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Pulmonary clearance of Mycoplasma pulmonis in C57BL/6N and C3H/HeN mice
R F Parker1, J K Davis, D K Blalock
1Department of Comparative Medicine, School of Medicine, University of Alabama, Birmingham 35294.
Abstract:
In C57BL/6N and C3H/HeN mice known to be free of all murine pathogens and matched for age, sex, and environmental factors, pulmonary clearance was measured over a 72-h time period after exposure to infectious aerosols of 35S-labeled Mycoplasma pulmonis. Reduced clearance of M. pulmonis in C3H/HeN mice relative to C57BL/6N mice was primarily due to impaired mycoplasmacidal activity in the lungs of the C3H/HeN mice. The C3H/HeN mice also had a slightly slower rate of mechanical transport of radiolabel from the lungs in the first 4 h after infection relative to the C57BL/6N mice but not at any later times. By 72 h after infection (relative to 0 h, C3H/HeN mice had an over 4,000% (1.75 X 10(7) versus 4.30 X 10(5] increase in neutrophils and an over 18,000% (more than 2 orders of magnitude) increase in numbers of M. pulmonis recovered from mechanically disaggregated lungs. In contrast, C57BL/6N mice reduced the number of M. pulmonis present by over 83% (nearly 2 orders of magnitude) before any increase in inflammatory cells, which was only a slight increase in lymphocytes and macrophages at 24 h after infection. These results directly link decreased mycoplasmal pulmonary clearance in C3H/HeN mice with the increased susceptibility to, and severity of, murine respiratory mycoplasmosis observed in this strain. The resistance of C57BL/6N mice appears to be related to nonspecific host defense mechanisms responsible for limiting the extent of infection.
Insights
C3H/HeN mice show reduced pulmonary clearance of Mycoplasma pulmonis due to impaired lung mycoplasmacidal activity, leading to increased susceptibility to respiratory mycoplasmosis. C57BL/6N mice exhibit resistance through effective host defense mechanisms.
Area of Science:
- Immunology
- Infectious Diseases
- Pulmonary Medicine
Background:
- Murine respiratory mycoplasmosis is a common infection in laboratory mice.
- Strain-dependent differences in susceptibility to Mycoplasma pulmonis infection are well-documented.
Purpose of the Study:
- To investigate the mechanisms underlying differential pulmonary clearance of Mycoplasma pulmonis in C57BL/6N and C3H/HeN mice.
- To elucidate the role of mycoplasmacidal activity and mechanical transport in host defense against M. pulmonis.
Main Methods:
- Exposure of pathogen-free C57BL/6N and C3H/HeN mice to 35S-labeled Mycoplasma pulmonis aerosols.
- Measurement of pulmonary clearance over 72 hours.
- Quantification of M. pulmonis load, neutrophil counts, and inflammatory cell infiltration.
Main Results:
- C3H/HeN mice exhibited significantly reduced pulmonary clearance of M. pulmonis compared to C57BL/6N mice.
- Impaired mycoplasmacidal activity in C3H/HeN mouse lungs was the primary cause of reduced clearance.
- C57BL/6N mice controlled M. pulmonis infection effectively through early host defense mechanisms, with minimal inflammation.
Conclusions:
- Decreased pulmonary clearance in C3H/HeN mice is directly linked to their increased susceptibility and disease severity in murine respiratory mycoplasmosis.
- Nonspecific host defense mechanisms in C57BL/6N mice are crucial for limiting M. pulmonis infection extent.