The inhibitory effect of human immune sera upon the in vitro development of Plasmodium falciparum

Sera from patients who had recovered from malaria were examined for their capacity to inhibit the growth of Plasmodium falciparum in vitro. The sera were dialysed to eliminate any residual drugs taken by the donor. IgG purified from inhibitory sera was found to be as effective as the original sera. The inhibitory activity of some of the immune serum was pronounced after the second day in culture. This may suggest that the mechanism of action of antibodies affects the merozoites which appear for a short period in the two day cycle of the parasite. There was no correlation between antibody titre measured by IFA and the inhibitory capacity of the sera: some samples with high IFA titres did not inhibit the growth while some with low IFA titres inhibited the parasite. Autoantibodies directed against the erythrocytes, which were found in some sera, had no antimalarial inhibitory role and the absorption of them did not alter the inhibitory effect. There were more inhibitory sera among Nigerian than amount Thai and Ethiopian sera. The experiments were performed with a Nigerian strain and therefore the results may be explained by differences between the various falciparum strains of malaria.