Nat. Immunol. 13, 1045–1054 (2012); published online 30 September 2012; corrected after print 8 April 2013

In the version of this article initially published, the eighth author was identified incorrectly. The correct name is Inma M Berenjeno, and the initials should be I.M.B. in the Author Contributions section. The error has been corrected in the HTML and PDF versions of the article.