Isolated pulmonary infection acts as a source of systemic tumor necrosis factor

To investigate the local secretion of tumor necrosis factor (TNF) in the lung as a source for systemic TNF.

Prospective, randomized experimental trials.

Laboratory.

Hartley guinea pigs.

Female guinea pigs were challenged intratracheally with 10(3) to 10(9) Escherichia coli. Two and eight hrs after the bacterial challenge, colony-forming units of bacteria in the lung and blood, TNF and prostaglandin E2 (PGE2) in the bronchoalveolar lavage fluid, and serum TNF concentrations were determined. At the same time, alveolar macrophages were harvested and cultured in vitro, and TNF and PGE2 secretions were measured.

TNF and PGE2 concentrations were either not detected in bronchoalveolar lavage fluid or were found in very low levels in control animals. High concentrations of TNF and PGE2, however, were found in bacteria-challenged animals. Two hours after inoculation of bacteria, TNF in the bronchoalveolar lavage fluid had a significant correlation with TNF values in the serum. The TNF concentration in aortic blood was significantly higher than TNF concentration in right atrial blood. For comparable inocula, TNF in the bronchoalveolar lavage fluid after 8 hrs was significantly lower than at 2 hrs, but PGE2 levels remained high. Lipopolysaccharide-stimulated alveolar macrophage secretion of TNF in vitro was depressed in animals with high PGE2 levels in bronchoalveolar lavage fluid and high numbers of viable bacteria in the lungs.

During pulmonary Gram-negative infection, the lungs may be a major source of TNF in the blood. The magnitude of TNF secretion by the lungs is highly dependent on the intensity of infection during its early stages. By 8 hrs after onset of infection, TNF secretion appears to downregulate, possibly by endogenous PGE2.