Study objectives: To examine the lung defense
mechanisms of both young and aged rats before and after pulmonary
challenge with a bacterial pathogen.
Fischer 344 rats, either 2.5 months or 20 months of age, were
intratracheally inoculated with 5 × 103,
5 × 104, or 5 × 105Listeria
monocytogenes, and the effects on mortality, lung inflammation,
pulmonary bacterial clearance, alveolar macrophage (AM) function, and
T-lymphocyte characterization were determined.
and results: In noninfected control animals, the older rats had
lower numbers of AMs on lavage and a lower percentage of total T, CD4+,
and CD8+ cells. No difference was observed between noninfected young
and old rats in AM function, assessing both chemiluminescence and
nitric oxide (NO) production. After bacterial challenge, aged rats
exhibited an increase in mortality, pulmonary infection, and edema, and
lung lesions, which were more extensive than those observed in the
younger rats. Interestingly, AM chemiluminescence was enhanced, while
AM NO, a highly important antibacterial defense product, was abrogated
in the aged rats as compared to the young rats.
Conclusions: This study demonstrated that advanced age is
associated with alterations in lung defense mechanisms and increased
susceptibility to pulmonary bacterial infection marked by elevated
mortality, slowed pulmonary bacterial clearance, and altered AM
function, specifically a decrease in NO production. These observations
are indicative of reduced pulmonary defense function in an older
population of rats.