Nat. Immunol. 14, 536–542 (2013); published online 20 May 2013; corrected after print 25 June 2013

In the version of this article initially published, an arrow was incorrectly included between the MPP2 cell and CD4+ cell in the top row of Figure 2. The correct figure has no arrow there. The error has been corrected in the HTML and PDF versions of the article.