Characterization of VAR2CSA-deficient Plasmodium falciparum-infected erythrocytes selected for adhesion to the BeWo placental cell line.
BACKGROUND
Malaria in pregnancy is characterized by accumulation of infected erythrocytes (IE) in the placenta. The key ligand identified as mediating this process is a Plasmodium falciparum erythrocyte membrane protein 1 family member, termed VAR2CSA. VAR2CSA appears to be the main ligand responsible for adhesion to chondroitin sulphate A (CSA). Whether other PfEMP1 molecules can also mediate placental adhesion, independent of CSA binding, is unclear.


METHODS
The parasite line CS2 carrying a disrupted var2csa gene (CS2KO) was selected for adhesion to the BeWo choriocarcinoma cell line, which has been proposed as a model for placental malaria. The selected and control IE were tested for adhesion to placental sections and flow cytometry was used to measure recognition of IE by three serum sets from malaria-exposed men and women.


RESULTS
Wild-type CS2 adhere to BeWo and placental tissue via CSA. CS2KO IE were successfully selected for adhesion to BeWo, and adhered by a CSA-independent mechanism. They bound to immobilized ICAM-1 and CD36. BeWo-selected CS2KO bound at moderate levels to placental sections, but most binding was to placental villi rather than to the syncytiotrophoblast to which IE adherence occurs in vivo. This binding was inhibited by a blocking antibody to CD36 but not to ICAM-1. As expected, sera from malaria-exposed adults recognized CS2 IE in a gender and parity dependent manner. In one serum set, there was a similar but less pronounced pattern of antibody binding to selected CS2KO IE, but this was not seen in two others. One var gene, It4var19, was particularly abundant in the selected line and was detected as full length transcripts in BeWo-selected IE, but not unselected CS2KO.


CONCLUSIONS
This study suggests that IE with characteristics similar to the CS2KO have a limited role in the pathogenesis of placental malaria. VAR2CSA appear to be the major ligand for placental adhesion, and could be the basis for a vaccine against pregnancy malaria.
Yosaatmadja
Francisca
F
Department of Medicine, University of Melbourne (RMH/WH), Post Office Royal Melbourne Hospital, Parkville VIC 3050, Australia. fyo@unimelb.edu.au
Andrews
Katherine T
KT
Duffy
Michael F
MF
Brown
Graham V
GV
Beeson
James G
JG
Rogerson
Stephen J
SJ
D000328:Adult; D000818:Animals; D000913:Antibodies, Protozoan / Q000276:immunology; D000953:Antigens, Protozoan / Q000235:genetics / Q000502:physiology*; D018955:CD36 Antigens / Q000276:immunology / Q000378:metabolism; D002448:Cell Adhesion; D045744:Cell Line, Tumor; D002809:Chondroitin Sulfates / Q000378:metabolism; D015331:Cohort Studies; D004912:Erythrocytes / Q000166:cytology / Q000469:parasitology*; D005260:Female; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D066298:In Vitro Techniques; D018799:Intercellular Adhesion Molecule-1 / Q000378:metabolism; D016778:Malaria, Falciparum / Q000276:immunology; D008297:Male; D008954:Models, Biological; D010920:Placenta / Q000469:parasitology; D010963:Plasmodium falciparum / Q000235:genetics* / Q000276:immunology / Q000502:physiology; D011247:Pregnancy; D015597:Pregnancy Complications, Parasitic / Q000276:immunology / Q000469:parasitology; D015800:Protozoan Proteins / Q000235:genetics
D000913:Antibodies, Protozoan; D000953:Antigens, Protozoan; D018955:CD36 Antigens; D007074:Immunoglobulin G; D015800:Protozoan Proteins; C512601:VAR2CSA protein, Plasmodium falciparum; C085731:erythrocyte membrane protein 1, Plasmodium falciparum; D018799:Intercellular Adhesion Molecule-1; D002809:Chondroitin Sulfates