A longitudinal study of antibodies to the Plasmodium falciparum antigen Pf155/RESA and immunity to malaria infection in adult Liberians

118 adult Liberians from 2 villages were studied prospectively for one year with monthly blood examinations for malaria parasites. The crude parasite rate was 41η5% and the crude gametocyte rate was 6η1%. The inoculation rate varied between 0η075 in the dry season and almost 0η4 in the rainy season, which is in accordance with other data from holoendemic areas. 47η5% (56) had a titre to the Pf155/RESA antigen ≤1/50(‘low responders’) and 52η5% (62) had a titre of ≥1/250 (‘high responders’). The response was not age-dependent in this adult population, which may suggest that genetic factors are determining whether the individual become a high or low responder. Antibodies against the Pf155/RESA antigen were measured in 2 surveys 8 months apart, and the mean antibody response to Pf155/RESA and its EENV sequence was constant without seasonal variation. Pf155/RESA high responders had lower parasite densities during all 3 seasons surveyed, and Pf155/RESA high responders, with high antibody reactivity against the (EENV)6 sequence from the 3' repeat region of Pf155/RESA, had significantly lower parasite densities in the rainy season of 1987. The data suggest that high titres of antibodies to the Pf155/RESA antigen, and especially to its EENV sequence, might play a role in protective immunity in adults. © 1990, Royal Society of Tropical Medicine and Hygiene. All rights reserved.