Chlamydia pneumoniaeInfection of Alveolar Macrophages: A Model

Chlamydia (Chlamydophila) pneumoniae is a common respiratory pathogen, and it seems likely that alveolar macrophages may have an important role in infection with this bacterium. In the present study, we examined the usefulness of a continuous cell line of murine alveolar macrophages, designated "MH-S," as an in vitro C. pneumoniae infection model. Infection of MH-S cells with C. pneumoniae resulted in the development of typical inclusion bodies in the cells, similar to that seen in primary alveolar macrophages. However, we noted that, although the number of bacteria in the cultures increased during the infection, there was a restricted production of infective elementary bodies. The analysis of bacterial messenger RNA in the cultures showed that the message levels for the omcB gene were present only at a moderate level, but the levels of hsp60 messages increased markedly during infection. Neutralization of tumor necrosis factor (TNF)-alpha induced by inoculation with antibody significantly enhanced the infection, but omcB message levels were still inhibited. These results indicate that the growth of C. pneumoniae in alveolar macrophages may be restricted. Endogenous TNF-alpha may be one of the factors responsible for such restriction, but other factors also may be involved.