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Murine respiratory mycoplasmosis in LEW and F344 rats: strain differences in lesion severity
Abstract:
Pathogen-free weaning rats of the LEW and F344 strains were caged together for two months to eliminate microbial and environmental differences, and then infected intranasally with 10-fold dilutions of viable Mycoplasma pulmonis. At necropsy 28 days post-inoculation, F344 rats had no gross lung lesions, even those given the maximum dose of 1.4 X 10(9) colony-forming units of M. pulmonis. LEW rats often had extensive gross lesions with a gross-pneumonia-dose50 of 1.1 X 10(7) colony-forming units/rat. Histological examination of the respiratory tract (nasal passages, larynges, tracheae, and lungs) and tympanic cavities showed both qualitative and quantitative differences in lesions between the two strains, particularly in the lungs. Hyperplasia of bronchus-associated lymphoid tissue occurred in both strains, but was more extensive in LEW rats. Atelectasis, alveolar consolidation (due primarily to mononuclear inflammatory cells), and suppurative bronchitis and bronchiolitis were seen only in LEW rats. Infiltrates of lymphoid cells into the lungs distal to bronchi and around blood vessels also were seen primarily in LEW rats. These differences between the two rat strains provide excellent model systems with which to dissect the role of cell responses in the pathogenesis of a naturally occurring chronic lung disease.
Insights
Different rat strains show varying susceptibility to Mycoplasma pulmonis infection. LEW rats developed severe pneumonia, while F344 rats remained largely unaffected, highlighting strain-specific immune responses in lung disease.
Area of Science:
- Immunology
- Pathology
- Respiratory Medicine
Background:
- Mycoplasma pulmonis is a common respiratory pathogen in rodents.
- Rat strain differences can influence disease susceptibility and severity.
- Understanding host-pathogen interactions is crucial for managing chronic lung diseases.
Purpose of the Study:
- To compare the susceptibility of LEW and F344 rat strains to Mycoplasma pulmonis infection.
- To characterize the resulting respiratory lesions and inflammatory responses.
- To evaluate these rat strains as models for studying chronic lung disease pathogenesis.
Main Methods:
- Pathogen-free LEW and F344 rats were co-housed and then intranasally inoculated with Mycoplasma pulmonis.
- Rats were necropsied 28 days post-inoculation for gross and histological examination of respiratory tissues and tympanic cavities.
- Lesion severity and inflammatory cell infiltration were assessed and compared between strains.
Main Results:
- F344 rats showed no gross lung lesions, even at high M. pulmonis doses.
- LEW rats exhibited extensive gross pneumonia with a lower pneumonia-dose50.
- Histological analysis revealed significant strain-dependent differences in lung pathology, including atelectasis, consolidation, and inflammatory cell infiltrates predominantly in LEW rats.
Conclusions:
- LEW rats are highly susceptible to M. pulmonis-induced pneumonia, whereas F344 rats are resistant.
- Significant qualitative and quantitative differences in respiratory tract lesions exist between the strains.
- These distinct responses establish LEW and F344 rats as valuable models for dissecting cellular mechanisms in chronic lung disease.