Epitope mapping was done using a peptide array covering the DBL4e domain. The peptide array consisted of 66 synthetic 16-28 amino acids long overlapping peptides, spanning amino acids 1607-1989 of the P. falciparum-FCR3 var2csa sequence (Table S1 ). The peptides were prepared by Schafer-N Copenhagen and the purity of the peptides was expected to be 70% or higher. Peptide binding was determined using ELISA. ELISA plates (Nunc Immunoplate) were coated overnight (4uC) with DBL4e peptides at a concentration of 3 mg/ml in 16PBS. Plates were blocked with ELISA dilution buffer (1% BSA and 1% Triton x-100) before animal serum samples were added. The serum samples were diluted 1:100. The following secondary horseradish peroxidaseconjugated (HRP) antibodies were used: anti-rabbit P0448 (DAKO), dilution 1:2000; and anti-rat A9037 (Invitrogen) and diluted 1:3000. The optical density was measured at 490 nm in an ELISA plate reader (VersaMax, Molecular Devices). The level of reactivity in this ELISA based peptide array was directly associated to the level of reactivity in an assay where identical peptides were synthesised directly on to a chip, confirming homogeneous coating of the peptides [17] .