Primary structure of the 175K Plasmodium falciparum erythrocyte binding antigen and identification of a peptide which elicits antibodies that inhibit malaria merozoite invasion.

Abstract

Abstract. The Plasmodium falciparum gene encoding erythrocyte binding antigen-175 (EBA-175), a putative receptor for red cell invasion (Camus, D., and T. J. Hadley. 1985. Science (Wash. DC). 230:553-556.), has been isolated and characterized. DNA sequencing demonstrated a single open reading frame encoding a translation product of 1,435 amino acid residues. Peptides corresponding to regions on the deduced amino acid sequence predicted to be B cell epitopes were assessed for immunogenicity. Immunization of mice and rabbits with EBA-peptide 4, a synthetic peptide encompassing amino acid residues 1,062-1,103, produced antibodies that recognized P. falciparum merozoites in an indirect fluorescent antibody assay. When compared to sera from rabbits immunized with the same adjuvant and carrier protein, sera from rabbits immunized with EBA-peptide 4 inhibited merozoite invasion of erythrocytes in vitro by 80% at a 1:5 dilution. Furthermore, these sera inhibited the binding of purified, authentic EBA-175 to erythrocytes, suggesting that their activity in inhibiting merozoite invasion of erythrocytes is mediated by blocking the binding of EBA-175 to erythrocytes. Since the nucleotide sequence of EBA-peptide 4 is conserved among seven strains of P. falciparum from throughout the world (Sim, B. K. L. 1990. Mol. Biochem. Parasitol. 41:293-296.), these data identify a region of the protein that should be a focus of vaccine development efforts.

Preerythrocytic, live-attenuated Plasmodium falciparum vaccine candidates by design

“…At 72 h after infection, the expression profile of p36 Ϫ and p52 Ϫ single knockouts and p52 Ϫ /p36 Ϫ double knockout resembled the staining profile of WT liver stages, including expression of LSA-1 (Table 3). At 144 h after infection, p36 Ϫ and p52 Ϫ continued to show expression of LSA-1, but we could not detect expression of EBA175 (a late liver-stage/blood-stage marker) (22). Staining of p52 Ϫ /p36 Ϫ liver stages at 144 h after infection could not be evaluated because no parasites were detectable at this time point with any of the tested antibodies ( The p52 Ϫ /p36 Ϫ parasites showed slightly lower gliding activity compared with WT parasites; the effect was not statistically significant at the 95% confidence level (P ϭ 0.11).…”

Variation in use of erythrocyte invasion pathways by Plasmodium falciparum mediates evasion of human inhibitory antibodies

“…This will facilitate a more precise understanding of the significance of these antigens as targets of inhibitory antibodies. Antibodies raised in rabbits against EBA175, EBA140, PfRh1, and PfRh2b have been shown to inhibit invasion (13,17,40), further supporting their role as targets of acquired inhibitory antibodies. Antibodies raised in rabbits against PfRh4 did not inhibit invasion (20); lack of inhibitory activity may have resulted from the use of only small regions of the protein to generate antibodies.…”

Erythrocyte invasion profiles are associated with a common invasion ligand polymorphism in Senegalese isolates ofPlasmodium falciparum

“…falciparum expresses multiple adhesive proteins that localize to the apical invasion organelles of the parasite, most notably members of 2 multigene families: the Erythrocyte Binding Antigen (EBA) family (Sim et al 1990 ;Peterson and Wellems, 2000 ;Thompson et al 2001 ;Gilberger et al 2003), and the P. falciparum Reticulocyte Binding Protein homologue (PfRh) family (Rayner et al 2000(Rayner et al , 2001Triglia et al 2001 ;Kaneko et al 2002 ;Cowman and Crabb, 2006). Differential expression of these proteins, particularly of members of the PfRh family, allows P. falciparum to engage alternative receptors for erythrocyte invasion, termed invasion pathways (Taylor et al 2002 ;Duraisingh et al 2003 a, b;Stubbs et al 2005 ;Triglia et al 2005).…”