An epidemiological study of humoral and cell-mediated immune response to the Plasmodium falciparum antigen Pf155/RESA in adult Liberians

We investigated the seroreactivity and T cell reactivity against the Plasmodium falciparum antigen Pf155/RESA, different oligopeptides from the 3' and 5' repeat regions of the Pf155/RESA antigen, and crude Plasmodium falciparum antigens in 164 adult Liberians. We compared 2 long-term residential groups with high and low exposure to malaria. The seropositive rate to the peptides was significantly higher with increased exposure. There was no significant difference in response rates to the Pf155/RESA. This may indicate the level of persistent T cell memory in previously primed donors. The seropositive rates to 3 Pf155/RESA peptides and the rates measured by either 3H-thymidine incorporation or IFN-γ-release after stimulation with Pf155/RESA and the peptides were all lower in parasite positive individuals. Even low grade, asymptomatic parasitemia can impair the T cell response in vitro. The lower antibody response in parasite positive subjects may be explained by either antibody consumption or lower protection against malaria parasitemia in subjects with low concentrations of antibodies against the Pf155/RESA antigen.