Recent studies indicate that polymicrobial sepsis can markedly increase inducible macrophage A(o) (non-necrotic cellular suicide) and that this is associated with decreased Mφ function. In vitro studies suggest that Mφ A(o) can be induced by IL-1β via interleukin-1β-converting enzyme (ICE, a cysteine protease), prostanoids, or reactive oxygen/nitrogen. However, the mechanism(s) underlying this process in septic Mφ remains unknown. To determine this, male C3H/HeN mice were subjected to sepsis (cecal ligation and puncture, CLP) or sham-operation. Twenty-four hours thereafter, Mφ were isolated from the peritoneum (PMφ) and liver (LMφ). Macrophage monolayers were treated with LPS (10 μg/ml) alone (Cont) or in the presence of iodoacetamide (Iodo, 5 mM), N-methylmalamide (meth, 5 mM), ibuprophen (Ibu, 40 μg/ml), N-methyl-L-arginine (LNMA, 0.4 mM), or superoxide dismutase (SOD, 60,000 U/ml) for 24 hr. The extent of A(o) was determined using an enzyme- linked immunosorbent cell-death assay, which detects the presence of cytoplasmic oligonucleosomes measured as optical density. The results indicate that both PMφ and LMφ from septic animals exhibit increased A(o) over cells from sham animals. However, only the nonspecific cysteine protease inhibitors (Iodo and meth) and the NO inhibitor LNMA blocked septic mouse MΦ A(o). Furthermore, only PMφ from CLP mice treated with Iodo, but not LNMA or IBU, showed an improved capacity to release IL-6. We conclude that increased Mφ A(o) seen during sepsis appears to be mediated by both ICE-like cysteine protease activation and NO release but the level/mechanism of action of these inhibitors differs.