The indoleamine 2,3-dioxygenase inhibitor 1-methyl-tryptophan suppresses mitochondrial function, induces aerobic glycolysis and decreases interleukin-10 production in human lymphocytes.

BACKGROUND: Indoleamine 2,3-dioxygenase (IDO) suppresses adaptive immunity. It is known that IDO induces T-cell differentiation to regulatory T-cells (Treg) through tryptophan depletion and/or kynurenine pathway products. CD4+ effector T-cells require distinct metabolic programs in order to support their function as compared to Treg cells. Furthermore, glucose metabolism is also known to affect B-cell survival and function. The effect of IDO on glucose metabolism of lymphocytes was evaluated by using its inhibitor 1-methyl-DL-tryptophan (1-MT).
METHODS: Ten healthy volunteers vaccinated against tetanus. Peripheral blood mononuclear cells (PBMC) were cultured with or without tetanus toxoid and/or 1-MT. Cell proliferation was assessed by optical microscopy, glucose uptake by measuring its concentration in the supernatant, aerobic glycolysis by assessing lactate concentration in the supernatant, mitochondrial function by XTT assay, and finally production of Tregs' signature cytokine IL-10 by means of ELISA.
RESULTS: Primarily, IDO decreases glucose uptake by stimulated lymphocytes. Secondly, IDO increases mitochondrial function in stimulated lymphocytes. In addition, IDO decreases aerobic glycolysis in stimulated lymphocytes. Finally, IDO induces the production of the immunosuppressive cytokine IL-10 by stimulated lymphocytes.
CONCLUSION: Considering that cell metabolism plays a significant role in lymphocyte differentiation and function, IDO may exert its immunomodulatory effect by interfering with cell metabolism.