Carbohydrate chains and phosphatidylserine successively work as signals for apoptotic cell removal

At an early stage of apoptosis, Jurkat cells transiently become susceptible to binding and phagocytosis by macrophages through the polylactosamine-type carbohydrate chains of CD43 [J. Biol. Chem. 279 (2004) 5967]. Susceptibility of apoptotic Jurkat cells to macrophage recognition was studied over an extended time range of 0-24 h including a later stage. Jurkat cells incubated with appropriate concentrations of apoptosis-inducing agents etoposide or anti-Fas antibody became susceptible to macrophage-binding at 2 h, and the susceptibility fell to the control level at 4 or 6 h. However, it increased again at later hours (6-24 h). Flow cytometric analyses of CD43 and phosphatidylserine (PS) on the apoptotic cells indicated that CD43 began to degrade at around 4 h, and PS is externalized significantly at 4 or 6 h. The macrophage-binding at 2 h was prevented by glycosidase treatment of Jurkat cells, but not by annexin V. Conversely, the later binding at 12 or 18 h was not prevented by glycosidase treatment, but was done so by annexin V. These results suggest that Jurkat cells become susceptible to phagocytic removal at an early stage of apoptosis by the carbohydrate-mediated mechanism, and at a later stage by the PS-mediated mechanism.