Anti-infective immunity of recombinant Bifidobacteria bifidum-Eg95 vaccine of Echinococcus granulosus in mice

Abstract

Objective To investigate the protective immunity in mice immunized with recombinantBifidobacteria bifidum(Bb)-Eg95 vaccine of Echinococcus granulosus (Eg) and challenged with Eg protoscoleces.Methods Fifty-six female BALB/c mice 12-14 weeks old and weighed 20-25 g were vaccinated with the recombinant Bb-Eg95 vaccine subcutaneously,intramuscularly,intranasally and orally,respectively,with blank vector,Bb and medium of solution(MRS) as control,8 mice in each group.Mice were challenged with Eg protoscoleces on week 8 after immunization and killed on week 25 after infection.The weight of hydatid cyst was measured and the decreased larva rate was calculated.Sera were collected to determine the levels of IgE,IgG and its subclasses by enzyme linked immunosorbent assay(ELISA).Splenocytes were collected and cultivated to test the proliferation of splenocytes using methyltetrazolium (MTT) assay under EgAg and concanavalin A (ConA) stimulation.The results were compared with analysis of variance and the comparison between two groups was performed with LSD-t test.Results There was significant difference in the weight of hydatid cyst between groups (F =11.062,P ＜ 0.05).Compared with MRS control group[(0.075 ± 0.019)g],the hydatid cyst weight decreased in subcutaneous group [(0.050 ± 0.013)g],intramuscular group[(0.050 ± 0.019)g],intranasal group[(0.028 ± 0.016)g] and oral group [(0.031 ± 0.018)g,all P ＜ 0.01).Compared with subcutaneous and intramuscular groups,the hydatid cyst weight decreased in intranasal and oral groups(all P ＜ 0.05).The decreased larva rate was inversely proportional to the weight of hydatid cyst.There was significant difference in the levels(obsorbancy,A) of IgG,IgG2a,IgG2b,IgG1,IgG3 and IgE between these groups(F =21.774,36.977,27.071,14.746,10.131,9.444,P ＜ 0.05 or P ＜ 0.01).Compared with MRS control group (0.015 ± 0.002,0.002 ± 0.001,0.003 ± 0.001),the levels of IgG,IgG2a and IgG2b increased in subcutaneous group(0.022 ± 0.004,0.007 ± 0.002,0.008 ± 0.002),intramuscular group (0.023 ± 0.003,0.008 ± 0.002,0.007 ± 0.002),intranasal group(0.032 ± 0.007,0.012 ± 0.002,0.013 ± 0.004)and oral group(0.028 ± 0.006,0.010 ± 0.003,0.010 ± 0.002,P ＜ 0.05 or P ＜ 0.01).Compared with subcutaneous and intramuscular groups,the levels of IgG,IgG2a and IgG2b increased in intranasal and oral groups(P ＜ 0.05 or P ＜ 0.01).Compared with MRS control group(0.009 ± 0.001,0.009 ± 0.002,0.009 ± 0.001),the levels of IgG1,IgG3 and IgE decreased in subcutaneous group(0.022 ± 0.004,0.007 ± 0.002,0.008 0.002),intramuscular group(0.004 ± 0.001,0.004 ± 0.001,0.004 ± 0.002),intranasal group(0.005 ± 0.002,0.005 ± 0.003,0.005 ± 0.002)and oral group(0.005 ± 0.001,0.004 ± 0.002,0.004 ± 0.003,all P ＜ 0.01).There was significant difference in the proliferation of splenocytes in the supernatant of cultured splenocyte,of cultured splenocyte + EgAg and of cultured splenocyte + ConA(F =63.975,359.833,167.399,P ＜ 0.01).There was significant difference in the proliferation of splenocytes inside groups(F =6741.955,4953.667,869.320,201.235,175.413,139.653,169.994,all P ＜0.01).Compared with the cultured splenocyte the proliferation of splenocytes increased in the cultured splenocyte +EgAg and splenocyte + ConA (all P ＜ 0.01).Compared with the cultured splenocyte + EgAg,the proliferation of splenocytes increased in the cultured splenocyte + ConA(P ＜ 0.01).Conclusion An effective and protective immunity is induced by the recombinant Bb-Eg95 vaccine of Eg in mice. Key words: Echinococcus granulosus; Vaccines, synthetic; Mice; Infection; Protective immunity