POLYMORPHONUCLEAR LEUKOCYTES AS A SIGNIFICANT SOURCE OF TUMOR-NECROSIS-FACTOR-ALPHA IN ENDOTOXIN-CHALLENGED LUNG-TISSUE

The kinetic expression and potential cellular source of tumor necrosis factor-alpha (TNF-alpha) in lipopolysaccharide- (LPS) induced acute l ung inflammation was investigated using a rat model by Northern blot a nalysis, in situ hybridization and immunohistochemistry. LPS induced a polymorphonuclear leukocyte infiltrate in the lung that peaked betwee n 6 and 24 hours. TNF-alpha messenger (m)RNA was strongly induced by L PS in whole lung tissues shown by Northern analysis. Both alveolar mac rophages and polymorphonuclear leukocytes (PMNs), purified from bronch oalveolar lavage fluids of LPS-treated rats, were shown to express TNF -alpha mRNA by Northern analysis. However, PMNs displayed several time s more TNF-alpha mRNA, relative to actin mRNA, than alveolar macrophag es at 6 and 12 hours. By in situ hybridization, most of the cells posi tive for TNF-alpha mRNA at 6 and 12 hours seemed to be PMNs located wi thin the tissue near bronchioles or vessels. By immunohistochemistry, TNF-alpha protein was localized mainly to alveolar macrophages at earl y times (1 to 3 hours) after LPS challenge, and thereafter, PMNs seeme d to be the predominant source of TNF-alpha protein as more than 90% o f total intraalveolar positive cells at 6 and 12 hours were PMN. Thus, our data provide the first in vivo evidence that PMNs can serve as a significant source of TNF-alpha at sites of acute inflammation.