IL-1β-converting enzyme (ICE), also known as caspase-1, subserves two dichotomous biologic roles. It processes newly synthesized pro-IL-1β to yield the active cytokine and, as the human homologue of the Caenorhabditis elegans gene product, ced-3, it also induces cellular apoptosis through the cleavage of key intracellular structural and regulatory proteins and through the catalytic activation of other caspase family members. We show here that two different proinflammatory stimuli, LPS and granulocyte-macrophage-CSF, up-regulate the expression of both ICE and IL-1β in human polymorphonuclear neutrophils, and that the ICE-dependent cleavage of pro-IL-1β results in delayed expression of the constitutive cell death program. The apoptotic delay can be blocked by inhibiting tyrosine kinases or NF-κB activation and by inhibiting protein synthesis. Since an antisense oligonucleotide for IL-1β, a blocking Ab to IL-1β, and preincubation with the IL-1R antagonist all prevent the delay in apoptosis, we conclude that IL-1β acts in an autocrine manner to inhibit granulocyte programmed cell death. We conclude that caspase-1 (ICE) subserves both pro-and antiapoptotic roles; the latter role is evident during inflammation as an inhibition of spontaneous neutrophil apoptosis through the processing of IL-1β. The ICE-dependent activation of IL-1β may represent a common autocrine pathway for the divergent stimuli that inhibit the constitutive expression of neutrophil programmed cell death during inflammation.