In this study, the full lipL21 gene fragment encoding outer membrane protein LipL21 was cloned from L. interrogans serovar Lai and inserted into eukaryotic expression vector pcDNA3.1（+）. The guinea pigs were immunized with pcDNA3.1（+）-lipL21, pcDNA3.1（+） or PBS. Six weeks after the second immunization, the splenocytes were isolated to detect their proliferative ability by lymphocyte transformation experiments. In addition, microscopic agglutination test was used for quantitative detection of specific antibodies. The rest guinea pigs were challenged intraperitoneally with L. interogans sorevar Lai. Then, protective effect was evaluated on the basis of survival and histopathological lesions in the kidneys, lungs, and liver. The lipL21 gene was successfully expressed in COS-7 cells through recombinant pcDNA3.1（+）-lipL21. The titer of specific antibodies substantially increased, and the stimulation index of splenocytes increased significantly. Hence, the pcDNA3.1（+）-lipL21 could protect the immunized guinea pigs from homotypic Leptospira infection. Furthermore, no obvious pathologic changes were observed in the pcDNA3.1（+）-lipL21 immunized guinea pigs. The results showed that the protective effect with pathogenic strains of Leptospira was shared by LipL21 mediated through a plasmid vector. Consequently, these results indicated that the lipL21 DNA vaccine was a promising candidate for the prevention of leptospirosis.
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