Although we could not dissect the T cell phenotype responsible for protective immunity, results from antigen-specific T-cell proliferation, NO production, increased mRNA expression of IL-2, IL-12, IFN-γ, robust DTH responses, and IgG2 antibody titer are indicative of durable T-cell response which is sustained at least up to 3 months post infection. This evidence concerns the gene IFNG and infection.