Detection of Plasmodium falciparum using a radioimmunoassay based on a crossreacting, monoclonal anti-P. berghei antibody-P. berghei antigen system

An antibody binding-inhibition test is described, which allows the detection of P. falciparum in red blood cells (RBC) infected in vitro, using a crossreacting, monoclonal anti-P. berghei antibody and P. berghei coated microtiter plates. Experiments carried out to determine the coating efficiency of various P. berghei and P. falciparum derived antigen preparations showed that intact, saponin freed P. berghei parasites and sonicated, RBC parasitized with P. falciparum had the highest binding activity. Binding of the monoclonal antibody to the antigen coated plates was effectively inhibited by preincubation with sonicated, P. falciparum infected RBC. The minimal degree of infection detectable was about 0.008% parasitemia (400 parasitized RBC/microliters blood). The sensitivity of detection was not appreciably affected by the source of the coating antigen. We conclude that the difficulty and expense involved in the use of P. falciparum based immunodiagnostic tests for large scale screening for malaria can be obviated by making use of P. berghei based assays.