Cytokines Induce Indoleamine 2,3-Dioxygenase Expression in Human Atheroma-Associated Cells: Implications for PersistentChlamydophila pneumoniaeInfection

Abstract

This study shows that vascular smooth muscle cells express significantly higher levels of gamma interferoninducible indoleamine 2,3-dioxygenase (IDO) activity than endothelium or mononuclear cells. Since IDO activity is linked to persistent Chlamydophila pneumoniae infection, our results suggest that smooth muscle cells may be an important reservoir of that organism in atherosclerosis.Ample evidence indicates that T cells respond to local antigens and produce gamma interferon (IFN-␥) in atheroma (16). Recent attention has focused on the association of Chlamydophila pneumoniae with lesion progression (5,19,25). C. pneumoniae localizes in human atherosclerotic lesions as assessed by electron microscopy (30) and by PCR and immunostaining (17,18). Furthermore, C. pneumoniae can infect and proliferate within endothelial cells, smooth muscle cells, and macrophages in vitro (14,15).The ability of C. pneumoniae to survive chronically in vascular host tissue may derive from its capacity to establish a persistent infection. The persistent form of C. pneumoniae, characterized by enlarged abnormal forms, differs structurally and metabolically from the elementary and reticulate bodies (3,10,22). This obligate intracellular pathogen, like other chlamydial species, requires tryptophan for growth (7,27). The mammalian enzyme indoleamine 2,3-dioxygenase (IDO) catabolizes tryptophan and can lower the concentration of this amino acid in host cells. Interestingly, IFN-␥, a cytokine present in atherosclerotic plaques, can regulate IDO expression in some cells. Numerous studies have investigated the effects of various cytokines on IDO regulation in multiple cell lines (4,8,11,23,24,27,33). IFN-␥-induced IDO activity can induce the persistent form of C. pneumoniae infection in cultured cells (26). This study compared the effects of IFN-␥ on IDO activity in different types of human vascular wall cells, including saphenous vein endothelial cells (SVEC), saphenous vein smooth muscle cells (SVSMC), aortic smooth muscle cells (ASMC), and peripheral blood mononuclear cells (PBMC). SVEC, SVSMC, and ASMC were isolated as previously described (20). PBMC were isolated from healthy donors by plateletpheresis (6), followed by adherence to plastic culture flasks (2 h at 37°C) (21).SVEC, SVSMC, ASMC, and PBMC were plated at a cell density of 1.5 ϫ 10 5 cells/cm 2 in 96-well plates. Confluent monolayers were overlaid with media containing IFN-␥ (Endogen) from 0 to 800 U/ml. In some experiments, tumor necrosis factor alpha (TNF-␣) (0 to 1,000 U/ml) (Endogen) was added 24 h later. After 72 h of incubation at 37°C, the medium was replaced with [ 3 H]tryptophan pulse media containing 0.05 mM L-tryptophan (Sigma) and 1 Ci of L-5-[ 3 H]tryptophan (New England Nuclides)/ml in Hanks balanced salt solution (Gibco BRL). Plates were incubated an additional 4 h at 37°C, after which the supernatants and cell lysates prepared by 10% trichloroacetic acid extraction were collected and frozen until analysis. Each data point was determined in triplicate for two dif...

<EMPH TYPE="ITAL">Chlamydia pneumoniae</EMPH> as an Emerging Risk Factor in Cardiovascular Disease

“…[81][82][83] Interferon gamma produced locally by these T lymphocytes may prime atheroma cells to harbor persistent infection with C pneumoniae. 55,84 Plaque destabilization may proceed through more direct mechanisms as well; C pneumoniae enhances the production of matrix-degrading metalloproteinases able to weaken plaques so that they rupture more readily.…”

Schizophrenia: From the brain to peripheral markers. A consensus paper of the WFSBP task force on biological markers

“…Cytokines, such as IL-1b, IL-2 and IFN-g, reduce the production of serotonin by stimulating the activity of indoleamine-2,3-dioxygenase (IDO), an enzyme that converts tryptophan, the precursor of 5-HT, to kynurenine (Guillemin et al 2001;Sakash et al 2002). The kynurenine is again metabolized (Dang et al 2000) into quinolinic acid and kynurenic acid.…”

Gamma interferon: a central mediator in atherosclerosis

“…In view of the stimulatory effects of GM-CSF on macrophage effector functions, reduced expression of GM-CSF, if demonstrable by IFN-g in vivo, could also have a vascular protective effect. Finally, IFN-g induces the expression of indoleamine 2, 3-dioxygenase (IDO) in vascular SMC [140,141]. A link between increased IDO activity and persistence of Chlamydia pneumoniae due to reduced levels of tryptophan, as well as the continued interest in the relationship between Chlamydial infections and atherosclerotic disease offer an additional perspective as to how IFN-g effects on vascular SMC can infl uence plaque progression.…”