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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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Specificity of affinity-purified human anti-pME6  antibodies shown by Western  blot analysis. An SDS extract of  FCB-1 merozoites was subjected to SDS-PAGE under  nonreducing conditions on a  12.5% gel, transferred to nitrocellulose, then probed with a  sample of pooled human immune serum taken before chromatography over the pME6 affinity column (lane 1); serum  taken after passage over the column (lane 2); affinity-purified  anti-pME6 antibodies (lane 3);  mAb 89.1 (specific for MSP-183;  lane 4); and mAb 111.4 (specific  for MSP-142 and MSP-119; lane  5). Positions of molecular mass  marker proteins are indicated, and  bands corresponding to the MSP-1  precursor, MSP-183, MSP-142,  and MSP-119 are arrowed.
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Figure 5: Specificity of affinity-purified human anti-pME6 antibodies shown by Western blot analysis. An SDS extract of FCB-1 merozoites was subjected to SDS-PAGE under nonreducing conditions on a 12.5% gel, transferred to nitrocellulose, then probed with a sample of pooled human immune serum taken before chromatography over the pME6 affinity column (lane 1); serum taken after passage over the column (lane 2); affinity-purified anti-pME6 antibodies (lane 3); mAb 89.1 (specific for MSP-183; lane 4); and mAb 111.4 (specific for MSP-142 and MSP-119; lane 5). Positions of molecular mass marker proteins are indicated, and bands corresponding to the MSP-1 precursor, MSP-183, MSP-142, and MSP-119 are arrowed.

Mentions: Antibodies which prevent MSP-1 processing and erythrocyte invasion may be involved in mediating protection against blood-stage parasitemia. If antibodies induced to other domains of MSP-1 can block the activity of processing-inhibitory antibodies specific for MSP-119, their presence in human sera may be disadvantageous to the host. In light of the above data, it was decided to investigate the ability of naturally acquired antibodies, specific for the region of MSP-1 corresponding to pME6, to block the processing-inhibitory activity of mAbs 12.8 and 12.10. This particular construct was chosen because pME6 is readily soluble (8), and the E. coli clone which expresses pME6 does so at very high levels. Human antibodies reactive with pME6 were isolated from pooled Gambian adult immune serum by affinity chromatography on immobilized pME6 fusion protein. The eluted Ig was judged to be >98% pure as assessed by SDS-PAGE under reducing conditions (data not shown). The Ig was concentrated by ultrafiltration and assayed by immunoblot for reactivity with FCB-1 merozoite polypeptides. Strong reactivity was observed with only two merozoite polypeptides of ∼83 and 195 kD (Fig. 5); these most likely correspond to MSP-183 and the residual MSP-1 precursor protein. Note that the purified antibodies showed no reactivity with the MSP-142 and MSP-119 species (Fig. 5, arrows). In confirmation of this, analysis of the affinity-purified Ig by indirect immunofluorescence showed strong reactivity with acetone-fixed FCB-1 or T9/96 schizonts, but none with newly invaded ring stage parasites, which contain only MSP-119 (9–12) (data not shown). Note that since the pME6 construct covers much of the highly conserved MSP-1 block 3 domain, as well as all of the conserved block 5 (see Fig. 3), antibodies against pME6 would be expected to recognize both allelic forms of MSP-1.


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)

Specificity of affinity-purified human anti-pME6  antibodies shown by Western  blot analysis. An SDS extract of  FCB-1 merozoites was subjected to SDS-PAGE under  nonreducing conditions on a  12.5% gel, transferred to nitrocellulose, then probed with a  sample of pooled human immune serum taken before chromatography over the pME6 affinity column (lane 1); serum  taken after passage over the column (lane 2); affinity-purified  anti-pME6 antibodies (lane 3);  mAb 89.1 (specific for MSP-183;  lane 4); and mAb 111.4 (specific  for MSP-142 and MSP-119; lane  5). Positions of molecular mass  marker proteins are indicated, and  bands corresponding to the MSP-1  precursor, MSP-183, MSP-142,  and MSP-119 are arrowed.
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Related In: Results  -  Collection

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Figure 5: Specificity of affinity-purified human anti-pME6 antibodies shown by Western blot analysis. An SDS extract of FCB-1 merozoites was subjected to SDS-PAGE under nonreducing conditions on a 12.5% gel, transferred to nitrocellulose, then probed with a sample of pooled human immune serum taken before chromatography over the pME6 affinity column (lane 1); serum taken after passage over the column (lane 2); affinity-purified anti-pME6 antibodies (lane 3); mAb 89.1 (specific for MSP-183; lane 4); and mAb 111.4 (specific for MSP-142 and MSP-119; lane 5). Positions of molecular mass marker proteins are indicated, and bands corresponding to the MSP-1 precursor, MSP-183, MSP-142, and MSP-119 are arrowed.
Mentions: Antibodies which prevent MSP-1 processing and erythrocyte invasion may be involved in mediating protection against blood-stage parasitemia. If antibodies induced to other domains of MSP-1 can block the activity of processing-inhibitory antibodies specific for MSP-119, their presence in human sera may be disadvantageous to the host. In light of the above data, it was decided to investigate the ability of naturally acquired antibodies, specific for the region of MSP-1 corresponding to pME6, to block the processing-inhibitory activity of mAbs 12.8 and 12.10. This particular construct was chosen because pME6 is readily soluble (8), and the E. coli clone which expresses pME6 does so at very high levels. Human antibodies reactive with pME6 were isolated from pooled Gambian adult immune serum by affinity chromatography on immobilized pME6 fusion protein. The eluted Ig was judged to be >98% pure as assessed by SDS-PAGE under reducing conditions (data not shown). The Ig was concentrated by ultrafiltration and assayed by immunoblot for reactivity with FCB-1 merozoite polypeptides. Strong reactivity was observed with only two merozoite polypeptides of ∼83 and 195 kD (Fig. 5); these most likely correspond to MSP-183 and the residual MSP-1 precursor protein. Note that the purified antibodies showed no reactivity with the MSP-142 and MSP-119 species (Fig. 5, arrows). In confirmation of this, analysis of the affinity-purified Ig by indirect immunofluorescence showed strong reactivity with acetone-fixed FCB-1 or T9/96 schizonts, but none with newly invaded ring stage parasites, which contain only MSP-119 (9–12) (data not shown). Note that since the pME6 construct covers much of the highly conserved MSP-1 block 3 domain, as well as all of the conserved block 5 (see Fig. 3), antibodies against pME6 would be expected to recognize both allelic forms of MSP-1.

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