Accessing invasion-competent Plasmodium vivax merozoites reveals antibody-dependent NK cell activation.

Malaria pathogenesis and clinical symptoms arise from blood-stage replication of Plasmodium parasites, which depends on rapid invasion of red blood cells by merozoites. Despite the central importance of this stage, direct functional studies of Plasmodium vivax (P. vivax) merozoites remain limited by the lack of continuous in vitro culture and restricted access to viable, invasion-competent merozoites from clinical isolates. Consequently, key aspects of P. vivax merozoite biology and immune recognition remain poorly defined. Here, we establish a robust platform enabling synchronized release and high-yield isolation of invasion-competent P. vivax merozoites from ex vivo cultures. Reversible inhibition of parasite egress using the PKG inhibitor ML10 enables synchronization at the segmented schizont stage, followed by rapid mechanical release of merozoites using a liposome-based extrusion approach. This workflow yields highly pure merozoites with recovery rates exceeding 75% while preserving structural integrity and invasive capacity. Leveraging this platform, we demonstrate that antibody-opsonized P. vivax merozoites activate human natural killer cells, revealing functional antibody-dependent immune responses.