Is circulating endotoxin the trigger for the systemic inflammatory response syndrome seen after injury?

Patients with severe traumatic or burn injury and a mouse model of burn injury were studied early after injury to determine the relation of plasma endotoxin (lipopolysaccharide [LPS]) to the production of proinflammatory cytokines and subsequent resistance to infection. Elevated levels of plasma LPS have been reported in patients after serious injury. It has been suggested that circulating LPS may be a trigger for increased proinflammatory cytokine production and may play a role in the septic syndromes seen in a substantial portion of such patients. Yet, despite multiple reports of leakage of LPS from the gut and bacterial translocation after injury in animal models, there is little direct evidence linking circulating LPS with production of inflammatory mediators. The authors studied serial samples of peripheral blood from 10 patients with 25% to 50% surface area burns and 8 trauma patients (injury Severity Score, 25-57). Patients were compared with 18 healthy volunteers. The study was focused on the first 10 days after injury before the onset of sepsis or the systemic inflammatory response syndrome. Plasma samples were assayed for LPS, and adherent cells from the blood were studied for basal and LPS-stimulated production of tumor necrosis factor-alpha (TNF-alpha), interleukin-1 beta (IL-1 beta), and interleukin-6 (IL-6). The correlation of increased plasma LPS with TNF-alpha production was studied as was the association of increased plasma LPS and increased TNF-alpha production with subsequent septic complications. We also studied a mouse model of 25% burn injury. Burn mice were compared with sham burn control subjects. Plasma samples were assayed at serial intervals for LPS, and adherent cells from the spleens were studied for basal- and LPS-stimulated production of TNF-alpha, IL-1 beta, and IL-6. Expression of the messenger RNAs for IL-1 beta and TNF-alpha also was measured. The relation of increased TNF-alpha production with mortality from a septic challenge, cecal ligation and puncture (CLP), was determined. Finally, the effect of administration of LPS to normal mice on subsequent mortality after CLP and on TNF-alpha production was studied. Elevated plasma LPS (> 1 pg/mL) was seen in 11 of the 18 patients within 10 days of injury and in no normal control subjects. In this period, patients as compared with control subjects showed increased stimulated production of TNF-alpha, IL-1 beta, and IL-6. Increased TNF-alpha production was not correlated with el