A CROSS-SECTIONAL STUDY OF ANTI-DNA ANTIBODIES IN THE SERUM AND IGG AND IGM FRACTION OF HEALTHY-INDIVIDUALS, PATIENTS WITH SYSTEMIC LUPUS-ERYTHEMATOSUS AND THEIR RELATIVES

Sera from healthy individuals, relatives of lupus patients, and lupus patients with active disease and in remission were screened for IgG an d IgM antibodies to ssDNA and dsDNA. The serum samples were also separ ated into IgG and IgM fractions which were screened for DNA reactivity at dilutions equivalent to those used for testing un-fractionated ser um. The results show that whilst, as expected, antibodies of IgG or Ig M isotype to both ss and dsDNA could be detected in high concentration in the serum of lupus patients with active disease, anti-ssDNA antibo dies of the IgG or IgM isotype are also detectable in healthy individu als, relatives and spouses of lupus patients. Furthermore when IgG and IgM serum fractions were separated and screened for DNA reactivity, t he IgM fraction in the healthy individuals frequently showed an increa se in the level of binding to ssDNA compared to the serum or separated IgM fraction of SLE relatives. In contrast no increase in DNA reactiv ity of the IgG fraction was detected in the separated IgG fraction fro m healthy individuals. These observations infer that IgM autoantibodie s are present in healthy individuals at levels higher than is reported normally, and at levels comparable with those found in relatives of S LE patients in which autoreactive antibodies are frequently reported, and their ability to bind ssDNA in whole serum is inhibited by IgG ant ibodies present within whole serum.