NK cells inhibit <i>Plasmodium falciparum</i> growth in red blood cells via antibody-dependent cellular cytotoxicity.

Abstract

Antibodies acquired naturally through repeated exposure to <i>Plasmodium falciparum</i> are essential in the control of blood-stage malaria. Antibody-dependent functions may include neutralization of parasite-host interactions, complement activation, and activation of Fc receptor functions. A role of antibody-dependent cellular cytotoxicity (ADCC) by natural killer (NK) cells in protection from malaria has not been established. Here we show that IgG isolated from adults living in a malaria-endemic region activated ADCC by primary human NK cells, which lysed infected red blood cells (RBCs) and inhibited parasite growth in an in vitro assay for ADCC-dependent growth inhibition. RBC lysis by NK cells was highly selective for infected RBCs in a mixed culture with uninfected RBCs. Human antibodies to <i>P. falciparum</i> antigens PfEMP1 and RIFIN were sufficient to promote NK-dependent growth inhibition. As these results implicate acquired immunity through NK-mediated ADCC, antibody-based vaccines that target bloodstream parasites should consider this new mechanism of action.