Four different interleukin-1 species sensitize to the lethal action of tumour necrosis factor

We studied the induction of lethal shock by Tumour Necrosis Factor (TNF) in mice and observed a remarkable difference between the effect of human and murine TNF, which could be eliminated by co-administration of sensitizing agents. We identified interleukin-1 (IL1) as a natural sensitizer, rendering mice as susceptible to human TNF as to murine TNF. This IL1 activity was found to be exerted to the same extent both by human and murine IL1-alpha or IL1-beta, and was also different from the sensitization obtained with galactosamine, since these agents had an additive effect. Pretreatment of the animals with indomethacin, a cyclooxygenase inhibitor, provided partial protection against TNF lethality in IL1-sensitized but not in galactosamine-sensitized mice.