Characterization of vesicle-associated exported immunodominant antigens of the human pathogen Babesia duncani.

Human babesiosis is an emerging disease caused by intraerythrocytic Babesia parasites, primarily transmitted through tick bites. Among the species of Babesia that infect humans, Babesia duncani causes severe disease in murine models, associated with excessive cytokine responses that contribute to immunopathology. The parasite factors that mediate host immune activation remain poorly defined. Here, we show that B. duncani, similar to B. microti, exports antigens through vesicle-mediated pathways. Screening a panel of 105 known and predicted secreted proteins using sera from B. duncani-infected and uninfected mice identified multiple immunodominant antigens. We further characterized two representative antigens and demonstrate using differential centrifugation, vesicle enrichment, immunofluorescence microscopy, and transmission electron microscopy that these antigens localize to vesicles released by B. duncani-infected erythrocytes into the extracellular environment. These findings reveal vesicle-mediated antigen export as a key feature of B. duncani infection and suggest a pathway through which parasite-derived antigens may be delivered to the host immune system. Such findings may guide future studies aimed at developing diagnostic or vaccine strategies.