Nat. Immunol.; doi:10.1038/ni.3318; corrected online 8 December 2015

In the version of this article initially published online, in the third and fourth paragraphs of the Discussion section, the mice are incorrectly identified as Rorcgfb/+. The correct genotype is Rorcgfp/+. The error has been corrected for the print, PDF and HTML versions of this article.