Nat. Immunol. 8, 882–892 (2007); published online 15 July 2007; corrected after print 13 November 2013

In the version of this article initially published, in Figure 4b the row labeled 'IB: α-PSGL-1 monomer' is incorrect; it is a duplicate of the row above. The error has been corrected in the HTML and PDF versions of the article.