Nur77-eGFP mice and hen egg lysozyme–specific BCR (IgHEL) Tg mice (MD4 line) were described previously (23 (link), 24 (link)). BoyJ and Nr4a1−/− mice were from The Jackson Laboratory (13 (link)). All mice were housed in a specific pathogen–free facility at University of California, San Francisco, according to university and National Institutes of Health guidelines.