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Chlamydia pneumoniae infection of alveolar macrophages: a model
Shusaku Haranaga1, Hiroyuki Yamaguchi, Hideaki Ikejima
1Department of Medical Microbiology and Immunology, University of South Florida College of Medicine, 12901 Bruce B. Downs Boulevard, Tampa, FL 33612, USA.
Abstract:
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.
Insights
This study shows that alveolar macrophages restrict Chlamydia (Chlamydophila) pneumoniae growth, evidenced by limited infective elementary body production. Tumor necrosis factor-alpha (TNF-alpha) contributes to this restriction in vitro.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Alveolar macrophages are crucial in respiratory infections.
- Chlamydia (Chlamydophila) pneumoniae is a common respiratory pathogen.
Purpose of the Study:
- To evaluate the MH-S murine alveolar macrophage cell line as an in vitro model for C. pneumoniae infection.
- To investigate the mechanisms of C. pneumoniae restriction within alveolar macrophages.
Main Methods:
- Infection of MH-S cells with C. pneumoniae.
- Analysis of bacterial messenger RNA (mRNA) levels for omcB and hsp60 genes.
- Neutralization of tumor necrosis factor-alpha (TNF-alpha) to assess its role in infection restriction.
Main Results:
- MH-S cells supported C. pneumoniae inclusion body formation but showed restricted production of infective elementary bodies.
- Moderate omcB mRNA levels and markedly increased hsp60 mRNA levels were observed during infection.
- TNF-alpha neutralization enhanced infection but did not fully restore omcB mRNA levels, suggesting other inhibitory factors.
Conclusions:
- Alveolar macrophage restriction of C. pneumoniae growth is a significant factor in infection dynamics.
- Endogenous TNF-alpha plays a role in this restriction, but other cellular mechanisms are also involved.