Evaluating IgG Antibody to Variant Surface Antigens Expressed on Plasmodium falciparum Infected Erythrocytes Using Flow Cytometry

Constant exposure to Plasmodium falciparum leads to acquisition of malarial antibodies that can protect against the clinical consequences of infection. One important target of such antibodies is against the parasite-infected erythrocyte (IEs). Current established assays to test the efficacy of antibodies in preventing parasite growth include direct parasite growth inhibition, the agglutination of IEs, and the inhibition of adhesion of IEs (to quantify antibody that inhibits adhesion to purified receptors or cells).However, many of these assays are labor-intensive and low-output which limits study sizes to small cohorts. Here we present an alternative assay that measures the levels of protective antibodies to variant surface antigens (VSA) of IEs. This assay can be performed using a microtitre plate and requires only a small volume of test serum sample. Serum samples are incubated with IEs and are then analyzed using a semi-automated autosampler attached to a flow cytometer. The assay is accurate, quick, and reproducible. Ultimately this assay could be used on large population-based studies, which could increase the statistical power of clinical studies.