Expression of truncated Babesia microti apical membrane protein 1 and rhoptry neck protein 2 and evaluation of their protective efficacy.

In this study, we evaluated the protective effect of recombinant Babesia microti apical membrane protein 1 (rBmAMA1) and rhoptry neck protein 2 (rBmRON2) against B. microti infection using a hamster model. The genes encoding the predicted domains I and II of BmAMA1 and the gene encoding the predicted transmembrane regions 2 and 3 of BmRON2 were expressed as His fusion recombinant proteins in Escherichia coli. Three groups with 5 hamsters in each group were immunized with rBmAMA1, rBmRON2 and rBmAMA1+rBmRON2, then challenged with B. microti. The result showed that only the group immunized with rBmAMA1+rBmRON2 exhibited limited protection against B. microti challenge infection, characterized by significant decreased of parasitemia and higher hematocrit values from day 6-10 post challenge infection. However, there was no significant difference in the groups immunized with rBmAMA1 or rBmRON2 alone. The absence of a significant difference in the total amount of antibodies against rBmAMA1 and rBmRON2 between the group immunized with single and combined proteins. This result suggests that the protection cannot be solely attributed to the quantity of antibodies produced, but also to their ability to target important epitopes from both antigens. These results suggest that combined immunization with rBmAMA1 and rBmRON2 is a promising strategy against B. microti.