Nat. Protoc. 4, 372–384 (2009); doi:10.1038/nprot.2009.3; published online 26 February 2009; corrected after print 24 January 2014

In the version of this article initially published, the sequence of primer VH3a-sense in Table 1 incorrectly indicated a ‘C’ at position 12 instead of a ‘G’. The error has been corrected in the HTML and PDF versions of the article.