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.

https://science.sciencemag.org/content/sci/234/4775/470.full.pdf

Shock and tissue injury induced by recombinant human cachectin.

https://science.sciencemag.org/content/sci/230/4726/630.full.pdf

Tumor necrosis factor (TNF)

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.

Passive immunization against cachectin/tumor necrosis factor protects mice from lethal effect of endotoxin

Inflammation, the most ancient aspect of the host immune response, is surely of great value to the host, insofar as agents that suppress inflam­ mation in a nonspecific fashion predispose to infection. Yet, the inflam­ matory response to invasive organisms may also, if sufficiently intense or inappropriately prolonged, cause injury or death. A delicate balance has thus been achieved, one which clinicians strive to maintain through judicious application of anti-inflammatory medications (e.g. glucocorti­ coids, nonsteroidal anti-inflammatory agents, and cytotoxic drugs). Only recently have we come to understand that many aspects of this primitive response to host invasion are governed by polypeptide hormones, in turn produced by immune effector cells. Moreover, we have come to appreciate the pleiotropic properties of these so-called "cytokines." It would appear that a ' limited number of cytokines are capable of orches­ trating disease states that scarcely resemble one another; among them, endotoxic shock, graft-vs-host disease, cerebral malaria, and cancer cachexia. Cells of monocyte/macrophage lineage play a central role in cytokine ("mono kine") production and so act to modulate many aspects of the inflammatory response. While devoid of specificity and immunologic mem-

The biology of cachectin/TNF--a primary mediator of the host response

In response to invasive stimuli macrophages secrete cachectin, a multipotent protein. Prominent among its biological effects is the ability to induce wasting (cachexia) as well as a lethal state of shock. The identity of cachectin and tumour necrosis factor has led to a new view of its therapeutic potential.

Cachectin and tumour necrosis factor as two sides of the same biological coin

Previous studies have indicated that endotoxin and other bacterial and protozoal products can stimulate macrophages to produce a factor that can suppress the activity of the enzyme lipoprotein lipase (LPL), in vivo and in vitro. In the present report we describe the purification of this factor, cachectin, to apparent homogeneity from the conditioned medium of endotoxin-stimulated RAW 264.7 cells. The isolated protein has an isoelectric point of 4.7 and a subunit molecular weight of 17,000. Although cachectin's isoelectric point and molecular weight are similar to those described for interleukin 1, pure cachectin has no leukocyte-activating factor (LAF) activity. Cachectin at a concentration of 10(-11) M has the ability to suppress the LPL activity of the 3T3-L1 adipocyte cell line by 80%. Binding studies using radio-labeled cachectin and 3T3-L1 adipocytes and C2 myotubules revealed approximately 10(4) high-affinity receptors per cell on both cell types (Ka, 3 X 10(9]. Cachectin receptors were also present on liver membranes but were absent on erythrocytes and lymphocytes. The isolation of cachectin and characterization of its receptor should facilitate further investigations into the role of cachectin and other macrophage mediators in the metabolic derangements that occur during infection and cachexia.

/pdf/purification-of-cachectin-a-lipoprotein-lipase-suppressing-4vnr9t6k90.pdf

P Pekala

Papers

Purification of cachectin, a lipoprotein lipase-suppressing hormone secreted by endotoxin-induced RAW 264.7 cells.