Tumor necrosis factor alone does not explain the lethal effect of lipopolysaccharide.

Lethality and tumor necrosis factor production induced by different types of lipopolysaccharide were studied in naive (non-primed) rats during the late phase of endotoxin tolerance. The correlation with antilipopolysaccharide antibodies was also analyzed. No correlation was found between tumor necrosis factor levels and lipopolysaccharide-induced mortality in naive animals. Low-toxicity lipopolysaccharide preparations induced levels of tumor necrosis factor similar to those induced with more toxic types of lipopolysaccharide. Late tolerance was associated with progressively lower levels of lipopolysaccharide-induced tumor necrosis factor and increasing titers of antilipopolysaccharide antibodies after repeated injections of homologous lipopolysaccharide. During late endotonxin tolerance, a direct correlation between the lipopolysaccharide dose and peak tumor necrosis factor serum levels was found. We conclude that since tumor necrosis factor serum levels do not correlate with mortality, tumor necrosis factor alone cannot explain the lethal effect of lipopolysaccharide.