Spherical body protein 4 from Babesia bigemina: A novel gene that contains conserved B-cell epitopes and induces cross-reactive neutralizing antibodies in Babesia ovata

Authors: MOSQUEDA, JUAN - Autonomous University Of Queretaro; HERNANDEZ-SILVA, DIEGO - Autonomous University Of Queretaro; Ueti, Massaro; CRUZ-RESÉNDIZ, ADOLFO - Autonomous University Of Queretaro; MARQUEZ-CERVANTEZ, RICARDO - Autonomous University Of Queretaro; VALDEZ-ESPINOZA, URIEL - Autonomous University Of Queretaro; DANG-TRINH, MINH-ANH - Obihiro University; NGUYEN, THU-THUY - Obihiro University; CAMACHO-NUEZ, MINERVA - Ciudad University - Mexico; MERCADO-URIOSTEGUI, MIGUEL - Autonomous University Of Queretaro; AGUILAR-TIPACAMÚ, GABRIELA - Autonomous University Of Queretaro; RAMOS-ARAGON, JUAN - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); HERNANDEZ-ORTIZ, RUBEN - Instituto Nacional De Investigaciones Forestales Y Agropecuarias (INIFAP); KAWAZU, SHIN-ICHIRO - Obihiro University; IGARASHI, IKUO - Obihiro University

Submitted to: Pathogens
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/20/2023
Publication Date: 3/22/2023
Citation: Mosqueda, J., Hernandez-Silva, D.J., Ueti, M.W., Cruz-Reséndiz, A., Marquez-Cervantez, R., Valdez-Espinoza, U.M., Dang-Trinh, M., Nguyen, T., Camacho-Nuez, M., Mercado-Uriostegui, M.A., Aguilar-Tipacamú, G., Ramos-Aragon, J.A., Hernandez-Ortiz, R., Kawazu, S., Igarashi, I. 2023. Spherical body protein 4 from Babesia bigemina: A novel gene that contains conserved B-cell epitopes and induces cross-reactive neutralizing antibodies in Babesia ovata. Pathogens. 12(3). Article 495. https://doi.org/10.3390/pathogens12030495.
DOI: https://doi.org/10.3390/pathogens12030495

Interpretive Summary: Babesia parasites secrete proteins stored in organelles of the apical complex, which are involved in all steps of the invasion process of vertebrate host cells. Babesia parasites have large, round intracellular organelles called spherical bodies. Evidence suggests that proteins from these organelles are released during the invasion of red blood cells, where spherical body proteins (SBPs) play a role in cytoskeleton reorganization. In this study, four peptides with predicted B-cell epitopes are conserved in different isolates from six countries. Sera from cattle infected with B. bigemina cattle recognized the individual peptides. An in vitro assay demonstrated that antibodies against these conserved peptides reduced parasite invasion by 57%, 44%, 42%, and 38% for peptides 1, 2, 3, and 4, respectively. These data support the concept of spb4 as a new gene in B. bigemina that should be considered a candidate for a vaccine to control bovine babesiosis.

Technical Abstract: Bovine babesiosis is a tick-transmitted disease caused by intraerythrocytic protozoan parasites of the genus Babesia. Its main causative agents in the Americas are Babesia bigemina and Babesia bovis, while Babesia ovata affects cattle in Asia. All Babesia species secrete proteins stored in organelles of the apical complex, which are involved in all steps of the invasion process of vertebrate host cells. Unlike other apicomplexans, which have dense granules, babesia parasites instead have large, round intracellular organelles called spherical bodies. Evidence suggests that proteins from these organelles are released during the process of invading red blood cells, where spherical body proteins (SBPs) play an important role in cytoskeleton reorganization. In this study, we characterized the gene that encodes SBP4 in B. bigemina. This gene is transcribed and expressed in the erythrocytic stages of B. bigemina. The sbp4 gene consists of 834 nucleotides without introns that encode a protein of 277 amino acids. In silico analysis predicted a signal peptide that is cleaved at residue 20, producing a 28.88-kDa protein. The presence of a signal peptide and the absence of transmembrane domains suggest that this protein is secreted. Importantly, when cattle were immunized with recombinant B. bigemina SBP4, antibodies identified B. bigemina and B. ovata merozoites according to confocal microscopy observations and were able to neutralize parasite multiplication in vitro for both species. Four peptides with predicted B-cell epitopes were identified to be conserved in 17 different isolates from six countries. Compared with the pre-immunization sera, antibodies against these conserved peptides reduced parasite invasion in vitro by 57%, 44%, 42%, and 38% for peptides 1, 2, 3, and 4, respectively (p < 0.05). Moreover, sera from cattle infected with B. bigemina cattle contained antibodies