Monocytes/macrophages are prominent in atherosclerotic plaques where the vascular remodeling and plaque rupture may be influenced by the lipids and cytokines at these sites. Therefore, we evaluated the effects of factors found within the vascular wall, such as cytokines, oxidized low-density lipoprotein (ox-LDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL), on monocyte-derived matrix metalloproteinase-1 (MMP-1) and -9 (MMP-9) and tissue inhibitor of metalloproteinases-1 (TIMP-1). ox-LDL, LDL, and HDL alone had no effect on MMP-1, MMP-9, or TIMP-1 production. However, in the presence of tumor necrosis factor (TNF)-alpha and GM-CSF, ox-LDL enhanced MMP-1 significantly by two- to threefold, increased MMP-9 slightly, and had no effect on TIMP-1 production. In contrast, HDL suppressed the induction of MMP-1 by TNF-alpha and GM-CSF as well as the ox-LDL-mediated increase in MMP-1 production. The enhancement of MMP-1 production by ox-LDL occurred through, in part, a prostaglandin E2 (PGE2)-dependent pathway as indomethacin suppressed and PGE2 restored MMP-1 production. This conclusion was supported further by ox-LDL-mediated increases in PGE2 and cyclooxygenase-2 (COX-2) production. These data suggest that the interaction of primary monocytes with ox-LDL and proinflammatory cytokines may contribute to vascular remodeling and plaque rupture.