Ifn-γ Activated Indoleamine 2,3-Dioxygenase Activity in Human Cells is an Antiparasitic and an Antibacterial Effector Mechanism

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Abstract
In nearly all human cells IFN-γ Stimulation leads to an activation of indoleamine 2,3-dioxygenase (IDO) activity, which is responsible for anti-toxoplasma and anti-chlamydia effects. We have recently shown that IDO activation is also a defense mechanism against extracellular β-hemolytic streptococci groups A,B,C and G in human glioblastoma cells, fibroblasts and macrophages. Similar effects were also seen with enterococci and in approximately 65% of staphylococci tested, including multiresistant strains of both species. In addition, we have found that IDO activity is differentially regulated in different cells. For example we have found that TNF-α enhances IFN-γ induced IDO activity and antimicrobial effect in human glioblastoma cells whereas both IFN-γ mediated effects were blocked by TNF-α as well as by IL-1 in a human uroepithelial cell line. We were able to show that the IL-1 and TNF-α mediated inhibition of IFN-γ-induced IDO activity in uroepithelial cells is due to stimulation of inducible nitric oxide synthase. In human astrocytoma cells, IL-1 and TNF-α did not inhibit IDO activity and in concordance with this finding these cells did not show a detectable nitric oxide production.