的 var 基因编码，这些基因显示出结构多样性和等位基因多态性。它们的血清学关系是理解该基因家族进化限制和合理疫苗设计的关键。在这里，我们研究了 Palo Alto/VarO 和 IT4/R29 和 3D7/PF13_003 寄生虫系。VarO 和 R29 与未感染的红细胞形成玫瑰花结，这是一种与严重疟疾相关的表型。它们表达一种与玫瑰花结相关的等位基因 Cys2/组 A NTS-DBL1α(1)PfEMP1 结构域，其 3D7 同源物由 PF13_0003 编码。使用这三个重组 NTS-DBL1α(1)结构域，我们在小鼠中引发了抗体，并用淘选选择法开发了单变体培养物。3D7/PF13_0003 寄生虫形成玫瑰花结，揭示了序列同一性与毒力表型之间的相关性。抗体在 ELISA 中与等位基因结构域发生交叉反应，但与 Cys4/组 B/C PFL1955w NTS-DBL1α 反应极小。相比之下，它们在单变体感染红细胞的表面血清反应性的 FACS 分析和玫瑰花结破坏试验中具有变体特异性。因此，虽然 ELISA 可以区分血清群，但表面反应性测定定义了更具限制性的血清型。无论感染的累积暴露如何，生活在疟疾流行地区的人获得的抗体也表现出变体特异性的表面反应性。虽然每条玫瑰花结线的血清阳性率都超过 90%，但年轻年龄组获得表面反应性抗体的动力学不同。这些数据表明，人类在一个血清群内获得了针对非重叠血清型的抗体 repertoire，这与人群水平上的抗体驱动的多样化压力一致。此外，这些数据为疫苗设计提供了重要信息，因为针对玫瑰花结 PfEMP1 黏附素的疫苗的生产将需要工程改造以诱导变体跨越反应，或结合多种血清型以引发广谱免疫。
