Elucidating the functional role of the novel BdP50 protein and extracellular vesicles in the human erythrocyte infection by Babesia divergens

Authors: GONZALEZ, LUIS MIGUEL - Instituto De Salud Carlos Iii; REVUELTA, BELÉN - Instituto De Salud Carlos Iii; AITOR, GIL - Instituto De Salud Carlos Iii; TERRON, MARIA - Instituto De Salud Carlos Iii; SACHSE, MARTIN CHRISTOP - Instituto De Salud Carlos Iii; SOTILLO, JAVIER - Instituto De Salud Carlos Iii; LUQUE, DANIEL - Instituto De Salud Carlos Iii; RAHMAN, RAIHAN - Washington State University; Bastos, Reginaldo; SUAREZ, CARLOS ESTEBAN - Retired ARS Employee; MONTERO, ESTRELLA - Instituto De Salud Carlos Iii

Submitted to: PLOS Neglected Tropical Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2025
Publication Date: 8/13/2025
Citation: Gonzalez, L., Revuelta, B., Aitor, G., Terron, M.C., Sachse, M., Sotillo, J., Luque, D., Rahman, R.S., Bastos, R.G., Suarez, C., Montero, E. 2025. Elucidating the functional role of the novel BdP50 protein and extracellular vesicles in the human erythrocyte infection by Babesia divergens. PLOS Neglected Tropical Diseases. 19(8). Article e0013401. https://doi.org/10.1371/journal.pntd.0013401.
DOI: https://doi.org/10.1371/journal.pntd.0013401

Interpretive Summary: Babesia divergens is a zoonotic tickborne blood parasite that replicates inside red blood cells (RBCs) and causes clinical babesiosis in humans and cattle. This study shows that P50 (BdP50), a novel protein of B. divergens, localizes on the surface of blood stage parasites and B. divergens vesicles secreted to the medium by parasites cultured using human RBCs. Furthermore, anti-BdP50 antibodies inhibited up to 88% of the de novo parasite entry into RBCs, reinforcing the role of BdP50 in both host cell interaction and invasion. Notably, the anti-BdP50 antibody inhibitory effect gradually decreased over time, despite the continued presence of antibodies in the medium. Additionally, we revealed that the BdP50-expressing B. divergens vesicles modify the extracellular environment and prime naïve RBCs, promoting invasion and growth of the parasite. In conclusion, this study highlights the role of BdP50 and Bd-derived EVs in the life cycle of B. divergens, which may serve as promising biomarkers for the development of new diagnostics, therapies and vaccines to control babesiosis.

Technical Abstract: Babesia divergens is a tickborne hemoparasite that replicates inside red blood cells (RBCs) during its asexual life cycle, causing clinical babesiosis in humans and cattle. The B. divergens P50 (BdP50) is a novel glycosylphosphatidylinositol-anchored protein that may play a role in the parasite complex life cycle. It was previously shown that BdP50 is synthesized as a preprotein (p48) and processed to its active form (p35), which localizes on the surface of both invasive merozoites and extracellular B. divergens vesicles (Bd-derived EVs) that are secreted to the medium by parasites cultured using human RBCs. Here we showed that BdP50 binds to RBCs, suggesting that both free merozoites and Bd-derived EVs can interact with the host RBC through BdP50. Furthermore, anti-BdP50 antibodies inhibited up to 88% of the de novo merozoite entry into RBCs after invasion, reinforcing the role of BdP50 in both host cell interaction and invasion. Notably, the inhibitory effect gradually decreased over time, despite the continued presence of antibodies against BdP50 in the medium. A plausible explication points to the Bd-derived EVs, as we revealed that they modify the extracellular environment and prime naïve RBCs, promoting invasion and growth of the parasite. This strategy, involving BdP50, may help counteract a hostile extracellular environment for the parasite due to the presence of anti-B. divergens antibodies. In conclusion, this study highlights the role of BdP50 and Bd-derived EVs in the life cycle of B. divergens, which may be promising as biomarkers for the development of new diagnostics, therapies and vaccines to control babesiosis.