Brucella abortus is a facultative intracellular bacterial pathogen that causes 
abortion in domestic animals and undulant fever in humans. IFN-γ, IL-12, and 
CD8+ T lymphocytes are important components of host immune responses against B. 
abortus. Herein, IFN-γ and IL-12/β2-microglobulin (β2-m) knockout mice were used 
to determine whether CD8+ T cells and IL-12-dependent IFN-γ deficiency would be 
more critical to control B. abortus infection compared to the lack of endogenous 
IFN-γ. At 1 week after infection, IFN-γ KO and IL-12/β2-m KO mice showed 
increased numbers of bacterial load in spleens; however, at 3 weeks 
postinfection (p.i.), only IFN-γ KO succumbed to Brucella. All IFN-γ KO had died 
at 16 days p.i. whereas death within the IL-12/β2-m KO group was delayed and 
occurred at 32 days until 47 days postinfection. Susceptibility of IL-12/β2-m KO 
animals to Brucella was associated to undetectable levels of IFN-γ in mouse 
splenocytes and inability of these cells to lyse Brucella-infected macrophages. 
However, the lack of endogenous IFN-γ was found to be more important to control 
brucellosis than CD8+ T cells and IL-12-dependent IFN-γ deficiencies.