As recent studies have shown that Th1 cytokines, such as interferon-γ (IFN-γ) and tumor necrosis factor α (TNF-α), induce abortion [24], we decided to determine if IFN-γ and TNF-α contribute to the induction of abortion by B. abortus infection and measured the production of IFN-γ and TNF-α by ELISA in pregnant mice infected on day 4.5 of gestation. This evidence concerns the gene IFNG and abortion.