Interestingly, although some of these models develop lupus-like features and abnormal accumulation of apoptotic cells (e.g., C1q-, C4-, SAP-, c-Mer-, DNase I-, and MFG-E8-deficient mice; Botto et al., 1998; Bickerstaff et al., 1999; Chen et al., 2000; Napirei et al., 2000; Cohen et al., 2002; Hanayama et al., 2004), disease expression is frequently dependent on background genes (e.g., C1q-, C4-, SAP-deficient mice; Botto et al., 1998; Bickerstaff et al., 1999; Chen et al., 2000; Mitchell et al., 2002; Paul et al., 2002; Gillmore et al., 2004). Here, APCS is linked to systemic lupus erythematosus.