Protein SP44 Is a Novel Protective Antigen in a Mouse Model of Babesiosis.

Babesiosis caused by species imposes an increasing threat to public-health and so far, there is no effective vaccine to prevent infections. surface antigen may participate in the invasion of erythrocytes. In our previous study, a surface antigen of merozoites, named as SP44 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 encoding SP44 was cloned and the recombinant protein was expressed. In consistent with the protein microarray result, recombinant SP44 (rSP44) can be recognized by sera from infected mice. Immunofluorescence assays (IFA) confirmed that SP44 is a secreted protein and localized principally in the cytoplasm of the parasites. The parasitemia and gene copies were lower in mice administered rSP44 antisera compared with normal controls. Active immunization with rSP44 also afforded protection against infection. The concentrations of hemoglobin in rSP44 immunization group were higher than those in the control group. Importantly, vaccination of mice with rSP44 resulted in a Th1/Th2 mixed immune response with significantly elevated IL-10 and IFN-γ levels during the early stage of infection. Taken together, our results indicated that rSP44 can induce a protective immune response against infection. Thus, SP44 can be used as both a diagnosis marker and a vaccine candidate.