title: Ex-vivo cytoadherence phenotypes of Plasmodium falciparum strains from Malian children with hemoglobins A, S, and C.
abstract: Sickle hemoglobin (Hb) S and HbC may protect against malaria by reducing the expression of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) on the surface of parasitized red blood cells (RBCs), thereby weakening their cytoadherence to microvascular endothelial cells (MVECs) and impairing their activation of MVECs to produce pathological responses. Therefore, we hypothesized that parasites causing malaria in HbAS or HbAC heterozygotes have overcome this protective mechanism by expressing PfEMP1 variants which mediate relatively strong binding to MVECs. To test this hypothesis, we performed 31 cytoadherence comparisons between parasites from HbAA and HbAS (or HbAC) Malian children with malaria. Ring-stage parasites from HbAA and HbAS (or HbAC) children were cultivated to trophozoites, purified, and then inoculated in parallel into the same wildtype uninfected RBCs. After one cycle of invasion and maturation to the trophozoite stage expressing PfEMP1, parasite strains were compared for binding to MVECs. In this assay, there were no significant differences in the binding of parasites from HbAS and HbAC children to MVECs compared to those from HbAA children (HbAS, fold-change  = 1.46, 95% CI 0.97-2.19, p = 0.07; HbAC, fold-change  = 1.19, 95% CI 0.77-1.84, p = 0.43). These data suggest that in-vitro reductions in cytoadherence by HbS and HbC may not be selecting for expression of high-avidity PfEMP1 variants in vivo. Future studies that identify PfEMP1 domains or amino-acid motifs which are selectively expressed in parasites from HbAS children may provide further insights into the mechanism of malaria protection by the sickle-cell trait.
authors.affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America; Nuffield Department of Clinical Medicine, University of Oxford, Oxford, United Kingdom.
authors.forename: Jeanette T
authors.initials: JT
authors.lastname: Beaudry
authors.affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Krause
authors.affiliation: Faculty of Medicine, Pharmacy and Odontostomatology, Malaria Research and Training Center, University of Bamako, Bamako, Mali.
authors.forename: Seidina A S
authors.initials: SA
authors.lastname: Diakite
authors.affiliation: Biostatistics Research Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Fay
authors.affiliation: Biostatistics Research Branch, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Gyan
authors.initials: G
authors.lastname: Joshi
authors.affiliation: Faculty of Medicine, Pharmacy and Odontostomatology, Malaria Research and Training Center, University of Bamako, Bamako, Mali.
authors.forename: Mahamadou
authors.initials: M
authors.lastname: Diakite
authors.affiliation: Mahidol-Oxford Tropical Diseases Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok, Thailand.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: White
authors.affiliation: Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Rick M
authors.initials: RM
authors.lastname: Fairhurst
mesh_terms: D000293:Adolescent; D000818:Animals; D001681:Biological Assay; D002448:Cell Adhesion; D002648:Child; D002675:Child, Preschool; D042783:Endothelial Cells / Q000378:metabolism / Q000473:pathology; D006441:Hemoglobin A / Q000378:metabolism*; D006444:Hemoglobin C / Q000378:metabolism*; D006451:Hemoglobin, Sickle / Q000378:metabolism*; D006801:Humans; D007223:Infant; D016778:Malaria, Falciparum / Q000469:parasitology; D008302:Mali; D055806:Microvessels / Q000473:pathology; D010271:Parasites / Q000166:cytology / Q000302:isolation & purification; D010641:Phenotype; D010963:Plasmodium falciparum / Q000166:cytology* / Q000302:isolation & purification
chemical_list: D006451:Hemoglobin, Sickle; D006444:Hemoglobin C; D006441:Hemoglobin A