Clearance of challenge infection with B. abortus 2308 measure as CFU in spleen in BALB/c, 129/Sv, C57BL/6, and 129/Sv mice previously vaccinated with mutant strains, B. abortus S19, RB51. IFN-γ production by spleen cells of IRF-1 KO mice vaccinated with S19, RB51, or the Δpgk mutant strain. Here, IRF1 is linked to infection.