Apoptotic macrophages are frequently observed in human atherosclerotic lesions, and are considered to be involved in plaque instability in atherosclerosis. However, the molecular mechanism that promotes programmed cell death of macrophages in atherosclerosis remains to be elucidated. In this study, we investigated the effects of interferon-γ (IFN-γ), a cytokine secreted by activated T helper 1 (Th1) lymphocytes, on apoptotic cell death of THP-1 macrophages. Further we studied whether these apoptotic macrophages could be simultaneously activated in vitro and subsequently overgenerate monocyte chemoattractant protein-1 (MCP-1). When THP-1 macrophages were cultured with various concentrations of IFN-γ, DNA synthesis was significantly decreased. IFN-γ was found significantly to induce apoptotic cell death in THP-1 macrophages. RNase protection assay revealed that IFN-γ up-regulated the mRNA levels of two pro-apoptotic molecules, tumor necrosis factor-α receptor 1 (TNFR1) and caspase-8, in THP-1 cells. Furthermore, TNF-α antibodies were found completely to neutralize the IFN-γ-induced inhibition in DNA synthesis as well as apoptotic cell death in macrophages. IFN-γ was found to activate these macrophages to stimulate MCP-1 production. The results suggest that IFN-γ not only exerted apoptotic effects on macrophages, but also activated them and subsequently overgenerated MCP-1, and was thus involved in the development and progression of atherosclerosis.