Protection of mice against lethal endotoxemia by a lipid A precursor

Lipid X, the major biosynthetic precursor of lipid A, has recently been described. Although lipid X is a mitogen and coagulates the Limulus amebocyte lysate, we found that it is not lethal for mice, even when given in large doses (2 X 10(6) micrograms/kg). Furthermore, lipid X was found to give partial protection against a 100% lethal dose of endotoxin, even if the lipid X was given as late as 6 h after endotoxin challenge.