Apoptosis, subcellular particles, and autoimmunity.

Firm evidence links the process of apoptosis to the induction of autoimmune disease. However, questions remain regarding the precise interactions of dying cells with the immune system. Genetic analyses indicate that deficiencies in serum proteins or receptors that mediate clearance of apoptotic cells increase the risk of autoimmunity. Moreover, administration of apoptotic cells to naive animals elicits transient autoimmune responses. Because known autoantigens are covalently modified and redistributed to cell surface blebs during the execution stage of apoptosis, increasing attention is being directed at this stage of programmed cell death, and researchers have identified a variety of autoantigens that are sequestered within blebs. However, blebs are merely a transition stage toward the complete cellular fragmentation, as blebs quickly convert into apoptotic bodies, subcellular particles (SCPs) of heterogeneous size, surface composition, and cargo. Because certain types of subcellular particles represent packets of highly enriched autoantigens, we propose that they are relevant to our understanding of autoimmunity.