C3 and systemic lupus erythematosus: Abnormal phagocytosis of apoptotic cells in clinical and experimental studies of lupus has been demonstrated [21,22]; and furthermore, Bijl et al. have demonstrated abnormal phagocytosis in SLE patients, showing reduced uptake of apoptotic cells by monocyte-derived macrophages as a serum-dependent defect that is associated with decreased levels of C1q, C4, and C3 [22].