Fever response in old and young mice after injection of interleukin 1.

In an attempt to determine why certain elderly humans show a blunted febrile response to infection, a mouse model was developed. Interleukin 1 (IL1), previously called endogenous pyrogen (EP), the predominantly macrophage-derived mediator of fever, was obtained from supernatants that were generated by stimulating macrophages obtained from young and old mice. The dose versus febrile response curves were generated by injecting crude or partially purified supernatants that contained IL1 into the tail veins of young and old mice. Old mice responded with less fever than young mice to both crude and partially purified supernatants, suggesting that one mechanism for the blunted fever response observed with aging may be an altered response to EP.