Jiang G, Daubenberger C, Huber W, Matile H, Tanner M, Pluschke G
Swiss Tropical Institute, Basel.
Acta Trop. 2000 Jan 5;74(1):51-61. doi: 10.1016/s0001-706x(99)00045-5.
Merozoite surface protein 1 of Plasmodium falciparum (PfMSP-1) is regarded as a key candidate antigen for malaria vaccine development. It exhibits significant antigenic polymorphism and has been divided into 17 building blocks based on the analysis of sequence diversity. Differences in the antigenic composition of PfMSP-1 in local P. falciparum populations may result in differences in the efficacy of vaccines, which contain sequences of particular allelic variant(s) of PfMSP-1. To contribute to the required knowledge of genetic diversity of malaria parasites in geographically diverse regions, we have used the polymerase chain reaction (PCR) to analyze the sequence diversity of blocks 1-4 of PfMSP-1 in disease isolates from the Kilombero District in Tanzania. In the semi-conserved block 1, in which dimorphic amino acid variances have been described at three positions, we found three of the five previously described combinations of these three pairs of amino acids. In addition one combination was found, which has not been reported before in parasite isolates from different locations worldwide. Of the two sequence variants, which were dominating, one (S44-Q47-V52) corresponded to the 83.1 sequence incorporated into the SPf66 malaria peptide vaccine, while the other one (G44-H47-I52) differed from the previous in all three dimorphic amino acids. The partial protection observed in a phase III SPf66 trial conducted in the Kilombero District in children aged 1-5, thus does not seem to be associated with a clear dominance of favourable variants of block 1 of PfMSP-1 in this area. All three different principle types of block 2, the major polymorphic region of PfMSP-1, were found in the Tanzanian isolates. Most of the sequences contained K1-type tripeptide repeats, but clones with MAD20-type repeats or no repetitive sequence (RO33-type block 2) were also present. K1- and MAD20-type tripeptide repeat motifs were never mixed within one parasite clone. In one sequence a hexapeptide repeat was found at the end of block 2, which has not been reported before. Dimorphism in 13 of the 17 previously described variable positions of the semi-conserved block 3 and three of four recombination types of block 4 (K/K, M/K and M/M) were found among the Tanzanian isolates. Apart from previously described dimorphic amino acid positions, polymorphism was rare in the non-repeated building blocks. Selection and spreading of parasite variants, which contain amino acid exchanges at other than the dimorphic positions thus, is not a common event. Parasite isolates frequently harboured more than one PfMSP-1 allele. Three of the four heterogeneous isolates analysed contained two different general types of sequences. One isolate contained at least four distinct clones, demonstrating the high endemicity of malaria in the Kilombero District, which is a well-established site for malaria vaccine field trials.
恶性疟原虫裂殖子表面蛋白1（PfMSP-1）被视为疟疾疫苗研发的关键候选抗原。它表现出显著的抗原多态性，基于序列多样性分析已被分为17个结构域。当地恶性疟原虫群体中PfMSP-1抗原组成的差异可能导致含有PfMSP-1特定等位基因变体序列的疫苗效力不同。为了增进对不同地理区域疟原虫遗传多样性的必要了解，我们利用聚合酶链反应（PCR）分析了来自坦桑尼亚基洛梅罗区疾病分离株中PfMSP-1结构域1-4的序列多样性。在半保守的结构域1中，已在三个位置描述了二态氨基酸变异，我们发现了这三对氨基酸的五种先前描述组合中的三种。此外还发现了一种组合，此前在全球不同地点的寄生虫分离株中尚未有过报道。在占主导地位的两个序列变体中，一个（S44-Q47-V52）对应于纳入SPf66疟疾肽疫苗的83.1序列，而另一个（G44-H47-I52）在所有三个二态氨基酸上均与前者不同。在基洛梅罗区对1-5岁儿童进行的III期SPf66试验中观察到的部分保护作用，因此似乎与该地区PfMSP-1结构域1有利变体的明显优势无关。PfMSP-1的主要多态性区域结构域2的所有三种不同主要类型在坦桑尼亚分离株中均有发现。大多数序列包含K1型三肽重复序列，但也存在具有MAD20型重复序列或无重复序列（RO33型结构域2）的克隆。K1型和MAD20型三肽重复基序从未在一个寄生虫克隆中混合出现。在一个序列中，在结构域2末端发现了一个六肽重复序列，此前尚未有过报道。在坦桑尼亚分离株中发现了半保守结构域3先前描述的17个可变位置中的13个位置存在二态性，以及结构域4的四种重组类型中的三种（K/K、M/K和M/M）。除了先前描述的二态氨基酸位置外，在非重复结构域中多态性很少见。因此，在二态位置以外含有氨基酸交换的寄生虫变体的选择和传播并非常见事件。寄生虫分离株经常携带不止一个PfMSP-1等位基因。分析的四个异质分离株中有三个包含两种不同的一般序列类型。一个分离株包含至少四个不同的克隆，这表明基洛梅罗区疟疾的高流行率，该地区是疟疾疫苗现场试验的成熟地点。
