[Changes in antibacterial activity of murine peritoneal macrophages against Mycobacterium tuberculosis after prolonged in vitro precultivation].

We examined profiles of intramacrophagial growth of M. tuberculosis (MTB) when mouse peritoneal macrophages (M phi s) were infected with the organisms at day 0 or day 7 after in vitro precultivation, and obtained the following results. First, the growth rate of the virulent MTB H37Rv strain as well as attenuated H37Ra strain was slower in M phi s which had been precultured for 7 days (M phi s [day 7]) than in freshly prepared M phi s without precultivation (M phi s [day 0]). The doubling time of MTB H37Rv was 2.2 and 2.9 days in M phi s [day 0] and M phi s [day 7], respectively, and that of MTB H37Ra was 2.9 and 3.6 days in M phi s [day 0] and M phi s [day 7], respectively. Second, MTB-mediated cytotoxicity in terms of the LDH release from infected M phi s was less marked in M phi s [day 7] than in M phi s [day 0], when they were infected with MTB of either the H37Rv or H37Ra strain. MTB H37Ra strain exhibited much weaker cytotoxic effects on host M phi s than did H37Rv strain. Third, when M phi s [day 7] were infected with MTB of either the H37Rv or H37Ra strain, they showed markedly lowered levels of reactive oxygen intermediate (ROI) production than did M phi s [day 0]. In contrast, the reactive nitrogen intermediate (RNI) producing ability of M phi s in response to MTB infection was not so markedly reduced in M phi s [day 7] from that of M phi s [day 0]. As mentioned above, the M phi s [day 7] did not permit accelerated growth of infected MTB, compared to the MTB growth in the M phi s [day 0]. It thus appears that ROI played a trivial role in the antimicrobial activity against MTB of murine peritoneal M phi s which had been precultured for long periods. Although it is regarded that RNI played more critical roles in M phi anti-MTB activity than did ROI, the present results also suggest that other kinds of antimicrobial effectors are required in M phi antimicrobial activity against MTB organisms, particularly in the case of M phi s after prolonged in vitro cultivation.