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Antibodies that inhibit malaria merozoite surface protein-1 processing and erythrocyte invasion are blocked by naturally acquired human antibodies.

Guevara Patiño JA, Holder AA, McBride JS, Blackman MJ - J. Exp. Med. (1997)

Bottom Line: Most significantly, affinity-purified, naturally acquired human antibodies specific for epitopes within the NH2-terminal 83-kD domain of MSP-1 very effectively block the processing-inhibitory activity of the anti-MSP-119 mAb 12.8.Blocking antibodies therefore (a) are part of the human response to malarial infection; (b) can be induced by MSP-1 structures unrelated to the MSP-119 target of processing-inhibitory antibodies; and (c) have the potential to abolish protection mediated by anti-MSP-119 antibodies.Our results suggest that an effective MSP-119-based falciparum malaria vaccine should aim to induce an antibody response that prevents MSP-1 processing on the merozoite surface.

View Article: PubMed Central - PubMed

Affiliation: Division of Parasitology, National Institute for Medical Research, London, United Kingdom.

ABSTRACT
Merozoite surface protein-1 (MSP-1) of the human malaria parasite Plasmodium falciparum undergoes at least two endoproteolytic cleavage events during merozoite maturation and release, and erythrocyte invasion. We have previously demonstrated that mAbs which inhibit erythrocyte invasion and are specific for epitopes within a membrane-proximal, COOH-terminal domain of MSP-1 (MSP-119) prevent the critical secondary processing step which occurs on the surface of the extracellular merozoite at around the time of erythrocyte invasion. Certain other anti-MSP-119 mAbs, which themselves inhibit neither erythrocyte invasion nor MSP-1 secondary processing, block the processing-inhibitory activity of the first group of antibodies and are termed blocking antibodies. We have now directly quantitated antibody-mediated inhibition of MSP-1 secondary processing and invasion, and the effects on this of blocking antibodies. We show that blocking antibodies function by competing with the binding of processing-inhibitory antibodies to their epitopes on the merozoite. Polyclonal rabbit antibodies specific for certain MSP-1 sequences outside of MSP-119 also act as blocking antibodies. Most significantly, affinity-purified, naturally acquired human antibodies specific for epitopes within the NH2-terminal 83-kD domain of MSP-1 very effectively block the processing-inhibitory activity of the anti-MSP-119 mAb 12.8. The presence of these blocking antibodies also completely abrogates the inhibitory effect of mAb 12.8 on erythrocyte invasion by the parasite in vitro. Blocking antibodies therefore (a) are part of the human response to malarial infection; (b) can be induced by MSP-1 structures unrelated to the MSP-119 target of processing-inhibitory antibodies; and (c) have the potential to abolish protection mediated by anti-MSP-119 antibodies. Our results suggest that an effective MSP-119-based falciparum malaria vaccine should aim to induce an antibody response that prevents MSP-1 processing on the merozoite surface.

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Schematic of recombinant (pME) MSP-1 constructs relative  to the MSP-1 gene and its products. Shown is a diagrammatic representation of the complete MSP-1 gene, divided into conserved (open) blocks 1,  3, 5, 12, and 17, semiconserved (hatched) blocks 7, 9, 11, 13, and 15, and  poorly conserved or polymorphic (filled) blocks 2, 4, 6, 8, 10, 14, and 16,  as defined by Tanabe et al. (48). The positions of the MSP-1 primary processing products (MSP-183, MSP-130, MSP-138 and MSP-142) are shown  relative to the gene, as are the relative positions of the pME series of recombinant expression constructs against which polyclonal rabbit antisera  have been raised (8). IgG purified from the anti-pME rabbit sera was used  in this study.
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Figure 3: Schematic of recombinant (pME) MSP-1 constructs relative to the MSP-1 gene and its products. Shown is a diagrammatic representation of the complete MSP-1 gene, divided into conserved (open) blocks 1, 3, 5, 12, and 17, semiconserved (hatched) blocks 7, 9, 11, 13, and 15, and poorly conserved or polymorphic (filled) blocks 2, 4, 6, 8, 10, 14, and 16, as defined by Tanabe et al. (48). The positions of the MSP-1 primary processing products (MSP-183, MSP-130, MSP-138 and MSP-142) are shown relative to the gene, as are the relative positions of the pME series of recombinant expression constructs against which polyclonal rabbit antisera have been raised (8). IgG purified from the anti-pME rabbit sera was used in this study.

