Longitudinal study of Plasmodium falciparum infection and immune responsesin infants with or without the sickle cell trait

Background Individuals may be homozygous (SS) or heterozygous (AS) sickle c ell gene carriers or have normal adult haemoglobin (AA). Haemoglobin S coul d have a protective role against malaria but evidence is sparse and the ope rating mechanisms are poorly known. Methods We followed two cohorts of children. The first was enrolled at birt h (156 newborn babies) and the second at 24-36 months old (84 children). Bo th cohorts were followed for 30 months; monthly for parasitological data an d half yearly for immunological data. Results In the first cohort, 22%, and in the second 13% of children were AS . Whatever their age parasite prevalence rates were similar in AA and AS in dividuals. Mean parasite densities increased less rapidly with age in AS th an in AA children, and were significantly lower in AS than in AA children > 48 months old. The AA children tended to be more often admitted to hospital than AS children (22% versus 11%, NS). Both anti-Plasmodium falciparum and anti-Pf155/RESA antibody rates increased more rapidly in AA than in AS chi ldren. Conversely, the prevalence rate of cellular responders to the Pf155/ RESA antigen was similar in AA and AS children during the first 2 years of life, then it was higher in AS than in AA children. Conclusions Sickle cell trait related antimalarial protection varies with a ge. The role of the modifications of the specific immune response to P. fal ciparum in explaining the protection of AS children against malaria is disc ussed.