Hoffmann E H, da Silveira L A, Tonhosolo R, Pereira F J, Ribeiro W L, Tonon A P, Kawamoto F, Ferreira M U
Department of Parasitology, Institute for Biomedical Sciences, University of São Paulo, São Paulo, Brazil.
Ann Trop Med Parasitol. 2001 Mar;95(2):117-32. doi: 10.1080/00034980120045833.
The polymorphic merozoite surface protein-2 (MSP-2) of Plasmodium falciparum is a major malaria-vaccine candidate. In the present study, PCR and hybridization with allelic-specific probes were used to type the Msp-2 gene from isolates from hypo-endemic Brazil (N = 113), meso-endemic Vietnam (N = 208) and holo-endemic Tanzania (N = 67). The typing methods were designed to group isolates into the dimorphic allelic families FC27 and IC1 and to detect possible between-family recombination events. The analysis was complemented by a comparison of 156 Msp-2 sequences from the GenBank database with 12 additional sequences obtained during the present study. Statistically significant differences were detected in pair-wise comparisons of the distribution of Msp-2 allelic types in Brazil and Vietnam, and in Brazil and Tanzania, but not in Vietnam and Tanzania. The extent of allelic diversity in the Msp-2 gene, as estimated by the total number of different alleles found in a given parasite population and the mean multiplicity of infections, clearly paralleled the levels of malaria endemicity in the study areas. However, no correlation between age and multiplicity of infections was found in the subjects. The patterns of Msp-2 diversity in Brazil appeared to be temporally stable, since no significant difference was observed in the distribution of Msp-2 allelic types among isolates collected, 10--13 years apart, in the same area of Rondônia. Despite the extensive sequence diversity found in Msp-2 alleles, especially in the central repetitive region of the molecule, several instances of identical or nearly identical alleles were found among isolates from different countries and regions, possibly as a result of extensive homoplasy. No recombinant allele was detected by molecular typing in any of the study sites, and the GenBank database included only 12 recombinant sequences (representing 7% of all reported Msp-2 sequences), all of them with an IC1-type 5' end and an FC27-type 3' end. A single, putative, crossover site was characterised for all recombinant alleles. Most of the allelic diversity observed was therefore attributable to variation in the repetitive region of the gene, instead of recombination between alleles of dimorphic families (as commonly found, for example, in the Msp-1 gene). The implications of these findings for studies on the genetic and antigenic diversity of malarial parasites are discussed.
恶性疟原虫的多态性裂殖子表面蛋白-2（MSP-2）是一种主要的疟疾疫苗候选物。在本研究中，采用聚合酶链反应（PCR）和等位基因特异性探针杂交技术，对来自低流行区巴西（N = 113）、中流行区越南（N = 208）和高流行区坦桑尼亚（N = 67）的疟原虫分离株的Msp-2基因进行分型。分型方法旨在将分离株分为双态等位基因家族FC27和IC1，并检测可能的家族间重组事件。通过将来自GenBank数据库的156条Msp-2序列与本研究中获得的另外12条序列进行比较，对分析进行了补充。在巴西和越南、巴西和坦桑尼亚的Msp-2等位基因类型分布的两两比较中检测到统计学上的显著差异，但在越南和坦桑尼亚之间未检测到。根据给定寄生虫群体中发现的不同等位基因总数和平均感染复数估计的Msp-2基因等位基因多样性程度，显然与研究地区的疟疾流行程度平行。然而，在研究对象中未发现年龄与感染复数之间的相关性。巴西Msp-2多样性模式似乎在时间上是稳定的，因为在朗多尼亚同一地区相隔10 - 13年收集的分离株中，Msp-2等位基因类型分布未观察到显著差异。尽管在Msp-2等位基因中发现了广泛的序列多样性，特别是在分子的中央重复区域，但在来自不同国家和地区的分离株中发现了几例相同或几乎相同的等位基因，这可能是广泛的平行进化的结果。在任何研究地点通过分子分型均未检测到重组等位基因，GenBank数据库仅包含12条重组序列（占所有报道的Msp-2序列的7%），所有这些序列均具有IC1型5'端和FC27型3'端。对所有重组等位基因确定了一个单一的推定交叉位点。因此，观察到的大多数等位基因多样性归因于基因重复区域的变异，而不是双态家族等位基因之间的重组（例如，在Msp-1基因中常见）。讨论了这些发现对疟原虫遗传和抗原多样性研究的意义。
