Recognition of dominant T cell-stimulating epitopes from the circumsporozoite protein of Plasmodium falciparum and relationship to malaria morbidity in Gambian children

Association between immune recognition of the malaria vaccine candidate antigen Pf155/RESA and resistance to clinical disease: a prospective study in a malaria-endemic region of west Africa

We have measured cellular and humoral immune responses to short synthetic peptides representing epitopes of the malaria vaccine candidate antigen Pf155/RESA in a longitudinal, prospective study of clinical immunity to Plasmodium falciparum malaria in a cohort of 354 Gambian children aged 3-8 years. A significant association was observed between presence of antibodies to the 3' repeat region peptide (EENV)6 and resistance to clinical malaria. The prevalence of protective antipeptide antibodies varied significantly between different ethnic groups, suggesting that immune recognition of some Pf155/RESA epitopes may be genetically regulated. There was no obvious association between proliferative or interferon gamma responses to T cell epitopes of Pf155/RESA and resistance to malaria infection or disease. At an individual level, the presence of peptide-binding antibodies was associated with the induction of interleukin 4 messenger ribonucleic acid expression in T cells activated with the overlapping T cell epitope EENVEHDA(EENV)2. This suggests that measurement of interleukin 4 production by T cells may represent a functional assay for T helper activity.

Immune response to soluble exoantigens of Plasmodium falciparum may contribute to both pathogenesis and protection in clinical malaria: evidence from a longitudinal, prospective study of semi-immune African children

Some soluble exoantigens of Plasmodium have lipopolysaccharide (LPS)-like properties and are believed to contribute to the pathogenesis of acute malaria. We have studied cellular and humoral immune responses to several purified exoantigens of Plasmodium falciparum in a cohort of children and compared these responses with their subsequent susceptibility to malaria infection and clinical disease. We found no evidence that either lymphoproliferative or interferon-gamma (IFN-gamma) responses to these antigens were associated with protective immunity. On the contrary, children whose cells produced IFN-gamma after in vitro activation with one of the soluble antigens (Ag7) were more likely to experience clinical manifestations of malaria infection (fever and malaise) than were children whose cells did not produce IFN-gamma. It is possible that exoantigen-induced IFN-gamma may exacerbate the LPS-like effects of these antigens. However, serum antibodies to another antigen (Ag2) were more prevalent in children with asymptomatic infections or low parasitemia than in children with fever and higher parasitemia (confirmed clinical malaria), suggesting that these antibodies may contribute to the development of protective immunity.

Differential antibody response of Gambian donors to soluble Plasmodium falciparum antigens

A seroepidemiological and clinical study was performed in an area of West Africa (The Gambia) where Plasmodium falciparum is endemic with seasonal transmission. Plasma samples were tested by intermediate gel immunoelectrophoresis for antibodies against 7 soluble P. falciparum antigens. There were marked differences in the age-related pattern of antibody response to the different antigens. Antibodies to 4 of the antigens were acquired slowly with a maximum prevalence reached after 25-35 years of age. Antibodies against the 3 remaining antigens, including the endotoxin-like antigen, Ag7, were acquired earlier with a plateau of maximum prevalence reached after 5-11 years, i.e. at the time when morbidity due to malaria decreased. Children who had not appeared to be infected with malaria during the preceding transmission season had lower levels of antibodies to soluble antigens than did children who had had a documented attack of clinical malaria or parasitaemia. There was no difference in antibody profiles to soluble antigens between children with sickle cell trait and children with normal haemoglobin.