In studying "hemorrhagic necrosis" of tumors produced by endotoxin, it was found that the serum of bacillus Calmette-Guerin (BCG)infected mice treated with endotoxin contains a substance (tumor necrosis factor; TNF) which mimics the tumor necrotic action of endotoxin itself. TNF-positive serum is as effective as endotoxin itself in causing necrosis of the sarcoma Meth A and other transplanted tumors. A variety of tests indicate that TNF is not residual endotoxin, but a factor released from host cells, probably macrophages, by endotoxin. Corynebacteria and Zymosan, which like BCG induce hyperplasia of the reticulo-endothelial system, can substitute for BCG in priming mice for release of TNF by endotoxin. TNF is toxic in vitro for two neoplastic cell lines; it is not toxic for mouse embryo cultures. We propose that TNF mediates endotoxin-induced tumor necrosis, and that it may be responsible for the suppression of transformed cells by activated macrophages.One of the best-known enigmas of cancer biology is the "hemorrhagic necrosis" of tumors induced by endotoxin (1-5). We report here that endotoxin acts indirectly by causing the host to release a substance, which we name tumor necrosis factor (TNF), that is selectively toxic for malignant cells.

Tumor necrosis can be induced in transplanted mouse methylcholanthrene-induced sarcoma by a tumor necrosis factor in the serum of mice infected with bacillus Calmette-Guerin and given bacterial endotoxin. Sera from normal mice, endotoxin-treated mice, and mice infected with bacillus Calmette-Guerin do not contain this factor. A 20-to 30-fold purification of the serum factor has been achieved by (NH4)2SO4 fractionation, Sephadex Fig. 1. No significant difference was found between normal and endotoxin-treated mice. Sera from the mice infected with BCG or infected with BCG followed by endotoxin showed increases in the a-globulin region and in the region between the ( and y globulins.Changes in Serum Enzymes. Table 1 shows that enzyme levels in endotoxin-treated mice were essentially similar to those of normal mice, with the exception of a small rise in lysozyme. The serum of BCG mice displayed marked elevation in all the enzymes measured; four of these-acid phosphatase, f3-glucuronidase, 0-glucosidase, and a-galactosidase-are lysosomal. In the BCG-endotoxin-treated group these elevations (with the exception of alkaline phosphatase) were even more marked. NADase, which is normally bound in microsomes (12), was present only in the serum of the BCG-endotoxin-treated mice. As we have shown previously (1), TNF was demonstrable only in serum of BCG-endotoxin-treated mice. Similar trace amounts of endotoxin (Limulus assay) were found in all four pools, indicating that TNF is not endotoxin.Partial Purification of TNF Obtained from Serum. All steps were carried out at 4°. Glassware was steam-sterilized at 2500F (1210C) for 20 min, and solutions were autoclaved. Sephadex gels were equilibrated and rinsed with 10 volumes of sterile 0.01 M potassium phosphate buffer, pH 7.0 containing 0.15 M NaCl (phosphate-buffered saline).A typical purification of TNF was as follows: 80 ml of TNF-rich serum was diluted with an equal volume of sterile 0.15 M NaCl, and 36.8 g of (NH4)2SO4 was added with con-381 Abbreviations: Meth A, methylcholanthrene-induced fibrosarcoma; TNF, tumor necrosis factor; BCG, bacillus Calmette-Guerin; NADase, NADI glycohydrolase (EC 3.2.2.5); Mr, molecular weight.

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