Nat. Immunol.; doi:10.1038/ni.3580; corrected online 10 October 2016

In the version of this article initially published online, the immunoblots in Figures 1a, 5a, 5b, 5c, 5d, 5f, 6a, 6b, 7a, 7b, 8a and 8b were in color. These have been replaced with black and white immunoblots. The error has been corrected for the print, PDF and HTML versions of this article.