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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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Inhibition of MSP-142 processing by anti–MSP119 mAbs.  Washed FCB-1 merozoites were either immediately detergent solubilized  (0h) or incubated for 1 h at 37°C in the presence of no antibodies (noAb),  1 mM PMSF as inhibitor control, or purified mAbs 12.10, 12.8, 1E1,  111.4, 8A12, 12D11, 7E5 or 117.2, all at a final concentration of 300 μg  ml−1. MSP-1 secondary processing in the samples was then quantified as  described. All samples were tested in triplicate, and percentage of processing was calculated as described in Materials and Methods.
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Figure 1: Inhibition of MSP-142 processing by anti–MSP119 mAbs. Washed FCB-1 merozoites were either immediately detergent solubilized (0h) or incubated for 1 h at 37°C in the presence of no antibodies (noAb), 1 mM PMSF as inhibitor control, or purified mAbs 12.10, 12.8, 1E1, 111.4, 8A12, 12D11, 7E5 or 117.2, all at a final concentration of 300 μg ml−1. MSP-1 secondary processing in the samples was then quantified as described. All samples were tested in triplicate, and percentage of processing was calculated as described in Materials and Methods.

Mentions: The assay was used to quantify MSP-1 secondary processing and its inhibition by a panel of anti–MSP-119 mAbs. Washed FCB-1 merozoites were incubated on ice in the presence of individual purified mAbs, then transferred to 37°C for 1 h to allow processing to occur. MSP-142 processing in the individual samples was then assessed using the above protocol. Fig. 1 shows that mAb 12.8, which recognizes a conserved epitope in the first EGF-like motif of MSP-119 (36, 37), inhibited processing by 96% of the control value, whereas mAb 12.10, which recognizes an epitope formed by the two EGF-like motifs together (37), inhibited processing by 98%. Monoclonal antibody 1E1 showed no processing-inhibitory activity in this assay system. Interestingly, our earlier data obtained using a semiquantitative Western blot–based assay indicated that mAb 1E1 appeared to induce abnormal processing rather than preventing the processing; in addition, mAb 1E1 does not prevent erythrocyte invasion in in vitro cultures of P. falciparum (25). Antibodies 8A12 and 117.2 inhibited MSP-142 processing by 18 and 12%, respectively, whereas mAbs 111.4, 12D11, and 7E5 did not detectably prevent processing. Neither mAb 89.1, which recognizes an epitope within the NH2-terminal domain of MSP-1 (MSP-183), nor the anti– P. yoelii MSP-1 mAb 25.1, had any effect on the processing (data not shown). These results confirm that mAbs 12.8 and 12.10 are potent inhibitors of MSP-142 processing. In similar assays using merozoites of the P. falciparum clone T9/96, which expresses the alternative dimorphic form of MSP-1 (31), but retains the nonpolymorphic epitopes recognized by mAbs 12.8 and 12.10 (38), both mAbs showed similarly potent processing inhibition activity (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)

Inhibition of MSP-142 processing by anti–MSP119 mAbs.  Washed FCB-1 merozoites were either immediately detergent solubilized  (0h) or incubated for 1 h at 37°C in the presence of no antibodies (noAb),  1 mM PMSF as inhibitor control, or purified mAbs 12.10, 12.8, 1E1,  111.4, 8A12, 12D11, 7E5 or 117.2, all at a final concentration of 300 μg  ml−1. MSP-1 secondary processing in the samples was then quantified as  described. All samples were tested in triplicate, and percentage of processing was calculated as described in Materials and Methods.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2199131&req=5

Figure 1: Inhibition of MSP-142 processing by anti–MSP119 mAbs. Washed FCB-1 merozoites were either immediately detergent solubilized (0h) or incubated for 1 h at 37°C in the presence of no antibodies (noAb), 1 mM PMSF as inhibitor control, or purified mAbs 12.10, 12.8, 1E1, 111.4, 8A12, 12D11, 7E5 or 117.2, all at a final concentration of 300 μg ml−1. MSP-1 secondary processing in the samples was then quantified as described. All samples were tested in triplicate, and percentage of processing was calculated as described in Materials and Methods.
Mentions: The assay was used to quantify MSP-1 secondary processing and its inhibition by a panel of anti–MSP-119 mAbs. Washed FCB-1 merozoites were incubated on ice in the presence of individual purified mAbs, then transferred to 37°C for 1 h to allow processing to occur. MSP-142 processing in the individual samples was then assessed using the above protocol. Fig. 1 shows that mAb 12.8, which recognizes a conserved epitope in the first EGF-like motif of MSP-119 (36, 37), inhibited processing by 96% of the control value, whereas mAb 12.10, which recognizes an epitope formed by the two EGF-like motifs together (37), inhibited processing by 98%. Monoclonal antibody 1E1 showed no processing-inhibitory activity in this assay system. Interestingly, our earlier data obtained using a semiquantitative Western blot–based assay indicated that mAb 1E1 appeared to induce abnormal processing rather than preventing the processing; in addition, mAb 1E1 does not prevent erythrocyte invasion in in vitro cultures of P. falciparum (25). Antibodies 8A12 and 117.2 inhibited MSP-142 processing by 18 and 12%, respectively, whereas mAbs 111.4, 12D11, and 7E5 did not detectably prevent processing. Neither mAb 89.1, which recognizes an epitope within the NH2-terminal domain of MSP-1 (MSP-183), nor the anti– P. yoelii MSP-1 mAb 25.1, had any effect on the processing (data not shown). These results confirm that mAbs 12.8 and 12.10 are potent inhibitors of MSP-142 processing. In similar assays using merozoites of the P. falciparum clone T9/96, which expresses the alternative dimorphic form of MSP-1 (31), but retains the nonpolymorphic epitopes recognized by mAbs 12.8 and 12.10 (38), both mAbs showed similarly potent processing inhibition activity (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