Induction of tumor necrosis factor, IFN-gamma, and acute lethality in mice by toxic and non-toxic forms of lipid A.

The effect of the i.v. administration of endotoxin (LPS), diphosphoryl lipid A, and the non-toxic derivative monophosphoryl lipid A (MPL), on the production of serum cachectin (TNF), IFN-gamma, and the appearance of endotoxin shock have been measured in mice primed with Listeria monocytogenes. All three of the lipid A varieties induced the production of TNF in a dose-dependent manner. Although comparable peak levels of TNF were produced (5 X 10(5) to 1 X 10(6) U/ml), treatments with LPS or diphosphoryl lipid A were lethal whereas those with MPL were not. A study following TNF in the mouse sera for up to 24 h after treatment with the lipid A types showed that serum levels of TNF peaked 90 min after the treatment, and that TNF levels induced by LPS treatment were maintained for several hours longer than those induced by lipid A or MPL. All three molecules also resulted in the production of IFN-gamma in the serum, which peaked at 4 to 5 h after treatment. After 90 min there were no significant differences in the levels of serum IFN-gamma in any of the groups of treated animals. However, as was observed with the TNF, the levels of IFN in animals treated with LPS persisted longer than those induced by MPL or lipid A. These results suggest that the non-toxic MPL as well as the toxic forms of lipid A can induce the production of TNF by macrophages. Furthermore, although it is essential, TNF alone is not necessarily sufficient to induce septic shock in mice.