Mentions: The above results showed that the binding of processing-inhibitory antibodies to MSP-119 can be specifically prevented by the interaction of other antibodies with the same polypeptide, and explained how blocking antibodies interfere with the processing-inhibitory activity of mAbs 12.8 and 12.10. Interestingly, Wilson et al. (38) found that mAb 13.2, which recognizes an epitope within the NH2-terminal domain of MSP-1, prevents the binding of mAb 12.8 to intact MSP-1, raising the possibility that antibodies specific to other components of the MSP-1–derived, merozoite surface protein complex might have blocking activity. To investigate this possibility, a series of rabbit antibodies, raised against recombinant proteins corresponding to regions covering all of MSP-1 (reference 8; Fig. 3) were tested for their ability to competitively prevent recognition of merozoite-derived MSP-1 by mAbs 12.8 and 12.10. Fig. 4 shows that binding of radioiodinated mAbs 12.8 and 12.10 to the merozoite antigen was significantly blocked by some but not all of the polyclonal antibodies. The fact that rabbit antibodies raised against pME12, 16, and 20 were able effectively to block binding was not unexpected, due to the presence of the 12.8 and 12.10 epitopes within the sequence of the recombinant proteins used to raise these rabbit sera. However, it was found that antibodies raised against constructs corresponding to domains of MSP-1 outside the COOH-terminal region also showed potent blocking activity; in particular, the anti-pME6, anti-pME14, and anti-pME3 sera inhibited binding of mAb 12.8 to the immobilized antigen by 68, 48, and 91%, respectively, and the rabbit anti-pME14, anti-pME1, and anti-pME3, but not the anti-pME6 antibodies, significantly prevented binding of mAb 12.10. These results show that polyclonal antibodies specific for fragments of the MSP-1 complex other than MSP-119 can act as blocking antibodies.


Antibodies that inhibit malaria merozoite surface protein-1 processing and erythrocyte invasion are blocked by naturally acquired human antibodies.

Guevara Patiño JA, Holder AA, McBride JS, Blackman MJ - J. Exp. Med. (1997)

Schematic of recombinant (pME) MSP-1 constructs relative  to the MSP-1 gene and its products. Shown is a diagrammatic representation of the complete MSP-1 gene, divided into conserved (open) blocks 1,  3, 5, 12, and 17, semiconserved (hatched) blocks 7, 9, 11, 13, and 15, and  poorly conserved or polymorphic (filled) blocks 2, 4, 6, 8, 10, 14, and 16,  as defined by Tanabe et al. (48). The positions of the MSP-1 primary processing products (MSP-183, MSP-130, MSP-138 and MSP-142) are shown  relative to the gene, as are the relative positions of the pME series of recombinant expression constructs against which polyclonal rabbit antisera  have been raised (8). IgG purified from the anti-pME rabbit sera was used  in this study.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2199131&req=5

