Mouse Model of Abortion Induced by Brucella abortus Infection

Abstract

The mechanisms of abortion induced by bacterial infection are largely unknown. We found that Brucella abortus, a causative agent of brucellosis and a facultative intracellular pathogen, caused abortion in pregnant mice. High rates of abortion are observed for bacterial infection on day 4.5 of gestation, but not for other days. Regardless of whether fetuses are aborted or not, the transmission of bacteria to the fetus and bacterial replication in the placenta are observed. There is a higher degree of bacterial colonization in the placenta than in other organs and many bacteria are detected in trophoblast giant cells in the placenta. The intracellular growth-defective virB4 mutant and attenuated vaccine strain S19 do not induce abortion. In the case of abortion, the induction of IFN-γ and RANTES production is observed at day 7.5 of gestation – the placental development period – for infection by the wild type strain but not by the virB4 mutant or S19. B. abortus-infected pregnant IFN-γ knockoutmice die within 15 days of infection, but nonpregnant IFN-γ knockout mice remain alive. The neutralization of IFN-γ or RANTES, in which production is induced by infection with B. abortus serves to prevent abortion. These results indicate that abortion induced by B. abortus infection is regulated by IFN-γ during the period of placental development, and the production and function of RANTES are correlated with IFN-γ.