Inhibition of Erythrocyte Invasion andPlasmodium falciparumMerozoite Surface Protein 1 Processing by Human Immunoglobulin G1 (IgG1) and IgG3 Antibodies

Abstract

Antigen-specific antibodies (Abs) to the 19-kDa carboxy-terminal region of Plasmodium falciparum merozoite surface protein 1 (MSP1 19 ) play an important role in protective immunity to malaria. Mouse monoclonal Abs (MAbs) 12.10 and 12.8 recognizing MSP1 19 can inhibit red cell invasion by interfering with MSP1 processing on the merozoite surface. We show here that this ability is dependent on the intact Ab since Fab and F(ab) 2 fragments derived from MAb 12.10, although capable of binding MSP1 with high affinity and competing with the intact antibody for binding to MSP1, were unable to inhibit erythrocyte invasion or MSP1 processing. The DNA sequences of the variable (V) regions of both MAbs 12.8 and 12.10 were obtained, and partial amino acid sequences of the same regions were confirmed by mass spectrometry. Human chimeric Abs constructed by using these sequences, which combine the original mouse V regions with human ␥1 and ␥3 constant regions, retain the ability to bind to both parasites and recombinant MSP1 19 , and both chimeric human immunoglobulin G1s (IgG1s) were at least as good at inhibiting erythrocyte invasion as the parental murine MAbs 12.8 and 12.10. Furthermore, the human chimeric Abs of the IgG1 class (but not the corresponding human IgG3), induced significant NADPHmediated oxidative bursts and degranulation from human neutrophils. These chimeric human Abs will enable investigators to examine the role of human Fc␥ receptors in immunity to malaria using a transgenic parasite and mouse model and may prove useful in humans for neutralizing parasites as an adjunct to antimalarial drug therapy.

Recombinant protein vaccines against the asexual blood-stages ofPlasmodium falciparum

“…The evidence that antibodies to asexual blood stage antigens are a major mediator of naturallyacquired adaptive immune responses to malaria is overwhelming, and consequently the focus of the subunit vaccine strategy has been to induce an antibody response that inhibits parasite growth. Antibodies to the two leading asexual blood stage vaccine candidates, MSP1 and AMA1, as well as many other merozoite surface proteins, block the invasion of erythrocytes by merozoites in in vitro GIA, 33,36,[84][85][86][87][88][89][90][91] and there is some evidence from studies in animal models that high GIA activity correlates with protection. 92 CP2.9 is a chimeric protein in which domain III of apical membrane antigen 1 (AMA1) is linked to MSP1 19 .…”

Plasmodium falciparum 19-Kilodalton Merozoite Surface Protein 1 (MSP1)-Specific Antibodies That Interfere with Parasite GrowthIn VitroCan Inhibit MSP1 Processing, Merozoite Invasion, and Intracellular Parasite Development

“…However, antibody fine specificity (12,32) and Fcmediated mechanisms (25,27) are important. Data acquired in this study suggest that polyclonal antibodies to MSP1 19 can inhibit parasite invasion of erythrocytes by inhibiting MSP1 processing and by a second, potentially more important mechanism, perhaps steric hindrance of parasite binding.…”

“…The fact that another factor other than MSP1 processing is involved means that the processing assay alone is an inadequate method to assay antibody-mediated inhibition of parasite growth. However, since some MAbs show good activity in both processing and invasion inhibition (7,19,25), it remains a viable tool to dissect the mode of action of MSP1-specific antibodies. The contribution inhibition of intracellular growth makes toward the protective effect of anti-MSP1 antibodies needs further investigation, but it is interesting that an engineered variant of MSP1 19 appears able to induce antibodies that are more active in this assay than those induced by the wild-type protein, suggesting that the fine specificity of the antibodies may contribute to this mechanism.…”

Correlates of protection forPlasmodium falciparummalaria vaccine development: current knowledge and future research

“…These approaches may be valuable for measuring antigen-specific inhibitory antibodies in human vaccine trials, especially when testing vaccines in populations with significant background immunity that can confound the assessment of vaccine-induced immunity. Assays have also been developed to measure antibodies that inhibit processing of MSP1 and AMA1 as an additional functional assay [80,81], but these have not been widely used.…”