3. Mer/kd (Mer knock-down) mice developed autoimmune disease Mer is a member of Ax1/Mer/Tyro3 receptor tyrosine kinase family. Growth arrest-specific gene 6 (GAS6) was shown to bridge Mer to phosphatidylserine on apoptotic cells. Mer-kd mice had macrophages deficient in clearance of apoptotic thymocytes. The phagocytic deficiency was restricted to apoptotic cells and was independent of Fc receptor-mediated phagocytosis or ingestion of other particles. Mer-kd mice developed progressive lupus-like immunity, with antibodies to chromatin, DNA, and IgG. The autoimmunity appears to be spontaneously, driven by endogenous antigens, with little polyclonal B cell activation.