Schematic model of the proposed mechanism by which histones liberated from nucleosomes upon DNA digestion are degraded by FSAP. Nucleosomes are not cytotoxic, but through digestion of nucleosome DNA by circulating nucleases, cytotoxic histones may be liberated. These histones induce the autoactivation of FSAP, and the histones are in turn rapidly degraded by FSAP, which neutralizes their cytotoxicity. FSAP is subsequently inactivated through irreversible complex formation with serin protease inhibitors, including AP.