Figure 3: Schematic of recombinant (pME) MSP-1 constructs relative to the MSP-1 gene and its products. Shown is a diagrammatic representation of the complete MSP-1 gene, divided into conserved (open) blocks 1, 3, 5, 12, and 17, semiconserved (hatched) blocks 7, 9, 11, 13, and 15, and poorly conserved or polymorphic (filled) blocks 2, 4, 6, 8, 10, 14, and 16, as defined by Tanabe et al. (48). The positions of the MSP-1 primary processing products (MSP-183, MSP-130, MSP-138 and MSP-142) are shown relative to the gene, as are the relative positions of the pME series of recombinant expression constructs against which polyclonal rabbit antisera have been raised (8). IgG purified from the anti-pME rabbit sera was used in this study.
Mentions: The above results showed that the binding of processing-inhibitory antibodies to MSP-119 can be specifically prevented by the interaction of other antibodies with the same polypeptide, and explained how blocking antibodies interfere with the processing-inhibitory activity of mAbs 12.8 and 12.10. Interestingly, Wilson et al. (38) found that mAb 13.2, which recognizes an epitope within the NH2-terminal domain of MSP-1, prevents the binding of mAb 12.8 to intact MSP-1, raising the possibility that antibodies specific to other components of the MSP-1–derived, merozoite surface protein complex might have blocking activity. To investigate this possibility, a series of rabbit antibodies, raised against recombinant proteins corresponding to regions covering all of MSP-1 (reference 8; Fig. 3) were tested for their ability to competitively prevent recognition of merozoite-derived MSP-1 by mAbs 12.8 and 12.10. Fig. 4 shows that binding of radioiodinated mAbs 12.8 and 12.10 to the merozoite antigen was significantly blocked by some but not all of the polyclonal antibodies. The fact that rabbit antibodies raised against pME12, 16, and 20 were able effectively to block binding was not unexpected, due to the presence of the 12.8 and 12.10 epitopes within the sequence of the recombinant proteins used to raise these rabbit sera. However, it was found that antibodies raised against constructs corresponding to domains of MSP-1 outside the COOH-terminal region also showed potent blocking activity; in particular, the anti-pME6, anti-pME14, and anti-pME3 sera inhibited binding of mAb 12.8 to the immobilized antigen by 68, 48, and 91%, respectively, and the rabbit anti-pME14, anti-pME1, and anti-pME3, but not the anti-pME6 antibodies, significantly prevented binding of mAb 12.10. These results show that polyclonal antibodies specific for fragments of the MSP-1 complex other than MSP-119 can act as blocking antibodies.

Bottom Line: Most significantly, affinity-purified, naturally acquired human antibodies specific for epitopes within the NH2-terminal 83-kD domain of MSP-1 very effectively block the processing-inhibitory activity of the anti-MSP-119 mAb 12.8.Blocking antibodies therefore (a) are part of the human response to malarial infection; (b) can be induced by MSP-1 structures unrelated to the MSP-119 target of processing-inhibitory antibodies; and (c) have the potential to abolish protection mediated by anti-MSP-119 antibodies.Our results suggest that an effective MSP-119-based falciparum malaria vaccine should aim to induce an antibody response that prevents MSP-1 processing on the merozoite surface.

View Article: PubMed Central - PubMed

Affiliation: Division of Parasitology, National Institute for Medical Research, London, United Kingdom.

ABSTRACT
Merozoite surface protein-1 (MSP-1) of the human malaria parasite Plasmodium falciparum undergoes at least two endoproteolytic cleavage events during merozoite maturation and release, and erythrocyte invasion. We have previously demonstrated that mAbs which inhibit erythrocyte invasion and are specific for epitopes within a membrane-proximal, COOH-terminal domain of MSP-1 (MSP-119) prevent the critical secondary processing step which occurs on the surface of the extracellular merozoite at around the time of erythrocyte invasion. Certain other anti-MSP-119 mAbs, which themselves inhibit neither erythrocyte invasion nor MSP-1 secondary processing, block the processing-inhibitory activity of the first group of antibodies and are termed blocking antibodies. We have now directly quantitated antibody-mediated inhibition of MSP-1 secondary processing and invasion, and the effects on this of blocking antibodies. We show that blocking antibodies function by competing with the binding of processing-inhibitory antibodies to their epitopes on the merozoite. Polyclonal rabbit antibodies specific for certain MSP-1 sequences outside of MSP-119 also act as blocking antibodies. Most significantly, affinity-purified, naturally acquired human antibodies specific for epitopes within the NH2-terminal 83-kD domain of MSP-1 very effectively block the processing-inhibitory activity of the anti-MSP-119 mAb 12.8. The presence of these blocking antibodies also completely abrogates the inhibitory effect of mAb 12.8 on erythrocyte invasion by the parasite in vitro. Blocking antibodies therefore (a) are part of the human response to malarial infection; (b) can be induced by MSP-1 structures unrelated to the MSP-119 target of processing-inhibitory antibodies; and (c) have the potential to abolish protection mediated by anti-MSP-119 antibodies. Our results suggest that an effective MSP-119-based falciparum malaria vaccine should aim to induce an antibody response that prevents MSP-1 processing on the merozoite surface.

Show MeSH
Related in: MedlinePlus