Minimal variation in the transmission-blocking vaccine candidate Pfs48/45 of the human malaria parasite Plasmodium falciparum

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Crystallization, sequence and preliminary crystallographic data for transmission-blocking anti-malaria Fab 4B7 with cyclic peptides from the Pfs25 protein of P. falciparum

X-ray quality crystals of an Fab fragment from a transmission-blocking monoclonal antibody 4B7 (MAb 4B7) against a sexual stage protein Pfs25 of Plasmodium falciparum were grown as uncomplexed and peptide-complexed forms. Initially, the intact immunoglobulin was crystallized because cleavage with pepsin or papain did not produce a homogeneous product. Further proteolytic trials with elastase produced a suitable Fab fragment from which crystals have been obtained, both for the free Fab and in complex with cyclic peptides and in the presence of linear peptides. While linear peptides bind to MAb 4B7, cyclic peptides modeled on a predicted -hairpin loop of the third EGF-like domain of Pfs25 bind better and readily co-crystallize with the Fab. The genes for the variable domain of the Fab have been cloned, sequenced and the primary amino-acid sequence for the complete Fab deduced. This work explores the use of glycerol as an additive and the modification of the peptide sequence outside the epitope for improving in the crystallization. Data sets have been collected from crystals of several Fab-peptide complexes and from uncomplexed Fab to resolutions ranging from 2.4 to 3.3 Å. The packing arrangements of several crystal forms have been determined by molecular replacement, and refinement of their three-dimensional structures is in progress. The three-dimensional structure of this Fab complexed with the various peptides will aid in an understanding of the mode by which this antibody recognizes and prevents transmission of the malaria parasite

Clinical immunity to Plasmodium falciparum malaria is associated with serum antibodies to the 19-kDa C-terminal fragment of the merozoite surface antigen PfMSP-1

The development of an effective malaria vaccine depends upon identification of antigens that are targets of protective immune responses. An immunoepidemiologic approach has been used to investigate the relationship between antibody responses to a defined region of the major merozoite surface protein of Plasmodium falciparum (PfMSP-1 19) and resistance to clinical malaria in 2 populations of children from West Africa. After allowing for the confounding effects of age, antibodies to PfMSP-1 19 were shown the provide 40% protection against clinical malaria in children in Sierra Leone. In Gambian children, antibodies to one of the epidermal growth factor-like motifs of PfMSP-1 19 were strongly associated with resistance to both clinical malaria and high levels of parasitemia

Program and abstract of the 45th annual meeting of the American Society of Tropical Medicine and Hygiene

To investigate the potential influence of antigen (Ag) presentation on the immune response to MSP1 19, the 19 kDa C-terminal domain of the #Plasmodium falciparum MSP1 Ag, 3 recombinant MSP 19 Ags expressed in baculovirus, #E. coli and #Saccharomyces cerevisiae were used to stimulate in vitro peripheral blood mononuclear cells (PBMCS) from #P. falciparum immune adults with no recent history of clinical malaria. Donors were recruited in 2 senegalese villages (Dielmo and Ndiop), where malaria transmission is perennial and seasonal, respectively. Each PBMC preparation was stimulated with a range of concentrations of the 3 recombinant Ags (cleaved from carrier molecules when appropriate). Most subjects responded to at least 1 recombinant Ag (SI > 3 in 8/10 at Dielmo and 14/15 at Ndiop). The dose-dependent response to #Saccharomyces cerevisiae MSP1 19 was similar in both villages. In contrast, there was a 10-fold difference in the optimal concentration of the #E. coli product between the two villages. Both the optimal dose and the concentration-dependence of the simulation by the baculovirus recombinant protein differed in each setting. These studies show that the 3 recombinant antigens differ in their capacity to stimulate lymphocyte proliferation, suggesting that protein structure (folding and/or glycosylation) affecting Ag processing, is critical. Futhermore, these data suggest that the malaria transmission pattern influences the immune response to the various MSP1 19 recombinants. (Résumé d'auteur