To determine the role of STAT4 in SLE-associated Spt-AFC and Spt-GC responses and SLE-like autoimmunity development, we crossed STAT4−/− mice to the SLE-prone FcγRIIB−/− mouse strain (designated RIIB−/−.STAT4−/−). This evidence concerns the gene FCGR2B and systemic lupus erythematosus.