The interplay between cellular and molecular determinants that lead to severe malaria in adults is unexplored. Here, we analyzed parasite virulence factors in an infected adult population in India and investigated whether severe malaria isolates impair endothelial protein C receptor (EPCR), a protein involved in coagulation and endothelial barrier permeability. Severe malaria isolates overexpressed specific members of the Plasmodium falciparum var gene/ PfEMP1 (P. falciparum erythrocyte membrane protein 1) family that bind EPCR, including DC8 var genes that have previously been linked to severe pediatric malaria. Machine learning analysis revealed that DC6-and DC8-encoding var transcripts in combination with high parasite biomass were the strongest indicators of patient hospitalization and disease severity. We found that DC8 CIDRα1 domains from severe malaria isolates had substantial differences in EPCR binding affinity and blockade activity for its ligand activated protein C. Additionally, even a low level of inhibition exhibited by domains from two cerebral malaria isolates was sufficient to interfere with activated protein C-barrier protective activities in human brain endothelial cells. Our findings demonstrate an interplay between parasite biomass and specific PfEMP1 adhesion types in the development of adult severe malaria, and indicate that low impairment of EPCR function may contribute to parasite virulence. malaria | Plasmodium falciparum | var | PfEMP1 | EPCR

Plasmodium vivax has two invasion ligand/host receptor pathways (PvDBP/DARC and PvRBP2b/TfR1) that are promising targets for therapeutic intervention. We optimized invasion assays with isogenic cultured reticulocytes. Using a receptor blockade approach with multiple P. vivax isolates, we found that all strains utilized both DARC and TfR1, however with significant variation in receptor usage. This suggests that P. vivax, like P. falciparum, uses alternative invasion pathways with implications for pathogenesis and vaccine development.

The clinical presentation of severePlasmodium falciparummalaria differs between children and adults, but the mechanistic basis for this remains unclear. Contributing factors to disease severity include total parasite biomass and the diverse cytoadhesive properties mediated by the polymorphicvargene parasite ligand family displayed on infected erythrocytes. To explore these factors, we performed a multicohort analysis of the contribution ofvarexpression and parasite biomass to severe malaria in two previously published pediatric cohorts in Tanzania and Malawi and an adult cohort in India. Machine learning analysis revealed independent and complementary roles forvaradhesion types and parasite biomass in adult and pediatric severe malaria and showed that similarvarprofiles, including upregulation of group A and DC8var, predict severe malaria in adults and children. Among adults, patients with multiorgan complications presented infections with significantly higher parasite biomass without significant differences invaradhesion types. Conversely, pediatric patients with specific complications showed distinctvarsignatures. Cerebral malaria patients showed broadly increased expression ofvargenes, in particular group A and DC8var, while children with severe malaria anemia were classified based on high transcription of DC8varonly. This study represents the first large multisite meta-analysis ofvarexpression, and it demonstrates the presence of commonvarprofiles in severe malaria patients of different ages across distant geographical sites, as well as syndrome-specific disease signatures. The complex associations between parasite biomass,varadhesion type, and clinical presentation revealed here represent the most comprehensive picture so far of the relationship between cytoadhesion, parasite load, and clinical syndrome.IMPORTANCEP. falciparummalaria can cause multiple disease complications that differ by patient age. Previous studies have attempted to address the roles of parasite adhesion and biomass in disease severity; however, these studies have been limited to single geographical sites, and there is limited understanding of how parasite adhesion and biomass interact to influence disease manifestations. In this meta-analysis, we compared parasite disease determinants in African children and Indian adults. This study demonstrates that parasite biomass and specific subsets ofvargenes are independently associated with detrimental outcomes in both childhood and adult malaria. We also explored how parasitevaradhesion types and biomass play different roles in the development of specific severe malaria pathologies, including childhood cerebral malaria and multiorgan complications in adults. This work represents the largest study to date of the role of bothvaradhesion types and biomass in severe malaria.