Complement mediated cell death is associated with DNA fragmentation

In this study, we demonstrate for the first time that complement attack of target cells, in the presence of suitably high levels of serum, can induce the oligonucleosomal DNA fragmentation characteristic of apoptosis. This phenomenon requires membrane permeabilisation induced by formation of the complete membrane attack complex and relies on physiologically relevant levels of serum. TUNEL analysis detected complement mediated DNA fragmentation as early as 30 min after the addition of serum and electron microscopy confirmed that chromatin became condensed after complement attack. Various experiments implicate serum DNase I as the mediator of this DNA fragmentation. Intriguingly, membrane permeability induced by melittin gave rise to similar serum dependent DNA fragmentation. The implications of these results for the study of apoptosis in vitro and in vivo are discussed.