Acute Lung Inflammation in Klebsiella pneumoniae B5055-Induced Pneumonia and Sepsis in BALB/c Mice: A Comparative Study

Lungs play an important role in the body's defense against a variety of pathogens, but this network of immune system-mediated defense can be deregulated during acute pulmonary infections. The present study compares acute lung inflammation occurring during Klebsiella pneumoniae B5055-induced pneumonia and sepsis in BALB/c mice. Pneumonia was induced by intranasal instillation of bacteria (10⁴ cfu), while sepsis was developed by placing the fibrin-thrombin clot containing known amount of bacteria (10² cfu) into the peritoneal cavity of animals. Mice with sepsis showed 100% mortality within five post-infection days, whereas all the animals with pneumonia survived. In animals suffering from K. pneumoniae B5055-induced pneumonia, all the inflammatory parameters (TNF-α, IL-1α, MPO, MDA, and NO) were found to be maximum till third post-infection day, after that, a decline was observed, whereas in septic animals, all the above-mentioned markers of inflammation kept on increasing. Histopathological study showed presence of alternatively activated alveolar macrophages (or foam cells) in lungs of mice with pneumonia after third post-infection day, which might have contributed to the induction of resolution of inflammation, but no such observation was made in lungs of septic mice. Hence, during pneumonia, controlled activation of macrophages may lead to resolution of inflammation.