Aging is accompanied by dysregulated immune function resulting in increased susceptibility of the elderly to diseases caused by microbial pathogens. There exists a multitude of data suggesting decreased resistance of the elderly to a variety of intracellular pathogens but there is no data relating the effect of aging on the immune response against Brucella. To elucidate the mechanism of immune dysregulation in old, old and young DBA/2 and BALB/c mice were infected with wild-type B. abortus strain 2308. The old and young mice were also vaccinated with vaccine B. abortus strain RB51 over-expressing Cu-Zn superoxide dismutase (SOD) and then challenged with B. abortus strain 2308 to determine the effect of vaccination in old vs. young mice. Specific IgG1 and IgG2a response to Brucella antigens were also evaluated to determine the effect of aging on Th-specificity of the immune response against Brucella infection. The immune response in aged vs. young mice was further assessed using RT-PCR and cytokine antibody array to determine the type of T-helper response. The experimental results indicate that all mice, regardless of age, survived infection ranging from doses of 2 x 104 to - 2 x 108 CFU. Though the older DBA/2 mice had a higher organism burden after 1 week of infection, these mice cleared Brucella infection more efficiently (5 weeks post-infection) than young mice. Vaccination with strain RB51 over-expressing SOD provided significant protection in young DBA/2, young BALB/c and old BALB/c mice but not in old DBA/2 mice after strain 2308 challenge. The results also suggest that old mice produced a different magnitude of IgG1 and IgG2a response to bacterioferritin and SOD of Brucella. The data suggests that both Th17 as well as Th1 responses were accentuated in old mice as compared to young mice following infection with Brucella. How the Th17 and Th1 branches of immune system work together enabling old mice to clear Brucella better than young mice warrants future investigation.