Fig. 1

Immunoreactivity of recombinant Plasmodium antigens in sera from adults living in endemic regions. a Expression plasmids encoding the entire ectodomains of the proteins from the named species were expressed as enzymatically monobiotinylated soluble recombinant proteins in HEK293 cells. Spent tissue culture supernatant was normalized and resolved by SDS-PAGE under reducing conditions, blotted and detected by Western blotting using streptavidin-HRP. All proteins contain a C-terminal rat Cd4d3+ 4 and enzymatically biotinylatable tag. The named proteins from each species were enzymatically monobiotinylated during expression and captured on streptavidin-coated plates. Pooled sera from Malawian adults was used to probe the P. malariae and P. ovale proteins (b), and sera from 10 Malaysian individuals with PCR-confirmed single P. knowlesi infections were used for the P. knowlesi (c). Immunoreactivity was quantified by ELISA using an anti-human alkaline-phosphatase conjugated secondary antibody that hydrolyzed a substrate forming a product with maximal absorbance at 405 nm; responses were normalized to a control protein