TNF and the Molecular Pathogenesis of Shock 
Bruce A. Beutler, M.D. — Associate Investigator 
Dr. Beutler is also Associate Professor of Internal Medicine at the University of Texas Southwestern Medical 
Center at Dallas. After receiving his M.D. degree from the University of Chicago (Pritzker School of 
Medicine), he served as an intern and resident at the Southwestern Medical Center. His postdoctoral 
fellowship with Anthony Cerami was completed at the Rockefeller University, which he left as an assistant 
professor to assume a position at the Southwestern Medical Center. 
THIS laboratory studies basic mechanisms that 
lead to septic shock, a serious condition aris- 
ing as a result of many types of infection. We have 
learned that the final common pathway leading to 
shock involves the production of certain cyto- 
kines, particularly tumor necrosis factor (TNF), 
by host cells known as macrophages and by other 
cell types as well. 
Once TNF has been produced, it alters the me- 
tabolism of cells throughout the body, triggering 
a breakdown of protein and fat stores. If TNF is 
chronically secreted at low levels, a state of wast- 
ing called cachexia will develop. This condition 
is seen in cancer and many other forms of chronic 
illness. On the other hand, if massive quantities 
of TNF are released over a short time, as in wide- 
spread injury, the protein activates neutrophils 
and endothelial cells in such a way that shock 
occurs. 
Because TNF is a critically important molecule 
in various human disease processes, we have 
sought to understand how its biosynthesis is con- 
trolled. Probably the most potent stimulus for 
TNF release is a molecule known as lipopolysac- 
charide, or endotoxin. This molecule is pro- 
duced by gram-negative bacteria, which have a 
remarkable tendency to cause shock. In the 
course of a gram-negative infection, endotoxin is 
released into the bloodstream. It is harmless to 
most cells but is a powerful activator of mono- 
cytes and macrophages, triggering their release of 
TNF with all of its attendant consequences. 
By studying different portions of the TNF gene, 
we have shown that endotoxin causes two sepa- 
rate responses within the macrophage: 1) It 
causes increased transcription of the TNF gene, 
leading to a marked accumulation of TNF mRNA 
within macrophages. 2) It causes far more effi- 
cient translation of the mRNA — i.e., increases the 
speed with which the mRNA is read to produce 
TNF protein. Acting in concert, these two effects 
are responsible for a 10,000-fold increase in the 
rate of TNF biosynthesis and thus a massive net 
effect. 
For a number of technical reasons, it has been 
very difficult to demonstrate the major sources of 
TNF in living animals. It is not clear, for example, 
whether it is made by normal tissues in healthy 
animals or whether such "baseline" production 
is important for maintenance of physiological or 
immunological processes. Similarly, it is not 
clear whether the TNF that arises in cancer is de- 
rived from cells of the tumor or from host cells 
that act in response to the tumor. TNF is believed 
to be made in a variety of autoimmune or allergic 
diseases, but again, the principal source of the 
protein remains uncertain. 
To address these questions, our laboratory has 
produced transgenic mice that express a reporter 
construct in which an easily measurable enzyme 
(chloramphenicol acetyltransferase, or CAT) is 
employed as a marker for TNF. In other words, 
CAT synthesis also occurs in cells that produce 
TNF. CAT remains confined, however, to the cell 
of origin, whereas TNF is secreted and becomes 
widely dispersed in the organism. Using these an- 
imals, we have found that during normal develop- 
ment TNF is made by cells of the thymus. Other 
investigators have further reported that thymic 
production of TNF is essential for normal devel- 
opment. Although the protein does not appear to 
be produced elsewhere in healthy animals, it is 
readily induced by administration of lipopolysac- 
charide or by various authentic infections. 
A second tissue in which CAT synthesis marks 
TNF production is the placenta, the organ that is 
formed in pregnant mammals to nourish the de- 
veloping fetus. The placenta contains cells of two 
separate origins: part of the placenta, the deci- 
dua, is derived from the mother. The remainder 
of the placenta, the trophoblast, is derived from 
the fertilized egg. Studies utilizing the reporter 
construct have effectively proved that the TNF 
gene is constitutively expressed by the tropho- 
blast. TNF may also be constitutively expressed 
by trophoblastic tumors. Its function within the 
placenta remains to be established; however, it is 
interesting to consider that the protein may play 
an important role in normal pregnancy. 
Our laboratory has also made progress in un- 
derstanding the mechanism of action of drugs 
that inhibit TNF biosynthesis and in devising mol- 
ecules that block the action of TNF once it has 
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