Antigens and antibodies in Plasmodium falciparum malaria studied by immunoelectrophoretic methods.

Soluble plasma antigens in 53 Liberian patients with P. falciparum malaria were analyzed in double diffusion using plasma from 27 immune adults. One immune plasma reacted with 17% of the plasma samples and was used in subsequent quantitative immunoelectrophoretic (IE) studies as antiserum. By fused rocket IE 2 antigens were found in samples with parasitaemia (P) above 0.6% and above 4.5% P the antigens had grossly increasing concentration. In 22 samples of 0.6% P or more, 7 antigens were demonstrated by crossed IE. Two electrophoretically heterogeneous antigens. Ag-1 and Ag-2, were found most frequently. Ag-1 was partly heat-stable and was in some samples amphiphilic as shown by charge shift crossed IE. Ag-1 and Ag-2 did not contain integral erythrocyte membrane proteins, and Ag-1 is suggested to be a structural protein of P. falciparum. Twenty-six immune plasma samples were screened for antibodies against 4 antigens in crossed IE with intermediate gel. It is suggested that an index for protective immunity may be obtained by summation of semiquantitative titers obtained by crossed IE with intermediate gel using an antigen pool representing e.g. 20--30 soluble antigens.