CD34 and systemic lupus erythematosus: The impaired clearance of apoptotic cells in SLE is due to their failed recognition by phagocytes because (a) the phagocytes are smaller (4), (b) the phagocytes have diminished and delayed phagocytic activity (46), (c) the phagocytes have reduced adherence (47), or (d) the differentiation of phagocytes from CD34-positive hematopoietic stem cells is reduced (48–50).