Vol. 206, No. 2, February 16, 2009. Pages 421–434.

Please note that two errors appeared in the references of the online early release version of this article. References 67 and 68 were listed incorrectly. The current html, pdf, and print versions appear correctly.

The corrected references appear below.

67. Fallarino, F., U. Grohmann, K.W. Hwang, C. Orabona, C. Vacca, R. Bianchi, M.L. Belladonna, M.C. Fioretti, M.L. Alegre, and P. Puccetti. 2003. Modulation of tryptophan catabolism by regulatory T cells. Nat. Immunol. 4:1206–1212.

68. Puccetti, P., and U. Grohmann. 2007. IDO and regulatory T cells: a role for reverse signalling and non-canonical NF-κB activation. Nat. Rev. Immunol. 7:817–823.