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 cell by merozoites. Despite the central importance of this stage, direct functional studies of Plasmodium vivax merozoites have been severely limited by the lack of continuous in vitro culture and the inability to routinely access 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 that enables synchronized release and high-yield isolation of invasion-competent P. vivax merozoites directly from ex vivo cultures. Reversible inhibition of parasite egress using the cGMP-dependent protein kinase inhibitor ML10 allows precise synchronization at the segmented schizont stage, followed by rapid mechanical liberation 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 provide direct functional evidence that antibody opsonized P. vivax merozoites activate human natural killer cells consistent with antibody-dependent cellular cytotoxicity mechanisms. Together, this study overcomes a long-standing technical barrier and enables direct investigation of P. vivax merozoite invasion biology and immune effector responses.