Immunization with rEmCRT provides protection against Echinococcus  multilocularis infection in BALB/c mice

Abstract

Background Alveolar echinococcosis (AE) is a severe parasitic zoonosis, caused by the larval stage of Echinococcus multilocularis. Identification of the antigens eliciting acquired immunity during infection is important for vaccine development against Echinococcus infection. Methods First of all, we predicted the physical and chemical properties and protein structure characteristics of E. multilocularis calreticulin (EmCRT), and then constructed the recombinant plasmid pET28a-EmCRT. Secondly, the constructed recombinant plasmid was transformed into E. coli BL21 and induced to produce recombinant EmCRT (rEmCRT). Then the antigen specificity and the calcium-binding property of rEmCRT was detected. Thirdly, the expression level and distribution of Emcrt gene in PSCs and vesicles were analysed. And the protective immunity induced by rEmCRT immunized mice and the corresponding mechanismwas investigated in the end. Results We identified that EmCRT, a ubiquitous protein with Ca2+-binding ability, elicited protective immunity against E. multilocularis infection. EmCRT was found to be expressed on the surface of E. multilocularis larvae as well as in the secreted products of metacestode vesicles and protoscoleces (PSCs). Recombinant EmCRT formulated with Freund’s adjuvant (FA) elicited both IgG1 and IgG2a antibodies, with a higher IgG1/IgG2a ratio indicating a predominant Th2 response in vaccinated mice, and stimulated mouse lymphocytes from the spleen to produce high levels of Th1 (IFN-γ, IL-2) and Th2 (IL-4, 5, 10) cytokines. The protection was around 43.7% after challenged with E. multilocularis PSCs. Conclusions Our results suggest that EmCRT is an immunodominant protein secreted by E. multilocularis larvae and contributes to the induction of partial protective immunity in vaccinated mice against Echinococcus infection. Therefore, EmCRT could be a novel and potential candidate vaccine against AE.