Nat. Med. 16, 279–285 (2010), published online 28 February 2010; corrected after print 6 May 2010

In the version of this article initially published, the symbol key in Figure 2g,h is incorrect. The correct symbol key is open circles for Ido1−/− and filled circles for WT. The error has been corrected in the HTML and PDF versions of the article.