Effects of Bacillus Calmette-Guérin and levamisole on immune responses in young adult and age-immunodepressed mice.

The immunomodulating effects of bacillus Calmette-Guérin (BCG) and levamisole were tested in young adult mice after a single administration and in 12-month-old mice after continuous administration. In young mice, BCG was shown to activate macrophages, to potentiate antibody responses and delayed hypersensitivity reaction, to increase antibody-dependent cell-mediated cytotoxicity, and to induce nonspecific suppressor cells. Levamisole was not able to modify any of these immune responses in young mice. The action of these adjuvants differed markedly when tested in age-immunodepressed mice. BCG was found to be strongly immunosuppressive on antibody formation and induced suppressor cell activity in the spleen. Moreover, the survival of immunodepressed mice continuously treated with BCG was shortened in comparison to untreated aged mice. In contrast, levamisole acted as an immunorestoring agent because it strongly stimulated the antibody response compared to aged controls and did not induce suppressor cell population. The survival of levamisole-treated mice was prolonged when compared to untreated aged mice. When the surviving mice were killed and autopsied at the age of 24 months, the incidence of spontaneous tumors was significantly lower in the group of mice treated by levamisole.