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[Effect of atypical mycobacterial infection on the cell-mediated immunity induced by Mycobacterium bovis BCG in mice. II. Suppression of protective immunity].

The protective immunity against virulent mycobacteria is induced by Mycobacterium bovis BCG in mice. It was found that a preceding infection with a strain of atypical mycobacteria, M. avium Mino, suppresses the BCG-induced protective immunity. In the present study, protective immunity was judged by the extended survival time after the challenge with virulent mycobacteria, M. bovis Ravenel. C57BL/10 mice receiving BCG vaccination with 10(7) live bacilli sc showed prolonged survival after 10(6) injection with M. bovis Ravenel iv. Infection of these mice with M. avium Mino, 10(6) iv, 2 weeks before BCG vaccination shortened the survival time significantly. This suppression of protective immunity was caused by CD8+ T cells. CD4+ T cells also had a weak suppressive effect on the protective immunity, but was not the main population of suppressor T cells. Thus, it was confirmed that atypical mycobacterial infection produces CD8+ suppressor T cells which inhibit both protective immunity and delayed-type hypersensitivity induced by BCG.