We investigated the regulation of elastase activity in murine peritoneal macrophages by different cytokines and bacterial LPS. Thioglycolate-elicited mouse peritoneal exudate macrophages secrete a metalloproteinase that degrades elastin. Incubation of peritoneal exudate macrophages with LPS and IFN-gamma significantly inhibited the production of elastase by a mechanism independent of nitric oxide, superoxide, and hydrogen peroxide. The cytokines IL-1alpha, IL-1beta, IL-2, IL-4, IL-6, IL-8, IL-10, TNF, TGF-alpha and -beta, basic fibroblast growth factor, monocyte chemotactic factor-1, and granulocyte CSF (G-CSF) had no significant effect on the production of elastase by macrophages. In contrast, granulocyte-macrophage CSF (GM-CSF) increased the production of elastase in a dose-dependent manner, and with macrophage CSF (M-CSF) inhibited it. Elastin zymography demonstrated that the modulation of elastolytic activity in macrophages was associated with changes in the level of metalloelastase protein. The stimulation of elastase activity by GM-CSF and the inhibition of elastase activity by LPS, IFN-gamma, and M-CSF occurred at the level of transcription. LPS and M-CSF also augmented the expression level of tissue inhibitors of metalloproteinase mRNA. The increased mRNA steady state level of murine macrophage elastase induced by GM-CSF resulted from both increased transcription and enhanced stability. The modulation of metalloelastase activity in macrophages by IFN-gamma, M-CSF, and GM-CSF suggests that these molecules may control the degradation of elastin fibers in lungs or blood vessels.