Characterization of a human monoclonal IgM with antibody activity to dsDNA.

We report here the characterization and fine specificity of a human monoclonal IgM lambda reacting with double stranded DNA. The purified IgM and its Fab fragment bind to DNA in the Farr or Crithidia lucilae assays as well as in an immunoenzymatic test. In the latter case, binding was inhibited by native DNA, by DNA alternative co-polymers and by some homopolymers only, but not by monodeoxyribonucleotides and ribonucleotides. Since cardiolipin and phosphatidic acid were good inhibitors, these data suggest that the monoclonal IgM reacts with the sugar phosphate backbone of deoxyribonucleic acids. Interestingly, the patient was affected with both Waldenström's macroglobulinaemia and pernicious anaemia without any symptoms of systemic lupus erythematosus.