Age-related differences in the neutrophil response to pulmonary pseudomonas infection

Background: Pseudomonas aeruginosa pneumonia is more common and more lethal in the elderly. The immunologic underpinnings of this increased incidence and mortality have not been evaluated, however are assumed to be a complication of age-associated immune dysfunction. Methods: Young (10-12 week old) and aged (18-20 month old) BALB/c mice were subjected to intratracheal infection of P. aeruginosa. Animals were sacrificed 24 h after inoculation. The lungs were collected for analysis of lung pathology, chemokine levels, neutrophil counts, and myeloperoxidase activity. Results: Pulmonary levels of the neutrophil chemokine KC are significantly higher in aged mice relative to young following P. aeruginosa infection. Despite this, neutrophil counts are higher in young mice compared to aged mice after infection. Furthermore, the neutrophils are predominantly found in the air space of young infected mice. This correlated with increased myeloperoxidase activity from bronchoalveolar lavage specimens of young mice relative to aged mice after infection. Conclusions: Neutrophil migration into the lungs is impaired in aged mice 24 h after intratracheal infection despite elevated chemokine levels, suggesting that immunosenescence is impairing neutrophil migration. (c) 2014 Elsevier Inc. All rights reserved.