Human antibodies to the 19 kDa C-terminal fragment of Plasmodium falciparum merozoite surface protein 1 inhibit parasite growth in vitro

The 19kDa, C-terminal fragment of the major surface protein of Plasmodium falciparum (PfMSP1(19)) is a candidate for inclusion in a subunit malaria vaccine. In this study, we show that PfMSP1(19)-specific antibodies, affinity purified from malaria-immune human serum can: (i) compete with invasion-inhibitory monoclonal antibodies for binding to PfMSP1(19) and (ii) mediate inhibition of parasite growth in vitro, in the absence of complement and mononuclear cells, at physiological antibody concentrations (100 mu g/ml). Parasites expressing either the K1 or 3D7 allele of PfMSP1(19) were equally susceptible to inhibition of merozoite invasion, indicating that the target epitopes of inhibitory antibodies are conserved or crossreactive. These studies suggest that vaccines designed to induce antibodies to PfMSP1(19) may protect against the high levels of malaria parasitaemia which are associated with clinical disease.