Nat. Immunol. 12, 284–286 (2011); published online 21 April 2011; addendum published after print 24 June 2011
The article to which this News and Views refers has been retracted (http://www.nature.com/ni/journal/v12/n4/abs/ni.2004.html). Nature Immunology wishes to inform readers that some of the comments made in this News and Views, although made in good faith based on the article's conclusions, may no longer be valid.