Yaa Reuben M, Kimenyi Kelvin M, Palasciano Henry Antonio, Obiero George, Ochola-Oyier L Isabella
Department of Biochemistry, University of Nairobi, Nairobi, Kenya.
UK Dementia Research Institute, Imperial College London, London, UK.
Malar J. 2025 Apr 28;24(1):136. doi: 10.1186/s12936-025-05378-7.
Individuals experiencing recurrent malaria infections encounter a variety of alleles with each new infection. This ongoing allelic diversity influences the development of naturally acquired immunity and it can inform vaccine efficacy. To investigate the diversity and infection variability, Plasmodium falciparum merozoite surface protein 1 (PfMSP1), a crucial protein for parasite invasion and immune response, was assessed in parasites isolated from children in the Junju cohort, Kilifi County, who experienced at least 10 febrile malaria episodes over a span of 5 years.
Pfmsp1 C-terminal region (Pfmsp1) was genotyped using PCR followed by capillary sequencing in blood samples collected from the children. Sequenced reads were trimmed and aligned to the P. falciparum 3D7 reference genome. Single nucleotide polymorphisms in the Pfmsp1 region were identified from the alignment and grouped to distinct microhaplotypes whose changing frequency over time were examined across the multiple infection episodes. In addition, the variability of infections in the population was assessed using nucleotide and haplotype diversity indices.
A total of eleven microhaplotypes were observed across all malaria episodes. There were 3 prevalent microhaplotypes, E-KSNG-L, Q-KSNG-L, and Q-KSNG-F in the population. Conversely, microhaplotypes such as Q-KNNG-L, E-KSSR-L, E-KNNG-L, E-KSSG-L, E-TSSR-L (3D7), Q-TSSR-L, E-TSSG-L, and E-KSNG-F were rare and maintained at low frequencies. High allelic replacements were observed, however some individuals experienced consecutive re-infections with the same microhaplotype. Notably, PfMSP1 allelic diversity as measured by haplotype diversity was stable, while nucleotide diversity decreased over time with decreasing parasitemia. Parasite PfMSP1 allelic diversity remained stable over the multiple malaria episodes, despite declining parasitaemia levels. In addition, there are reveal dynamic PfMSP1 allelic replacements across parasite infection episodes.
Allelic diversity was stable over time in individuals, based on this limited polymorphic region and small sample size, suggesting that there are no significant shifts in allele frequencies or replacements due to alleles being maintained under balancing selection. The dominant alleles in the population are those frequently observed in these children with multiple malaria episodes, further suggesting that early exposure to dominant alleles does not shift their frequency in the population or prevent repeat infection with the same alleles in subsequent infections. However, a blood stage merozoite vaccine is likely to require a multi-allelic formulation.
经历复发性疟疾感染的个体每次新感染都会接触到多种等位基因。这种持续的等位基因多样性会影响自然获得性免疫的发展，并能为疫苗效力提供信息。为了研究多样性和感染变异性，对来自基利菲县琼朱队列中经历了5年至少10次发热性疟疾发作的儿童分离出的疟原虫中的恶性疟原虫裂殖子表面蛋白1（PfMSP1）进行了评估，PfMSP1是一种对寄生虫入侵和免疫反应至关重要的蛋白质。
使用聚合酶链反应（PCR）对从儿童采集的血样中的Pfmsp1 C末端区域（Pfmsp1）进行基因分型，随后进行毛细管测序。对测序读数进行修剪并与恶性疟原虫3D7参考基因组比对。从比对中识别出Pfmsp1区域的单核苷酸多态性，并将其分组为不同的微单倍型，在多次感染发作期间检查其随时间变化的频率。此外，使用核苷酸和单倍型多样性指数评估人群中感染的变异性。
在所有疟疾发作中总共观察到11种微单倍型。人群中有3种常见的微单倍型，即E-KSNG-L、Q-KSNG-L和Q-KSNG-F。相反，诸如Q-KNNG-L、E-KSSR-L、E-KNNG-L、E-KSSG-L、E-TSSR-L（3D7）、Q-TSSR-L、E-TSSG-L和E-KSNG-F等微单倍型很少见且频率维持在较低水平。观察到了高频率的等位基因替换，然而一些个体经历了相同微单倍型的连续再感染。值得注意的是，通过单倍型多样性测量的PfMSP1等位基因多样性是稳定的，而核苷酸多样性随着寄生虫血症的降低而随时间下降。尽管寄生虫血症水平下降，但寄生虫PfMSP1等位基因多样性在多次疟疾发作中保持稳定。此外，还揭示了跨寄生虫感染发作的动态PfMSP1等位基因替换。
基于这个有限的多态性区域和小样本量，个体中的等位基因多样性随时间保持稳定，这表明由于等位基因在平衡选择下得以维持，等位基因频率没有显著变化或替换。人群中的优势等位基因是在这些多次疟疾发作的儿童中经常观察到的那些，这进一步表明早期接触优势等位基因不会改变其在人群中的频率，也不会阻止在随后的感染中再次感染相同的等位基因。然而，一种血液阶段裂殖子疫苗可能需要多等位基因配方。
