Antibodies to Plasmodium falciparum rifin proteins are associated with rapid parasite clearance and asymptomatic infections.

Plasmodium falciparum rifin proteins, belonging to the largest known family of variable infected-erythrocyte surface-expressed proteins encoded by rif genes, were recently shown to be capable of inducing a strong immune response in P. falciparum-infected adults living in an area in Gabon where malaria is endemic. In the present study, the levels of antirifin antibodies were analyzed in serum obtained from 60 children from the same area who were admitted to hospital and diagnosed with severe malaria. High antirifin antibody concentrations in these individuals correlated significantly with their capacity to rapidly clear their parasites from the circulation after the start of chemotherapy. A doubling of antirifin antibody concentrations reduced the clearance time by 5 h (95% confidence interval, 4.1 to 6.9 h). In the same group of children, who were followed up for 2 years, antirifin antibody levels did not correlate with a reduced rate of reinfection or with a delay in the time to the first reinfection. However, the initial antirifin antibody levels were sustained over the study period. The likelihood that these antibodies could confer a certain degree of protection against malaria is supported by our findings of statistically higher levels of antirifin antibodies to all four rifin proteins in a group of 42 asymptomatic parasitemic children.