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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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Affinity-purified, naturally acquired human anti-pME6 antibodies are potent blocking antibodies. (A) Equal aliquots of washed FCB-1  merozoites were solubilized directly into detergent (0 h control), or preincubated either with reaction buffer only or with affinity-purified human  anti-pME6 antibodies at a final concentration of 300 μg ml−1. An equal  concentration of mAb 12.10 or 12.8 was then added to some samples as  shown, and processing was allowed to proceed for 1 h in all but the 0 h  control. Inhibition of MSP-1 processing mediated by mAb 12.8 alone (96%)  was almost completely reversed by preincubation with the anti-pME6 antibodies, whereas the inhibition of processing mediated by mAb 12.10  alone (97%) was completely unaffected by preincubation with anti-pME6  antibodies. (B) RIA plates coated with merozoite antigen were pretreated  with nonradioactive mAb 12.10 or 12.8 at a saturating concentration (100 μg  ml−1), or affinity-purified anti-pME6 antibodies at a saturating concentration (300 μg ml−1), or nonimmune human serum (NI Hs) at an equivalent final antibody concentration, before assessing the ability of radioiodinated mAb 12.8 or 12.10 to bind. All samples were assayed in triplicate,  and SE bars are shown.
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Figure 6: Affinity-purified, naturally acquired human anti-pME6 antibodies are potent blocking antibodies. (A) Equal aliquots of washed FCB-1 merozoites were solubilized directly into detergent (0 h control), or preincubated either with reaction buffer only or with affinity-purified human anti-pME6 antibodies at a final concentration of 300 μg ml−1. An equal concentration of mAb 12.10 or 12.8 was then added to some samples as shown, and processing was allowed to proceed for 1 h in all but the 0 h control. Inhibition of MSP-1 processing mediated by mAb 12.8 alone (96%) was almost completely reversed by preincubation with the anti-pME6 antibodies, whereas the inhibition of processing mediated by mAb 12.10 alone (97%) was completely unaffected by preincubation with anti-pME6 antibodies. (B) RIA plates coated with merozoite antigen were pretreated with nonradioactive mAb 12.10 or 12.8 at a saturating concentration (100 μg ml−1), or affinity-purified anti-pME6 antibodies at a saturating concentration (300 μg ml−1), or nonimmune human serum (NI Hs) at an equivalent final antibody concentration, before assessing the ability of radioiodinated mAb 12.8 or 12.10 to bind. All samples were assayed in triplicate, and SE bars are shown.

Mentions: The ability of the affinity-purified human antibodies to block the processing-inhibitory effects of mAbs 12.8 and 12.10 was then assessed. Merozoites were incubated on ice in the presence or absence of the human anti-pME6 antibodies, and then mAb 12.8 or 12.10 was added and the samples were incubated for 20 min on ice before transfer to 37°C for 1 h to allow processing to take place. Fig. 6 A shows that pretreatment with the anti-pME6 antibodies virtually abolished the processing-inhibitory activity of mAb 12.8, but interestingly had no effect on the inhibitory activity of mAb 12.10. In parallel binding assays (Fig. 6 B), the anti-pME6 antibodies competed effectively with binding of mAb 12.8, but not mAb 12.10, to immobilized merozoite-derived antigen.


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)

Affinity-purified, naturally acquired human anti-pME6 antibodies are potent blocking antibodies. (A) Equal aliquots of washed FCB-1  merozoites were solubilized directly into detergent (0 h control), or preincubated either with reaction buffer only or with affinity-purified human  anti-pME6 antibodies at a final concentration of 300 μg ml−1. An equal  concentration of mAb 12.10 or 12.8 was then added to some samples as  shown, and processing was allowed to proceed for 1 h in all but the 0 h  control. Inhibition of MSP-1 processing mediated by mAb 12.8 alone (96%)  was almost completely reversed by preincubation with the anti-pME6 antibodies, whereas the inhibition of processing mediated by mAb 12.10  alone (97%) was completely unaffected by preincubation with anti-pME6  antibodies. (B) RIA plates coated with merozoite antigen were pretreated  with nonradioactive mAb 12.10 or 12.8 at a saturating concentration (100 μg  ml−1), or affinity-purified anti-pME6 antibodies at a saturating concentration (300 μg ml−1), or nonimmune human serum (NI Hs) at an equivalent final antibody concentration, before assessing the ability of radioiodinated mAb 12.8 or 12.10 to bind. All samples were assayed in triplicate,  and SE bars are shown.
© Copyright Policy
Related In: Results  -  Collection

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Figure 6: Affinity-purified, naturally acquired human anti-pME6 antibodies are potent blocking antibodies. (A) Equal aliquots of washed FCB-1 merozoites were solubilized directly into detergent (0 h control), or preincubated either with reaction buffer only or with affinity-purified human anti-pME6 antibodies at a final concentration of 300 μg ml−1. An equal concentration of mAb 12.10 or 12.8 was then added to some samples as shown, and processing was allowed to proceed for 1 h in all but the 0 h control. Inhibition of MSP-1 processing mediated by mAb 12.8 alone (96%) was almost completely reversed by preincubation with the anti-pME6 antibodies, whereas the inhibition of processing mediated by mAb 12.10 alone (97%) was completely unaffected by preincubation with anti-pME6 antibodies. (B) RIA plates coated with merozoite antigen were pretreated with nonradioactive mAb 12.10 or 12.8 at a saturating concentration (100 μg ml−1), or affinity-purified anti-pME6 antibodies at a saturating concentration (300 μg ml−1), or nonimmune human serum (NI Hs) at an equivalent final antibody concentration, before assessing the ability of radioiodinated mAb 12.8 or 12.10 to bind. All samples were assayed in triplicate, and SE bars are shown.
Mentions: The ability of the affinity-purified human antibodies to block the processing-inhibitory effects of mAbs 12.8 and 12.10 was then assessed. Merozoites were incubated on ice in the presence or absence of the human anti-pME6 antibodies, and then mAb 12.8 or 12.10 was added and the samples were incubated for 20 min on ice before transfer to 37°C for 1 h to allow processing to take place. Fig. 6 A shows that pretreatment with the anti-pME6 antibodies virtually abolished the processing-inhibitory activity of mAb 12.8, but interestingly had no effect on the inhibitory activity of mAb 12.10. In parallel binding assays (Fig. 6 B), the anti-pME6 antibodies competed effectively with binding of mAb 12.8, but not mAb 12.10, to immobilized merozoite-derived antigen.

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