Abstract：Seven-day-age and 35-day-age mice (BalB/C) were inoculated with 2×103 and 4×104 cfu of bacillus calmette-guerin (BCG), respectively, and challenged with 105 cfu of BCG at 28 days post inoculation. The ratios of protection against tuberculosis (TB) were observed and the expressions of interferon-γ（IFN-γ）/ interleukin-4（IL-4） were detected with enzyme-linked immunospot (ELISPOT). The results indicated that 100% of protection could be induced with 2×103 cfu of BCG and 75% of protection with 4×104 cfu of BCG in 7-day-age mice, but 67 % of protection could be induced with 2×103 cfu of BCG in 35-day-age mice. In 7-day-age mice inoculated with 2×103 cfu of BCG, the expressed quantity of Th1 type cytokines mainly produced IFN-γin spleen were improved significantly post inoculation and Th2 type cytokines mainly produced IL-4 were reduced; However, whether in 7-day-mice inoculated with 4×104 cfu of BCG or in 35-day-age mice inoculated with 2×103 cfu of BCG,both IFN-γ and IL-4 were significantly improved. It can be concluded that the protection against TB induced with BCG may be correlated to the doses of BCG and the ages of inoculated animals and Th1/Th2 type cell immune responses induced with BCG may cause these differences.
