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Bronchopulmonary macrophage activation in the pathogenesis of hypersensitivity pneumonitis
Abstract:
Repeated intratracheal (IT) inoculation of rabbits with a homogenized, saline suspension of Micropolspora faeni produced bronchopulmonary (BP) histologic lesions resembling those of human hypersensitivity pneumonitis. With an in vitro phagocytic and bactericidal assay, an analysis of BP macrophages from M. faeni-injected rabbits demonstrated activation at both 2 and 4 weeks after the initiation of immunization. No BP macrophage activation was observed in immunized rabbits 6 weeks post-inoculation. BP macrophage activation was capable of recall after 6 weeks in M. faeni-sensitized animals that received a booster IT injection (2 mg) that did not activate "normal" alveolar wash cells. This recall of BP macrophage activation was accompanied by both a marked migration of mononuclear cells into the lung and positive delayed hypersensitivity skin reactions after intradermal injection of M. faeni antigen. Pulmonary histologic examination of sensitized, boosted rabbits suggested an enhanced cellular parenchymal infiltrate when compared with appropriate controls. The above observations confirm the occurrence of immunologically activated BP macrophages in rabbits inoculated witn M. faeni via the respiratory tract route and suggest a correlation between macrophage activation and histopathology.
Insights
Repeated Micropolspora faeni inoculation in rabbits caused lung inflammation similar to human hypersensitivity pneumonitis. Bronchopulmonary macrophages showed activation, which could be recalled with booster injections.
Area of Science:
- Immunology
- Pulmonology
- Pathology
Background:
- Hypersensitivity pneumonitis is an immune-mediated lung disease.
- Micropolspora faeni is a known environmental antigen implicated in hypersensitivity pneumonitis.
Purpose of the Study:
- To investigate the role of bronchopulmonary (BP) macrophages in a rabbit model of hypersensitivity pneumonitis induced by Micropolspora faeni.
- To assess the temporal dynamics of BP macrophage activation and its correlation with lung histopathology.
Main Methods:
- Rabbits were repeatedly inoculated intratracheally with Micropolspora faeni.
- Bronchopulmonary macrophages were analyzed for phagocytic and bactericidal activity.
- Delayed hypersensitivity skin reactions and lung histology were evaluated.
Main Results:
- Intratracheal inoculation induced lung lesions similar to human hypersensitivity pneumonitis.
- BP macrophages showed activation at 2 and 4 weeks post-immunization, but not at 6 weeks.
- Booster injections in sensitized rabbits recalled BP macrophage activation, accompanied by mononuclear cell infiltration and positive skin reactions.
Conclusions:
- Immunologically activated BP macrophages occur in rabbits following respiratory inoculation with Micropolspora faeni.
- Macrophage activation correlates with observed lung histopathology in this hypersensitivity pneumonitis model.