Institut de Recherche pour le Développement, IRD UMR 216, Mère et Enfant Face aux Infections Tropicales, Paris, France.
PLoS One. 2010 Oct 1;5(10):e13105. doi: 10.1371/journal.pone.0013105.
Protection against pregnancy associated malaria (PAM) is associated with high levels of anti-VAR2CSA antibodies. This protection is obtained by the parity dependent acquisition of anti-VAR2CSA antibodies. Distinct parity-associated molecular signatures have been identified in VAR2CSA domains. These two observations combined point to the importance of identifying VAR2CSA sequence variation, which facilitate parasitic evasion or subversion of host immune response. Highly conserved domains of VAR2CSA such as DBL5ε are likely to contain conserved epitopes, and therefore do constitute attractive targets for vaccine development.
METHODOLOGY/PRINCIPAL FINDINGS: VAR2CSA DBL5ε-domain sequences obtained from cDNA of 40 placental isolates were analysed by a combination of experimental and in silico methods. Competition ELISA assays on two DBL5ε variants, using plasma samples from women from two different areas and specific mice hyperimmune plasma, indicated that DBL5ε possess conserved and cross-reactive B cell epitopes. Peptide ELISA identified conserved areas that are recognised by naturally acquired antibodies. Specific antibodies against these peptides labelled the native proteins on the surface of placental parasites. Despite high DBL5ε sequence homology among parasite isolates, sequence analyses identified motifs in DBL5ε that discriminate parasites according to donor's parity. Moreover, recombinant proteins of two VAR2CSA DBL5ε variants displayed diverse recognition patterns by plasma from malaria-exposed women, and diverse proteoglycan binding abilities.
CONCLUSIONS/SIGNIFICANCE: This study provides insights into conserved and exposed B cell epitopes in DBL5ε that might be a focus for cross reactivity. The importance of sequence variation in VAR2CSA as a critical challenge for vaccine development is highlighted. VAR2CSA conformation seems to be essential to its functionality. Therefore, identification of sequence variation sites in distinct locations within VAR2CSA, affecting antigenicity and/or binding properties, is critical to the effort of developing an efficient VAR2CSA-based vaccine. Motifs associated with parasite segregation according to parity constitute one such site.
妊娠相关疟疾（PAM）的保护与高水平的抗 VAR2CSA 抗体有关。这种保护是通过获得抗 VAR2CSA 抗体的产次依赖性获得的。在 VAR2CSA 结构域中已经确定了不同的与产次相关的分子特征。这两个观察结果结合起来表明，确定 VAR2CSA 序列变异的重要性，这有助于寄生虫逃避或颠覆宿主的免疫反应。VAR2CSA 的高度保守结构域，如 DBL5ε，可能含有保守的表位，因此确实构成了疫苗开发的有吸引力的目标。
方法/主要发现：通过实验和计算方法相结合，对从 40 个胎盘分离物的 cDNA 中获得的 VAR2CSA DBL5ε 结构域序列进行了分析。使用来自两个不同地区的妇女的血浆样本和特定的小鼠高免疫血浆，对两种 DBL5ε 变体进行竞争 ELISA 测定，表明 DBL5ε 具有保守和交叉反应的 B 细胞表位。肽 ELISA 确定了被天然获得的抗体识别的保守区域。针对这些肽的特异性抗体标记了胎盘寄生虫表面的天然蛋白。尽管寄生虫分离物之间的 DBL5ε 序列同源性很高，但序列分析确定了 DBL5ε 中的基序，可以根据供体的产次来区分寄生虫。此外，两种 VAR2CSA DBL5ε 变体的重组蛋白显示出对来自疟疾暴露妇女的血浆的不同识别模式，以及不同的蛋白聚糖结合能力。
结论/意义：本研究提供了对 DBL5ε 中保守和暴露的 B 细胞表位的深入了解，这些表位可能是交叉反应的焦点。VAR2CSA 中的序列变异作为疫苗开发的关键挑战的重要性得到了强调。VAR2CSA 的构象对其功能至关重要。因此，确定 VAR2CSA 内不同位置的序列变异位点，影响抗原性和/或结合特性，对于开发有效的基于 VAR2CSA 的疫苗至关重要。与产次相关的寄生虫分离的基序就是这样一个位点。
