Interleukin-1 is a master cytokine regulating inflammatory and immune responses. But there are two faces to the biology of IL-1: IL-1 can be causative in the manifestations of a broad spectrum of diseases, 2 but IL-1 can also provide the host with protective mechanisms required to fight infection. For example, IL-1 stimulates hematopoiesis, particularly for neutrophils. Indeed, IL-1 was given to patients to shorten the nadir of bone-marrow suppression after chemotherapy. 3 New data suggest that this latter property of IL-1 is enhanced at elevated temperatures during in vivo mouse models of neutrophil recovery from radiation. 1 This observation is consistent with what we know about IL-1.

Early research on IL-1 was carried out to isolate the endogenous fever–producing protein then called leukocytic pyrogen (reviewed in Dinarello4). Indeed, recombinant IL-1 (either IL-1 or IL-1) is the most potent pyrogen for humans, producing fever at doses as low as 1 ng/kg (reviewed in Dinarello5). Human responses to IL-1 also target the hematopoietic system as IL-1 induces neutrophilia via induction of G-CSF. In fact, fever and neutrophilia are the two most consistent