Antibodies to sequences in a non-repeat region of Plasmodium falciparum antigen Pf155/RESA inhibit either cytoadherence or parasite growth in vitro

Abstract

Antibodies to a non-repeat region of the Plasmodium falciparum antigen Pf155/RESA were investigated for their capacity to inhibit parasite cytoadherence to melanoma cells and parasite growth in vitro. The activities of these antibodies were studied since the target region in Pf155/RESA includes a cytoadherence-related motif also found in loop 3 and 7 of human erythrocyte band 3 protein. Overlapping multiple antigen peptides (MAPs) together spanning residues 199-220 of Pf155/RESA were used to raise antibodies in rabbits. Analysis of the fine specificity of these antibodies revealed that antibodies raised against largely overlapping sequences displayed highly different specificity patterns. Similarly, striking differences were seen when analysing the biological effect of antibodies to these MAPs. Antibodies to the cytoadherence-related motif of Pf155/RESA, as well as antibodies raised against a MAP based on a corresponding band 3 motif, inhibited cytoadherence but not parasite growth. In contrast, antibodies to sequences adjacent to the Pf155/RESA cytoadherence motif inhibited parasite growth in vitro but had no effect on cytoadherence.

Antibodies to a non-repeat region ofPlasmodium falciparumantigen Pf155/RESA in individuals from malaria-endemic areas

“…Furthermore, pepscan analysis of those antibodies revealed marked differences in their ®ne speci®city. In spite of this structural difference between MAP16 and MAP18, the peptides as well as rabbit antibodies to them inhibited the cytoadherence of P. falciparum-infected erythrocytes to endothelial cells with similar ef®ciency [43]. With regard to MAP11 and MAP12, presenting the cytoadherence related motifs of erythrocyte band 3 loops 3 and 7, respectively, the latter MAP was better recognized by antibodies.…”

“…A possible cross-reactive target antigen in this context is RESA2, which shows a high degree of homology with Pf155/RESA, but lacks the repeat sequences of this antigen [45]. Accordingly, there is a high degree of homology between the Pf155/RESA sequences presented in MAP14 and 15 and a RESA2 sequence, while the homology between the sequences in MAP16 and 18 and the corresponding sequence in RESA2 is considerably lower [43]. However, although the RESA2 gene has been shown to be transcribed in several independent P. falciparum isolates [46], its expression at the protein level has not yet been identi®ed.…”

“…The structural difference between the two MAPs was also re¯ected in the speci®city of rabbit antibodies against them, which showed only a very low degree of cross-reactivity [43]. Furthermore, pepscan analysis of those antibodies revealed marked differences in their ®ne speci®city.…”

“…We have recently also shown that rabbit antibodies to non-repeat sequences in the N-terminal part of Pf155/RESA, including antibodies to MAP14 and 15, inhibit parasite growth in vitro [18,43]. However, antibodies to the cytoadherence related motifs in Pf155/RESA as presented in MAP16 and 18 were without effect in this respect [43]. In the present study we show that af®nity-puri®ed human antibodies reactive with Pf155/RESA non-repeat sequences as presented in MAP14 and 15 also have the capacity to inhibit parasite growth in vitro.…”

“…Furthermore, B cell epitopes, frequently recognized by antibodies from individuals living in malaria-endemic areas, have been detected in the N-terminal non-repeat region of Pf155/RESA [17,22,42]. Rabbit antibodies induced by synthetic peptides corresponding to certain sequences in this region have the capacity to inhibit P. falciparum growth in vitro [18,43], indicating that this region of the antigen may also constitute an important target for immune responses during malaria infection. We now report that individuals living in malaria-endemic regions show a high level of seroreactivity to sequences in the N-terminal non-repeat region of Pf155/RESA.…”