Abstract
(Englisch)
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Chemical synthesis of overlapping long synthetic peptides (LSP) corresponding to the Plasmodium falciparum exo-erythrocytic protein LSA-3 comprising 1786 amino acids has been completed. These LSP which range from 44 to 186 aa have now been tested for their immunogenicity in mice and antigenicity in humans. Using the 17 LSA3 LSP we performed a mapping of B cell epitopes in sera from 20 villagers living in Dielmo, an African hyper-endemic malaria region. Each of the peptides was recognised by at least one individual, and many by most individuals. The LSP strategy led us to identify several antigenically dominant regions. A first, highly antigenic region, lies within the R2 repeats region since almost all of the individuals recognised the three peptides covering the sequence 501-854. This region includes repeats of octamers, which vary in numbers but are highly conserved among various parasite strains. In addition, in the NR-B region represented by 8 polypeptides, the prevalence of responders is also high, despite the fact that it is a non-repetitive region, and, in fact, the response for the 3 peptides is as high as that observed for the repeat region . In the NR-A from N-terminal region, sequence 100-222 is also recognized by antibodies as previously observed with smaller peptides. Many of the peptides proved to be immunogenic in mice as evaluated by the proliferative or IFN-g response and by the antibody production. The frequency of specific IFN-g producing cells were measured by ex-vivo Elispot on freshly isolated LN cells from each immunised mouse. Epitopes can be classified in three different categories as follows: a) sequences 1081 to 1255 and 1601-1712 corresponding to three peptides induced both proliferative response and IFN-g production in most of the mice, b) sequences 893-999 and 1698 to 1786 induced moderate to high proliferative response; however, only one mouse per group produced significant levels of IFN-g against the homologous peptide, and c) for sequences 840-907, 985 to 1095 and 1241 to 1517, T-cell responses were poor; a few mice (one or two per group) showed a proliferative response in the absence of IFN-g production.
In conclusion, results show a strong and rather homogeneous antibody response against each of the 17 LSP studied. All peptides proved to define at least one B cell epitope in Balb/C mice and many were capable of inducing high levels of antibodies and T cell responses.
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