Baruch Dror I, Gamain Benoit, Miller Louis H
Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Infect Immun. 2003 Aug;71(8):4536-43. doi: 10.1128/IAI.71.8.4536-4543.2003.
The variant surface antigens of Plasmodium falciparum are an important component of naturally acquired immunity and an important vaccine target. However, these proteins appear to elicit primarily variant-specific antibodies. We tested if naked DNA immunization can elicit more cross-reactive antibody responses and allow simultaneous immunization with several variant constructs. Mice immunized with plasmid DNA expressing variant cysteine-rich interdomain region 1 (CIDR1) domains of the P. falciparum erythrocyte membrane protein 1 (PfEMP1) developed antibodies that were reactive to the corresponding PfEMP1s as measured by an enzyme-linked immunosorbent assay, flow cytometry, and agglutination of parasitized erythrocytes (PEs). We observed some cross-reactive immune responses; for example, sera from mice immunized with one domain agglutinated PEs of various lines and recognized heterologous domains expressed on the surface of Chinese hamster ovary (CHO) cells. We found no significant antigenic competition when animals were immunized with a mixture of plasmids or immunized sequentially with individual constructs. Moreover, mixed or sequential immunizations resulted in greater cross-reactive agglutination responses than immunization with a single domain. Recombinant protein (Sc y179) immunization after priming with DNA (prime-boost regimen) increased antibody titers to the homologous domain substantially but seemed to diminish the cross-reactive responses somewhat. The titer of agglutinating antibodies was previously shown to correlate with protection. Surprisingly, the agglutination titers of sera from DNA immunization were high, similar to those of pooled human hyperimmune sera. These sera also appeared to give limited low-titer variant transcending agglutination. Thus, DNA immunization appears to be a very useful tool for developing variant antigen vaccines.
恶性疟原虫的可变表面抗原是自然获得性免疫的重要组成部分，也是重要的疫苗靶点。然而，这些蛋白质似乎主要引发变体特异性抗体。我们测试了裸DNA免疫是否能引发更多的交叉反应性抗体反应，并允许同时用几种变体构建体进行免疫。用表达恶性疟原虫红细胞膜蛋白1（PfEMP1）的富含半胱氨酸的结构域间区域1（CIDR1）变体的质粒DNA免疫小鼠后，通过酶联免疫吸附测定、流式细胞术和对寄生红细胞（PEs）的凝集作用检测到，小鼠产生了对相应PfEMP1有反应的抗体。我们观察到了一些交叉反应性免疫反应；例如，用一个结构域免疫的小鼠血清能凝集各种品系的PEs，并识别在中国仓鼠卵巢（CHO）细胞表面表达的异源结构域。当用质粒混合物免疫动物或依次用单个构建体免疫时，我们没有发现明显的抗原竞争。此外，混合或顺序免疫比用单个结构域免疫产生更大的交叉反应性凝集反应。用DNA进行初免后再用重组蛋白（Sc y179）免疫（初免-加强方案），可显著提高同源结构域的抗体滴度，但似乎在一定程度上降低了交叉反应性反应。先前已证明凝集抗体的滴度与保护作用相关。令人惊讶的是，DNA免疫血清的凝集滴度很高，与汇集的人超免疫血清相似。这些血清似乎也产生有限的低滴度变体超越凝集反应。因此，DNA免疫似乎是开发变体抗原疫苗的一种非常有用的工具。
