Serum amyloid P component (SAP) binds DNA and chromatin in a calcium dependent manner in physiological conditions (Pepys et al. 1987). This binding displaces H1-type histones (Butler et al. 1990), solubilizing chromatin which is otherwise insoluble in extracellular fluids. SAP may therefore participate in the in vivo handling of chromatin exposed by cell death. SAP knockout mice spontaneously develop antinuclear autoimmunity and severe glomerulonephritis, a phenotype resembling human systemic lupus erythematosus, a serious autoimmune disease, suggesting that SAP binding may play a role in reducing the immunogenicity of chromatin and preventing autoimmunity (Bickerstaff et al. 1999).