The contribution of CD8+ and CD4+ T cell-mediated effector functions against Mycobacterium tuberculosis infection elicited by i.m. vaccination with plasmid DNA encoding the immunodominant Ag85A antigen of M. tuberculosis was studied. Ag85A DNA-vaccinated beta2-microglobulin gene-deficient (beta2m-/-) mice, which lack CD8+ T cells, produced Ag85-specific antibodies and Th1 type cytokines similar to wild-type mice. Although beta2m-/- mice were more susceptible to M. tuberculosis infection, following vaccination they efficiently controlled bacterial replication in spleen and lungs 4 weeks post-infection. In contrast, mice lacking CD4+ T cells were neither sensitized by the Ag85A DNA vaccine to produce Ag85-specific antibodies or Th1 type cytokines nor did they contain a M. tuberculosis challenge infection. In addition, Ag85A DNA-vaccinated IFN-gamma gene knockout mice produced Ag85-specific antibodies and IL-2 but died rapidly following a M. tuberculosis challenge infection. Collectively, these data support the view that IFN-gamma-producing CD4+ T cells, independently of CD8+ T cells, may mediate the protective effect of the Ag85A DNA vaccine.