Background:Cholesterol 27-hydroxylase, an enzyme expressed at high levels by human monocytes/macrophages, provides a first line of defense against the development of atherosclerosis. Prior studies have suggested that the cytokine interferon-gamma (IFN-γ) promotes atherosclerosis. We therefore examined the effect of IFN-g on macrophage foam cell formation and on expression of the anti-atherogenic 27-hydroxylase in THP-1 human monocytes/macrophages.Material/Methods: THP-1 monocytes and acetylated LDL-treated THP-1 macrophages were incubated in the presence or absence of IFN-γ (500 U/ml) with or without the addition of IFN- γ receptor blocking or neutralizing antibody. Foam cell formation was quantified based on percentage of macrophages harboring oil red O-stained globules. Cellular mRNA and protein were isolated. 27-Hydroxylase message was measured by RT-PCR and 27-hydroxylase protein by immunoblot.Results: IFN-γ -treated THP-1 macrophages exhibit increased foam cell transformation compared to untreated cells under cholesterol loading conditions. IFN-γ-promoted foam cell formation is abolished by pre-treatment with either IFN-γ neutralizing or IFN-&#x03B3 receptor blocking antibody. IFN-γ diminishes cholesterol 27-hydroxylase expression in THP-1, and this IFN-γ -induced downregulation is prevented by pre-treating the cultured cells with either IFN-γ neutralizing or IFN-&#x03B3 receptor blocking antibody.Conclusions: Imbalances in cellular cholesterol flux within macrophages lead to formation of lipid-laden foam cells, a critical step in the pathogenesis of atherosclerosis. We have demonstrated that IFN-γ, acting through the IFN-γ receptor, decreases expression of 27-hydroxylase and increases propensity to foam cell formation in the cell line THP-1. These observations suggest that one mechanism by which IFN-g promotes atherosclerosis may involve affecting expression of cholesterol 27-hydroxylase, a cholesterol homeostatic protein.

Keywords: Antibodies - immunology, Arteriosclerosis - etiology, Biological Transport - drug effects, Cell Differentiation, Cholesterol - metabolism, Cholesterol, LDL - metabolism, Cytochrome P-450 CYP27A1, Down-Regulation - genetics, Foam Cells - chemistry, Foam Cells - drug effects, Foam Cells - metabolism, Interferon Type II - immunology, Interferon Type II - metabolism, Interferon Type II - pharmacology, Macrophages - cytology, Monocytes - cytology, Steroid Hydroxylases - genetics, Steroid Hydroxylases - metabolism, Antibodies - immunology, Arteriosclerosis - etiology, Biological Transport - drug effects, Cholestanetriol 26-Monooxygenase, Cholesterol - metabolism, Cholesterol, LDL - metabolism, Down-Regulation - genetics, Foam Cells - metabolism, Interferon-gamma - pharmacology, Macrophages - cytology, Monocytes - cytology, Steroid Hydroxylases - metabolism