Babesia microti Protein Bm SP44 Is a Novel Protective Antigen in a Mouse Model of Babesiosis

Babesiosis caused byBabesiaspecies imposes an increasing threat to public-health and so far, there is no effective vaccine to preventBabesiainfections.Babesiasurface antigen may participate in the invasion of erythrocytes. In our previous study, a surface antigen ofB. microtimerozoites, named asBmSP44 was identified as a dominant reactive antigen by protein microarray screening. To evaluate its potential applications in diagnosis and prevention of Babesiosis, the open reading frame encodingBmSP44 was cloned and the recombinant protein was expressed. In consistent with the protein microarray result, recombinantBmSP44 (rBmSP44) can be recognized by sera fromB. microtiinfected mice. Immunofluorescence assays (IFA) confirmed thatBmSP44 is a secreted protein and localized principally in the cytoplasm of the parasites. The parasitemia andBabesiagene copies were lower in mice administered rBmSP44 antisera compared with normal controls. Active immunization with rBmSP44 also afforded protection againstB. microtiinfection. The concentrations of hemoglobin in rBmSP44 immunization group were higher than those in the control group. Importantly, vaccination of mice with rBmSP44 resulted in a Th1/Th2 mixed immune response with significantly elevated IL-10 and IFN-gamma levels during the early stage of infection. Taken together, our results indicated that rBmSP44 can induce a protective immune response againstBabesiainfection. Thus,BmSP44 can be used as both a diagnosis marker and a vaccine candidate.