The IFN-γ production from splenocytes stimulated with OVA in BCG vaccinated young and middle-aged mice. Splenocytes were prepared from BCG-vaccinated or non-vaccinated a)13-week old, b) 89-week old mice, and plated in a 24-well plate, at a concentration of 5 × 105 cells per well. Cells were stimulated with 100 μg/ml of ovalbumin (OVA, gray column), 10 μg/ml of PPD (solid column) or PBS (open column) and incubated for 48 h. Then, supernatants were collected and the concentration of IFN-γ was measured by ELISA. Results are shown by mean ± SD from groups of 3 mice. ** p < 0.01, * p <0.05, N.S.: not significant.