We found that IRF5 was critical for disease development in the FcγRIIB−/−Yaa and FcγRIIB−/− lupus models as IRF5-deficient FcγRIIB−/−Yaa and FcγRIIB−/− mice developed minimal disease manifestations [21]. The gene discussed is IRF5; the disease is systemic lupus erythematosus.