Little is known about endogenous systemic lupus erythematosus (SLE) plasma DNA even though it is the presumed precursor of DNA-containing immune complexes, thought to play a central role in lupus glomerulonephritis. DNA purified from SLE plasma formed discrete bands, corresponding to sizes of about 150-200, 400, 600, and 800 bp, closely resembling the characteristic 200 bp "ladder" found with oligonucleosomal (ON) DNA. By radiolabeling DNA while in whole plasma, the very small amounts present could be further characterized. All of 24 such specimens formed two or more discrete bands on 6% PAGE. Detergent treatment of plasma resulted in a DNA migration pattern similar to that of purified DNA, suggesting disruption of DNA-protein complexes. DNA purified from authentic ON and detergent-treated ON behaved similarly. A significant portion of DNA, labeled in SLE plasma could be specifically immunoprecipitated with monoclonal antihistone antibody as was the case with ON. These immunoprecipitates, when redissolved, exhibited the expected size distribution upon PAGE. It is concluded that DNA in SLE plasma occurs as a series of multimeric complexes, at least a portion of which is noncovalently bound to histone. These results are consistent with an ON-like structure for SLE plasma DNA as had been suggested by theoretical considerations and may have important implications for its immunologic behavior in SLE and perhaps other disorders. (J. Clin. Invest. 1990.86:69-74.)

A B S T R A C T Circulating DNA has been associated with several human disorders, including the nephritis of systemic lupus erythematosus (SLE), in which it is thought to play an etiological role. However, it remains unclear whether its appearance in the circulation is truly pathological. Several reports, each generally based on a single assay method, have disagreed as to whether DNA may circulate in normals. Some, but not all, of this disagreement may be explained by the recently described appearance of DNA in serum, but not plasma, apparently as the result of release from leukocytes in vitro.In the present report an attempt is made to clarify this problem. Normal plasma and serum samples were examined by four assays for DNA that were newly modified to enhance their specificity and/or sensitivity. Plasma DNA was undetectable by all four methods, the most sensitive of which could detect 0.05 tJg/ml of native DNA (nDNA) or 0.1 tg/ml of single-stranded DNA (ssDNA). Serum DNA was present in 14 of 16 samples tested in variable concentrations with an estimated mean of 1.9 ig/ml. It is concluded that the appearance of DNA in adult human plasma is a pathological event. Presumably, previous reports describing detection of DNA in normal plasma were based on the measurement of non-DNAase-sensitive interfering substances. Furthermore, it is emphasized that the use of serum in studies dependent on sensitive assays for DNA (or anti-DNA antibody) introduces an ambiguity that may be avoided by substitution of carefully collected plasma for serum.

B burgdorferi can invade the CNS early in the course of infection. Careful consideration should be given to choosing antibiotics that achieve adequate CSF levels in patients with disseminated infection.

SUMMARYThe rale of clearance of exiracellular plasma DNA in man ha.s importani inipiitalions for palhogenelie mechanisms in systemic lupus erythemalosus (SLE), as well as for eeriain oihcr clinical states. Present knowledge of this parameter is derived exelusively from studies of injected, naked DNA in animals. Recent informalion indicates that the physiologic form of plasma DNA in SLE is that of oligonucleosome-like molecules rather than of naked DNA and eonsists of multimcric complexes of DNA bound to histone, probably arising from an apoplotic process. In order to study the rale at which ihese oligonucleosome-like complexes are removed from plasma and to do so in man rather than experimental animals, we exploited the observation that during haemodialysis large amounts of DNA are released, apparently within the dialysis coil, inlo the paiieni's plasma. Since this release appears lo cease promptly with termination of the procedure, it offered the potential for estimating the rate of removal of such DNA from human plasma. Moreover, if that DNA. as postulated, were shown to possess an oligonucleosome-like structure resembling that fotind endogenously in human SLE, the relevance of such information to the human disease state would be further enhanced. The present results support the conclusion that DNA released into plasma during haemodialysis possesses such an oligonucleosome-like structure. The plasma half-life of ihat DNA in man was found nol lo exceed 4 min. The highly dynamic state thus implied for extracellular endogenous plasma DNA in man has important implications for pathogenetic mechanisms dependent on dsDNA in SLE. Moreover, individuals undergoing chronic hacmodialysi,s, who are thereby exposed to a very large cumulative amount of such DNA., might serve as models for studying its long-term sequelae.