Identification and Characterization of B-Cell Epitopes in the DBL4ε Domain of VAR2CSA

Malaria during pregnancy in Plasmodium falciparum endemic regions is a major cause of mortality and severe morbidity. VAR2CSA is the parasite ligand responsible for sequestration of Plasmodium falciparum infected erythrocytes to the receptor chondroitin sulfate A (CSA) in the placenta and is the leading candidate for a placental malaria vaccine. Antibodies induced in rats against the recombinant DBL4ε domain of VAR2CSA inhibit the binding of a number of laboratory and field parasite isolates to CSA. In this study, we used a DBL4ε peptide-array to identify epitopes targeted by DBL4ε-specific antibodies that inhibit CSA-binding of infected erythrocytes. We identified three regions of overlapping peptides which were highly antigenic. One peptide region distinguished itself particularly by showing a clear difference in the binding profile of highly parasite blocking IgG compared to the IgG with low capacity to inhibit parasite adhesion to CSA. This region was further characterized and together these results suggest that even though antibodies against the synthetic peptides which cover this region did not recognize native protein, the results using the mutant domain suggest that this linear epitope might be involved in the induction of inhibitory antibodies induced by the recombinant DBL4ε domain.

在恶性疟原虫(Plasmodium falciparum)流行区域，孕期疟疾是导致死亡与严重发病的主要诱因。VAR2CSA是负责将恶性疟原虫感染红细胞黏附至胎盘内受体硫酸软骨素A(chondroitin sulfate A, CSA)的疟原虫配体，同时也是胎盘疟疾疫苗的首要候选靶点。在大鼠体内由VAR2CSA重组DBL4ε结构域诱导产生的抗体，可抑制多种实验室株与野外分离株的疟原虫感染红细胞与CSA结合。本研究中，我们利用DBL4ε肽阵列，鉴定可抑制感染红细胞与CSA结合的VAR2CSA特异性抗体所靶向的表位。我们共鉴定出3个抗原性极强的重叠肽段区域。其中一个肽段区域表现尤为突出：高寄生虫阻断活性免疫球蛋白G(IgG)的结合谱与抑制疟原虫黏附CSA能力较弱的IgG存在显著差异。对该区域进行进一步表征后，结合本次研究结果表明：尽管针对覆盖该区域的合成肽段的抗体无法识别天然蛋白，但突变结构域实验结果提示，该线性表位可能参与重组DBL4ε结构域诱导的抑制性抗体生成过程。