[Inhibition on apoptosis of splenocytes in infected mice by immunization with recombinant Bb-Eg95-EgA31 protein of Echinococcus granulosus].

Objective: To investigate the weight reduction of hydatid cysts and apoptosis of splenocytes in infected mice by recombinant Bifidobacteria bifidum (Bb)-Eg95-EgA31 protein of Echinococcus granulosus (Eg) and challenged with Eg protoscoleces.

Methods: 56 female BALB/c mice were randomly divided into 7 groups. Groups A and B were injected subcutaneously and intramuscularly respectively with 5 x 10(6) colony-forming unit (CFU) recombinant Bb-Eg95-EgA31 protein, group C was immunized intranasally by 5 x 10(5) CFU protein, group D was vaccinated transgastrically by 5 x 10(8) CFU protein, groups E and F were injected subcutaneously with 5 x 10(6) CFU blank vector [Bb (pGEX-1 lambda T)] and Bb respectively, and group G was injected subcutaneously with 100 microl MRS. Mice in all groups were challenged with 50 Eg protoscoleces on the 8th week after vaccination and sacrificed on the 25th week after infection. The weight of hydatid cysts was measured and weight-reduction rate was calculated. Spleens were collected to prepare splenocytes which were cultured under stimulation with concanavalin A (ConA). The apoptotic rate was determined by flow cytometry (FCM).

Results: The average weight of hydatid cysts in groups A [(41.0 +/- 23.0) mg], B [(44.0 +/- 22.0) mg], C [(22.0 +/- 21.0) mg], and D [(28.0 +/- 16.0) mg] was lower than that of group G [(75.0 +/- 33.0) mg] (P<0.05, P<0.01), and there was no significant difference among groups A, B, C and D (P>0.05); no significant difference was found between group G and groups E [(63.0 +/- 30.0) mg], F [(69.0 +/- 22.0) mg] (P>0.05). The apoptotic rate of splenocytes cultured with no ConA in groups A (0.14 +/- 0.01), B (0.14 +/- 0.01), C (0.13 +/- 0.01), and D (0.141 +/- 0.01) was lower than that of group G (0.21 +/- 0.01) (P<0.05); that of group C was lower than groups A, B, and D (P<0.05); there was no significant difference between groups D and A, between groups A and B, and between groups E (0.20 +/- 0.01), F (0.20 +/- 0.01) and group G. The apoptotic rate of splenocytes cultured with ConA in group A (0.19 +/- 0.01), B (0.20 +/- 0.00), C (0.17 +/- 0.01), and D (0.19 +/- 0.01) were lower than that of group G (0.26 +/- 0.01) (P<0.01), that of group C was lower than groups A and B (P<0.01), group C was lower than group D (P<0.05), group D was lower than group B (P<0.05); there was no significant difference between groups A and B, and between groups A and D, and between groups E (0.25 +/- 0.01), F (0.25 +/- 0.01), and group G (P>0.05). The apoptotic rate of splenocytes cultured with ConA was higher than those cultured without ConA (P<0.01).

Conclusions: Apoptosis of splenocytes may be induced by infection of Echinococcus granulosus protoscoleces in mice, while the recombinant Bb-Eg95-EgA31 protein may inhibit the apoptosis of splenocytes in mice challenged with Eg, and induce certain protective immunity in the host.