Purchase this article with an account.
Eleni Konstantinou, Jeroen P.J. Saeij, Lucy H. Young; Cell death of gamma interferon (IFNg)-stimulated human macrophages upon Toxoplasma gondii infection limits parasite replication. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1892.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Toxoplasmosis is the most common cause of infectious retinochoroiditis. It is caused by the parasite Toxoplasma gondii, which affects both immune compromised and immune competent patients. The cytokine interferon gamma (IFNg) plays an important role in the inhibition of Toxoplasma growth. In some cell types (such as HeLa cells) IFNg induces the enzyme indoleamine 2,3-dioxygenase (IDO) leading to tryptophan depletion and restriction of Toxoplasma growth while other cell types restrict Toxoplasma growth through an unknown mechanism. Macrophages and other innate immunity cells that infiltrate the retina in ocular toxoplasmosis play an important role in fighting the infection but can also contribute to the inflammation in the eye. It is unclear how human macrophages inhibit Toxoplasma growth. The goal of this study is to determine how IFNg-stimulated human cells inhibit Toxoplasma replication.
An in vitro study using the MM6 and THP-1human macrophage cell lines was performed. Cells were stimulated with IFNg for 24 h and subsequently infected with Toxoplasma expressing luciferase and GFP. Parasite growth over time was determined by microscopy and by measuring luciferase activity. Macrophage cell death was determined by measuring the release of lactate dehydrogenase into the culture medium. To assess whether tryptophan depletion was implicated in cell death, cells were supplemented with tryptophan or treated with an inhibitor of IDO.
IFNg-stimulated human macrophages rapidly died upon Toxoplasma infection and thereby restricted parasite growth. We obtained similar results in two different human macrophage cell lines and in human fibroblasts. Cell death was independent of tryptophan depletion. Cell death of human fibroblasts was also independent of necroptosis and apoptosis. We are currently determining the role of a variety of candidate genes in the induction of cell death by making knockout macrophage cell lines using CRISPR/Cas9.
Increased death of IFNg-stimulated cells upon Toxoplasma infection is an effective mechanism of Toxoplasma growth restriction. Unraveling this mechanism of cell death could eventually lead to better therapeutics to treat ocular toxoplasmosis.
This PDF is available to Subscribers Only