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The pathogenesis of human and simian immunodeficiency viruses is characterized by CD4+ T cell depletion and chronic T cell activation, leading ultimately to AIDS. CD4+ T helper (TH) cells provide protective immunity and immune regulation through different immune cell functional subsets, including TH1, TH2, T regulatory (Treg), and interleukin-17 (IL-17)–secreting TH17 cells. Because IL-17 can enhance host defenses against microbial agents, thus maintaining the integrity of the mucosal barrier, loss of TH17 cells may foster microbial translocation and sustained inflammation. Here, we study HIV-seropositive subjects and find that progressive disease is associated with the loss of TH17 cells and a reciprocal increase in the fraction of the immunosuppressive Treg cells both in peripheral blood and in rectosigmoid biopsies. The loss of TH17/Treg balance is associated with induction of indoleamine 2,3-dioxygenase 1 (IDO1) by myeloid antigen-presenting dendritic cells and with increased plasma concentration of microbial products. In vitro, the loss of TH17/Treg balance is mediated directly by the proximal tryptophan catabolite from IDO metabolism, 3-hydroxyanthranilic acid. We postulate that induction of IDO may represent a critical initiating event that results in inversion of the TH17/Treg balance and in the consequent maintenance of a chronic inflammatory state in progressive HIV disease.
↵* These authors contributed equally to this work.
↵† Present address: National Immune Monitoring Laboratory, Montréal, Quebec H7N 4A4, Canada.
↵‡ Present address: Department of Medical Parasitology, New York University, New York, NY 10010, USA.
Citation: D. Favre, J. Mold, P. W. Hunt, B. Kanwar, P. Loke, L. Seu, J. D. Barbour, M. M. Lowe, A. Jayawardene, F. Aweeka, Y. Huang, D. C. Douek, J. M. Brenchley, J. N. Martin, F. M. Hecht, S. G. Deeks, J. M. McCune, Tryptophan Catabolism by Indoleamine 2,3-Dioxygenase 1 Alters the Balance of TH17 to Regulatory T Cells in HIV Disease. Sci. Transl. Med. 2, 32ra36 (2010).
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