Although bacille Calmette-Guerin (BCG) has been used worldwide as the only
vaccine for
tuberculosis, its protective efficacy in human adults is controversial. To investigate human immunological responses to Mycobacterium tuberculosis after BCG vaccination, we analyzed IFN-gamma and
IL-10 production by peripheral blood mononuclear cells (PBMC) from health-care workers five times throughout the year after BCG vaccination. Of 449 health-care workers, 36 (8.0%) were negative by the
tuberculin skin test, and of these, 20 were vaccinated with BCG. Because all the subjects had received BCG vaccination as infants, the present vaccination was considered to be a revaccination. The
cytokine responses of the vaccinated and control
tuberculin skin-test-positive subjects (n = 6) were followed at 0, 2, 4, and 8 weeks and at 12 months. The mean IFN-gamma production by PBMC when cultured with purified
protein derivative (
PPD) gradually increased, reached a peak at week 8, and then declined until 12 months, with four exceptions who showed no IFN-gamma elevation. The IFN-gamma level of the vaccinated group at week 0 was significantly lower than that of the controls. The mean
IL-10 production in response to
PPD reached a peak at week 2, and then declined to its lowest point at week 8. These results indicate that the
BCG vaccine can induce a type I
cytokine response to M.
tuberculosis in most
tuberculin skin-test-negative adults at week 8, suggesting the immunological efficacy of vaccination.