Fig. (1) IFN-γ-producing capabilities of spleen cells from LPS and/or Ni pre-treated mice. Mice (6 weeks old) were inoculated with LPS. After the 3rd week of the LPS inoculation, they (9 weeks old) were immunized with NiCl2. IFN-γ-producing capability of spleen cells extracted from the mice (12 weeks old) were examined (a). After the NiCl2 immunization, the same mice (12 weeks old) were secondly immunized with NiCl4. Then, IFN-γ-producing capability of spleen cells extracted from the mice (15 weeks old) were examined (b). Five mice from each group (40 mice in 8 groups) were applied in one experiment. This figure showed representative results from 4 repeated experiments. **, p < 0.01.