Cachectin (tumor necrosis factor), a protein produced in large quantities by endotoxin-activated macrophages, has been implicated as an important mediator of the lethal effect of endotoxin. Recombinant human cachectin was infused into rats in an effort to determine whether cachectin, by itself, can elicit the derangements of host physiology caused by administration of endotoxin. When administered in quantities similar to those produced endogenously in response to endotoxin, cachectin causes hypotension, metabolic acidosis, hemoconcentration, and death within minutes to hours, as a result of respiratory arrest. Hyperglycemia and hyperkalemia were also observed after infusion. At necropsy, diffuse pulmonary inflammation and hemorrhage were apparent on gross and histopathologic examination, along with ischemic and hemorrhagic lesions of the gastrointestinal tract, and acute renal tubular necrosis. Thus, it appears that a single protein mediator (cachectin) is capable of inducing many of the deleterious effects of endotoxin.

A highly specific polyclonal rabbit antiserum directed against murine cachectin/tumor necrosis factor (TNF) was prepared. When BALB/c mice were passively immunized with the antiserum or with purified immune globulin, they were protected against the lethal effect of the endotoxin lipopolysaccharide produced by Escherichia coli. The prophylactic effect was dose-dependent and was most effective when the antiserum was administered prior to the injection of the endotoxin. Antiserum to cachectin/TNF did not mitigate the febrile response of endotoxin-treated animals, and very high doses of endotoxin could overcome the protective effect. The median lethal dose of endotoxin in mice pretreated with 50 microliters of the specific antiserum was approximately 2.5 times greater the median lethal dose for controls given nonimmune serum. The data suggest that cachectin/TNF is one of the principal mediators of the lethal effect of endotoxin.

Cachectin (tumor necrosis factor) is a macrophage hormone strongly implicated in the pathogenesis of endotoxin-induced shock. The availability of a DNA probe complementary to the cachectin messenger RNA (mRNA), as well as a specific antibody capable of recognizing the cachectin gene product, has made it possible to analyze the regulation of cachectin gene expression under a variety of conditions. Thioglycollate-elicited peritoneal macrophages obtained from mice contain a pool of cachectin mRNA that is not expressed as protein. When the cells are stimulated with endotoxin, large quantity of additional cachectin mRNA is produced, and immunoreactive cachectin is secreted. Macrophages from mice of the C3H/HeJ strain do not produce cachectin in response to endotoxin. A dual defect appears to prevent cachectin expression. First, a diminished quantity of cachectin mRNA is expressed in response to low concentrations of endotoxin. Second, a post-transcriptional defect prevents the production of cachectin protein. Macrophages from endotoxin-sensitive mice do not produce cachectin if they are first treated with dexamethasone, apparently for similar reasons. These findings give new insight into the nature of the C3H/HeJ mutation and suggest an important mechanism by which glucocorticoids may act to suppress inflammation.

IFN-gamma permits the endotoxin-induced production of cachectin by C3H/HeJ (endotoxin resistant) macrophages, apparently by facilitating endotoxin-induced cachectin biosynthesis at both transcriptional and posttranscriptional levels. IFN-gamma cannot induce cachectin biosynthesis by itself, nor does it markedly enhance cachectin production by endotoxin-induced peritoneal macrophages obtained from endotoxin-responsive mice. Elucidation of the precise mechanism through which IFN-gamma influences cachectin biosynthesis may permit a better understanding of the molecular events that follow endotoxin-induced activation of macrophages. Moreover, the permissive effect of IFN-gamma on cachectin biosynthesis might elicit enhanced endotoxin sensitivity in vivo.