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−/−). The gene discussed is STAT4; the disease is systemic lupus erythematosus.