Nat. Immunol. 15, 676–686 (2014); published online 8 June 2014; corrected after print 21 August 2014

In the version of this article initially published, the labels along the horizontal axes of the graphs Figure 6e,f (right), indicating the presence or absence of IL-9, are reversed. Each '−' should be '+', and each '+' should be '–'. The error has been corrected in the HTML and PDF versions of this article.