Independence of plasma membrane blebbing from other biochemical and biological characteristics of apoptotic cells

Plasma membrane blebs are observed in many types of apoptotic cells, but their physiological roles remain to be clarified. We examined whether there is a causative connection between membrane blebbing and other apoptotic changes in Jurkat cells induced to undergo apoptosis by doxorubicin in the presence or absence of Y-27632, an inhibitor of the Rho kinase ROCK-I. The inclusion of the drug made most membrane blebs disappear, while other changes, such as chromatin condensation, inactivation of mitochondrial enzymes, externalization of the membrane phospholipid phosphatidylserine, and removal of cell surface sialic acid, remained unaffected. Furthermore, these apoptotic cells were phagocytosed by macrophages as efficiently as normally apoptosing cells. These results indicate that blebbing of the plasma membrane occurs independently from other apoptotic changes and is not involved in the recognition and engulfment of apoptotic cells by macrophages.