Nat. Immunol. 14, 346–355 (2013); published online 17 February 2013; corrected after print 22 April 2013

In the version of this article initially published, the second affiliation for Young-Joon Kim was missing. The correct affiliation includes the following: Department of Integrated Omics for Biomedical Science, WCU Program of Graduate School, Yonsei University, Seoul, Republic of Korea. The error has been corrected in the HTML and PDF versions of the article.