Complexes of serum amyloid P component and DNA in serum from healthy individuals and systemic lupus erythematosus patients

Serum amyloid P component (SAP) binds in vitro to DNA; based on findings in SAP-deficient mice it was proposed that SAP's role is to handle chromatin and DNA, thereby preventing formation of anti-DNA antibodies. For the first time we have shown the presence of Ca2+-dependent SAP-DNA complexes, measu red by ELISA, in sera from both healthy volunteers and systemic lupus eryth ematosus patients (SLE). The concentration of SAP-DNA complexes in SLE sera was significantly lower than in normal sera and particularly low in sera f rom patients with anti-DNA titers exceeding 50. The complexes were dissocia ted by the SAP ligand heparin and were not demonstrable in EDTA plasma. Normal sera showed similar capacity to form SAP-DNA complexes with both thy mus and Escherichia coli DNA, whereas significantly lower amounts of comple xes, in particular with E. coli DNA, were formed in SLE sera. SLE patients with moderate to high anti-DNA titers showed a significant negative correla tion between serum SAP's binding of E. coli DNA and the anti-DNA titer.