Ceesay Sukai, Kampmann Martin, Votborg-Novél Lasse, Hansson Helle Smedegaard, Jensen Rasmus Weisel, Carrasquilla Manuela, Cisse Hamidou, Turner Louise, Dabbas Usama, Ntalla Christina, Bandermann Silke, Doumbo Safiatou, Doumtabe Didier, Ongoiba Aissata, Kayentao Kassoum, Traore Boubacar, Crompton Peter D, Lavstsen Thomas, Portugal Silvia
Max-Planck-Institute for Infection Biology, Berlin, Germany.
Charité - Universitätsmedizin Berlin, Berlin, Germany.
PLoS Pathog. 2025 Jun 10;21(6):e1013210. doi: 10.1371/journal.ppat.1013210. eCollection 2025 Jun.
In seasonal transmission areas, clinical malaria occurs during the wet season when mosquitoes are present, while in the dry season, malaria transmission is interrupted and clinical cases are rare. In Mali, Plasmodium falciparum can persist in low parasitaemic asymptomatic individuals through the six-month dry season and shows circulation of more developed parasite stages compared to clinical malaria cases, indicative of reduced cytoadhesion of infected erythrocytes. How prolonged circulation of infected erythrocytes is achieved remains unknown. Here, we explored var gene expression in subclinical infections and clinical malaria cases of Malian children, collected during the dry and wet seasons. We sequenced expressed var DBLα-tags, used bioinformatic tools to predict their domain composition, binding phenotype and upstream sequence type; and determined their relationship to seasonality and clinical presentation. We found that parasites of asymptomatic infections expressed fewer var genes, with a larger proportion of var transcripts attributed to one or a few vars. In contrast, clinical cases exhibited expression of many var genes at lower proportions. We found that parasites of asymptomatic carriers expressed a mixture of CD36- and EPCR-binding PfEMP1, which changed over time. We confirmed that vars encoding CD36-binding PfEMP1 dominated in non-severe malaria cases, and found no significant difference in expressed var types between dry and wet seasons. Asymptomatic carriers were older, had higher titers of anti-P. falciparum antibodies, and broader reactivity to PfEMP1, suggesting that host immunity was the main determinant limiting var transcript variation in asymptomatic carriers. However, qRT-PCR analyses also indicated higher total var transcript levels in malaria cases compared to asymptomatic carriers, suggesting that in addition to the parasite's switching and the host's immune selection of expressed var genes, parasites able to sustain long-term infections may be poised for reduced PfEMP1 expression.
在季节性传播地区，临床疟疾在雨季有蚊子时出现，而在旱季，疟疾传播中断，临床病例罕见。在马里，恶性疟原虫可在低寄生虫血症的无症状个体中持续存在六个月的旱季，并且与临床疟疾病例相比，显示出更发达的寄生虫阶段的循环，这表明受感染红细胞的细胞粘附减少。感染红细胞如何实现长期循环仍不清楚。在这里，我们探索了在旱季和雨季收集的马里儿童亚临床感染和临床疟疾病例中的var基因表达。我们对表达的var DBLα标签进行了测序，使用生物信息学工具预测其结构域组成、结合表型和上游序列类型；并确定它们与季节性和临床表现的关系。我们发现无症状感染的寄生虫表达的var基因较少，较大比例的var转录本归因于一个或几个var。相比之下，临床病例表现出许多var基因以较低比例表达。我们发现无症状携带者的寄生虫表达了结合CD36和EPCR的PfEMP1的混合物，并且随时间变化。我们证实编码结合CD36的PfEMP1的var在非重症疟疾病例中占主导地位，并且发现旱季和雨季之间表达的var类型没有显著差异。无症状携带者年龄较大，抗恶性疟原虫抗体滴度较高，对PfEMP1的反应性更广，这表明宿主免疫是限制无症状携带者var转录本变异的主要决定因素。然而，qRT-PCR分析还表明，疟疾病例中的总var转录本水平高于无症状携带者，这表明除了寄生虫的转换和宿主对表达的var基因的免疫选择外，能够维持长期感染的寄生虫可能准备降低PfEMP1的表达。
