BCG vaccination to young and aged mice augments Th1 cytokine production by PPD stimulated splenocytes. Young (a, c) and aged (b, d) mice were immunized with 1 × 106 CFU of BCG or phosphate buffered saline (PBS). Eight weeks after immunization, the animals were intravenously challenged with 1 × 105 CFU of M. tuberculosis strain H37Rv. Four weeks after challenge, the levels of IL-2 (a, b) and IFN-γ (c, d) in the culture supernatants of splenocytes stimulated with PBS (open column) or PPD (solid column) were measured by ELISA (BD Biosciences). Data represent mean ± SD of three mice. *, p < 0.05, compared with PBS-stimulation (student's t-test).