APCS and systemic lupus erythematosus: Aged MBL-deficient mice do not develop autoimmunity even on a lupus-prone genetic background 129 × C57BL/6.55 Moreover, SAP−/− and C1q−/− mice only develop autoimmunity on the mixed 129 × C57BL/6 or MRL/Mp background.30, 31 To our knowledge, MFG-E8−/− mice are the only opsonin-deficient model that spontaneously develop an autoimmune phenotype with aging.29