Antimicrobial and immunoregulatory properties of human tryptophan 2,3-dioxygenase

Eur J Immunol. 2009 Oct;39(10):2755-64. doi: 10.1002/eji.200939535.


In mammals, the regulation of local tryptophan concentrations by the IFN-gamma-i inducible enzyme IDO is a prominent antimicrobial and immunoregulatory effector mechanism. Here, we show for the first time that another tryptophan-degrading enzyme, the liver-specific tryptophan 2,3-dioxygenase (TDO), is also capable of mediating antimicrobial and immunoregulatory effects. Using a tetracycline inducible eukaryotic system, we were able to express recombinant TDO protein, which exhibits functional properties of native TDO. We found that HeLa cells expressing recombinant TDO were capable of inhibiting the growth of bacteria (Staphylococcus aureus), parasites (Toxoplasma gondii) and viruses (herpes simplex virus). These TDO-mediated antimicrobial effects could be blocked by the addition of tryptophan. In addition, we observed that, similar to IDO-positive cells, TDO-positive cells were capable of inhibiting anti CD3-driven T-cell proliferation and IFN-gamma production. Furthermore, TDO-positive cells also restricted alloantigen-induced T-cell activation. Here, we describe for the first time that TDO mediates antimicrobial and immunoregulatory effects and suggest that TDO-dependent inhibition of T-cell growth might be involved in the immunotolerance observed in vivo during allogeneic liver transplantation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Coculture Techniques
  • Culture Media, Conditioned / pharmacology
  • Gene Expression / drug effects
  • HeLa Cells
  • Humans
  • Immunologic Factors / genetics
  • Immunologic Factors / immunology*
  • Immunologic Factors / metabolism*
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / antagonists & inhibitors
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / metabolism
  • Interferon-gamma / metabolism
  • Interferon-gamma / pharmacology
  • Isoantigens / immunology
  • Kynurenine / metabolism
  • Leukocytes, Mononuclear / immunology
  • Lymphocyte Activation / drug effects
  • Lymphocyte Activation / immunology
  • Lymphocyte Culture Test, Mixed
  • Simplexvirus / growth & development
  • Staphylococcus aureus / growth & development
  • T-Lymphocytes / immunology
  • T-Lymphocytes / metabolism
  • Tetracycline / pharmacology
  • Toxoplasma / growth & development
  • Transfection
  • Tryptophan / metabolism
  • Tryptophan / pharmacology
  • Tryptophan Oxygenase / genetics
  • Tryptophan Oxygenase / immunology*
  • Tryptophan Oxygenase / metabolism*


  • Culture Media, Conditioned
  • Immunologic Factors
  • Indoleamine-Pyrrole 2,3,-Dioxygenase
  • Isoantigens
  • Kynurenine
  • Interferon-gamma
  • Tryptophan
  • Tryptophan Oxygenase
  • Tetracycline