Endotoxin, a constituent of Gram-negative bacteria, stimulates macrophages to release large quantities of tumor necrosis factor (TNF) and interleukin-1 (IL-1), which can precipitate tissue injury and lethal shock (endotoxemia). Antagonists of TNF and IL-1 have shown limited efficacy in clinical trials, possibly because these cytokines are early mediators in pathogenesis. Here a potential late mediator of lethality is identified and characterized in a mouse model. High mobility group-1 (HMG-1) protein was found to be released by cultured macrophages more than 8 hours after stimulation with endotoxin, TNF, or IL-1. Mice showed increased serum levels of HMG-1 from 8 to 32 hours after endotoxin exposure. Delayed administration of antibodies to HMG-1 attenuated endotoxin lethality in mice, and administration of HMG-1 itself was lethal. Septic patients who succumbed to infection had increased serum HMG-1 levels, suggesting that this protein warrants investigation as a therapeutic target.

Bacterial infection of the mammalian bloodstream can lead to overwhelming sepsis, a potentially fatal syndrome of irreversible cardiovascular collapse (shock) and critical organ failure. Cachectin, also known as tumour necrosis factor, is a macrophage-derived peptide hormone released in response to bacterial lipopolysaccharide, and it has been implicated as a principal mediator of endotoxic shock, although its function in bacterial sepsis is not known. Anaesthetized baboons were passively immunized against endogenous cachectin and subsequently infused with an LD100 dose of live Escherichia coli. Control animals (not immunized against cachectin) developed hypotension followed by lethal renal and pulmonary failure. Neutralizing monoclonal anti-cachectin antibody fragments (F(ab')2) administered to baboons only one hour before bacterial challenge protected against shock, but did not prevent critical organ failure. Complete protection against shock, vital organ dysfunction, persistent stress hormone release and death was conferred by administration of antibodies 2 h before bacterial infusion. These results indicate that cachectin is a mediator of fatal bacteraemic shock, and suggest that antibodies against cachectin offer a potential therapy of life-threatening infection.

Cytokines are critical in the often fatal cascade of events that cause septic shock. One regulatory system that is likely to be important in controlling inflammatory responses is the neuroendocrine axis. The pituitary, for example, is ideally situated to integrate central and peripheral stimuli, and initiates the increase in systemic glucocorticoids that accompanies host stress responses. To assess further the contribution of the pituitary to systemic inflammatory processes, we examined the secretory profile of cultured pituitary cells and whole pituitaries in vivo after stimulation with bacterial lipopolysaccharide (LPS). Here we identify macrophage migration inhibitory factor (MIF) as a major secreted protein release by anterior pituitary cells in response to LPS stimulation. Serum analysis of control, hypophysectomized and T-cell-deficient (nude) mice suggests that pituitary-derived MIF contributes to circulating MIF present in the post-acute phase of endotoxaemia. Recombinant murine MIF greatly enhances lethality when co-injected with LPS and anti-MIF antibody confers full protection against lethal endotoxaemia. We conclude that MIF plays a central role in the toxic response to endotoxaemia and possibly septic shock.

Cytokines, products of stimulated macrophages, are thought to mediate many host responses to bacterial infection, but increased circulating cytokine concentrations have not been detected consistently in infected patients. We measured plasma concentrations of circulating tumor necrosis factor alpha (cachectin), interleukin-1 beta, and gamma interferon, together with physiologic and hormonal responses, in 13 healthy men after intravenous administration of Escherichia coli endotoxin (4 ng per kilogram of body weight) and during a control period of saline administration. Eight additional subjects received ibuprofen before receiving endotoxin or saline. Plasma levels of tumor necrosis factor were generally less than 35 pg per milliliter throughout the control period, but increased 90 to 180 minutes after endotoxin administration to mean peak concentrations of 240 +/- 70 pg per milliliter, as compared with 35 +/- 5 pg per milliliter after saline administration. Host responses were temporally associated with the increase in circulating tumor necrosis factor at 90 minutes, and the extent of symptoms, changes in white-cell count, and production of ACTH were temporally related to the peak concentration of tumor necrosis factor. Ibuprofen pretreatment did not prevent the rise in circulating tumor necrosis factor (mean peak plasma level, 170 +/- 70 pg per milliliter) but greatly attenuated the symptoms and other responses after endotoxin administration. Concentrations of circulating interleukin-1 beta and gamma interferon did not change after endotoxin administration. We conclude that the response to endotoxin is associated with a brief pulse of circulating tumor necrosis factor and that the resultant responses are effected through the cyclooxygenase pathway.

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