The Apcs-deficient mice (Apcs−/−) were chosen as an example of a gene-targeted strain previously reported to develop a lupus-like disease on the hybrid genetic background (129 × C57BL/6); autoimmunity in Apcs−/− mice persists even after backcrossing the mutated gene onto C57BL/6 (Bickerstaff et al. 1999). The gene discussed is APCS; the disease is Autoimmunity.