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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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The binding of processing-inhibitory mAbs 12.8 and 12.10  to FCB-1 merozoite-derived MSP-1 is competitively prevented by certain other anti–MSP-1 mAbs. Plates coated with a merozoite antigen extract were preincubated in triplicate with either no antibody (noAb; control wells), or with predetermined saturating concentrations of mAbs 12.10,  12.8, 2.2, 111.4, 7.5, 1E1, or 89.1. The effects of this pretreatment on  binding of radioiodinated mAbs 12.8 (A) or 12.10 (B) to the immobilized  antigen was then assessed. All samples were tested in triplicate. Blocking  activity of individual mAbs was calculated as described in Materials and  Methods.
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Figure 2: The binding of processing-inhibitory mAbs 12.8 and 12.10 to FCB-1 merozoite-derived MSP-1 is competitively prevented by certain other anti–MSP-1 mAbs. Plates coated with a merozoite antigen extract were preincubated in triplicate with either no antibody (noAb; control wells), or with predetermined saturating concentrations of mAbs 12.10, 12.8, 2.2, 111.4, 7.5, 1E1, or 89.1. The effects of this pretreatment on binding of radioiodinated mAbs 12.8 (A) or 12.10 (B) to the immobilized antigen was then assessed. All samples were tested in triplicate. Blocking activity of individual mAbs was calculated as described in Materials and Methods.

Mentions: Wells of 96-well polyvinyl chloride plates coated with merozoite antigen extract were incubated with anti–MSP-119 mAbs at saturating concentrations. The plates were then washed and an optimal concentration of radioiodinated mAb 12.8 or 12.10 was added. After further incubation, plates were washed and individual wells were counted directly in a gamma counter. Fig. 2 shows that antibodies known to interfere with the processing activity of mAbs 12.8 and 12.10 prevented these mAbs from binding to immobilized antigen. Although mAbs 7.5 and 1E1 prevented binding of both radiolabeled mAbs, mAb 2.2 only significantly prevented binding of mAb 12.8, consistent with its ability to interfere with the processing-inhibitory activity of mAb 12.8 but not 12.10 (25). Preincubation with mAb 111.4 had little or no effect on binding of the radiolabeled mAbs, consistent with its lack of blocking activity (25); mAb 89.1 was similarly ineffective in competing with 12.8 or 12.10 binding. Identical results were obtained when rMSP-119 was used to coat RIA plates (data not shown).


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)

The binding of processing-inhibitory mAbs 12.8 and 12.10  to FCB-1 merozoite-derived MSP-1 is competitively prevented by certain other anti–MSP-1 mAbs. Plates coated with a merozoite antigen extract were preincubated in triplicate with either no antibody (noAb; control wells), or with predetermined saturating concentrations of mAbs 12.10,  12.8, 2.2, 111.4, 7.5, 1E1, or 89.1. The effects of this pretreatment on  binding of radioiodinated mAbs 12.8 (A) or 12.10 (B) to the immobilized  antigen was then assessed. All samples were tested in triplicate. Blocking  activity of individual mAbs was calculated as described in Materials and  Methods.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2199131&req=5

Figure 2: The binding of processing-inhibitory mAbs 12.8 and 12.10 to FCB-1 merozoite-derived MSP-1 is competitively prevented by certain other anti–MSP-1 mAbs. Plates coated with a merozoite antigen extract were preincubated in triplicate with either no antibody (noAb; control wells), or with predetermined saturating concentrations of mAbs 12.10, 12.8, 2.2, 111.4, 7.5, 1E1, or 89.1. The effects of this pretreatment on binding of radioiodinated mAbs 12.8 (A) or 12.10 (B) to the immobilized antigen was then assessed. All samples were tested in triplicate. Blocking activity of individual mAbs was calculated as described in Materials and Methods.
Mentions: Wells of 96-well polyvinyl chloride plates coated with merozoite antigen extract were incubated with anti–MSP-119 mAbs at saturating concentrations. The plates were then washed and an optimal concentration of radioiodinated mAb 12.8 or 12.10 was added. After further incubation, plates were washed and individual wells were counted directly in a gamma counter. Fig. 2 shows that antibodies known to interfere with the processing activity of mAbs 12.8 and 12.10 prevented these mAbs from binding to immobilized antigen. Although mAbs 7.5 and 1E1 prevented binding of both radiolabeled mAbs, mAb 2.2 only significantly prevented binding of mAb 12.8, consistent with its ability to interfere with the processing-inhibitory activity of mAb 12.8 but not 12.10 (25). Preincubation with mAb 111.4 had little or no effect on binding of the radiolabeled mAbs, consistent with its lack of blocking activity (25); mAb 89.1 was similarly ineffective in competing with 12.8 or 12.10 binding. Identical results were obtained when rMSP-119 was used to coat RIA plates (data not shown).

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