[Anti-fecundity effect of soluble immature egg antigen of Schistosoma japonicum in mice].

OBJECTIVE: To study anti-female fecundity effect in mice immunized with soluble immature egg antigen (SIEA) of Schistosoma japonicum, and observe possible mechanism.

METHODS: Immature eggs were collected from the liver of a rabbit 34 days after being infected with 3000 cercariae of S. japonicum, and soluble antigen was prepared routinely. 20 ICR mice were divided randomly to 2 groups. 11 mice were immunized with SIEA (100 microg per mouse) and Freund adjuvant and the other 9 were injected with equal volume of sterile normal saline and Freund adjuvant as control. All mice received injection 5 times in 2 weeks interval. One week following the last vaccination, mice were challenged with 30 +/- 2 cercariae of S. japonicum Yunnan isolate. Feces were collected on day 45. All mice were sacrificed on day 46. The number of worms collected, number of eggs in feces, female uterus and liver, and the number of egg granulomas on the liver surface were compared between the 2 groups. The vitelline gland of female and testes of male worms were examined by transmission electron microscopy.

RESULTS: There was no significant difference on the worm number between the immunized group and control (P > 0.05). The eggs per gram feces and liver, eggs in uterus per female, and egg granulomas on the liver surface were (56.68 +/- 24.78), (5 826 +/- 437), (49.94 +/- 12.53) and (10.04 +/- 1.13)/0.25 cm2, respectively in immunized group, while in control group these were (89.93 +/- 32.18), (10016 +/- 3541), (76.54 +/- 19.77) and (19.22 +/- 2.45)/0.25 cm2 respectively, all with significant difference (P < 0.05). Ultrastructure of the reproductive organs of paired adult worms showed that mature vitelline cells and lipid droplets in the cytoplasm of the cells decreased in the vitelline glands of immunized mice. More sustentacular cells and fewer spermatids were seen in testes of immunized mice. Vacuoles were seen in the cytoplasm of vitelline cells and sustentacular cells.

CONCLUSION: The results indicated that SIEA may have an anti-fecundity effect possibly through inhibiting the maturation of germinal cells.