A solid-phase antibody binding-inhibition test, for the assay of Plasmodium berghei antigen and antibodies, using radioiodinated protein A.

Sonicated red blood cells (RBC) of rats infected with Plasmodium berghei (Pb) were used to coat plastic tubes with Pb antigens. The antigen-coated tubes were employed to detect Pb antigens and antibodies, with high efficiency. Anti-Pb antibodies were estimated by treating the tubes with rabbit or rat anti-Pb sera and assaying the bound Ig with radiolabeled Staphylococcus PrA. Pb antigens were detected by their capacity to inhibit the binding of the anti-Pb antibodies. Using a rabbit-Pb serum, sonicated, infected RBC (50% parasitemia) gave detectable inhibition up to 1 : 106 dilution.