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 f alciparum (PfMSP1(19)) is a candidate for inclusion in a subunit malaria va ccine. In this study, we show that PfMSP1(19)-specific antibodies, affinity purified from malaria-immune human serum can: (i) compete with invasion-in hibitory monoclonal antibodies for binding to PfMSP1(19) and (ii) mediate i nhibition of parasite growth in vitro, in the absence of complement and mon onuclear cells, at physiological antibody concentrations (100 mu g/ml). Par asites expressing either the K1 or 3D7 allele of PfMSP1(19) were equally su sceptible to inhibition of merozoite invasion, indicating that the target e pitopes of inhibitory antibodies are conserved or crossreactive. These stud ies suggest that vaccines designed to induce antibodies to PfMSP1(19) may p rotect against the high levels of malaria parasitaemia which are associated with clinical disease.