Single cell analysis of kynurenine and System L amino acid transport in T cells

The tryptophan metabolite kynurenine has critical immunomodulatory properties and can function as an aryl hydrocarbon receptor (AHR) ligand. Here we show that the ability of T cells to transport kynurenine is restricted to cells activated by the T cell antigen receptor or pro-inflammatory cytokines. Kynurenine is transported across the T cell membrane by the System L transporter SLC7A5. Accordingly, the ability of kynurenine to activate AHR is restricted to T cells that express SLC7A5. We use the fluorescence spectral properties of kynurenine to develop a flow cytometry based assay for rapid, sensitive and quantitative measurement of the kynurenine transport capacity in a single cell. Our findings provide a method to assess the susceptibility of T cells to kynurenine, and a sensitive single cell assay to monitor system L amino acid transport