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 ph enomenon requires membrane permeabilisation induced by formation of the com plete 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 confir med that chromatin became condensed after complement attack. Various experi ments implicate serum DNase I as the mediator of this DNA fragmentation. In triguingly, membrane permeability induced by melittin gave rise to similar serum dependent DNA fragmentation. The implications of these results for th e study of apoptosis in vitro and in vivo are discussed.