Grimberg Brian T, Udomsangpetch Rachanee, Xainli Jia, McHenry Amy, Panichakul Tasanee, Sattabongkot Jetsumon, Cui Liwang, Bockarie Moses, Chitnis Chetan, Adams John, Zimmerman Peter A, King Christopher L
The Center for Global Health and Diseases, Case Western Reserve University, Cleveland, Ohio, United States of America.
PLoS Med. 2007 Dec;4(12):e337. doi: 10.1371/journal.pmed.0040337.
Plasmodium vivax invasion requires interaction between the human Duffy antigen on the surface of erythrocytes and the P. vivax Duffy binding protein (PvDBP) expressed by the parasite. Given that Duffy-negative individuals are resistant and that Duffy-negative heterozygotes show reduced susceptibility to blood-stage infection, we hypothesized that antibodies directed against region two of P. vivax Duffy binding protein (PvDBPII) would inhibit P. vivax invasion of human erythrocytes.
Using a recombinant region two of the P. vivax Duffy binding protein (rPvDBPII), polyclonal antibodies were generated from immunized rabbits and affinity purified from the pooled sera of 14 P. vivax-exposed Papua New Guineans. It was determined by ELISA and by flow cytometry, respectively, that both rabbit and human antibodies inhibited binding of rPvDBPII to the Duffy antigen N-terminal region and to Duffy-positive human erythrocytes. Additionally, using immunofluorescent microscopy, the antibodies were shown to attach to native PvDBP on the apical end of the P. vivax merozoite. In vitro invasion assays, using blood isolates from individuals in the Mae Sot district of Thailand, showed that addition of rabbit anti-PvDBPII Ab or serum (antibodies against, or serum containing antibodies against, region two of the Plasmodium vivax Duffy binding protein) (1:100) reduced the number of parasite invasions by up to 64%, while pooled PvDBPII antisera from P. vivax-exposed people reduced P. vivax invasion by up to 54%.
These results show, for what we believe to be the first time, that both rabbit and human antibodies directed against PvDBPII reduce invasion efficiency of wild P. vivax isolated from infected patients, and suggest that a PvDBP-based vaccine may reduce human blood-stage P. vivax infection.
间日疟原虫的入侵需要红细胞表面的人类达菲抗原与该寄生虫表达的间日疟原虫达菲结合蛋白（PvDBP）之间相互作用。鉴于达菲阴性个体具有抗性，且达菲阴性杂合子对血液阶段感染的易感性降低，我们推测针对间日疟原虫达菲结合蛋白区域二（PvDBPII）的抗体将抑制间日疟原虫对人类红细胞的入侵。
使用重组的间日疟原虫达菲结合蛋白区域二（rPvDBPII），从免疫兔中产生多克隆抗体，并从14名暴露于间日疟原虫的巴布亚新几内亚人的混合血清中进行亲和纯化。通过酶联免疫吸附测定（ELISA）和流式细胞术分别确定，兔抗体和人抗体均能抑制rPvDBPII与达菲抗原N端区域以及达菲阳性人类红细胞的结合。此外，使用免疫荧光显微镜观察发现，这些抗体可附着于间日疟原虫裂殖子顶端的天然PvDBP上。使用来自泰国湄索地区个体的血液分离株进行的体外入侵试验表明，添加兔抗PvDBPII抗体或血清（针对间日疟原虫达菲结合蛋白区域二的抗体或含有该抗体的血清）（1:100）可使寄生虫入侵数量减少多达64%，而来自暴露于间日疟原虫人群的PvDBPII混合抗血清可使间日疟原虫入侵减少多达54%。
我们认为这些结果首次表明，针对PvDBPII的兔抗体和人抗体均可降低从感染患者分离出的野生间日疟原虫的入侵效率，并提示基于PvDBP的疫苗可能会减少人类血液阶段的间日疟原虫感染。
