Anti-merozoite antibodies induce natural killer cell effector function and are associated with immunity against malaria.

Natural killer (NK) cells are potent immune effectors that can be activated via antibody-mediated Fc receptor engagement. Using multiparameter flow cytometry, we found that NK cells degranulate and release IFN-γ upon stimulation with antibody-opsonized Plasmodium falciparum merozoites. Antibody-dependent NK (Ab-NK) activity was largely strain transcending and enhanced invasion inhibition into erythrocytes. Ab-NK was associated with the successful control of parasitemia after experimental malaria challenge in African adults. In an independent cohort study in children, Ab-NK increased with age, was boosted by concurrent P. falciparum infections, and was associated with a lower risk of clinical episodes of malaria. Nine of the 14 vaccine candidates tested induced Ab-NK, including some less well-characterized antigens: P41, P113, MSP11, RHOPH3, and Pf_11363200. These data highlight an important role of Ab-NK activity in immunity against malaria and provide a potential mechanism for evaluating vaccine candidates. A different antibody angle: Natural killer (NK) cells have been shown to mediate immune responses against Plasmodium falciparum using multiple effector functions. Odera et al. now show that antibody-opsonized P. falciparum merozoites can induce NK cell degranulation and IFN-γ production. This response was not strain specific and reduced invasion of merozoites into uninfected red blood cells. Using a controlled human malaria infection study in adults, they observed that antibody-dependent NK (Ab-NK) cell activity correlated directly with the control of parasitemia. In addition, in a cohort of children living in an endemic malaria setting, Ab-NK frequency increased with age, was boosted during P. falciparum infection, and was linked to a reduced risk of clinical malaria. These findings highlight a key role for antibody-mediated NK cell responses during malaria. —CF [ABSTRACT FROM AUTHOR]